fgerlits commented on code in PR #1682:
URL: https://github.com/apache/nifi-minifi-cpp/pull/1682#discussion_r1394163260


##########
extensions/standard-processors/tests/unit/SplitTextTests.cpp:
##########
@@ -0,0 +1,860 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "FlowFileRecord.h"
+#include "TestBase.h"
+#include "Catch.h"
+#include "processors/SplitText.h"
+#include "SingleProcessorTestController.h"
+#include "io/BufferStream.h"
+
+namespace org::apache::nifi::minifi::test {
+
+TEST_CASE("Test LineReader with nullptr") {
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with empty stream") {
+  auto stream = std::make_shared<io::BufferStream>();
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 10, 
.endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader without trailing endlines") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 9, .endline_size 
= 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size +1 , .size = 
second_line_size + 1, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2 - 
1, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size + 1, .size = 
second_line_size, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, 
'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with starts with filter") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "header this is a new line\nheader and another 
line\r\nthirdline\nheader line\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 26, .endline_size 
= 1, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 26, .size = 25, 
.endline_size = 2, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 51, .size = 10, 
.endline_size = 1, .matches_starts_with = false});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 61, .size = 12, 
.endline_size = 1, .matches_starts_with = true});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+struct ExpectedSplitTextResult {
+  std::string content;
+  uint64_t fragment_index = 0;
+  uint64_t fragment_count = 0;
+  uint64_t text_line_count = 0;
+};
+
+struct SplitTextProperties {
+  uint64_t line_split_count = 0;
+  std::optional<bool> trim_trailing_newlines;
+  std::optional<uint64_t> maximum_fragment_size;
+  std::optional<uint64_t> header_line_count;
+  std::optional<std::string> header_line_marker_characters;
+};

Review Comment:
   This looks just slightly different from `SplitTextConfiguration`.  Could we 
use that instead, or somehow merge the two into one?



##########
extensions/standard-processors/processors/SplitText.h:
##########
@@ -0,0 +1,234 @@
+/**
+ * @file SplitText.h
+ * SplitText class declaration
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <memory>
+#include <string_view>
+#include <utility>
+#include <optional>
+
+#include "core/Processor.h"
+#include "core/ProcessSession.h"
+#include "core/PropertyDefinitionBuilder.h"
+#include "core/PropertyDefinition.h"
+#include "core/PropertyType.h"
+#include "core/RelationshipDefinition.h"
+#include "FlowFileRecord.h"
+#include "utils/Export.h"
+#include "utils/expected.h"
+
+namespace org::apache::nifi::minifi::processors {
+
+struct SplitTextConfiguration {
+  uint64_t line_split_count = 0;
+  std::optional<uint64_t> maximum_fragment_size;
+  uint64_t header_line_count = 0;
+  std::optional<std::string> header_line_marker_characters;
+  bool remove_trailing_new_lines = true;
+};
+
+namespace detail {
+
+constexpr size_t SPLIT_TEXT_BUFFER_SIZE = 8192;
+
+enum class StreamReadState {
+  Ok,
+  StreamReadError,
+  EndOfStream
+};
+
+class LineReader {
+ public:
+  struct LineInfo {
+    uint64_t offset = 0;
+    uint64_t size = 0;
+    uint8_t endline_size = 0;
+    bool matches_starts_with = true;
+
+    bool operator==(const LineInfo& line_info) const = default;
+  };
+
+  explicit LineReader(const std::shared_ptr<io::InputStream>& stream);
+  std::optional<LineInfo> readNextLine(const std::optional<std::string>& 
starts_with = std::nullopt);
+  StreamReadState getState() const { return state_; }
+
+ private:
+  uint8_t getEndLineSize(size_t newline_index);
+  void setLastLineInfoAttributes(uint8_t endline_size, const 
std::optional<std::string>& starts_with);
+  bool readNextBuffer();
+  std::optional<LineReader::LineInfo> finalizeLineInfo(uint8_t endline_size, 
const std::optional<std::string>& starts_with);
+
+  size_t buffer_offset_ = 0;
+  uint64_t current_buffer_count_ = 0;
+  size_t last_read_size_ = 0;
+  uint64_t read_size_ = 0;
+  std::array<char, SPLIT_TEXT_BUFFER_SIZE> buffer_{};
+  std::shared_ptr<io::InputStream> stream_;
+  std::optional<LineInfo> last_line_info_;
+  StreamReadState state_ = StreamReadState::Ok;
+};
+
+class SplitTextFragmentGenerator {
+ public:
+  struct Fragment {
+    uint64_t text_line_count = 0;
+    uint64_t processed_line_count = 0;
+    uint64_t fragment_size = 0;
+    uint64_t fragment_offset = 0;
+    uint8_t endline_size = 0;
+  };
+
+  SplitTextFragmentGenerator(const std::shared_ptr<io::InputStream>& stream, 
const SplitTextConfiguration& split_text_config);
+  std::optional<Fragment> readNextFragment();
+  nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
readHeaderFragment();

Review Comment:
   Why do we sometimes write `Fragment` and sometimes 
`SplitTextFragmentGenerator::Fragment`?  I'm fine with either version, but 
mixing them looks strange.



##########
extensions/standard-processors/processors/SplitText.cpp:
##########
@@ -0,0 +1,383 @@
+/**
+ * @file SplitText.cpp
+ * SplitText class implementation
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "SplitText.h"
+#include "core/ProcessContext.h"
+#include "core/ProcessSession.h"
+#include "core/Resource.h"
+#include "core/FlowFile.h"
+#include "utils/gsl.h"
+#include "utils/ProcessorConfigUtils.h"
+
+namespace org::apache::nifi::minifi::processors {
+
+namespace detail {
+
+LineReader::LineReader(const std::shared_ptr<io::InputStream>& stream)
+    : stream_(stream) {
+  if (!stream_ || stream_->size() == 0) {
+    state_ = StreamReadState::EndOfStream;
+  }
+}
+
+uint8_t LineReader::getEndLineSize(size_t newline_index) {
+  gsl_Expects(buffer_.size() > newline_index);
+  if (buffer_[newline_index] != '\n') {
+    return 0;
+  }
+  if (newline_index == 0 || buffer_[newline_index - 1] != '\r') {
+    return 1;
+  }
+  return 2;
+}
+
+void LineReader::setLastLineInfoAttributes(uint8_t endline_size, const 
std::optional<std::string>& starts_with) {
+  const uint64_t size_from_beginning_of_stream = (current_buffer_count_ - 1) * 
SPLIT_TEXT_BUFFER_SIZE + buffer_offset_;
+  if (last_line_info_) {
+    LineInfo previous_line_info = *last_line_info_;
+    last_line_info_->offset = previous_line_info.offset + 
previous_line_info.size;
+    last_line_info_->size = size_from_beginning_of_stream - 
previous_line_info.offset - previous_line_info.size;
+    last_line_info_->endline_size = endline_size;
+    last_line_info_->matches_starts_with = true;
+  } else {
+    last_line_info_ = LineInfo{.offset = 0, .size = read_size_ - 
last_read_size_ + buffer_offset_, .endline_size = endline_size, 
.matches_starts_with = true};
+  }
+
+  if (starts_with) {
+    last_line_info_->matches_starts_with = last_line_info_->size >= 
starts_with->size() &&
+      std::equal(starts_with->begin(), starts_with->end(), buffer_.begin() + 
last_line_info_->offset, buffer_.begin() + last_line_info_->offset + 
starts_with->size());
+  }
+}
+
+bool LineReader::readNextBuffer() {
+  buffer_offset_ = 0;
+  last_read_size_ = (std::min)(gsl::narrow<size_t>(stream_->size() - 
read_size_), SPLIT_TEXT_BUFFER_SIZE);
+  const auto read_ret = 
stream_->read(as_writable_bytes(std::span(buffer_).subspan(0, 
last_read_size_)));
+  read_size_ += read_ret;
+  if (io::isError(read_ret)) {
+    state_ = StreamReadState::StreamReadError;
+    return false;
+  }
+  ++current_buffer_count_;
+  return true;
+}
+
+std::optional<LineReader::LineInfo> LineReader::finalizeLineInfo(uint8_t 
endline_size, const std::optional<std::string>& starts_with) {
+  setLastLineInfoAttributes(endline_size, starts_with);
+  if (last_line_info_->size == 0) {
+    return std::nullopt;
+  }
+  return last_line_info_;
+}
+
+std::optional<LineReader::LineInfo> LineReader::readNextLine(const 
std::optional<std::string>& starts_with) {
+  if (state_ != StreamReadState::Ok) {
+    return std::nullopt;
+  }
+
+  const auto isLastReadProcessed = [this]() { return last_read_size_ <= 
buffer_offset_; };
+  while (read_size_ < stream_->size() || !isLastReadProcessed()) {
+    if (isLastReadProcessed() && !readNextBuffer()) {
+      return std::nullopt;
+    }
+
+    for (auto i = buffer_offset_; i < last_read_size_; ++i) {
+      if (buffer_[i] == '\n') {
+        buffer_offset_ = i + 1;
+        return finalizeLineInfo(getEndLineSize(i), starts_with);
+      }
+    }
+    buffer_offset_ = last_read_size_;
+  }
+
+  state_ = StreamReadState::EndOfStream;
+  return finalizeLineInfo(0, starts_with);
+}
+
+SplitTextFragmentGenerator::SplitTextFragmentGenerator(const 
std::shared_ptr<io::InputStream>& stream, const SplitTextConfiguration& 
split_text_config)
+    : line_reader_(stream),
+      split_text_config_(split_text_config) {
+}
+
+void SplitTextFragmentGenerator::finalizeFragmentOffset(Fragment& 
current_fragment) {
+  current_fragment.fragment_offset = flow_file_offset_;
+  flow_file_offset_ += current_fragment.fragment_size;
+}
+
+void SplitTextFragmentGenerator::addLineToFragment(Fragment& current_fragment, 
const LineReader::LineInfo& line) {
+  if (line.endline_size == line.size) {  // if line consists only of endline 
characters, we need to append the fragment trim size
+    current_fragment.endline_size += line.endline_size;
+  } else {
+    current_fragment.endline_size = line.endline_size;
+  }
+  current_fragment.text_line_count += line.endline_size == line.size ? 0 : 1;
+  current_fragment.fragment_size += line.size;
+}
+
+bool SplitTextFragmentGenerator::lineSizeWouldExceedMaxFragmentSize(const 
LineReader::LineInfo& line, uint64_t fragment_size) const {
+  return split_text_config_.maximum_fragment_size && fragment_size + line.size 
+ header_fragment_size_ > split_text_config_.maximum_fragment_size.value();
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::createHeaderFragmentUsingLineCount() {
+  Fragment header_fragment;
+  for (uint64_t i = 0; i < split_text_config_.header_line_count; ++i) {
+    auto line = line_reader_.readNextLine();
+    if (!line) {
+      if (getState() == StreamReadState::EndOfStream) {
+        return nonstd::make_unexpected("The flow file's line count is less 
than the specified header line count!");
+      } else {
+        return nonstd::make_unexpected("Error while reading flow file 
stream!");
+      }
+    }
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
header_fragment.fragment_size)) {
+      return nonstd::make_unexpected("Header line would exceed the maximum 
fragment size!");
+    }
+
+    addLineToFragment(header_fragment, *line);
+  }
+
+  flow_file_offset_ += header_fragment.fragment_size;
+  header_fragment_size_ = header_fragment.fragment_size;
+  return header_fragment;
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::createHeaderFragmentUsingHeaderMarkerCharacters() {
+  Fragment header_fragment;
+  while (auto line = 
line_reader_.readNextLine(split_text_config_.header_line_marker_characters)) {
+    if (line->size < split_text_config_.header_line_marker_characters->size() 
|| !line->matches_starts_with) {
+      buffered_line_info_ = line;
+      break;
+    }
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
header_fragment.fragment_size)) {
+      return nonstd::make_unexpected("Header line would exceed the maximum 
fragment size!");
+    }
+
+    addLineToFragment(header_fragment, *line);
+  }
+
+  flow_file_offset_ += header_fragment.fragment_size;
+  header_fragment_size_ = header_fragment.fragment_size;
+  return header_fragment;
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::readHeaderFragment() {
+  gsl_Expects(flow_file_offset_ == 0);
+  if (split_text_config_.header_line_count == 0 && 
!split_text_config_.header_line_marker_characters) {
+    return nonstd::make_unexpected("No header properties were set!");
+  }

