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GH-33823: [C++][IPC] Improve error messages when opening files that are the wrong format #49771

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GH-33823: [C++][IPC] Improve error messages when opening files that are the wrong format #49771

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abd2b9c
#33823 Improve err msgs when opening files that are the wrong format
RobertLD Apr 16, 2026
db7dd63
33823 Formatting + linting
RobertLD Apr 16, 2026
d025ab0
Update cpp/src/arrow/ipc/reader.cc
RobertLD Apr 24, 2026
1d9b536
Update cpp/src/arrow/ipc/message.cc
RobertLD Apr 24, 2026
407c134
33823 Add tests to verify new err msgs
RobertLD Apr 29, 2026
d01cb5d
33823 PR suggestions
RobertLD May 12, 2026
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18 changes: 18 additions & 0 deletions cpp/src/arrow/ipc/message.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -563,7 +563,25 @@ Status DecodeMessage(MessageDecoder* decoder, io::InputStream* file) {
}

auto metadata_length = decoder->next_required_size();

// "ARRO" (first 4 bytes of kArrowMagicBytes) as little-endian int32.
constexpr int32_t kArrowMagicPrefix = 0x4F525241;

// Did we misinterpret the metadata as a length?
if (metadata_length == kArrowMagicPrefix) {
constexpr std::string_view kRemainingMagic =
internal::kArrowMagicBytes.substr(sizeof(int32_t));
ARROW_ASSIGN_OR_RAISE(auto peek, file->Read(kRemainingMagic.size()));
if (peek->size() >= static_cast<int64_t>(kRemainingMagic.size()) &&
std::string_view(reinterpret_cast<const char*>(peek->data()),
kRemainingMagic.size()) == kRemainingMagic) {
Comment on lines +575 to +577

@pitrou pitrou May 13, 2026

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What happens if this check fails? Are we assuming that the file is a valid IPC stream that happens to have a metadata size exactly 0x4F525241 bytes?

In any case, we have read kRemainingMagic bytes that are discarded below, so we'll be out of sync anyway.

@RobertLD RobertLD Jun 15, 2026

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@pitrou Okay I see what you're saying and this was an oversight on my part. My idea is to continue to let it fall through and add a separate check immediately below it to reject metadata over 1GB. I think this is the best solution but it does change the behavior of the library (and I'm concerned there may be a single user somewhere who has 10Gb of metadata) and it's a bit of stretch scope wise considering this ticket is about error messages.

What are your thoughts? I'm thinking I just go forward with the above (or alternatively, just throw a failure with a different message on specifically 0x4F525241 even if it's not IPC)

@pitrou pitrou Jun 16, 2026

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Letting it fall through means a mythical user with a valid 0x4F525241 bytes metadata block will get a regression with a weird message decoding the Flatbuffers metadata. I'd rather an explicit message.

return Status::Invalid(
"This appears to be an Arrow IPC file. "
"Try the IPC file reader instead of the IPC stream reader.");
}
}
ARROW_ASSIGN_OR_RAISE(auto metadata, file->Read(metadata_length));

if (metadata->size() != metadata_length) {
return Status::Invalid("Expected to read ", metadata_length, " metadata bytes, but ",
"only read ", metadata->size());
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47 changes: 47 additions & 0 deletions cpp/src/arrow/ipc/read_write_test.cc
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Expand Up @@ -2265,6 +2265,53 @@ TEST(TestRecordBatchStreamReader, MalformedInput) {
ASSERT_RAISES(Invalid, RecordBatchStreamReader::Open(&garbage_reader));
}

TEST(TestRecordBatchStreamReader, OpenFileFormatSuggestsFileReader) {
std::shared_ptr<RecordBatch> batch;
ASSERT_OK(MakeIntRecordBatch(&batch));

FileWriterHelper helper;
ASSERT_OK(helper.Init(batch->schema(), IpcWriteOptions::Defaults()));
ASSERT_OK(helper.WriteBatch(batch));
ASSERT_OK(helper.Finish());

io::BufferReader reader(helper.buffer_);
// Check we mention using the file_reader when we detect file format
EXPECT_RAISES_WITH_MESSAGE_THAT(Invalid,
::testing::HasSubstr("Try the IPC file reader"),
RecordBatchStreamReader::Open(&reader));
}

TEST(TestRecordBatchStreamReader, CorruptDataDoesNotSuggestFileReader) {
// Continuation marker + metadata_length = 100, then 8 bytes of non-magic data.
const std::string corrupt(
"\xff\xff\xff\xff"
"\x64\x00\x00\x00"
"ABABABAB",
16);
auto buffer = std::make_shared<Buffer>(corrupt);
io::BufferReader reader(buffer);
// Validate that we don't suggest file reader when file is just corrupt
EXPECT_RAISES_WITH_MESSAGE_THAT(
Invalid, ::testing::Not(::testing::HasSubstr("Try the IPC file reader")),
RecordBatchStreamReader::Open(&reader));
}

TEST(TestRecordBatchFileReader, OpenStreamFormatSuggestsStreamReader) {
std::shared_ptr<RecordBatch> batch;
ASSERT_OK(MakeIntRecordBatch(&batch));

StreamWriterHelper helper;
ASSERT_OK(helper.Init(batch->schema(), IpcWriteOptions::Defaults()));
ASSERT_OK(helper.WriteBatch(batch));
ASSERT_OK(helper.Finish());

auto buf_reader = std::make_shared<io::BufferReader>(helper.buffer_);
// Check we mention using the stream_reader when we detect stream format
EXPECT_RAISES_WITH_MESSAGE_THAT(
Invalid, ::testing::HasSubstr("use the IPC stream reader"),
RecordBatchFileReader::Open(buf_reader.get(), helper.buffer_->size()));
}

class EndlessCollectListener : public CollectListener {
public:
EndlessCollectListener() : CollectListener(), decoder_(nullptr) {}
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4 changes: 3 additions & 1 deletion cpp/src/arrow/ipc/reader.cc
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Expand Up @@ -1890,7 +1890,9 @@ class RecordBatchFileReaderImpl : public RecordBatchFileReader {
const auto magic_start = buffer->data() + sizeof(int32_t);
if (std::string_view(reinterpret_cast<const char*>(magic_start), kMagicSize) !=
kArrowMagicBytes) {
return Status::Invalid("Not an Arrow file");
return Status::Invalid(
"Not an Arrow file. If this is an Arrow IPC stream, use "
"the IPC stream reader instead.");
}

int32_t footer_length = bit_util::FromLittleEndian(
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