stdlib.go

Documentation: github.com/klauspost/compress/gzhttp/writer/gzstd

     1  // package gzstd provides gzip compression through the standard library.
     2  
     3  package gzstd
     4  
     5  import (
     6  	"compress/gzip"
     7  	"io"
     8  	"sync"
     9  
    10  	"github.com/klauspost/compress/gzhttp/writer"
    11  )
    12  
    13  // gzipWriterPools stores a sync.Pool for each compression level for reuse of
    14  // gzip.Writers. Use poolIndex to covert a compression level to an index into
    15  // gzipWriterPools.
    16  var gzipWriterPools [gzip.BestCompression - gzip.HuffmanOnly + 1]*sync.Pool
    17  
    18  func init() {
    19  	for i := gzip.HuffmanOnly; i <= gzip.BestCompression; i++ {
    20  		addLevelPool(i)
    21  	}
    22  }
    23  
    24  // poolIndex maps a compression level to its index into gzipWriterPools. It
    25  // assumes that level is a valid gzip compression level.
    26  func poolIndex(level int) int {
    27  	if level > gzip.BestCompression {
    28  		level = gzip.BestCompression
    29  	}
    30  	if level < gzip.HuffmanOnly {
    31  		level = gzip.BestSpeed
    32  	}
    33  	return level - gzip.HuffmanOnly
    34  }
    35  
    36  func addLevelPool(level int) {
    37  	gzipWriterPools[poolIndex(level)] = &sync.Pool{
    38  		New: func() interface{} {
    39  			// NewWriterLevel only returns error on a bad level, we are guaranteeing
    40  			// that this will be a valid level so it is okay to ignore the returned
    41  			// error.
    42  			w, _ := gzip.NewWriterLevel(nil, level)
    43  			return w
    44  		},
    45  	}
    46  }
    47  
    48  type pooledWriter struct {
    49  	*gzip.Writer
    50  	index int
    51  }
    52  
    53  func (pw *pooledWriter) Close() error {
    54  	err := pw.Writer.Close()
    55  	gzipWriterPools[pw.index].Put(pw.Writer)
    56  	pw.Writer = nil
    57  	return err
    58  }
    59  
    60  func NewWriter(w io.Writer, level int) writer.GzipWriter {
    61  	index := poolIndex(level)
    62  	gzw := gzipWriterPools[index].Get().(*gzip.Writer)
    63  	gzw.Reset(w)
    64  	return &pooledWriter{
    65  		Writer: gzw,
    66  		index:  index,
    67  	}
    68  }
    69  
    70  // SetHeader will override the gzip header on pw.
    71  func (pw *pooledWriter) SetHeader(h writer.Header) {
    72  	pw.Name = h.Name
    73  	pw.Extra = h.Extra
    74  	pw.Comment = h.Comment
    75  	pw.ModTime = h.ModTime
    76  	pw.OS = h.OS
    77  }
    78  
    79  func Levels() (min, max int) {
    80  	return gzip.HuffmanOnly, gzip.BestCompression
    81  }
    82  
    83  func ImplementationInfo() string {
    84  	return "compress/gzip"
    85  }
    86
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