Review Comment:
   could this be checked in `onSchedule`?



##########
extensions/standard-processors/processors/SplitText.cpp:
##########
@@ -0,0 +1,383 @@
+/**
+ * @file SplitText.cpp
+ * SplitText class implementation
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "SplitText.h"
+#include "core/ProcessContext.h"
+#include "core/ProcessSession.h"
+#include "core/Resource.h"
+#include "core/FlowFile.h"
+#include "utils/gsl.h"
+#include "utils/ProcessorConfigUtils.h"
+
+namespace org::apache::nifi::minifi::processors {
+
+namespace detail {
+
+LineReader::LineReader(const std::shared_ptr<io::InputStream>& stream)
+    : stream_(stream) {
+  if (!stream_ || stream_->size() == 0) {
+    state_ = StreamReadState::EndOfStream;
+  }
+}
+
+uint8_t LineReader::getEndLineSize(size_t newline_index) {
+  gsl_Expects(buffer_.size() > newline_index);
+  if (buffer_[newline_index] != '\n') {
+    return 0;
+  }
+  if (newline_index == 0 || buffer_[newline_index - 1] != '\r') {
+    return 1;
+  }
+  return 2;
+}
+
+void LineReader::setLastLineInfoAttributes(uint8_t endline_size, const 
std::optional<std::string>& starts_with) {
+  const uint64_t size_from_beginning_of_stream = (current_buffer_count_ - 1) * 
SPLIT_TEXT_BUFFER_SIZE + buffer_offset_;
+  if (last_line_info_) {
+    LineInfo previous_line_info = *last_line_info_;
+    last_line_info_->offset = previous_line_info.offset + 
previous_line_info.size;
+    last_line_info_->size = size_from_beginning_of_stream - 
previous_line_info.offset - previous_line_info.size;
+    last_line_info_->endline_size = endline_size;
+    last_line_info_->matches_starts_with = true;
+  } else {
+    last_line_info_ = LineInfo{.offset = 0, .size = read_size_ - 
last_read_size_ + buffer_offset_, .endline_size = endline_size, 
.matches_starts_with = true};
+  }
+
+  if (starts_with) {
+    last_line_info_->matches_starts_with = last_line_info_->size >= 
starts_with->size() &&
+      std::equal(starts_with->begin(), starts_with->end(), buffer_.begin() + 
last_line_info_->offset, buffer_.begin() + last_line_info_->offset + 
starts_with->size());
+  }
+}
+
+bool LineReader::readNextBuffer() {
+  buffer_offset_ = 0;
+  last_read_size_ = (std::min)(gsl::narrow<size_t>(stream_->size() - 
read_size_), SPLIT_TEXT_BUFFER_SIZE);
+  const auto read_ret = 
stream_->read(as_writable_bytes(std::span(buffer_).subspan(0, 
last_read_size_)));
+  read_size_ += read_ret;
+  if (io::isError(read_ret)) {
+    state_ = StreamReadState::StreamReadError;
+    return false;
+  }
+  ++current_buffer_count_;
+  return true;
+}
+
+std::optional<LineReader::LineInfo> LineReader::finalizeLineInfo(uint8_t 
endline_size, const std::optional<std::string>& starts_with) {
+  setLastLineInfoAttributes(endline_size, starts_with);
+  if (last_line_info_->size == 0) {
+    return std::nullopt;
+  }
+  return last_line_info_;
+}
+
+std::optional<LineReader::LineInfo> LineReader::readNextLine(const 
std::optional<std::string>& starts_with) {
+  if (state_ != StreamReadState::Ok) {
+    return std::nullopt;
+  }
+
+  const auto isLastReadProcessed = [this]() { return last_read_size_ <= 
buffer_offset_; };
+  while (read_size_ < stream_->size() || !isLastReadProcessed()) {
+    if (isLastReadProcessed() && !readNextBuffer()) {
+      return std::nullopt;
+    }
+
+    for (auto i = buffer_offset_; i < last_read_size_; ++i) {
+      if (buffer_[i] == '\n') {
+        buffer_offset_ = i + 1;
+        return finalizeLineInfo(getEndLineSize(i), starts_with);
+      }
+    }
+    buffer_offset_ = last_read_size_;
+  }
+
+  state_ = StreamReadState::EndOfStream;
+  return finalizeLineInfo(0, starts_with);
+}
+
+SplitTextFragmentGenerator::SplitTextFragmentGenerator(const 
std::shared_ptr<io::InputStream>& stream, const SplitTextConfiguration& 
split_text_config)
+    : line_reader_(stream),
+      split_text_config_(split_text_config) {
+}
+
+void SplitTextFragmentGenerator::finalizeFragmentOffset(Fragment& 
current_fragment) {
+  current_fragment.fragment_offset = flow_file_offset_;
+  flow_file_offset_ += current_fragment.fragment_size;
+}
+
+void SplitTextFragmentGenerator::addLineToFragment(Fragment& current_fragment, 
const LineReader::LineInfo& line) {
+  if (line.endline_size == line.size) {  // if line consists only of endline 
characters, we need to append the fragment trim size
+    current_fragment.endline_size += line.endline_size;
+  } else {
+    current_fragment.endline_size = line.endline_size;
+  }
+  current_fragment.text_line_count += line.endline_size == line.size ? 0 : 1;
+  current_fragment.fragment_size += line.size;
+}
+
+bool SplitTextFragmentGenerator::lineSizeWouldExceedMaxFragmentSize(const 
LineReader::LineInfo& line, uint64_t fragment_size) const {
+  return split_text_config_.maximum_fragment_size && fragment_size + line.size 
+ header_fragment_size_ > split_text_config_.maximum_fragment_size.value();
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::createHeaderFragmentUsingLineCount() {
+  Fragment header_fragment;
+  for (uint64_t i = 0; i < split_text_config_.header_line_count; ++i) {
+    auto line = line_reader_.readNextLine();
+    if (!line) {
+      if (getState() == StreamReadState::EndOfStream) {
+        return nonstd::make_unexpected("The flow file's line count is less 
than the specified header line count!");
+      } else {
+        return nonstd::make_unexpected("Error while reading flow file 
stream!");
+      }
+    }
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
header_fragment.fragment_size)) {
+      return nonstd::make_unexpected("Header line would exceed the maximum 
fragment size!");
+    }
+
+    addLineToFragment(header_fragment, *line);
+  }
+
+  flow_file_offset_ += header_fragment.fragment_size;
+  header_fragment_size_ = header_fragment.fragment_size;
+  return header_fragment;
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::createHeaderFragmentUsingHeaderMarkerCharacters() {
+  Fragment header_fragment;
+  while (auto line = 
line_reader_.readNextLine(split_text_config_.header_line_marker_characters)) {
+    if (line->size < split_text_config_.header_line_marker_characters->size() 
|| !line->matches_starts_with) {
+      buffered_line_info_ = line;
+      break;
+    }
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
header_fragment.fragment_size)) {
+      return nonstd::make_unexpected("Header line would exceed the maximum 
fragment size!");
+    }
+
+    addLineToFragment(header_fragment, *line);
+  }
+
+  flow_file_offset_ += header_fragment.fragment_size;
+  header_fragment_size_ = header_fragment.fragment_size;
+  return header_fragment;
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::readHeaderFragment() {
+  gsl_Expects(flow_file_offset_ == 0);
+  if (split_text_config_.header_line_count == 0 && 
!split_text_config_.header_line_marker_characters) {
+    return nonstd::make_unexpected("No header properties were set!");
+  }
+
+  if (split_text_config_.header_line_count > 0) {
+    return createHeaderFragmentUsingLineCount();
