Method try_next_batch

parquet/src/arrow/push_decoder/mod.rs:657–705

Current state --> next state + output This function is called to get the next RecordBatch This structure is used to reduce the indentation level of the main loop in try_build

(self)

    /// This structure is used to reduce the indentation level of the main loop
    /// in try_build
    fn try_next_batch(self) -> Result<(Self, DecodeResult<RecordBatch>), ParquetError> {
        let mut current_state = self;
        loop {
            let (new_state, decode_result) = current_state.transition()?;
            // if more data is needed to transition, can't proceed further without it
            match decode_result {
                DecodeResult::NeedsData(ranges) => {
                    return Ok((new_state, DecodeResult::NeedsData(ranges)));
                }
                // act next based on state
                DecodeResult::Data(()) | DecodeResult::Finished => {}
            }
            match new_state {
                // not ready to read yet, continue transitioning
                Self::ReadingRowGroup { .. } => current_state = new_state,
                // have a reader ready, so decode the next batch
                Self::DecodingRowGroup {
                    mut record_batch_reader,
                    remaining_row_groups,
                } => {
                    match record_batch_reader.next() {
                        // Successfully decoded a batch, return it
                        Some(Ok(batch)) => {
                            let result = DecodeResult::Data(batch);
                            let next_state = Self::DecodingRowGroup {
                                record_batch_reader,
                                remaining_row_groups,
                            };
                            return Ok((next_state, result));
                        }
                        // No more batches in this row group, move to the next row group
                        None => {
                            current_state = Self::ReadingRowGroup {
                                remaining_row_groups,
                            }
                        }
                        // some error occurred while decoding, so return that
                        Some(Err(e)) => {
                            // TODO: preserve ArrowError in ParquetError (rather than convert to a string)
                            return Err(ParquetError::ArrowError(e.to_string()));
                        }
                    }
                }
                Self::Finished => {
                    return Ok((Self::Finished, DecodeResult::Finished));
                }
            }
        }
    }

    /// Transition to the next state with a reader (data can be produced), if not end of stream
    ///