ryanschneider opened a new issue, #451:
URL: https://github.com/apache/arrow-go/issues/451
### Describe the bug, including details regarding any error messages,
version, and platform.
I'm using `flight.StreamChunksFromReader` in my `DoGetStatement` statement
handler to serve chunks from a parquet file, more or less like so (err checks
removed, how I get the ReaderAtSeeker abstracted out)
```golang
func (s *flightServer) DoGetStatement(ctx context.Context, cmd
flightsql.StatementQueryTicket) (*arrow.Schema, <-chan flight.StreamChunk,
error) {
r := getParquetFile(...) // returns a ReaderAtSeeker
pqr, err := file.NewParquetReader(r,
file.WithReadProps(&parquet.ReaderProperties{
BufferedStreamEnabled: true,
}))
arr, err := pqarrow.NewFileReader(
pqr,
pqarrow.ArrowReadProperties{
Parallel: false,
BatchSize: batchSize,
},
memory.DefaultAllocator,
)
schema, err := arr.Schema()
rr, err := arr.GetRecordReader(ctx, nil, nil)
ch := make(chan flight.StreamChunk)
go streamChunksFromReader(rr, ch)
return schema, ch, nil
}
```
But this consistently returns `EOF` to the client _after_ sending all the
records, basically the reader returned by `client.DoGet()` fails on
`rdr.Read()` w/ `rpc error: code = Unknown desc = EOF` after reading the last
chunk, instead of returning `io.EOF` like it should.
I tracked this down to the trailing error check in
`flight.StreamChunksFromReader`:
https://github.com/apache/arrow-go/blob/main/arrow/flight/record_batch_reader.go#L235-L238
It seems like the `RecordReader` returned by
`pqarrow.FileReader.GetRecordReader` sets it's internal err state to `io.EOF`
after the last record is read. I was able to work around this using a slightly
modified local `streamChunksFromReader` implementation:
```golang
func streamChunksFromReader(rdr array.RecordReader, ch chan<-
flight.StreamChunk) {
defer close(ch)
defer func() {
if err := recover(); err != nil {
slog.Warn("panic while reading", slog.Any("err", err))
ch <- flight.StreamChunk{Err: fmt.Errorf("panic while
reading: %v", err)}
}
}()
defer rdr.Release()
for rdr.Next() {
rec := rdr.Record()
rec.Retain()
slog.Debug("record received", slog.Any("rows", rec.NumRows()),
slog.Any("cols", rec.NumCols()))
ch <- flight.StreamChunk{Data: rec}
if err := rdr.Err(); err != nil {
slog.Warn("error while reading", slog.Any("err", err))
ch <- flight.StreamChunk{Err: err}
}
}
if err := rdr.Err(); err != nil && err != io.EOF {
slog.Warn("error after reading", slog.Any("err", err))
ch <- flight.StreamChunk{Err: err}
}
}
```
The changes are two-fold:
- If `rdr.Err()` returns when `.Next()` returned true, always report that.
- If after `.Next()` returns false, only report non-EOF errors.
The added logging and other minors changes were just for pinpointing the
issue. I'm not sure if this is a bug in `pqarrow` or
`flight.StreamChunksFromReader`
### Component(s)
Other, Parquet
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