[I] [IPC] Expose `schema` on `StreamDecoder` [arrow-rs]

["wjones127 (via GitHub)" <gi...@apache.org>]

wjones127 opened a new issue, #6420:
URL: https://github.com/apache/arrow-rs/issues/6420

   **Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
   
   There is a nice example in the `StreamDecoder::decode` docs from reading from a stream:
   
   > ```rust
   > fn print_stream<I>(src: impl Iterator<Item = Buffer>) -> Result<(), ArrowError> {
   >    let mut decoder = StreamDecoder::new();
   >    for mut x in src {
   >        while !x.is_empty() {
   >            if let Some(x) = decoder.decode(&mut x)? {
   >                println!("{x:?}");
   >            }
   >        }
   >    }
   >    decoder.finish().unwrap();
   >    Ok(())
   > }
   > ```
   
   https://docs.rs/arrow-ipc/latest/arrow_ipc/reader/struct.StreamDecoder.html#method.decode
   
   **However, it doesn't show how to get the schema.** This would be useful if someone wanted to construct a `RecordBatchReader` or `SendableRecordBatchStream` from a stream of `Bytes` / `Buffer`. And it would be particularly helpful in cases where there were zero batches but we still wanted to get the schema.
   
   **Describe the solution you'd like**
   
   Minimally, it would be nice to do this:
   
   ```rust
   impl StreamDecoder {
       /// Return the schema, if decoded yet. Returns `None` if the schema message
       /// has yet to be decoded.
       fn schema(&self) -> Option<SchemaRef> { ... }
   }
   ```
   
   But it might also be nice to parallel the decode method:
   
   ```rust
   impl StreamDecoder {
       /// Return the schema, if decoded yet. Returns `None` if the schema message
       /// has yet to be decoded.
       fn decode_schema(&mut self, buffer: &mut Buffer) -> Option<SchemaRef> { ... }
   }
   ```
   
   
   **Describe alternatives you've considered**
   
   I asked in Slack if there were other straight forward ways, but didn't see anything easy from the suggestions. https://the-asf.slack.com/archives/C01QUFS30TD/p1726636373388569
   
   **Additional context**
   <!--
   Add any other context or screenshots about the feature request here.
   -->
   


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Re: [I] [IPC] Expose `schema` on `StreamDecoder` [arrow-rs]

["fsdvh (via GitHub)" <gi...@apache.org>]

fsdvh commented on issue #6420:
URL: https://github.com/apache/arrow-rs/issues/6420#issuecomment-2459832778

   Also interested in this one


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Re: [I] [IPC] Expose `schema` on `StreamDecoder` [arrow-rs]

["crepererum (via GitHub)" <gi...@apache.org>]

crepererum closed issue #6420: [IPC] Expose `schema` on `StreamDecoder`
URL: https://github.com/apache/arrow-rs/issues/6420


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