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118 lines
3.5 KiB
118 lines
3.5 KiB
// Copyright 2020 Google LLC All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package gzip provides helper functions for interacting with gzipped streams.
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package gzip
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import (
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"bufio"
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"bytes"
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"compress/gzip"
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"io"
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"github.com/google/go-containerregistry/internal/and"
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)
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// MagicHeader is the start of gzip files.
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var MagicHeader = []byte{'\x1f', '\x8b'}
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// ReadCloser reads uncompressed input data from the io.ReadCloser and
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// returns an io.ReadCloser from which compressed data may be read.
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// This uses gzip.BestSpeed for the compression level.
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func ReadCloser(r io.ReadCloser) io.ReadCloser {
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return ReadCloserLevel(r, gzip.BestSpeed)
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}
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// ReadCloserLevel reads uncompressed input data from the io.ReadCloser and
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// returns an io.ReadCloser from which compressed data may be read.
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// Refer to compress/gzip for the level:
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// https://golang.org/pkg/compress/gzip/#pkg-constants
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func ReadCloserLevel(r io.ReadCloser, level int) io.ReadCloser {
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pr, pw := io.Pipe()
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// For highly compressible layers, gzip.Writer will output a very small
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// number of bytes per Write(). This is normally fine, but when pushing
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// to a registry, we want to ensure that we're taking full advantage of
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// the available bandwidth instead of sending tons of tiny writes over
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// the wire.
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// 64K ought to be small enough for anybody.
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bw := bufio.NewWriterSize(pw, 2<<16)
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// Returns err so we can pw.CloseWithError(err)
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go func() error {
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// TODO(go1.14): Just defer {pw,gw,r}.Close like you'd expect.
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// Context: https://golang.org/issue/24283
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gw, err := gzip.NewWriterLevel(bw, level)
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if err != nil {
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return pw.CloseWithError(err)
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}
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if _, err := io.Copy(gw, r); err != nil {
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defer r.Close()
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defer gw.Close()
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return pw.CloseWithError(err)
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}
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// Close gzip writer to Flush it and write gzip trailers.
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if err := gw.Close(); err != nil {
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return pw.CloseWithError(err)
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}
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// Flush bufio writer to ensure we write out everything.
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if err := bw.Flush(); err != nil {
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return pw.CloseWithError(err)
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}
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// We don't really care if these fail.
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defer pw.Close()
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defer r.Close()
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return nil
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}()
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return pr
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}
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// UnzipReadCloser reads compressed input data from the io.ReadCloser and
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// returns an io.ReadCloser from which uncompressed data may be read.
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func UnzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
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gr, err := gzip.NewReader(r)
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if err != nil {
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return nil, err
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}
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return &and.ReadCloser{
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Reader: gr,
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CloseFunc: func() error {
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// If the unzip fails, then this seems to return the same
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// error as the read. We don't want this to interfere with
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// us closing the main ReadCloser, since this could leave
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// an open file descriptor (fails on Windows).
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gr.Close()
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return r.Close()
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},
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}, nil
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}
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// Is detects whether the input stream is compressed.
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func Is(r io.Reader) (bool, error) {
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magicHeader := make([]byte, 2)
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n, err := r.Read(magicHeader)
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if n == 0 && err == io.EOF {
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return false, nil
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}
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if err != nil {
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return false, err
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}
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return bytes.Equal(magicHeader, MagicHeader), nil
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}
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