+  }
+
+  return createHeaderFragmentUsingHeaderMarkerCharacters();
+}
+
+std::optional<SplitTextFragmentGenerator::Fragment> 
SplitTextFragmentGenerator::readNextFragment() {
+  Fragment current_fragment;
+  while (auto line = buffered_line_info_ ? buffered_line_info_ : 
line_reader_.readNextLine()) {
+    buffered_line_info_.reset();
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
current_fragment.fragment_size)) {
+      if (current_fragment.processed_line_count == 0) {  // first fragment 
line would be bigger than maximum fragment size (we don't have any other line 
in the fragment yet)
+        addLineToFragment(current_fragment, *line);
+      } else {
+        buffered_line_info_ = line;
+      }
+
+      finalizeFragmentOffset(current_fragment);
+      return current_fragment;
+    }
+
+    ++current_fragment.processed_line_count;
+    addLineToFragment(current_fragment, *line);
+    if (split_text_config_.line_split_count == 
current_fragment.processed_line_count) {
+      finalizeFragmentOffset(current_fragment);
+      return current_fragment;
+    }
+  }
+
+  if (current_fragment.fragment_size > 0) {
+    finalizeFragmentOffset(current_fragment);
+    return current_fragment;
+  }
+  return std::nullopt;
+}
+
+}  // namespace detail
+
+void SplitText::initialize() {
+  setSupportedProperties(Properties);
+  setSupportedRelationships(Relationships);
+}
+
+void SplitText::onSchedule(const std::shared_ptr<core::ProcessContext> 
&context, const std::shared_ptr<core::ProcessSessionFactory>& 
/*sessionFactory*/) {
+  gsl_Expects(context);
+  split_text_config_.line_split_count = 
utils::getRequiredPropertyOrThrow<uint64_t>(*context, LineSplitCount.name);
+  logger_->log_debug("SplitText line split count: {}", 
split_text_config_.line_split_count);
+  auto max_fragment_data_size_value = 
context->getProperty<core::DataSizeValue>(MaximumFragmentSize);
+  if (max_fragment_data_size_value) {
+    split_text_config_.maximum_fragment_size = 
max_fragment_data_size_value->getValue();
+    logger_->log_debug("SplitText maximum fragment size: {}", 
split_text_config_.maximum_fragment_size.value());
+  }
+  if (split_text_config_.maximum_fragment_size && 
split_text_config_.maximum_fragment_size.value() == 0) {
+    throw Exception(PROCESS_SCHEDULE_EXCEPTION, "Maximum Fragment Size cannot 
be 0!");
+  }
+  if (split_text_config_.line_split_count == 0 && 
!split_text_config_.maximum_fragment_size) {
+    throw Exception(PROCESS_SCHEDULE_EXCEPTION, "Line Split Count is set to 0, 
but Maximum Fragment Size is not set!");
+  }
+  split_text_config_.header_line_count = 
utils::getRequiredPropertyOrThrow<uint64_t>(*context, HeaderLineCount.name);
+  logger_->log_debug("SplitText header line count: {}", 
split_text_config_.header_line_count);
+  split_text_config_.header_line_marker_characters = 
context->getProperty(HeaderLineMarkerCharacters);
+  if (split_text_config_.header_line_marker_characters && 
split_text_config_.header_line_marker_characters->size() >= 
detail::SPLIT_TEXT_BUFFER_SIZE) {
+    throw Exception(PROCESS_SCHEDULE_EXCEPTION, fmt::format("SplitText header 
line marker characters length is larger than the maximum allowed: {}", 
detail::SPLIT_TEXT_BUFFER_SIZE));
+  }
+  if (split_text_config_.header_line_marker_characters) {
+    logger_->log_debug("SplitText header line marker characters were set: {}", 
*split_text_config_.header_line_marker_characters);
+  }
+  split_text_config_.remove_trailing_new_lines = 
utils::getRequiredPropertyOrThrow<bool>(*context, RemoveTrailingNewlines.name);
+  logger_->log_debug("SplitText should remove trailing new lines: {}", 
split_text_config_.remove_trailing_new_lines ? "true" : "false");
+}
+
+void SplitText::onTrigger(const std::shared_ptr<core::ProcessContext> 
&context, const std::shared_ptr<core::ProcessSession> &session) {
+  gsl_Expects(context && session);
+  std::shared_ptr<core::FlowFile> flow_file = session->get();
+  if (!flow_file) {
+    return;
+  }

Review Comment:
   we usually yield in these cases; should we do that here, as well?



##########
extensions/standard-processors/tests/unit/SplitTextTests.cpp:
##########
@@ -0,0 +1,860 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "FlowFileRecord.h"
+#include "TestBase.h"
+#include "Catch.h"
+#include "processors/SplitText.h"
+#include "SingleProcessorTestController.h"
+#include "io/BufferStream.h"
+
+namespace org::apache::nifi::minifi::test {
+
+TEST_CASE("Test LineReader with nullptr") {
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with empty stream") {
+  auto stream = std::make_shared<io::BufferStream>();
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});

Review Comment:
   This would be UB if the return value of `readNextLine()` is `nullopt`.  I 
think
   ```suggestion
     CHECK(reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
   ```
   would work, because `optional<T>` can be compared to `T`.



##########
extensions/standard-processors/processors/SplitText.h:
##########
@@ -0,0 +1,234 @@
+/**
+ * @file SplitText.h
+ * SplitText class declaration
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <memory>
+#include <string_view>
+#include <utility>
+#include <optional>
+
+#include "core/Processor.h"
+#include "core/ProcessSession.h"
+#include "core/PropertyDefinitionBuilder.h"
+#include "core/PropertyDefinition.h"
+#include "core/PropertyType.h"
+#include "core/RelationshipDefinition.h"
+#include "FlowFileRecord.h"
+#include "utils/Export.h"
+#include "utils/expected.h"
+
+namespace org::apache::nifi::minifi::processors {
+
+struct SplitTextConfiguration {
+  uint64_t line_split_count = 0;
+  std::optional<uint64_t> maximum_fragment_size;
+  uint64_t header_line_count = 0;
+  std::optional<std::string> header_line_marker_characters;
+  bool remove_trailing_new_lines = true;
+};
+
+namespace detail {
+
+constexpr size_t SPLIT_TEXT_BUFFER_SIZE = 8192;

Review Comment:
   it doesn't matter much here because a `size_t` is small, but `constexpr` 
variables at namespace scope should always be marked `inline`, especially if 
they are in a header, otherwise we'll have a copy of the constant in every 
translation unit that includes the header



##########
extensions/standard-processors/tests/unit/SplitTextTests.cpp:
##########
@@ -0,0 +1,860 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "FlowFileRecord.h"
+#include "TestBase.h"
+#include "Catch.h"
+#include "processors/SplitText.h"
+#include "SingleProcessorTestController.h"
+#include "io/BufferStream.h"
+
+namespace org::apache::nifi::minifi::test {
+
+TEST_CASE("Test LineReader with nullptr") {
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with empty stream") {
+  auto stream = std::make_shared<io::BufferStream>();
+  processors::detail::LineReader reader{nullptr};

Review Comment:
   I think this should be
   ```suggestion
   TEST_CASE("Test LineReader with empty stream") {
     auto stream = std::make_shared<io::BufferStream>();
     processors::detail::LineReader reader{stream};
   ```



