[professor-moody]

Rationale for this change

The ReadMessage overload that takes a body_length and ReadMessageAsync in cpp/src/arrow/ipc/message.cc read metadata_length + body_length bytes with a single read and then give the first metadata_length bytes to the message decoder. Nothing checks body_length: a negative value makes the read shorter than metadata_length while the metadata slice keeps its full length (the only consistency check in ReadMessageContinued is a DCHECK_EQ), and a large value overflows the sum. RecordBatchFileReader validates footer blocks in FileBlockFromFlatbuffer before calling these functions, but other callers of these public functions get no such check.

What changes are included in this PR?

ReadMessageInternal and ReadMessageAsync return Status::Invalid when body_length is negative or when metadata_length + body_length would overflow int64_t, before any IO is issued.

Are these changes tested?

Yes, in cpp/src/arrow/ipc/message_internal_test.cc (MessageDecodingTest fixture):

• ReadMessageValidBodyLength reads the sample messages with their actual body length through ReadMessage and ReadMessageAsync and checks the returned body length.
• ReadMessageInvalidBodyLength checks that body lengths of -1, -8 and INT64_MAX are rejected with Invalid by both functions.

Are there any user-facing changes?

Invalid body_length arguments return Invalid. Valid calls are unaffected.

Was AI used for this PR?

In accordance to the AI generation guidelines, please disclose below whether and how AI was used in this PR.

PR code and description written by:

• Human
• AI

Reviewed before submission by:

• Human
• AI
• Not reviewed

[github-actions]

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