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Source file src/github.com/google/go-containerregistry/internal/zstd/zstd.go

Documentation: github.com/google/go-containerregistry/internal/zstd

     1  // Copyright 2022 Google LLC All Rights Reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //    http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package zstd provides helper functions for interacting with zstd streams.
    16  package zstd
    17  
    18  import (
    19  	"bufio"
    20  	"bytes"
    21  	"io"
    22  
    23  	"github.com/google/go-containerregistry/internal/and"
    24  	"github.com/klauspost/compress/zstd"
    25  )
    26  
    27  // MagicHeader is the start of zstd files.
    28  var MagicHeader = []byte{'\x28', '\xb5', '\x2f', '\xfd'}
    29  
    30  // ReadCloser reads uncompressed input data from the io.ReadCloser and
    31  // returns an io.ReadCloser from which compressed data may be read.
    32  // This uses zstd level 1 for the compression.
    33  func ReadCloser(r io.ReadCloser) io.ReadCloser {
    34  	return ReadCloserLevel(r, 1)
    35  }
    36  
    37  // ReadCloserLevel reads uncompressed input data from the io.ReadCloser and
    38  // returns an io.ReadCloser from which compressed data may be read.
    39  func ReadCloserLevel(r io.ReadCloser, level int) io.ReadCloser {
    40  	pr, pw := io.Pipe()
    41  
    42  	// For highly compressible layers, zstd.Writer will output a very small
    43  	// number of bytes per Write(). This is normally fine, but when pushing
    44  	// to a registry, we want to ensure that we're taking full advantage of
    45  	// the available bandwidth instead of sending tons of tiny writes over
    46  	// the wire.
    47  	// 64K ought to be small enough for anybody.
    48  	bw := bufio.NewWriterSize(pw, 2<<16)
    49  
    50  	// Returns err so we can pw.CloseWithError(err)
    51  	go func() error {
    52  		// TODO(go1.14): Just defer {pw,zw,r}.Close like you'd expect.
    53  		// Context: https://golang.org/issue/24283
    54  		zw, err := zstd.NewWriter(bw, zstd.WithEncoderLevel(zstd.EncoderLevelFromZstd(level)))
    55  		if err != nil {
    56  			return pw.CloseWithError(err)
    57  		}
    58  
    59  		if _, err := io.Copy(zw, r); err != nil {
    60  			defer r.Close()
    61  			defer zw.Close()
    62  			return pw.CloseWithError(err)
    63  		}
    64  
    65  		// Close zstd writer to Flush it and write zstd trailers.
    66  		if err := zw.Close(); err != nil {
    67  			return pw.CloseWithError(err)
    68  		}
    69  
    70  		// Flush bufio writer to ensure we write out everything.
    71  		if err := bw.Flush(); err != nil {
    72  			return pw.CloseWithError(err)
    73  		}
    74  
    75  		// We don't really care if these fail.
    76  		defer pw.Close()
    77  		defer r.Close()
    78  
    79  		return nil
    80  	}()
    81  
    82  	return pr
    83  }
    84  
    85  // UnzipReadCloser reads compressed input data from the io.ReadCloser and
    86  // returns an io.ReadCloser from which uncompressed data may be read.
    87  func UnzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
    88  	gr, err := zstd.NewReader(r)
    89  	if err != nil {
    90  		return nil, err
    91  	}
    92  	return &and.ReadCloser{
    93  		Reader: gr,
    94  		CloseFunc: func() error {
    95  			// If the unzip fails, then this seems to return the same
    96  			// error as the read.  We don't want this to interfere with
    97  			// us closing the main ReadCloser, since this could leave
    98  			// an open file descriptor (fails on Windows).
    99  			gr.Close()
   100  			return r.Close()
   101  		},
   102  	}, nil
   103  }
   104  
   105  // Is detects whether the input stream is compressed.
   106  func Is(r io.Reader) (bool, error) {
   107  	magicHeader := make([]byte, 4)
   108  	n, err := r.Read(magicHeader)
   109  	if n == 0 && err == io.EOF {
   110  		return false, nil
   111  	}
   112  	if err != nil {
   113  		return false, err
   114  	}
   115  	return bytes.Equal(magicHeader, MagicHeader), nil
   116  }
   117  

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