##########
extensions/standard-processors/processors/SplitText.h:
##########
@@ -0,0 +1,234 @@
+/**
+ * @file SplitText.h
+ * SplitText class declaration
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <memory>
+#include <string_view>
+#include <utility>
+#include <optional>
+
+#include "core/Processor.h"
+#include "core/ProcessSession.h"
+#include "core/PropertyDefinitionBuilder.h"
+#include "core/PropertyDefinition.h"
+#include "core/PropertyType.h"
+#include "core/RelationshipDefinition.h"
+#include "FlowFileRecord.h"
+#include "utils/Export.h"
+#include "utils/expected.h"
+
+namespace org::apache::nifi::minifi::processors {
+
+struct SplitTextConfiguration {
+  uint64_t line_split_count = 0;
+  std::optional<uint64_t> maximum_fragment_size;
+  uint64_t header_line_count = 0;
+  std::optional<std::string> header_line_marker_characters;
+  bool remove_trailing_new_lines = true;
+};
+
+namespace detail {
+
+constexpr size_t SPLIT_TEXT_BUFFER_SIZE = 8192;
+
+enum class StreamReadState {
+  Ok,
+  StreamReadError,
+  EndOfStream
+};
+
+class LineReader {
+ public:
+  struct LineInfo {
+    uint64_t offset = 0;
+    uint64_t size = 0;
+    uint8_t endline_size = 0;
+    bool matches_starts_with = true;
+
+    bool operator==(const LineInfo& line_info) const = default;
+  };
+
+  explicit LineReader(const std::shared_ptr<io::InputStream>& stream);
+  std::optional<LineInfo> readNextLine(const std::optional<std::string>& 
starts_with = std::nullopt);
+  StreamReadState getState() const { return state_; }
+
+ private:
+  uint8_t getEndLineSize(size_t newline_index);
+  void setLastLineInfoAttributes(uint8_t endline_size, const 
std::optional<std::string>& starts_with);
+  bool readNextBuffer();
+  std::optional<LineReader::LineInfo> finalizeLineInfo(uint8_t endline_size, 
const std::optional<std::string>& starts_with);
+
+  size_t buffer_offset_ = 0;
+  uint64_t current_buffer_count_ = 0;
+  size_t last_read_size_ = 0;
+  uint64_t read_size_ = 0;
+  std::array<char, SPLIT_TEXT_BUFFER_SIZE> buffer_{};
+  std::shared_ptr<io::InputStream> stream_;
+  std::optional<LineInfo> last_line_info_;
+  StreamReadState state_ = StreamReadState::Ok;
+};
+
+class SplitTextFragmentGenerator {
+ public:
+  struct Fragment {
+    uint64_t text_line_count = 0;
+    uint64_t processed_line_count = 0;
+    uint64_t fragment_size = 0;
+    uint64_t fragment_offset = 0;
+    uint8_t endline_size = 0;
+  };
+
+  SplitTextFragmentGenerator(const std::shared_ptr<io::InputStream>& stream, 
const SplitTextConfiguration& split_text_config);
+  std::optional<Fragment> readNextFragment();
+  nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
readHeaderFragment();
+  StreamReadState getState() const { return line_reader_.getState(); }
+
+ private:
+  static void addLineToFragment(Fragment& fragment, const 
LineReader::LineInfo& line);
+  void finalizeFragmentOffset(Fragment& current_fragment);
+  bool lineSizeWouldExceedMaxFragmentSize(const LineReader::LineInfo& line, 
uint64_t fragment_size) const;
+  nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
createHeaderFragmentUsingLineCount();
+  nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
createHeaderFragmentUsingHeaderMarkerCharacters();
+
+  LineReader line_reader_;
+  // In case the read line would exceed the maximum fragment size, we need to 
buffer it for the next fragment
+  std::optional<LineReader::LineInfo> buffered_line_info_;
+  uint64_t flow_file_offset_ = 0;
+  const SplitTextConfiguration& split_text_config_;
+  uint64_t header_fragment_size_ = 0;
+};
+
+}  // namespace detail
+
+class SplitText : public core::Processor {
+ public:
+  explicit SplitText(std::string_view name,  const utils::Identifier& uuid = 
{})
+      : Processor(name, uuid) {
+  }
+
+  EXTENSIONAPI static constexpr const char* Description = "Splits a text file 
into multiple smaller text files on line boundaries limited by maximum number 
of lines or total size of fragment. "
+    "Each output split file will contain no more than the configured number of 
lines or bytes. If both Line Split Count and Maximum Fragment Size are 
specified, the split occurs at whichever "
+    "limit is reached first. If the first line of a fragment exceeds the 
Maximum Fragment Size, that line will be output in a single split file which 
exceeds the configured maximum size limit. "
+    "This component also allows one to specify that each split should include 
a header lines. Header lines can be computed by either specifying the amount of 
lines that should constitute a header "
+    "or by using header marker to match against the read lines. If such match 
happens then the corresponding line will be treated as header. Keep in mind 
that upon the first failure of header "
+    "marker match, no more matches will be performed and the rest of the data 
will be parsed as regular lines for a given split. If after computation of the 
header there are no more data, "
+    "the resulting split will consists of only header lines.";
+
+  EXTENSIONAPI static constexpr auto LineSplitCount = 
core::PropertyDefinitionBuilder<>::createProperty("Line Split Count")
+      .withDescription("The number of lines that will be added to each split 
file, excluding header lines. A value of zero requires Maximum Fragment Size to 
be set, and line count will not "
+        "be considered in determining splits.")
+      .withPropertyType(core::StandardPropertyTypes::UNSIGNED_LONG_TYPE)
+      .isRequired(true)
+      .build();
+  EXTENSIONAPI static constexpr auto MaximumFragmentSize = 
core::PropertyDefinitionBuilder<>::createProperty("Maximum Fragment Size")
+      .withDescription("The maximum size of each split file, including header 
lines. NOTE: in the case where a single line exceeds this property (including 
headers, if applicable), "
+        "that line will be output in a split of its own which exceeds this 
Maximum Fragment Size setting.")
+      .withPropertyType(core::StandardPropertyTypes::DATA_SIZE_TYPE)
+      .build();
+  EXTENSIONAPI static constexpr auto HeaderLineCount = 
core::PropertyDefinitionBuilder<>::createProperty("Header Line Count")
+      .withDescription("The number of lines that should be considered part of 
the header; the header lines will be duplicated to all split files.")
+      .withPropertyType(core::StandardPropertyTypes::UNSIGNED_LONG_TYPE)
+      .withDefaultValue("0")
+      .isRequired(true)
+      .build();
+  EXTENSIONAPI static constexpr auto HeaderLineMarkerCharacters = 
core::PropertyDefinitionBuilder<>::createProperty("Header Line Marker 
Characters")
+      .withDescription("The first character(s) on the line of the datafile 
which signifies a header line. This value is ignored when Header Line Count is 
non-zero. The first line not containing "
+        "the Header Line Marker Characters and all subsequent lines are 
considered non-header")
+      .build();
+  EXTENSIONAPI static constexpr auto RemoveTrailingNewlines = 
core::PropertyDefinitionBuilder<>::createProperty("Remove Trailing Newlines")
+      .withDescription("Whether to remove newlines at the end of each split 
file. This should be false if you intend to merge the split files later. If 
this is set to 'true' and a FlowFile is "
+        "generated that contains only 'empty lines' (i.e., consists only of 
and characters), the FlowFile will not be emitted. Note, however, that if 
header lines are specified, the resultant "
+        "FlowFile will never be empty as it will consist of the header lines, 
so a FlowFile may be emitted that contains only the header lines.")
+      .withPropertyType(core::StandardPropertyTypes::BOOLEAN_TYPE)
+      .withDefaultValue("true")
+      .isRequired(true)
+      .build();
+
+  EXTENSIONAPI static constexpr auto Properties = 
std::array<core::PropertyReference, 5>{
+      LineSplitCount,
+      MaximumFragmentSize,
+      HeaderLineCount,
+      HeaderLineMarkerCharacters,
+      RemoveTrailingNewlines
+  };
+
+  EXTENSIONAPI static constexpr auto Failure =
+    core::RelationshipDefinition{"failure", "If a file cannot be split for 
some reason, the original file will be routed to this destination and nothing 
will be routed elsewhere"};
+  EXTENSIONAPI static constexpr auto Original =
+    core::RelationshipDefinition{"original", "The original input file will be 
routed to this destination when it has been successfully split into 1 or more 
files"};
+  EXTENSIONAPI static constexpr auto Splits =
+    core::RelationshipDefinition{"splits", "The split files will be routed to 
this destination when an input file is successfully split into 1 or more split 
files"};
+  EXTENSIONAPI static constexpr auto Relationships = std::array{Failure, 
Original, Splits};
+
+  EXTENSIONAPI static constexpr auto TextLineCountOutputAttribute =
+    core::OutputAttributeDefinition<0>{"text.line.count", {}, "The number of 
lines of text from the original FlowFile that were copied to this FlowFile 
(does not count empty lines)"};
+  EXTENSIONAPI static constexpr auto FragmentSizeOutputAttribute =
+    core::OutputAttributeDefinition<0>{"fragment.size", {},
+      "The number of bytes from the original FlowFile that were copied to this 
FlowFile, including header, if applicable, which is duplicated in each split 
FlowFile"};
+  EXTENSIONAPI static constexpr auto FragmentIdentifierOutputAttribute =
+    core::OutputAttributeDefinition<0>{"fragment.identifier", {}, "All split 
FlowFiles produced from the same parent FlowFile will have the same randomly 
generated UUID added for this attribute"};
+  EXTENSIONAPI static constexpr auto FragmentIndexOutputAttribute =
+    core::OutputAttributeDefinition<0>{"fragment.index", {}, "A one-up number 
that indicates the ordering of the split FlowFiles that were created from a 
single parent FlowFile"};
+  EXTENSIONAPI static constexpr auto FragmentCountOutputAttribute =
+    core::OutputAttributeDefinition<0>{"fragment.count", {}, "The number of 
split FlowFiles generated from the parent FlowFile"};
+  EXTENSIONAPI static constexpr auto SegmentOriginalFilenameOutputAttribute =
+    core::OutputAttributeDefinition<0>{"segment.original.filename", {}, "The 
filename of the parent FlowFile"};
+  EXTENSIONAPI static constexpr auto OutputAttributes = 
std::array<core::OutputAttributeReference, 6>{TextLineCountOutputAttribute, 
FragmentSizeOutputAttribute, FragmentIdentifierOutputAttribute,
+    FragmentIndexOutputAttribute, FragmentCountOutputAttribute, 
SegmentOriginalFilenameOutputAttribute};
+
+  EXTENSIONAPI static constexpr bool SupportsDynamicProperties = true;
+  EXTENSIONAPI static constexpr bool SupportsDynamicRelationships = false;
+  EXTENSIONAPI static constexpr core::annotation::Input InputRequirement = 
core::annotation::Input::INPUT_REQUIRED;
+  EXTENSIONAPI static constexpr bool IsSingleThreaded = false;
+  ADD_COMMON_VIRTUAL_FUNCTIONS_FOR_PROCESSORS
+
+  void onSchedule(const std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSessionFactory> &session_factory) override;
+  void onTrigger(const std::shared_ptr<core::ProcessContext> &context, const 
std::shared_ptr<core::ProcessSession> &session) override;
+  void initialize() override;
+
+  class ReadCallback {

