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merged 2 commits into from
Oct 10, 2025
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Fix doctests of parquet push decoded without default features #8577

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7e4afd6
Fix doctests of parquet push decoded without default features
mbrobbel Oct 9, 2025
0d9b92e
Fix typo
mbrobbel Oct 9, 2025
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269 changes: 141 additions & 128 deletions parquet/src/file/metadata/push_decoder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -47,53 +47,58 @@ use std::ops::Range;
/// requires the most IO operations - one to read the footer and then one
/// to read the metadata, and possibly more if page indexes are requested.
///
/// ```rust
/// # use std::ops::Range;
/// # use bytes::Bytes;
/// # use arrow_array::record_batch;
/// # use parquet::DecodeResult;
/// # use parquet::arrow::ArrowWriter;
/// # use parquet::errors::ParquetError;
/// # use parquet::file::metadata::{ParquetMetaData, ParquetMetaDataPushDecoder};
/// #
/// # fn decode_metadata() -> Result<ParquetMetaData, ParquetError> {
/// # let file_bytes = {
/// # let mut buffer = vec![0];
/// # let batch = record_batch!(("a", Int32, [1, 2, 3])).unwrap();
/// # let mut writer = ArrowWriter::try_new(&mut buffer, batch.schema(), None).unwrap();
/// # writer.write(&batch).unwrap();
/// # writer.close().unwrap();
/// # Bytes::from(buffer)
/// # };
/// # // mimic IO by returning a function that returns the bytes for a given range
/// # let get_range = |range: &Range<u64>| -> Bytes {
/// # let start = range.start as usize;
/// # let end = range.end as usize;
/// # file_bytes.slice(start..end)
/// # };
/// #
/// # let file_len = file_bytes.len() as u64;
/// // The `ParquetMetaDataPushDecoder` needs to know the file length.
/// let mut decoder = ParquetMetaDataPushDecoder::try_new(file_len).unwrap();
/// // try to decode the metadata. If more data is needed, the decoder will tell you what ranges
/// loop {
/// match decoder.try_decode() {
/// Ok(DecodeResult::Data(metadata)) => { return Ok(metadata); } // decode successful
/// Ok(DecodeResult::NeedsData(ranges)) => {
/// // The decoder needs more data
/// //
/// // In this example, we call a function that returns the bytes for each given range.
/// // In a real application, you would likely read the data from a file or network.
/// let data = ranges.iter().map(|range| get_range(range)).collect();
/// // Push the data into the decoder and try to decode again on the next iteration.
/// decoder.push_ranges(ranges, data).unwrap();
/// }
/// Ok(DecodeResult::Finished) => { unreachable!("returned metadata in previous match arm") }
/// Err(e) => return Err(e),
/// }
/// }
/// # }
/// ```
#[cfg_attr(
feature = "arrow",
doc = r##"
```rust
# use std::ops::Range;
# use bytes::Bytes;
# use arrow_array::record_batch;
# use parquet::DecodeResult;
# use parquet::arrow::ArrowWriter;
# use parquet::errors::ParquetError;
# use parquet::file::metadata::{ParquetMetaData, ParquetMetaDataPushDecoder};
#
# fn decode_metadata() -> Result<ParquetMetaData, ParquetError> {
# let file_bytes = {
# let mut buffer = vec![0];
# let batch = record_batch!(("a", Int32, [1, 2, 3])).unwrap();
# let mut writer = ArrowWriter::try_new(&mut buffer, batch.schema(), None).unwrap();
# writer.write(&batch).unwrap();
# writer.close().unwrap();
# Bytes::from(buffer)
# };
# // mimic IO by returning a function that returns the bytes for a given range
# let get_range = |range: &Range<u64>| -> Bytes {
# let start = range.start as usize;
# let end = range.end as usize;
# file_bytes.slice(start..end)
# };
#
# let file_len = file_bytes.len() as u64;
// The `ParquetMetaDataPushDecoder` needs to know the file length.
let mut decoder = ParquetMetaDataPushDecoder::try_new(file_len).unwrap();
// try to decode the metadata. If more data is needed, the decoder will tell you what ranges
loop {
match decoder.try_decode() {
Ok(DecodeResult::Data(metadata)) => { return Ok(metadata); } // decode successful
Ok(DecodeResult::NeedsData(ranges)) => {
// The decoder needs more data
//
// In this example, we call a function that returns the bytes for each given range.
