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ARROW-1002: [C++] Fix inconsistency with padding at start of IPC file format #693

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ARROW-1002: [C++] Fix inconsistency with padding at start of IPC file format #693

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20 changes: 8 additions & 12 deletions cpp/src/arrow/ipc/writer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -509,7 +509,7 @@ class DictionaryWriter : public RecordBatchSerializer {
};

// Adds padding bytes if necessary to ensure all memory blocks are written on
// 8-byte boundaries.
// 64-byte boundaries.
Status AlignStreamPosition(io::OutputStream* stream) {
int64_t position;
RETURN_NOT_OK(stream->Tell(&position));
Expand Down Expand Up @@ -687,9 +687,9 @@ class RecordBatchStreamWriter::RecordBatchStreamWriterImpl {
}

// Adds padding bytes if necessary to ensure all memory blocks are written on
// 8-byte boundaries.
Status Align() {
int64_t remainder = PaddedLength(position_) - position_;
// 64-byte (or other alignment) boundaries.
Status Align(int64_t alignment = kArrowAlignment) {
int64_t remainder = PaddedLength(position_, alignment) - position_;
if (remainder > 0) { return Write(kPaddingBytes, remainder); }
return Status::OK();
}
Expand All @@ -701,12 +701,6 @@ class RecordBatchStreamWriter::RecordBatchStreamWriterImpl {
return Status::OK();
}

// Write and align
Status WriteAligned(const uint8_t* data, int64_t nbytes) {
RETURN_NOT_OK(Write(data, nbytes));
return Align();
}

void set_memory_pool(MemoryPool* pool) { pool_ = pool; }

protected:
Expand Down Expand Up @@ -762,8 +756,10 @@ class RecordBatchFileWriter::RecordBatchFileWriterImpl
using BASE = RecordBatchStreamWriter::RecordBatchStreamWriterImpl;

Status Start() override {
RETURN_NOT_OK(WriteAligned(
reinterpret_cast<const uint8_t*>(kArrowMagicBytes), strlen(kArrowMagicBytes)));
// It is only necessary to align to 8-byte boundary at the start of the file
RETURN_NOT_OK(Write(reinterpret_cast<const uint8_t*>(kArrowMagicBytes),
strlen(kArrowMagicBytes)));
RETURN_NOT_OK(Align(8));

// We write the schema at the start of the file (and the end). This also
// writes all the dictionaries at the beginning of the file
Expand Down