Review Comment:
   Does `ReadCallback` need to be in the `SplitText` class?  I think it would 
be better to move it outside, into the `detail` namespace, if possible.



##########
extensions/standard-processors/tests/unit/SplitTextTests.cpp:
##########
@@ -0,0 +1,860 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "FlowFileRecord.h"
+#include "TestBase.h"
+#include "Catch.h"
+#include "processors/SplitText.h"
+#include "SingleProcessorTestController.h"
+#include "io/BufferStream.h"
+
+namespace org::apache::nifi::minifi::test {
+
+TEST_CASE("Test LineReader with nullptr") {
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with empty stream") {
+  auto stream = std::make_shared<io::BufferStream>();
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 10, 
.endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader without trailing endlines") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 9, .endline_size 
= 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size +1 , .size = 
second_line_size + 1, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2 - 
1, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size + 1, .size = 
second_line_size, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, 
'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with starts with filter") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "header this is a new line\nheader and another 
line\r\nthirdline\nheader line\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 26, .endline_size 
= 1, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 26, .size = 25, 
.endline_size = 2, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 51, .size = 10, 
.endline_size = 1, .matches_starts_with = false});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 61, .size = 12, 
.endline_size = 1, .matches_starts_with = true});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+struct ExpectedSplitTextResult {
+  std::string content;
+  uint64_t fragment_index = 0;
+  uint64_t fragment_count = 0;
+  uint64_t text_line_count = 0;
+};
+
+struct SplitTextProperties {
+  uint64_t line_split_count = 0;
+  std::optional<bool> trim_trailing_newlines;
+  std::optional<uint64_t> maximum_fragment_size;
+  std::optional<uint64_t> header_line_count;
+  std::optional<std::string> header_line_marker_characters;
+};
+
+void verifySplitResults(const SingleProcessorTestController& controller, const 
ProcessorTriggerResult& trigger_results, const 
std::vector<ExpectedSplitTextResult>& expected_results) {
+  REQUIRE(trigger_results.at(processors::SplitText::Splits).size() == 
expected_results.size());
+  std::string identifier;
+  for (size_t i = 0; i < expected_results.size(); ++i) {
+    
CHECK(controller.plan->getContent(trigger_results.at(processors::SplitText::Splits)[i])
 == expected_results[i].content);
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::TextLineCountOutputAttribute.name)
 == std::to_string(expected_results[i].text_line_count));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentSizeOutputAttribute.name)
 == std::to_string(expected_results[i].content.size()));

Review Comment:
   very minor, but introducing a
   ```c++
   const auto& actual_results = 
trigger_results.at(processors::SplitText::Splits)
   ```
   alias before the loop would make the code below shorter, and in my opinion 
more readable



##########
PROCESSORS.md:
##########
@@ -2862,6 +2863,44 @@ In the list below, the names of required properties 
appear in bold. Any other pr
 | success | All files, containing log events, are routed to success |
 
 
+## SplitText
+
+### Description
+
+Splits a text file into multiple smaller text files on line boundaries limited 
by maximum number of lines or total size of fragment. Each output split file 
will contain no more than the configured number of lines or bytes. If both Line 
Split Count and Maximum Fragment Size are specified, the split occurs at 
whichever limit is reached first. If the first line of a fragment exceeds the 
Maximum Fragment Size, that line will be output in a single split file which 
exceeds the configured maximum size limit. This component also allows one to 
specify that each split should include a header lines. Header lines can be 
computed by either specifying the amount of lines that should constitute a 
header or by using header marker to match against the read lines. If such match 
happens then the corresponding line will be treated as header. Keep in mind 
that upon the first failure of header marker match, no more matches will be 
performed and the rest of the data will be parsed as regular lines for a g
 iven split. If after computation of the header there are no more data, the 
resulting split will consists of only header lines.
+
+### Properties
+
+In the list below, the names of required properties appear in bold. Any other 
properties (not in bold) are considered optional. The table also indicates any 
default values, and whether a property supports the NiFi Expression Language.
+
+| Name                          | Default Value | Allowable Values | 
Description                                                                     
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
      |
+|-------------------------------|---------------|------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| **Line Split Count**          |               |                  | The 
number of lines that will be added to each split file, excluding header lines. 
A value of zero requires Maximum Fragment Size to be set, and line count will 
not be considered in determining splits.                                        
                                                                                
                                                                                
                                                                                
     |
+| Maximum Fragment Size         |               |                  | The 
maximum size of each split file, including header lines. NOTE: in the case 
where a single line exceeds this property (including headers, if applicable), 
that line will be output in a split of its own which exceeds this Maximum 
Fragment Size setting.                                                          
                                                                                
                                                                                
               |
+| **Header Line Count**         | 0             |                  | The 
number of lines that should be considered part of the header; the header lines 
will be duplicated to all split files.                                          
                                                                                
                                                                                
                                                                                
                                                                                
   |
+| Header Line Marker Characters |               |                  | The first 
character(s) on the line of the datafile which signifies a header line. This 
value is ignored when Header Line Count is non-zero. The first line not 
containing the Header Line Marker Characters and all subsequent lines are 
considered non-header                                                           
                                                                                
                                                                                
             |
+| **Remove Trailing Newlines**  | true          | true<br/>false   | Whether 
to remove newlines at the end of each split file. This should be false if you 
intend to merge the split files later. If this is set to 'true' and a FlowFile 
is generated that contains only 'empty lines' (i.e., consists only of and 
characters), the FlowFile will not be emitted. Note, however, that if header 
lines are specified, the resultant FlowFile will never be empty as it will 
consist of the header lines, so a FlowFile may be emitted that contains only 
the header lines. |

Review Comment:
   This is a typo in NiFi, but we don't have to be typo-for-typo compatible :)
   ```suggestion
   | **Remove Trailing Newlines**  | true          | true<br/>false   | Whether 
to remove newlines at the end of each split file. This should be false if you 
intend to merge the split files later. If this is set to 'true' and a FlowFile 
is generated that contains only 'empty lines' (i.e., consists only of \r and \n 
characters), the FlowFile will not be emitted. Note, however, that if header 
lines are specified, the resultant FlowFile will never be empty as it will 
consist of the header lines, so a FlowFile may be emitted that contains only 
the header lines. |
   ```



