Copilot commented on code in PR #3854:
URL: https://github.com/apache/avro/pull/3854#discussion_r3567559356


##########
lang/c++/test/DecompressionLimitTests.cc:
##########
@@ -0,0 +1,177 @@
+/*
+ * 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
+ *
+ *     https://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.
+ */
+
+// AVRO-4285: a data-file block is decompressed according to the file's codec. 
A
+// block with a very high compression ratio (or a malformed block) can expand 
to
+// far more memory than its compressed size. Reading such a block must be
+// rejected once its decompressed size would exceed the configured maximum, 
which
+// these tests set to a small value via AVRO_MAX_DECOMPRESS_LENGTH.
+
+#include <cstdlib>
+#include <filesystem>
+#include <optional>
+#include <sstream>
+#include <string>
+
+#include <boost/test/included/unit_test.hpp>
+
+#include "Compiler.hh"
+#include "DataFile.hh"
+#include "Exception.hh"
+#include "ValidSchema.hh"
+
+namespace avro {
+
+static void setDecompressLimit(const char *value) {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", value);

Review Comment:
   The return value of `_putenv_s` is ignored. If it fails, the tests may 
silently run with the default decompression limit, producing misleading 
pass/fail results. Assert success so failures are surfaced immediately.



##########
lang/c++/test/DecompressionLimitTests.cc:
##########
@@ -0,0 +1,177 @@
+/*
+ * 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
+ *
+ *     https://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.
+ */
+
+// AVRO-4285: a data-file block is decompressed according to the file's codec. 
A
+// block with a very high compression ratio (or a malformed block) can expand 
to
+// far more memory than its compressed size. Reading such a block must be
+// rejected once its decompressed size would exceed the configured maximum, 
which
+// these tests set to a small value via AVRO_MAX_DECOMPRESS_LENGTH.
+
+#include <cstdlib>
+#include <filesystem>
+#include <optional>
+#include <sstream>
+#include <string>
+
+#include <boost/test/included/unit_test.hpp>
+
+#include "Compiler.hh"
+#include "DataFile.hh"
+#include "Exception.hh"
+#include "ValidSchema.hh"
+
+namespace avro {
+
+static void setDecompressLimit(const char *value) {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", value);
+#else
+    setenv("AVRO_MAX_DECOMPRESS_LENGTH", value, 1);

Review Comment:
   The return value of `setenv` is ignored. If setting the environment variable 
fails, the test could pass while the decompression limit was never applied. 
Assert `setenv` succeeds to avoid false positives.



##########
lang/c++/test/DecompressionLimitTests.cc:
##########
@@ -0,0 +1,177 @@
+/*
+ * 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
+ *
+ *     https://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.
+ */
+
+// AVRO-4285: a data-file block is decompressed according to the file's codec. 
A
+// block with a very high compression ratio (or a malformed block) can expand 
to
+// far more memory than its compressed size. Reading such a block must be
+// rejected once its decompressed size would exceed the configured maximum, 
which
+// these tests set to a small value via AVRO_MAX_DECOMPRESS_LENGTH.
+
+#include <cstdlib>
+#include <filesystem>
+#include <optional>
+#include <sstream>
+#include <string>
+
+#include <boost/test/included/unit_test.hpp>
+
+#include "Compiler.hh"
+#include "DataFile.hh"
+#include "Exception.hh"
+#include "ValidSchema.hh"
+
+namespace avro {
+
+static void setDecompressLimit(const char *value) {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", value);
+#else
+    setenv("AVRO_MAX_DECOMPRESS_LENGTH", value, 1);
+#endif
+}
+
+static void unsetDecompressLimit() {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", "");
+#else
+    unsetenv("AVRO_MAX_DECOMPRESS_LENGTH");

Review Comment:
   The return value of `unsetenv` is ignored. If it fails, 
`DecompressLimitGuard` may not actually restore the previous environment state, 
potentially impacting later test cases. Assert `unsetenv` succeeds to keep 
tests deterministic.



##########
lang/c++/test/DecompressionLimitTests.cc:
##########
@@ -0,0 +1,177 @@
+/*
+ * 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
+ *
+ *     https://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.
+ */
+
+// AVRO-4285: a data-file block is decompressed according to the file's codec. 
A
+// block with a very high compression ratio (or a malformed block) can expand 
to
+// far more memory than its compressed size. Reading such a block must be
+// rejected once its decompressed size would exceed the configured maximum, 
which
+// these tests set to a small value via AVRO_MAX_DECOMPRESS_LENGTH.
+
+#include <cstdlib>
+#include <filesystem>
+#include <optional>
+#include <sstream>
+#include <string>
+
+#include <boost/test/included/unit_test.hpp>
+
+#include "Compiler.hh"
+#include "DataFile.hh"
+#include "Exception.hh"
+#include "ValidSchema.hh"
+
+namespace avro {
+
+static void setDecompressLimit(const char *value) {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", value);
+#else
+    setenv("AVRO_MAX_DECOMPRESS_LENGTH", value, 1);
+#endif
+}
+
+static void unsetDecompressLimit() {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", "");

Review Comment:
   The return value of `_putenv_s` is ignored. If clearing the environment 
variable fails, later tests in the same process may see a stale limit and 
behave unexpectedly. Assert success so failures are visible.