// In a real application, you would likely read the data from a file or network.
let data = ranges.iter().map(|range| get_range(range)).collect();
// Push the data into the decoder and try to decode again on the next iteration.
decoder.push_ranges(ranges, data).unwrap();
}
Ok(DecodeResult::Finished) => { unreachable!("returned metadata in previous match arm") }
Err(e) => return Err(e),
}
}
# }
```
"##
)]
///
/// # Example with "prefetching"
///
Expand All @@ -114,44 +119,48 @@ use std::ops::Range;
///
/// This approach can also be used when you have the entire file already in memory
/// for other reasons.
///
/// ```rust
/// # use std::ops::Range;
/// # use bytes::Bytes;
/// # use arrow_array::record_batch;
/// # use parquet::DecodeResult;
/// # use parquet::arrow::ArrowWriter;
/// # use parquet::errors::ParquetError;
/// # use parquet::file::metadata::{ParquetMetaData, ParquetMetaDataPushDecoder};
/// #
/// # fn decode_metadata() -> Result<ParquetMetaData, ParquetError> {
/// # let file_bytes = {
/// # let mut buffer = vec![0];
/// # let batch = record_batch!(("a", Int32, [1, 2, 3])).unwrap();
/// # let mut writer = ArrowWriter::try_new(&mut buffer, batch.schema(), None).unwrap();
/// # writer.write(&batch).unwrap();
/// # writer.close().unwrap();
/// # Bytes::from(buffer)
/// # };
/// #
/// let file_len = file_bytes.len() as u64;
/// // For this example, we "prefetch" all the bytes which we have in memory,
/// // but in a real application, you would likely read a chunk from the end
/// // for example 1MB.
/// let prefetched_bytes = file_bytes.clone();
/// let mut decoder = ParquetMetaDataPushDecoder::try_new(file_len).unwrap();
/// // push the prefetched bytes into the decoder
/// decoder.push_ranges(vec![0..file_len], vec![prefetched_bytes]).unwrap();
/// // The decoder will now be able to decode the metadata. Note in a real application,
/// // unless you can guarantee that the pushed data is enough to decode the metadata,
/// // you still need to call `try_decode` in a loop until it returns `DecodeResult::Data`
/// // as shown in the previous example
/// match decoder.try_decode() {
/// Ok(DecodeResult::Data(metadata)) => { return Ok(metadata); } // decode successful
/// other => { panic!("expected DecodeResult::Data, got: {other:?}") }
/// }
/// # }
/// ```
#[cfg_attr(
feature = "arrow",
doc = r##"
```rust
# use std::ops::Range;
# use bytes::Bytes;
# use arrow_array::record_batch;
# use parquet::DecodeResult;
# use parquet::arrow::ArrowWriter;
# use parquet::errors::ParquetError;
# use parquet::file::metadata::{ParquetMetaData, ParquetMetaDataPushDecoder};
#
# fn decode_metadata() -> Result<ParquetMetaData, ParquetError> {
# let file_bytes = {
# let mut buffer = vec![0];
# let batch = record_batch!(("a", Int32, [1, 2, 3])).unwrap();
# let mut writer = ArrowWriter::try_new(&mut buffer, batch.schema(), None).unwrap();
# writer.write(&batch).unwrap();
# writer.close().unwrap();
# Bytes::from(buffer)
# };
#
let file_len = file_bytes.len() as u64;
// For this example, we "prefetch" all the bytes which we have in memory,
// but in a real application, you would likely read a chunk from the end
// for example 1MB.
let prefetched_bytes = file_bytes.clone();
let mut decoder = ParquetMetaDataPushDecoder::try_new(file_len).unwrap();
// push the prefetched bytes into the decoder
decoder.push_ranges(vec![0..file_len], vec![prefetched_bytes]).unwrap();
// The decoder will now be able to decode the metadata. Note in a real application,
// unless you can guarantee that the pushed data is enough to decode the metadata,
// you still need to call `try_decode` in a loop until it returns `DecodeResult::Data`
// as shown in the previous example
match decoder.try_decode() {
Ok(DecodeResult::Data(metadata)) => { return Ok(metadata); } // decode successful
other => { panic!("expected DecodeResult::Data, got: {other:?}") }
}
# }
```
"##
)]
///
/// # Example using [`AsyncRead`]
///
Expand All @@ -160,49 +169,53 @@ use std::ops::Range;
/// implement async IO itself. To use async IO, you simply write an async
/// wrapper around it that reads the required byte ranges and pushes them into the
/// decoder.