##########
extensions/standard-processors/processors/SplitText.cpp:
##########
@@ -0,0 +1,383 @@
+/**
+ * @file SplitText.cpp
+ * SplitText class implementation
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "SplitText.h"
+#include "core/ProcessContext.h"
+#include "core/ProcessSession.h"
+#include "core/Resource.h"
+#include "core/FlowFile.h"
+#include "utils/gsl.h"
+#include "utils/ProcessorConfigUtils.h"
+
+namespace org::apache::nifi::minifi::processors {
+
+namespace detail {
+
+LineReader::LineReader(const std::shared_ptr<io::InputStream>& stream)
+    : stream_(stream) {
+  if (!stream_ || stream_->size() == 0) {
+    state_ = StreamReadState::EndOfStream;
+  }
+}
+
+uint8_t LineReader::getEndLineSize(size_t newline_index) {
+  gsl_Expects(buffer_.size() > newline_index);
+  if (buffer_[newline_index] != '\n') {
+    return 0;
+  }
+  if (newline_index == 0 || buffer_[newline_index - 1] != '\r') {
+    return 1;
+  }
+  return 2;
+}
+
+void LineReader::setLastLineInfoAttributes(uint8_t endline_size, const 
std::optional<std::string>& starts_with) {
+  const uint64_t size_from_beginning_of_stream = (current_buffer_count_ - 1) * 
SPLIT_TEXT_BUFFER_SIZE + buffer_offset_;
+  if (last_line_info_) {
+    LineInfo previous_line_info = *last_line_info_;
+    last_line_info_->offset = previous_line_info.offset + 
previous_line_info.size;
+    last_line_info_->size = size_from_beginning_of_stream - 
previous_line_info.offset - previous_line_info.size;
+    last_line_info_->endline_size = endline_size;
+    last_line_info_->matches_starts_with = true;
+  } else {
+    last_line_info_ = LineInfo{.offset = 0, .size = read_size_ - 
last_read_size_ + buffer_offset_, .endline_size = endline_size, 
.matches_starts_with = true};
+  }
+
+  if (starts_with) {
+    last_line_info_->matches_starts_with = last_line_info_->size >= 
starts_with->size() &&
+      std::equal(starts_with->begin(), starts_with->end(), buffer_.begin() + 
last_line_info_->offset, buffer_.begin() + last_line_info_->offset + 
starts_with->size());
+  }
+}
+
+bool LineReader::readNextBuffer() {
+  buffer_offset_ = 0;
+  last_read_size_ = (std::min)(gsl::narrow<size_t>(stream_->size() - 
read_size_), SPLIT_TEXT_BUFFER_SIZE);
+  const auto read_ret = 
stream_->read(as_writable_bytes(std::span(buffer_).subspan(0, 
last_read_size_)));
+  read_size_ += read_ret;
+  if (io::isError(read_ret)) {
+    state_ = StreamReadState::StreamReadError;
+    return false;
+  }
+  ++current_buffer_count_;
+  return true;
+}
+
+std::optional<LineReader::LineInfo> LineReader::finalizeLineInfo(uint8_t 
endline_size, const std::optional<std::string>& starts_with) {
+  setLastLineInfoAttributes(endline_size, starts_with);
+  if (last_line_info_->size == 0) {
+    return std::nullopt;
+  }
+  return last_line_info_;
+}
+
+std::optional<LineReader::LineInfo> LineReader::readNextLine(const 
std::optional<std::string>& starts_with) {
+  if (state_ != StreamReadState::Ok) {
+    return std::nullopt;
+  }
+
+  const auto isLastReadProcessed = [this]() { return last_read_size_ <= 
buffer_offset_; };
+  while (read_size_ < stream_->size() || !isLastReadProcessed()) {
+    if (isLastReadProcessed() && !readNextBuffer()) {
+      return std::nullopt;
+    }
+
+    for (auto i = buffer_offset_; i < last_read_size_; ++i) {
+      if (buffer_[i] == '\n') {
+        buffer_offset_ = i + 1;
+        return finalizeLineInfo(getEndLineSize(i), starts_with);
+      }
+    }
+    buffer_offset_ = last_read_size_;
+  }
+
+  state_ = StreamReadState::EndOfStream;
+  return finalizeLineInfo(0, starts_with);
+}
+
+SplitTextFragmentGenerator::SplitTextFragmentGenerator(const 
std::shared_ptr<io::InputStream>& stream, const SplitTextConfiguration& 
split_text_config)
+    : line_reader_(stream),
+      split_text_config_(split_text_config) {
+}
+
+void SplitTextFragmentGenerator::finalizeFragmentOffset(Fragment& 
current_fragment) {
+  current_fragment.fragment_offset = flow_file_offset_;
+  flow_file_offset_ += current_fragment.fragment_size;
+}
+
+void SplitTextFragmentGenerator::addLineToFragment(Fragment& current_fragment, 
const LineReader::LineInfo& line) {
+  if (line.endline_size == line.size) {  // if line consists only of endline 
characters, we need to append the fragment trim size
+    current_fragment.endline_size += line.endline_size;
+  } else {
+    current_fragment.endline_size = line.endline_size;
+  }
+  current_fragment.text_line_count += line.endline_size == line.size ? 0 : 1;
+  current_fragment.fragment_size += line.size;
+}
+
+bool SplitTextFragmentGenerator::lineSizeWouldExceedMaxFragmentSize(const 
LineReader::LineInfo& line, uint64_t fragment_size) const {
+  return split_text_config_.maximum_fragment_size && fragment_size + line.size 
+ header_fragment_size_ > split_text_config_.maximum_fragment_size.value();
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::createHeaderFragmentUsingLineCount() {
+  Fragment header_fragment;
+  for (uint64_t i = 0; i < split_text_config_.header_line_count; ++i) {
+    auto line = line_reader_.readNextLine();
+    if (!line) {
+      if (getState() == StreamReadState::EndOfStream) {
+        return nonstd::make_unexpected("The flow file's line count is less 
than the specified header line count!");
+      } else {
+        return nonstd::make_unexpected("Error while reading flow file 
stream!");
+      }
+    }
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
header_fragment.fragment_size)) {
+      return nonstd::make_unexpected("Header line would exceed the maximum 
fragment size!");
+    }
+
+    addLineToFragment(header_fragment, *line);
+  }
+
+  flow_file_offset_ += header_fragment.fragment_size;
+  header_fragment_size_ = header_fragment.fragment_size;
+  return header_fragment;
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::createHeaderFragmentUsingHeaderMarkerCharacters() {
+  Fragment header_fragment;
+  while (auto line = 
line_reader_.readNextLine(split_text_config_.header_line_marker_characters)) {
+    if (line->size < split_text_config_.header_line_marker_characters->size() 
|| !line->matches_starts_with) {
+      buffered_line_info_ = line;
+      break;
+    }
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
header_fragment.fragment_size)) {
+      return nonstd::make_unexpected("Header line would exceed the maximum 
fragment size!");
+    }
+
+    addLineToFragment(header_fragment, *line);
+  }
+
+  flow_file_offset_ += header_fragment.fragment_size;
+  header_fragment_size_ = header_fragment.fragment_size;
+  return header_fragment;
+}
+
+nonstd::expected<SplitTextFragmentGenerator::Fragment, std::string> 
SplitTextFragmentGenerator::readHeaderFragment() {
+  gsl_Expects(flow_file_offset_ == 0);
+  if (split_text_config_.header_line_count == 0 && 
!split_text_config_.header_line_marker_characters) {
+    return nonstd::make_unexpected("No header properties were set!");
+  }
+
+  if (split_text_config_.header_line_count > 0) {
+    return createHeaderFragmentUsingLineCount();
+  }
+
+  return createHeaderFragmentUsingHeaderMarkerCharacters();
+}
+
+std::optional<SplitTextFragmentGenerator::Fragment> 
SplitTextFragmentGenerator::readNextFragment() {
+  Fragment current_fragment;
+  while (auto line = buffered_line_info_ ? buffered_line_info_ : 
line_reader_.readNextLine()) {
+    buffered_line_info_.reset();
+    if (lineSizeWouldExceedMaxFragmentSize(*line, 
current_fragment.fragment_size)) {
+      if (current_fragment.processed_line_count == 0) {  // first fragment 
line would be bigger than maximum fragment size (we don't have any other line 
in the fragment yet)
+        addLineToFragment(current_fragment, *line);
+      } else {
+        buffered_line_info_ = line;
+      }
+
+      finalizeFragmentOffset(current_fragment);
+      return current_fragment;
+    }
+
+    ++current_fragment.processed_line_count;
+    addLineToFragment(current_fragment, *line);
+    if (split_text_config_.line_split_count == 
current_fragment.processed_line_count) {
+      finalizeFragmentOffset(current_fragment);
+      return current_fragment;
+    }
+  }
+
+  if (current_fragment.fragment_size > 0) {
+    finalizeFragmentOffset(current_fragment);
+    return current_fragment;
+  }
+  return std::nullopt;
+}
+
+}  // namespace detail
+
+void SplitText::initialize() {
+  setSupportedProperties(Properties);
+  setSupportedRelationships(Relationships);
+}
+
+void SplitText::onSchedule(const std::shared_ptr<core::ProcessContext> 
&context, const std::shared_ptr<core::ProcessSessionFactory>& 
/*sessionFactory*/) {
+  gsl_Expects(context);
+  split_text_config_.line_split_count = 
utils::getRequiredPropertyOrThrow<uint64_t>(*context, LineSplitCount.name);
+  logger_->log_debug("SplitText line split count: {}", 
split_text_config_.line_split_count);
+  auto max_fragment_data_size_value = 
context->getProperty<core::DataSizeValue>(MaximumFragmentSize);
+  if (max_fragment_data_size_value) {
+    split_text_config_.maximum_fragment_size = 
max_fragment_data_size_value->getValue();
+    logger_->log_debug("SplitText maximum fragment size: {}", 
split_text_config_.maximum_fragment_size.value());
+  }
+  if (split_text_config_.maximum_fragment_size && 
split_text_config_.maximum_fragment_size.value() == 0) {
+    throw Exception(PROCESS_SCHEDULE_EXCEPTION, "Maximum Fragment Size cannot 
be 0!");
+  }
+  if (split_text_config_.line_split_count == 0 && 
!split_text_config_.maximum_fragment_size) {
+    throw Exception(PROCESS_SCHEDULE_EXCEPTION, "Line Split Count is set to 0, 
but Maximum Fragment Size is not set!");
+  }
+  split_text_config_.header_line_count = 
utils::getRequiredPropertyOrThrow<uint64_t>(*context, HeaderLineCount.name);
+  logger_->log_debug("SplitText header line count: {}", 
split_text_config_.header_line_count);
+  split_text_config_.header_line_marker_characters = 
context->getProperty(HeaderLineMarkerCharacters);
+  if (split_text_config_.header_line_marker_characters && 
split_text_config_.header_line_marker_characters->size() >= 
detail::SPLIT_TEXT_BUFFER_SIZE) {
+    throw Exception(PROCESS_SCHEDULE_EXCEPTION, fmt::format("SplitText header 
line marker characters length is larger than the maximum allowed: {}", 
detail::SPLIT_TEXT_BUFFER_SIZE));
+  }
+  if (split_text_config_.header_line_marker_characters) {
+    logger_->log_debug("SplitText header line marker characters were set: {}", 
*split_text_config_.header_line_marker_characters);
+  }
+  split_text_config_.remove_trailing_new_lines = 
utils::getRequiredPropertyOrThrow<bool>(*context, RemoveTrailingNewlines.name);
+  logger_->log_debug("SplitText should remove trailing new lines: {}", 
split_text_config_.remove_trailing_new_lines ? "true" : "false");

