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// Copyright 2020 Google LLC All Rights Reserved.
//
// Licensed 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 gzip provides helper functions for interacting with gzipped streams.
package gzip
import (
"bufio"
"bytes"
"compress/gzip"
"io"
"github.com/google/go-containerregistry/internal/and"
)
// MagicHeader is the start of gzip files.
var MagicHeader = []byte{'\x1f', '\x8b'}
// ReadCloser reads uncompressed input data from the io.ReadCloser and
// returns an io.ReadCloser from which compressed data may be read.
// This uses gzip.BestSpeed for the compression level.
func ReadCloser(r io.ReadCloser) io.ReadCloser {
return ReadCloserLevel(r, gzip.BestSpeed)
}
// ReadCloserLevel reads uncompressed input data from the io.ReadCloser and
// returns an io.ReadCloser from which compressed data may be read.
// Refer to compress/gzip for the level:
// https://golang.org/pkg/compress/gzip/#pkg-constants
func ReadCloserLevel(r io.ReadCloser, level int) io.ReadCloser {
pr, pw := io.Pipe()
// For highly compressible layers, gzip.Writer will output a very small
// number of bytes per Write(). This is normally fine, but when pushing
// to a registry, we want to ensure that we're taking full advantage of
// the available bandwidth instead of sending tons of tiny writes over
// the wire.
// 64K ought to be small enough for anybody.
bw := bufio.NewWriterSize(pw, 2<<16)
// Returns err so we can pw.CloseWithError(err)
go func() error {
// TODO(go1.14): Just defer {pw,gw,r}.Close like you'd expect.
// Context: https://golang.org/issue/24283
gw, err := gzip.NewWriterLevel(bw, level)
if err != nil {
return pw.CloseWithError(err)
}
if _, err := io.Copy(gw, r); err != nil {
defer r.Close()
defer gw.Close()
return pw.CloseWithError(err)
}
// Close gzip writer to Flush it and write gzip trailers.
if err := gw.Close(); err != nil {
return pw.CloseWithError(err)
}
// Flush bufio writer to ensure we write out everything.
if err := bw.Flush(); err != nil {
return pw.CloseWithError(err)
}
// We don't really care if these fail.
defer pw.Close()
defer r.Close()
return nil
}()
return pr
}
// UnzipReadCloser reads compressed input data from the io.ReadCloser and
// returns an io.ReadCloser from which uncompressed data may be read.
func UnzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
gr, err := gzip.NewReader(r)
if err != nil {
return nil, err
}
return &and.ReadCloser{
Reader: gr,
CloseFunc: func() error {
// If the unzip fails, then this seems to return the same
// error as the read. We don't want this to interfere with
// us closing the main ReadCloser, since this could leave
// an open file descriptor (fails on Windows).
gr.Close()
return r.Close()
},
}, nil
}
// Is detects whether the input stream is compressed.
func Is(r io.Reader) (bool, error) {
magicHeader := make([]byte, 2)
n, err := r.Read(magicHeader)
if n == 0 && err == io.EOF {
return false, nil
}
if err != nil {
return false, err
}
return bytes.Equal(magicHeader, MagicHeader), nil
}
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