///
/// ```rust
/// # use std::ops::Range;
/// # use bytes::Bytes;
/// use tokio::io::{AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt};
/// # use arrow_array::record_batch;
/// # use parquet::DecodeResult;
/// # use parquet::arrow::ArrowWriter;
/// # use parquet::errors::ParquetError;
/// # use parquet::file::metadata::{ParquetMetaData, ParquetMetaDataPushDecoder};
/// #
/// // This function decodes Parquet Metadata from anything that implements
/// // [`AsyncRead`] and [`AsyncSeek`] such as a tokio::fs::File
/// async fn decode_metadata(
/// file_len: u64,
/// mut async_source: impl AsyncRead + AsyncSeek + Unpin
/// ) -> Result<ParquetMetaData, ParquetError> {
/// // We need a ParquetMetaDataPushDecoder to decode the metadata.
/// let mut decoder = ParquetMetaDataPushDecoder::try_new(file_len).unwrap();
/// loop {
/// match decoder.try_decode() {
/// Ok(DecodeResult::Data(metadata)) => { return Ok(metadata); } // decode successful
/// Ok(DecodeResult::NeedsData(ranges)) => {
/// // The decoder needs more data
/// //
/// // In this example we use the AsyncRead and AsyncSeek traits to read the
/// // required ranges from the async source.
/// let mut data = Vec::with_capacity(ranges.len());
/// for range in &ranges {
/// let mut buffer = vec![0; (range.end - range.start) as usize];
/// async_source.seek(std::io::SeekFrom::Start(range.start)).await?;
/// async_source.read_exact(&mut buffer).await?;
/// data.push(Bytes::from(buffer));
/// }
/// // Push the data into the decoder and try to decode again on the next iteration.
/// decoder.push_ranges(ranges, data).unwrap();
/// }
/// Ok(DecodeResult::Finished) => { unreachable!("returned metadata in previous match arm") }
/// Err(e) => return Err(e),
/// }
/// }
/// }
/// ```
#[cfg_attr(
feature = "arrow",
doc = r##"
```rust
# use std::ops::Range;
# use bytes::Bytes;
use tokio::io::{AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt};
# use arrow_array::record_batch;
# use parquet::DecodeResult;
# use parquet::arrow::ArrowWriter;
# use parquet::errors::ParquetError;
# use parquet::file::metadata::{ParquetMetaData, ParquetMetaDataPushDecoder};
#
// This function decodes Parquet Metadata from anything that implements
// [`AsyncRead`] and [`AsyncSeek`] such as a tokio::fs::File
async fn decode_metadata(
file_len: u64,
mut async_source: impl AsyncRead + AsyncSeek + Unpin
) -> Result<ParquetMetaData, ParquetError> {
// We need a ParquetMetaDataPushDecoder to decode the metadata.
let mut decoder = ParquetMetaDataPushDecoder::try_new(file_len).unwrap();
loop {
match decoder.try_decode() {
Ok(DecodeResult::Data(metadata)) => { return Ok(metadata); } // decode successful
Ok(DecodeResult::NeedsData(ranges)) => {
// The decoder needs more data
//
// In this example we use the AsyncRead and AsyncSeek traits to read the
// required ranges from the async source.
let mut data = Vec::with_capacity(ranges.len());
for range in &ranges {
let mut buffer = vec![0; (range.end - range.start) as usize];
async_source.seek(std::io::SeekFrom::Start(range.start)).await?;
async_source.read_exact(&mut buffer).await?;
data.push(Bytes::from(buffer));
}
// Push the data into the decoder and try to decode again on the next iteration.
decoder.push_ranges(ranges, data).unwrap();
}
Ok(DecodeResult::Finished) => { unreachable!("returned metadata in previous match arm") }
Err(e) => return Err(e),
}
}
}
```
"##
)]
/// [`AsyncRead`]: tokio::io::AsyncRead
#[derive(Debug)]
pub struct ParquetMetaDataPushDecoder {
Expand Down
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