##########
lang/c++/test/DecompressionLimitTests.cc:
##########
@@ -0,0 +1,177 @@
+/*
+ * 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
+ *
+ *     https://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.
+ */
+
+// AVRO-4285: a data-file block is decompressed according to the file's codec. 
A
+// block with a very high compression ratio (or a malformed block) can expand 
to
+// far more memory than its compressed size. Reading such a block must be
+// rejected once its decompressed size would exceed the configured maximum, 
which
+// these tests set to a small value via AVRO_MAX_DECOMPRESS_LENGTH.
+
+#include <cstdlib>
+#include <filesystem>
+#include <optional>
+#include <sstream>
+#include <string>
+
+#include <boost/test/included/unit_test.hpp>
+
+#include "Compiler.hh"
+#include "DataFile.hh"
+#include "Exception.hh"
+#include "ValidSchema.hh"
+
+namespace avro {
+
+static void setDecompressLimit(const char *value) {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", value);
+#else
+    setenv("AVRO_MAX_DECOMPRESS_LENGTH", value, 1);
+#endif
+}
+
+static void unsetDecompressLimit() {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", "");
+#else
+    unsetenv("AVRO_MAX_DECOMPRESS_LENGTH");
+#endif
+}
+
+// Saves AVRO_MAX_DECOMPRESS_LENGTH on construction and restores it on
+// destruction, so a test's override does not leak into other test cases that
+// share the process.
+struct DecompressLimitGuard {
+    std::optional<std::string> previous;
+    DecompressLimitGuard() {
+        const char *env = std::getenv("AVRO_MAX_DECOMPRESS_LENGTH");
+        if (env != nullptr) {
+            previous = std::string(env);
+        }
+    }
+    ~DecompressLimitGuard() {
+        if (previous) {
+            setDecompressLimit(previous->c_str());
+        } else {
+            unsetDecompressLimit();
+        }
+    }
+};
+
+static ValidSchema stringSchema() {
+    std::istringstream iss("\"string\"");
+    ValidSchema vs;
+    compileJsonSchema(iss, vs);
+    return vs;
+}
+
+static std::string tempFile(const char *name) {
+    return (std::filesystem::temp_directory_path() / name).string();
+}
+
+// Write a single, highly compressible value with the given codec, then read it
+// back with a small decompression limit and confirm the read is rejected.
+static void checkCodecRejectsOversized(Codec codec, const char *name) {
+    DecompressLimitGuard guard;
+    ValidSchema schema = stringSchema();
+    std::string path = tempFile(name);
+    std::string big(4 * 1024 * 1024, 'a'); // 4 MiB, compresses tiny
+
+    // Let any writer exception propagate: a failure here is a real problem
+    // (e.g. permissions or I/O), not a reason to silently skip. Codecs that 
are
+    // not compiled in are excluded via the #ifdef guards on the callers below.
+    {
+        DataFileWriter<std::string> writer(path.c_str(), schema, 64 * 1024 * 
1024, codec);
+        writer.write(big);
+        writer.close();
+    }
+
+    setDecompressLimit("1048576"); // 1 MiB, smaller than the 4 MiB block
+
+    bool rejected = false;
+    try {
+        DataFileReader<std::string> reader(path.c_str(), schema);
+        std::string out;
+        reader.read(out); // triggers block decompression
+    } catch (const Exception &e) {
+        // Assert it failed specifically because of the decompression limit, 
not
+        // an unrelated I/O or corruption error that would give a false 
positive.
+        rejected = std::string(e.what()).find("exceeds the maximum allowed") 
!= std::string::npos;
+        BOOST_CHECK_MESSAGE(rejected,
+                            std::string("unexpected exception for ") + name + 
": " + e.what());
+    }
+    std::filesystem::remove(path);
+    BOOST_CHECK_MESSAGE(rejected, std::string("codec not bounded: ") + name);
+}
+
+static void testDeflateDecompressionLimit() {
+    checkCodecRejectsOversized(DEFLATE_CODEC, 
"avro_decompress_limit_deflate.avro");
+}
+
+static void testSnappyDecompressionLimit() {
+#ifdef SNAPPY_CODEC_AVAILABLE
+    checkCodecRejectsOversized(SNAPPY_CODEC, 
"avro_decompress_limit_snappy.avro");
+#else
+    BOOST_TEST_MESSAGE("Snappy codec not available; skipping");
+#endif
+}
+
+static void testZstdDecompressionLimit() {
+#ifdef ZSTD_CODEC_AVAILABLE
+    checkCodecRejectsOversized(ZSTD_CODEC, "avro_decompress_limit_zstd.avro");
+#else
+    BOOST_TEST_MESSAGE("Zstandard codec not available; skipping");
+#endif
+}
+
+static void testWithinLimitStillReads() {
+    DecompressLimitGuard guard;
+    ValidSchema schema = stringSchema();
+    std::string path = tempFile("avro_decompress_within_limit.avro");
+    std::string payload = "hello world";
+
+    {
+        DataFileWriter<std::string> writer(path.c_str(), schema, 64 * 1024 * 
1024, DEFLATE_CODEC);
+        writer.write(payload);
+        writer.close();
+    }
+
+    setDecompressLimit("1048576");
+
+    std::string out;
+    {
+        DataFileReader<std::string> reader(path.c_str(), schema);
+        BOOST_CHECK(reader.read(out));
+    }
+    std::filesystem::remove(path);

