bkietz commented on a change in pull request #7033: URL: https://github.com/apache/arrow/pull/7033#discussion_r416235260
########## File path: cpp/src/arrow/dataset/file_csv.cc ########## @@ -0,0 +1,99 @@ +// 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 "arrow/dataset/file_csv.h" + +#include <memory> +#include <string> + +#include "arrow/csv/options.h" +#include "arrow/csv/reader.h" +#include "arrow/dataset/dataset_internal.h" +#include "arrow/dataset/file_base.h" +#include "arrow/dataset/type_fwd.h" +#include "arrow/dataset/visibility.h" +#include "arrow/result.h" +#include "arrow/util/iterator.h" + +namespace arrow { +namespace dataset { + +using internal::checked_cast; +using internal::checked_pointer_cast; + +static inline csv::ReadOptions default_read_options() { + auto defaults = csv::ReadOptions::Defaults(); + defaults.use_threads = false; + return defaults; +} + +static inline Result<std::shared_ptr<csv::StreamingReader>> OpenReader( + const FileSource& source, const CsvFileFormat& format) { + ARROW_ASSIGN_OR_RAISE(auto input, source.Open()); + + auto maybe_reader = csv::StreamingReader::Make( + default_memory_pool(), std::move(input), default_read_options(), + format.parse_options, format.convert_options); + if (!maybe_reader.ok()) { + return maybe_reader.status().WithMessage("Could not open IPC input source '", + source.path(), "': ", maybe_reader.status()); + } + + return std::move(maybe_reader).ValueOrDie(); +} + +/// \brief A ScanTask backed by an Csv file. +class CsvScanTask : public ScanTask { + public: + CsvScanTask(std::shared_ptr<const CsvFileFormat> format, FileSource source, + std::shared_ptr<ScanOptions> options, std::shared_ptr<ScanContext> context) + : ScanTask(std::move(options), std::move(context)), + format_(std::move(format)), + source_(std::move(source)) {} + + Result<RecordBatchIterator> Execute() override { + ARROW_ASSIGN_OR_RAISE(auto reader, OpenReader(source_, *format_)); Review comment: Reading using a predetermined schema is already supported for CSV and for all the other formats. The first chunk (as determined by `CsvFileFormat::chunk_size`) is used to sniff the schema which is assumed for the rest of the file, and this inspection can be applied to just one or to all the files in a dataset at discovery time. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