Review Comment:
   `fmt::format` can do this automagically:
   ```suggestion
     logger_->log_debug("SplitText should remove trailing new lines: {}", 
split_text_config_.remove_trailing_new_lines);
   ```



##########
extensions/standard-processors/tests/unit/SplitTextTests.cpp:
##########
@@ -0,0 +1,860 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "FlowFileRecord.h"
+#include "TestBase.h"
+#include "Catch.h"
+#include "processors/SplitText.h"
+#include "SingleProcessorTestController.h"
+#include "io/BufferStream.h"
+
+namespace org::apache::nifi::minifi::test {
+
+TEST_CASE("Test LineReader with nullptr") {
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with empty stream") {
+  auto stream = std::make_shared<io::BufferStream>();
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 10, 
.endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader without trailing endlines") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 9, .endline_size 
= 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size +1 , .size = 
second_line_size + 1, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2 - 
1, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size + 1, .size = 
second_line_size, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, 
'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with starts with filter") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "header this is a new line\nheader and another 
line\r\nthirdline\nheader line\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 26, .endline_size 
= 1, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 26, .size = 25, 
.endline_size = 2, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 51, .size = 10, 
.endline_size = 1, .matches_starts_with = false});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 61, .size = 12, 
.endline_size = 1, .matches_starts_with = true});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+struct ExpectedSplitTextResult {
+  std::string content;
+  uint64_t fragment_index = 0;
+  uint64_t fragment_count = 0;
+  uint64_t text_line_count = 0;
+};
+
+struct SplitTextProperties {
+  uint64_t line_split_count = 0;
+  std::optional<bool> trim_trailing_newlines;
+  std::optional<uint64_t> maximum_fragment_size;
+  std::optional<uint64_t> header_line_count;
+  std::optional<std::string> header_line_marker_characters;
+};
+
+void verifySplitResults(const SingleProcessorTestController& controller, const 
ProcessorTriggerResult& trigger_results, const 
std::vector<ExpectedSplitTextResult>& expected_results) {
+  REQUIRE(trigger_results.at(processors::SplitText::Splits).size() == 
expected_results.size());
+  std::string identifier;
+  for (size_t i = 0; i < expected_results.size(); ++i) {
+    
CHECK(controller.plan->getContent(trigger_results.at(processors::SplitText::Splits)[i])
 == expected_results[i].content);
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::TextLineCountOutputAttribute.name)
 == std::to_string(expected_results[i].text_line_count));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentSizeOutputAttribute.name)
 == std::to_string(expected_results[i].content.size()));
+    if (i > 0) {
+      
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentIdentifierOutputAttribute.name).value()
 == identifier);
+    } else {
+      identifier = 
trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentIdentifierOutputAttribute.name).value();
+      CHECK(!identifier.empty());
+    }
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(core::SpecialFlowAttribute::FILENAME)
 ==
+      "a.foo.fragment." + identifier + "." + 
std::to_string(expected_results[i].fragment_index));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentIndexOutputAttribute.name)
 == std::to_string(expected_results[i].fragment_index));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentCountOutputAttribute.name)
 == std::to_string(expected_results[i].fragment_count));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::SegmentOriginalFilenameOutputAttribute.name)
 == "a.foo");
+  }
+}
+
+void runSplitTextTest(const std::string& input, const 
std::vector<ExpectedSplitTextResult>& expected_results, const 
SplitTextProperties& properties) {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, 
std::to_string(properties.line_split_count));
+  if (properties.maximum_fragment_size) {
+    split_text->setProperty(processors::SplitText::MaximumFragmentSize, 
std::to_string(*properties.maximum_fragment_size) + " B");
+  }
+  if (properties.trim_trailing_newlines) {
+    split_text->setProperty(processors::SplitText::RemoveTrailingNewlines, 
properties.trim_trailing_newlines.value() ? "true" : "false");
+  }
+  if (properties.header_line_count) {
+    split_text->setProperty(processors::SplitText::HeaderLineCount, 
std::to_string(*properties.header_line_count));
+  }
+  if (properties.header_line_marker_characters) {
+    split_text->setProperty(processors::SplitText::HeaderLineMarkerCharacters, 
*properties.header_line_marker_characters);
+  }
+  const auto trigger_results = controller.trigger(input, 
{{std::string(core::SpecialFlowAttribute::FILENAME), "a.foo"}});
+  CHECK(trigger_results.at(processors::SplitText::Failure).empty());
+  CHECK(trigger_results.at(processors::SplitText::Original).size() == 1);
+  
CHECK(trigger_results.at(processors::SplitText::Original)[0]->getAttribute(core::SpecialFlowAttribute::FILENAME)
 == "a.foo");
+  
CHECK(controller.plan->getContent(trigger_results.at(processors::SplitText::Original)[0])
 == input);
+  verifySplitResults(controller, trigger_results, expected_results);
+}
+
+TEST_CASE("Line Split Count property is required") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+TEST_CASE("Line Split Count property can only be 0 if Maximum Fragment Size is 
set") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "0");
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+TEST_CASE("Maximum Fragment Size cannot be set to 0") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "0");
+  split_text->setProperty(processors::SplitText::MaximumFragmentSize, "0 B");
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+TEST_CASE("Header Line Marker Characters size cannot be equal or larger than 
split text buffer size") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "1");
+  std::string 
header_marker_character(static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE),
 'A');
+  split_text->setProperty(processors::SplitText::HeaderLineMarkerCharacters, 
header_marker_character);
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+
+TEST_CASE("SplitText only forwards empty flowfile") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "1");
+  const auto trigger_results = controller.trigger("", 
{{std::string(core::SpecialFlowAttribute::FILENAME), "a.foo"}});
+  CHECK(trigger_results.at(processors::SplitText::Splits).empty());
+  CHECK(trigger_results.at(processors::SplitText::Failure).empty());
+  CHECK(trigger_results.at(processors::SplitText::Original).size() == 1);
+  
CHECK(trigger_results.at(processors::SplitText::Original)[0]->getAttribute(core::SpecialFlowAttribute::FILENAME)
 == "a.foo");
+  
CHECK(controller.plan->getContent(trigger_results.at(processors::SplitText::Original)[0]).empty());
+}
+
+TEST_CASE("SplitText creates new flow file for a single line") {
+  std::vector<ExpectedSplitTextResult> expected_results(1, 
ExpectedSplitTextResult{});
+  expected_results[0].fragment_index = 1;
+  expected_results[0].fragment_count = 1;
+  expected_results[0].text_line_count = 1;
+  std::string line;
+  SECTION("Empty line with LF endline") {
+    line = "\n";
+    expected_results[0].content = line;
+    expected_results[0].text_line_count = 0;
+  }
+  SECTION("LF endline") {
+    line = "this is a new line\n";
+    expected_results[0].content = line;
+  }
+  SECTION("CRLF endline") {
+    line = "this is a new line\r\n";
+    expected_results[0].content = line;
+  }
+  SECTION("Line size larger than buffer size") {
+    line = 
std::string(static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 
1.5), 'a') + "\n";
+    expected_results[0].content = line;
+  }
+  SECTION("Content without endline is a single line") {
+    line = "this is a new line";
+    expected_results[0].content = line;
+  }
+
+  SplitTextProperties properties;
+  properties.line_split_count = 1;
+  properties.trim_trailing_newlines = false;
+  runSplitTextTest(line, expected_results, properties);
+}
+
+TEST_CASE("SplitText creates new flow file with 2 lines") {
+  std::vector<ExpectedSplitTextResult> expected_results(1, 
ExpectedSplitTextResult{});
+  expected_results[0].fragment_index = 1;
+  expected_results[0].fragment_count = 1;
+  expected_results[0].text_line_count = 2;
+  std::string input;
+  bool remove_trailing_endline = false;
+  SECTION("Only LF endlines") {
+    input = "\n\n";
+    expected_results[0].text_line_count = 0;
+    expected_results[0].content = input;
+  }
+  SECTION("LF endline") {
+    input = "this is a new line\nand another line\n";
+    expected_results[0].content = input;
+  }
+  SECTION("LF endline removing trailing endlines") {
+    input = "this is a new line\nand another line\n\n";
+    remove_trailing_endline = true;
+    expected_results[0].content = "this is a new line\nand another line";
+  }
+  SECTION("CRLF endline") {
+    input = "this is a new line\r\nand another line\r\n";
+    expected_results[0].content = input;
+  }
+  SECTION("CRLF endline removing trailing endlines") {
+    input = "this is a new line\r\nand another line\r\n\r\n";
+    remove_trailing_endline = true;
+    expected_results[0].content = "this is a new line\r\nand another line";
+  }
+  SECTION("Line size larger than buffer size") {
+    std::string 
str(static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5), 'a');
+    input = str + "\n" + str + "\n";
+    expected_results[0].content = input;
+  }
+  SECTION("Line size larger than buffer size without endline at the end") {
+    std::string 
str(static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5), 'a');
+    input = str + "\n" + str;
+    expected_results[0].content = input;
+  }
+
+  SplitTextProperties properties;
+  properties.line_split_count = 2;
+  properties.trim_trailing_newlines = remove_trailing_endline;
+  runSplitTextTest(input, expected_results, properties);
+}
+
+TEST_CASE("SplitText creates seperate flow files from 2 lines") {