Review Comment:
   Test cleanup currently ignores whether the temporary file was actually 
removed. As in other tests (e.g., `DataFileTests.cc`), asserting `remove()` 
succeeds makes it easier to catch environment/permission issues rather than 
silently leaving files behind.



##########
lang/c++/test/DecompressionLimitTests.cc:
##########
@@ -0,0 +1,177 @@
+/*
+ * 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
+ *
+ *     https://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.
+ */
+
+// AVRO-4285: a data-file block is decompressed according to the file's codec. 
A
+// block with a very high compression ratio (or a malformed block) can expand 
to
+// far more memory than its compressed size. Reading such a block must be
+// rejected once its decompressed size would exceed the configured maximum, 
which
+// these tests set to a small value via AVRO_MAX_DECOMPRESS_LENGTH.
+
+#include <cstdlib>
+#include <filesystem>
+#include <optional>
+#include <sstream>
+#include <string>
+
+#include <boost/test/included/unit_test.hpp>
+
+#include "Compiler.hh"
+#include "DataFile.hh"
+#include "Exception.hh"
+#include "ValidSchema.hh"
+
+namespace avro {
+
+static void setDecompressLimit(const char *value) {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", value);
+#else
+    setenv("AVRO_MAX_DECOMPRESS_LENGTH", value, 1);
+#endif
+}
+
+static void unsetDecompressLimit() {
+#ifdef _WIN32
+    _putenv_s("AVRO_MAX_DECOMPRESS_LENGTH", "");
+#else
+    unsetenv("AVRO_MAX_DECOMPRESS_LENGTH");
+#endif
+}
+
+// Saves AVRO_MAX_DECOMPRESS_LENGTH on construction and restores it on
+// destruction, so a test's override does not leak into other test cases that
+// share the process.
+struct DecompressLimitGuard {
+    std::optional<std::string> previous;
+    DecompressLimitGuard() {
+        const char *env = std::getenv("AVRO_MAX_DECOMPRESS_LENGTH");
+        if (env != nullptr) {
+            previous = std::string(env);
+        }
+    }
+    ~DecompressLimitGuard() {
+        if (previous) {
+            setDecompressLimit(previous->c_str());
+        } else {
+            unsetDecompressLimit();
+        }
+    }
+};
+
+static ValidSchema stringSchema() {
+    std::istringstream iss("\"string\"");
+    ValidSchema vs;
+    compileJsonSchema(iss, vs);
+    return vs;
+}
+
+static std::string tempFile(const char *name) {
+    return (std::filesystem::temp_directory_path() / name).string();
+}
+
+// Write a single, highly compressible value with the given codec, then read it
+// back with a small decompression limit and confirm the read is rejected.
+static void checkCodecRejectsOversized(Codec codec, const char *name) {
+    DecompressLimitGuard guard;
+    ValidSchema schema = stringSchema();
+    std::string path = tempFile(name);
+    std::string big(4 * 1024 * 1024, 'a'); // 4 MiB, compresses tiny
+
+    // Let any writer exception propagate: a failure here is a real problem
+    // (e.g. permissions or I/O), not a reason to silently skip. Codecs that 
are
+    // not compiled in are excluded via the #ifdef guards on the callers below.
+    {
+        DataFileWriter<std::string> writer(path.c_str(), schema, 64 * 1024 * 
1024, codec);
+        writer.write(big);
+        writer.close();
+    }
+
+    setDecompressLimit("1048576"); // 1 MiB, smaller than the 4 MiB block
+
+    bool rejected = false;
+    try {
+        DataFileReader<std::string> reader(path.c_str(), schema);
+        std::string out;
+        reader.read(out); // triggers block decompression
+    } catch (const Exception &e) {
+        // Assert it failed specifically because of the decompression limit, 
not
+        // an unrelated I/O or corruption error that would give a false 
positive.
+        rejected = std::string(e.what()).find("exceeds the maximum allowed") 
!= std::string::npos;
+        BOOST_CHECK_MESSAGE(rejected,
+                            std::string("unexpected exception for ") + name + 
": " + e.what());
+    }
+    std::filesystem::remove(path);

Review Comment:
   Test cleanup currently ignores whether the temporary file was actually 
removed. Other C++ tests in this repo assert removal succeeds (e.g., 
`DataFileTests.cc` uses `BOOST_CHECK(std::filesystem::remove(filename))`). 
Checking the return value makes cleanup failures visible (permissions, path 
issues, etc.).



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