pitrou commented on code in PR #49771:
URL: https://github.com/apache/arrow/pull/49771#discussion_r3234304108
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cpp/src/arrow/ipc/message.cc:
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@@ -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) {
Review Comment:
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.
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