Review Comment:
   typo: seperate -> separate



##########
extensions/standard-processors/tests/unit/SplitTextTests.cpp:
##########
@@ -0,0 +1,860 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "FlowFileRecord.h"
+#include "TestBase.h"
+#include "Catch.h"
+#include "processors/SplitText.h"
+#include "SingleProcessorTestController.h"
+#include "io/BufferStream.h"
+
+namespace org::apache::nifi::minifi::test {
+
+TEST_CASE("Test LineReader with nullptr") {
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with empty stream") {
+  auto stream = std::make_shared<io::BufferStream>();
+  processors::detail::LineReader reader{nullptr};
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 10, 
.endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader without trailing endlines") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "this is a new line\nand another line\r\nthirdline";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 19, .endline_size 
= 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 19, .size = 18, 
.endline_size = 2});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 37, .size = 9, .endline_size 
= 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size +1 , .size = 
second_line_size + 1, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2 - 
1, 'b') + "\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 1});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input larger than buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  const auto first_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.5);
+  const auto second_line_size = 
static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 1.7);
+  std::string input = std::string(first_line_size, 'a') + "\n" + 
std::string(second_line_size, 'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = first_line_size + 
1, .endline_size = 1});
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = first_line_size + 1, .size = 
second_line_size, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with input of same size as buffer length without 
trailing endline") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE - 
1, 'a') + "\n" + std::string(processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, 
'b');
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine() == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .endline_size = 1});
+  CHECK(*reader.readNextLine() ==
+    processors::detail::LineReader::LineInfo{.offset = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE, .size = 
processors::detail::SPLIT_TEXT_BUFFER_SIZE * 2, .endline_size = 0});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+TEST_CASE("Test LineReader with starts with filter") {
+  auto stream = std::make_shared<io::BufferStream>();
+  std::string input = "header this is a new line\nheader and another 
line\r\nthirdline\nheader line\n";
+  stream->write(reinterpret_cast<const uint8_t*>(input.data()), input.size());
+  processors::detail::LineReader reader{stream};
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 0, .size = 26, .endline_size 
= 1, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 26, .size = 25, 
.endline_size = 2, .matches_starts_with = true});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 51, .size = 10, 
.endline_size = 1, .matches_starts_with = false});
+  CHECK(*reader.readNextLine("header") == 
processors::detail::LineReader::LineInfo{.offset = 61, .size = 12, 
.endline_size = 1, .matches_starts_with = true});
+  CHECK(reader.readNextLine() == std::nullopt);
+  CHECK(reader.getState() == processors::detail::StreamReadState::EndOfStream);
+}
+
+struct ExpectedSplitTextResult {
+  std::string content;
+  uint64_t fragment_index = 0;
+  uint64_t fragment_count = 0;
+  uint64_t text_line_count = 0;
+};
+
+struct SplitTextProperties {
+  uint64_t line_split_count = 0;
+  std::optional<bool> trim_trailing_newlines;
+  std::optional<uint64_t> maximum_fragment_size;
+  std::optional<uint64_t> header_line_count;
+  std::optional<std::string> header_line_marker_characters;
+};
+
+void verifySplitResults(const SingleProcessorTestController& controller, const 
ProcessorTriggerResult& trigger_results, const 
std::vector<ExpectedSplitTextResult>& expected_results) {
+  REQUIRE(trigger_results.at(processors::SplitText::Splits).size() == 
expected_results.size());
+  std::string identifier;
+  for (size_t i = 0; i < expected_results.size(); ++i) {
+    
CHECK(controller.plan->getContent(trigger_results.at(processors::SplitText::Splits)[i])
 == expected_results[i].content);
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::TextLineCountOutputAttribute.name)
 == std::to_string(expected_results[i].text_line_count));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentSizeOutputAttribute.name)
 == std::to_string(expected_results[i].content.size()));
+    if (i > 0) {
+      
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentIdentifierOutputAttribute.name).value()
 == identifier);
+    } else {
+      identifier = 
trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentIdentifierOutputAttribute.name).value();
+      CHECK(!identifier.empty());
+    }
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(core::SpecialFlowAttribute::FILENAME)
 ==
+      "a.foo.fragment." + identifier + "." + 
std::to_string(expected_results[i].fragment_index));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentIndexOutputAttribute.name)
 == std::to_string(expected_results[i].fragment_index));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::FragmentCountOutputAttribute.name)
 == std::to_string(expected_results[i].fragment_count));
+    
CHECK(trigger_results.at(processors::SplitText::Splits)[i]->getAttribute(processors::SplitText::SegmentOriginalFilenameOutputAttribute.name)
 == "a.foo");
+  }
+}
+
+void runSplitTextTest(const std::string& input, const 
std::vector<ExpectedSplitTextResult>& expected_results, const 
SplitTextProperties& properties) {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, 
std::to_string(properties.line_split_count));
+  if (properties.maximum_fragment_size) {
+    split_text->setProperty(processors::SplitText::MaximumFragmentSize, 
std::to_string(*properties.maximum_fragment_size) + " B");
+  }
+  if (properties.trim_trailing_newlines) {
+    split_text->setProperty(processors::SplitText::RemoveTrailingNewlines, 
properties.trim_trailing_newlines.value() ? "true" : "false");
+  }
+  if (properties.header_line_count) {
+    split_text->setProperty(processors::SplitText::HeaderLineCount, 
std::to_string(*properties.header_line_count));
+  }
+  if (properties.header_line_marker_characters) {
+    split_text->setProperty(processors::SplitText::HeaderLineMarkerCharacters, 
*properties.header_line_marker_characters);
+  }
+  const auto trigger_results = controller.trigger(input, 
{{std::string(core::SpecialFlowAttribute::FILENAME), "a.foo"}});
+  CHECK(trigger_results.at(processors::SplitText::Failure).empty());
+  CHECK(trigger_results.at(processors::SplitText::Original).size() == 1);
+  
CHECK(trigger_results.at(processors::SplitText::Original)[0]->getAttribute(core::SpecialFlowAttribute::FILENAME)
 == "a.foo");
+  
CHECK(controller.plan->getContent(trigger_results.at(processors::SplitText::Original)[0])
 == input);
+  verifySplitResults(controller, trigger_results, expected_results);
+}
+
+TEST_CASE("Line Split Count property is required") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+TEST_CASE("Line Split Count property can only be 0 if Maximum Fragment Size is 
set") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "0");
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+TEST_CASE("Maximum Fragment Size cannot be set to 0") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "0");
+  split_text->setProperty(processors::SplitText::MaximumFragmentSize, "0 B");
+  REQUIRE_THROWS_AS(controller.trigger("", {}), minifi::Exception);
+}
+
+TEST_CASE("Header Line Marker Characters size cannot be equal or larger than 
split text buffer size") {
+  const auto split_text = std::make_shared<processors::SplitText>("SplitText");
+  SingleProcessorTestController controller{split_text};
+  split_text->setProperty(processors::SplitText::LineSplitCount, "1");
+  std::string 
header_marker_character(static_cast<size_t>(processors::detail::SPLIT_TEXT_BUFFER_SIZE),
 'A');

Review Comment:
   it's already a `size_t`, no cast is needed



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