zeroshade commented on a change in pull request #9817: URL: https://github.com/apache/arrow/pull/9817#discussion_r604336715
########## File path: go/parquet/compress/compress.go ########## @@ -0,0 +1,150 @@ +// 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. + +// Package compress contains the interfaces and implementations for handling compression/decompression +// of parquet data at the column levels. +package compress + +import ( + "compress/flate" + "io" + "io/ioutil" + + "github.com/apache/arrow/go/parquet/internal/gen-go/parquet" +) + +// Compression is an alias to the thrift compression codec enum type for easy use +type Compression parquet.CompressionCodec + +func (c Compression) String() string { + return parquet.CompressionCodec(c).String() +} + +// DefaultCompressionLevel will use flate.DefaultCompression since many of the compression libraries +// use that to denote "use the default". +const DefaultCompressionLevel = flate.DefaultCompression + +// Codecs is a useful struct to provide namespaced enum values to use for specifying the compression type to use +// which make for easy internal swapping between them and the thrift enum since they are initialized to the same +// constant values. +var Codecs = struct { + Uncompressed Compression + Snappy Compression + Gzip Compression + Lzo Compression + Brotli Compression + Lz4 Compression + Zstd Compression +}{ + Uncompressed: Compression(parquet.CompressionCodec_UNCOMPRESSED), + Snappy: Compression(parquet.CompressionCodec_SNAPPY), + Gzip: Compression(parquet.CompressionCodec_GZIP), + Lzo: Compression(parquet.CompressionCodec_LZO), + Brotli: Compression(parquet.CompressionCodec_BROTLI), + Lz4: Compression(parquet.CompressionCodec_LZ4), + Zstd: Compression(parquet.CompressionCodec_ZSTD), +} + +// Codec is an interface which is implemented for each compression type in order to make the interactions easy to +// implement. Most consumers won't be calling GetCodec directly. +type Codec interface { + // NewReader provides a reader that wraps a stream with compressed data to stream the uncompressed data + NewReader(io.Reader) io.ReadCloser + // NewWriter provides a wrapper around a write stream to compress data before writing it. + NewWriter(io.Writer) io.WriteCloser + // NewWriterLevel is like NewWrapper but allows specifying the compression level + NewWriterLevel(io.Writer, int) (io.WriteCloser, error) + // Encode encodes a block of data given by src and returns the compressed block. dst needs to be either nil + // or sized large enough to fit the compressed block (use CompressBound to allocate). dst and src should not + // overlap since some of the compression types don't allow it. + // + // The returned slice *might* be a slice of dst if it was able to fit the whole compressed data in it. + Encode(dst, src []byte) []byte + // EncodeLevel is like Encode, but specifies a particular encoding level instead of the default. + EncodeLevel(dst, src []byte, level int) []byte + // CompressBound returns the boundary of maximum size of compressed data under the chosen codec. + CompressBound(int64) int64 + // Decode is for decoding a single block rather than a stream, like with Encode, dst must be either nil or + // sized large enough to accommodate the uncompressed data and should not overlap with src. + // + // the returned slice *might* be a slice of dst. + Decode(dst, src []byte) []byte +} + +var codecs = map[Compression]Codec{} + +type nocodec struct{} + +func (nocodec) NewReader(r io.Reader) io.ReadCloser { + ret, ok := r.(io.ReadCloser) + if !ok { + return ioutil.NopCloser(r) + } + return ret +} + +func (nocodec) Decode(dst, src []byte) []byte { + if dst != nil { + copy(dst, src) + } + return dst +} + +type writerNopCloser struct { + io.Writer +} + +func (writerNopCloser) Close() error { + return nil +} + +func (nocodec) Encode(dst, src []byte) []byte { + copy(dst, src) + return dst +} + +func (nocodec) EncodeLevel(dst, src []byte, _ int) []byte { + copy(dst, src) + return dst +} + +func (nocodec) NewWriter(w io.Writer) io.WriteCloser { + ret, ok := w.(io.WriteCloser) + if !ok { + return writerNopCloser{w} + } + return ret +} + +func (n nocodec) NewWriterLevel(w io.Writer, _ int) (io.WriteCloser, error) { + return n.NewWriter(w), nil +} + +func (nocodec) CompressBound(len int64) int64 { return len } + +func init() { + codecs[Codecs.Uncompressed] = nocodec{} +} + +// GetCodec returns a Codec interface for the requested Compression type +func GetCodec(typ Compression) Codec { + ret, ok := codecs[typ] + if !ok { + // return codecs[Codecs.Uncompressed] Review comment: For now i liked the idea of erroring when trying to retrieve a codec if we haven't implemented it rather than silently returning the uncompressed one. The alternative here to panicing would be to change this to return `(Codec, error)` and have it return nil and an unimplemented error if it can't find the desired codec. -- 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. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
