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https://issues.apache.org/jira/browse/ARROW-4213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16738706#comment-16738706
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Wes McKinney commented on ARROW-4213:
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I would be OK with sending the schema always in DoGet.
On the IPC message, I think we are saying different things. We have the
Flatbuffers {{Message}} type which has the metadata version and can represent
different kinds of IPC messages
https://github.com/apache/arrow/blob/master/format/Message.fbs#L93
In
https://github.com/apache/arrow/blob/87feee3d941ee41fb39b25411e108bef40a55995/java/vector/src/main/java/org/apache/arrow/vector/types/pojo/Schema.java#L168,
the schema is being serialized as the Schema type. I'm just saying to put the
Schema inside a Message. It has the side benefit of including the metadata
version so the reader can check for protocol version compatibility.
In C++, the Schema is serialized here
*
https://github.com/apache/arrow/blob/master/cpp/src/arrow/flight/internal.cc#L205
This calls {{WriteSchemaMessage}}
https://github.com/apache/arrow/blob/e0f70bbf9bc8eb909373abaaf0b4c9f50bc0a2d6/cpp/src/arrow/ipc/writer.cc#L784
which puts the Schema inside the Message union
https://github.com/apache/arrow/blob/ce9c6e3914274dcaf7806159ea5373e0cb632727/cpp/src/arrow/ipc/metadata-internal.cc#L690
> [Flight] C++ and Java implementations are incompatible
> ------------------------------------------------------
>
> Key: ARROW-4213
> URL: https://issues.apache.org/jira/browse/ARROW-4213
> Project: Apache Arrow
> Issue Type: Bug
> Components: FlightRPC
> Reporter: David Li
> Priority: Major
> Labels: flight
> Fix For: 0.13.0
>
>
> A C++ client cannot request streams from a Java service, nor can it decode
> the schema from GetFlightInfo.
> Schema: in Java, GetFlightInfo encodes the schema directly via flatbuffers.
> C++ expects it to be encoded as an IPC message. This isn't a problem in Java
> as a method exists to decode such schemas, but in C++ the API for reading
> such a schema isn't really exposed. I'm willing to submit a patch for this,
> but it's not clear to me which scheme is preferred.
> Streams: in Java, DoGet starts with an ArrowMessage containing a schema. C++
> does not expect this and segfaults when it tries to decode the message as a
> record batch. Based on the presentations I've seen, I think C++ is in the
> wrong here; I have a patch to fix this that I could clean up and submit.
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