Jefffrey commented on code in PR #7962:
URL: https://github.com/apache/arrow-datafusion/pull/7962#discussion_r1379219105
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datafusion/core/src/datasource/file_format/arrow.rs:
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@@ -99,7 +102,177 @@ impl FileFormat for ArrowFormat {
}
}
-fn read_arrow_schema_from_reader<R: Read + Seek>(reader: R) ->
Result<SchemaRef> {
- let reader = FileReader::try_new(reader, None)?;
- Ok(reader.schema())
+const ARROW_MAGIC: [u8; 6] = [b'A', b'R', b'R', b'O', b'W', b'1'];
Review Comment:
> What do you think about moving this logic upstream into the arrow-rs
reader.
Yes, this logic was essentially ripped from `StreamReader` and `FileReader`
of `arrow-ipc`, but adjusted to be made compatible with async stream of bytes.
We could move this logic to `arrow-ipc`, but we need to keep in mind that
though we are getting a stream of bytes, this is a stream of bytes in the IPC
file format and not the IPC streaming format. So an `AsyncStreamReader` might
not exactly fit our use, whereas an `AsyncFileReader` could but might be
limited if we don't read its footer when attempting to decode the rest of the
data.
> I think I would rather the approach described on
https://github.com/apache/arrow-rs/issues/5021, reading the footer is more
generally useful, providing information beyond just the schema
It seems this ticket could be appropriate for that. Just to note, that we
can't exactly read the footer in a stream without reverting to the old method
of reading the entire stream just to decode the schema.
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