mbutrovich commented on code in PR #8080: URL: https://github.com/apache/arrow-rs/pull/8080#discussion_r2291883386
########## parquet/src/file/metadata/push_decoder.rs: ########## @@ -0,0 +1,556 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +use crate::errors::ParquetError; +use crate::file::metadata::{PageIndexPolicy, ParquetMetaData, ParquetMetaDataReader}; +use crate::DecodeResult; + +/// A push decoder for [`ParquetMetaData`]. +/// +/// This structure implements a push API based version of the [`ParquetMetaDataReader`], which +/// decouples the IO from the metadata decoding logic. +/// +/// You can use this decoder to customize your IO operations, as shown in the +/// examples below for minimizing bytes read, prefetching data, or +/// using async IO. +/// +/// # Example +/// +/// The most basic usage is to feed the decoder with the necessary byte ranges +/// as requested as shown below. +/// +/// ```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" +/// +/// By default, the [`ParquetMetaDataPushDecoder`] will requests only the exact byte Review Comment: "will requests" -> "will request" -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@arrow.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
