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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gzip
import (
"compress/flate"
"errors"
"fmt"
"hash/crc32"
"io"
"time"
)
// These constants are copied from the flate package, so that code that imports
// "compress/gzip" does not also have to import "compress/flate".
const (
NoCompression = flate.NoCompression
BestSpeed = flate.BestSpeed
BestCompression = flate.BestCompression
DefaultCompression = flate.DefaultCompression
HuffmanOnly = flate.HuffmanOnly
)
// A Writer is an io.WriteCloser.
// Writes to a Writer are compressed and written to w.
type Writer struct {
Header // written at first call to Write, Flush, or Close
w io.Writer
level int
wroteHeader bool
compressor *flate.Writer
digest uint32 // CRC-32, IEEE polynomial (section 8)
size uint32 // Uncompressed size (section 2.3.1)
closed bool
buf [10]byte
err error
}
// NewWriter returns a new [Writer].
// Writes to the returned writer are compressed and written to w.
//
// It is the caller's responsibility to call Close on the [Writer] when done.
// Writes may be buffered and not flushed until Close.
//
// Callers that wish to set the fields in Writer.Header must do so before
// the first call to Write, Flush, or Close.
func NewWriter(w io.Writer) *Writer {
z, _ := NewWriterLevel(w, DefaultCompression)
return z
}
// NewWriterLevel is like [NewWriter] but specifies the compression level instead
// of assuming [DefaultCompression].
//
// The compression level can be [DefaultCompression], [NoCompression], [HuffmanOnly]
// or any integer value between [BestSpeed] and [BestCompression] inclusive.
// The error returned will be nil if the level is valid.
func NewWriterLevel(w io.Writer, level int) (*Writer, error) {
if level < HuffmanOnly || level > BestCompression {
return nil, fmt.Errorf("gzip: invalid compression level: %d", level)
}
z := new(Writer)
z.init(w, level)
return z, nil
}
func (z *Writer) init(w io.Writer, level int) {
compressor := z.compressor
if compressor != nil {
compressor.Reset(w)
}
*z = Writer{
Header: Header{
OS: 255, // unknown
},
w: w,
level: level,
compressor: compressor,
}
}
// Reset discards the [Writer] z's state and makes it equivalent to the
// result of its original state from [NewWriter] or [NewWriterLevel], but
// writing to w instead. This permits reusing a [Writer] rather than
// allocating a new one.
func (z *Writer) Reset(w io.Writer) {
z.init(w, z.level)
}
// writeBytes writes a length-prefixed byte slice to z.w.
func (z *Writer) writeBytes(b []byte) error {
if len(b) > 0xffff {
return errors.New("gzip.Write: Extra data is too large")
}
le.PutUint16(z.buf[:2], uint16(len(b)))
_, err := z.w.Write(z.buf[:2])
if err != nil {
return err
}
_, err = z.w.Write(b)
return err
}
// writeString writes a UTF-8 string s in GZIP's format to z.w.
// GZIP (RFC 1952) specifies that strings are NUL-terminated ISO 8859-1 (Latin-1).
func (z *Writer) writeString(s string) (err error) {
// GZIP stores Latin-1 strings; error if non-Latin-1; convert if non-ASCII.
needconv := false
for _, v := range s {
if v == 0 || v > 0xff {
return errors.New("gzip.Write: non-Latin-1 header string")
}
if v > 0x7f {
needconv = true
}
}
if needconv {
b := make([]byte, 0, len(s))
for _, v := range s {
b = append(b, byte(v))
}
_, err = z.w.Write(b)
} else {
_, err = io.WriteString(z.w, s)
}
if err != nil {
return err
}
// GZIP strings are NUL-terminated.
z.buf[0] = 0
_, err = z.w.Write(z.buf[:1])
return err
}
// Write writes a compressed form of p to the underlying [io.Writer]. The
// compressed bytes are not necessarily flushed until the [Writer] is closed.
func (z *Writer) Write(p []byte) (int, error) {
if z.err != nil {
return 0, z.err
}
var n int
// Write the GZIP header lazily.
if !z.wroteHeader {
z.wroteHeader = true
z.buf = [10]byte{0: gzipID1, 1: gzipID2, 2: gzipDeflate}
if z.Extra != nil {
z.buf[3] |= 0x04
}
if z.Name != "" {
z.buf[3] |= 0x08
}
if z.Comment != "" {
z.buf[3] |= 0x10
}
if z.ModTime.After(time.Unix(0, 0)) {
// Section 2.3.1, the zero value for MTIME means that the
// modified time is not set.
le.PutUint32(z.buf[4:8], uint32(z.ModTime.Unix()))
}
if z.level == BestCompression {
z.buf[8] = 2
} else if z.level == BestSpeed {
z.buf[8] = 4
}
z.buf[9] = z.OS
_, z.err = z.w.Write(z.buf[:10])
if z.err != nil {
return 0, z.err
}
if z.Extra != nil {
z.err = z.writeBytes(z.Extra)
if z.err != nil {
return 0, z.err
}
}
if z.Name != "" {
z.err = z.writeString(z.Name)
if z.err != nil {
return 0, z.err
}
}
if z.Comment != "" {
z.err = z.writeString(z.Comment)
if z.err != nil {
return 0, z.err
}
}
if z.compressor == nil {
z.compressor, _ = flate.NewWriter(z.w, z.level)
}
}
z.size += uint32(len(p))
z.digest = crc32.Update(z.digest, crc32.IEEETable, p)
n, z.err = z.compressor.Write(p)
return n, z.err
}
// Flush flushes any pending compressed data to the underlying writer.
//
// It is useful mainly in compressed network protocols, to ensure that
// a remote reader has enough data to reconstruct a packet. Flush does
// not return until the data has been written. If the underlying
// writer returns an error, Flush returns that error.
//
// In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
func (z *Writer) Flush() error {
if z.err != nil {
return z.err
}
if z.closed {
return nil
}
if !z.wroteHeader {
z.Write(nil)
if z.err != nil {
return z.err
}
}
z.err = z.compressor.Flush()
return z.err
}
// Close closes the [Writer] by flushing any unwritten data to the underlying
// [io.Writer] and writing the GZIP footer.
// It does not close the underlying [io.Writer].
func (z *Writer) Close() error {
if z.err != nil {
return z.err
}
if z.closed {
return nil
}
z.closed = true
if !z.wroteHeader {
z.Write(nil)
if z.err != nil {
return z.err
}
}
z.err = z.compressor.Close()
if z.err != nil {
return z.err
}
le.PutUint32(z.buf[:4], z.digest)
le.PutUint32(z.buf[4:8], z.size)
_, z.err = z.w.Write(z.buf[:8])
return z.err
}