gtsocial-umbx

gzip.go (6940B)

---

 // 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 (
 	"errors"
 	"fmt"
 	"hash/crc32"
 	"io"
 
 	"github.com/klauspost/compress/flate"
 )
 
 // 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
 	ConstantCompression = flate.ConstantCompression
 	HuffmanOnly         = flate.HuffmanOnly
 
 	// StatelessCompression will do compression but without maintaining any state
 	// between Write calls.
 	// There will be no memory kept between Write calls,
 	// but compression and speed will be suboptimal.
 	// Because of this, the size of actual Write calls will affect output size.
 	StatelessCompression = -3
 )
 
 // 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
 	err         error
 	compressor  *flate.Writer
 	digest      uint32 // CRC-32, IEEE polynomial (section 8)
 	size        uint32 // Uncompressed size (section 2.3.1)
 	wroteHeader bool
 	closed      bool
 	buf         [10]byte
 }
 
 // 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 WriteCloser 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, 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 < StatelessCompression || 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 level != StatelessCompression {
 		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[0] = gzipID1
 		z.buf[1] = gzipID2
 		z.buf[2] = gzipDeflate
 		z.buf[3] = 0
 		if z.Extra != nil {
 			z.buf[3] |= 0x04
 		}
 		if z.Name != "" {
 			z.buf[3] |= 0x08
 		}
 		if z.Comment != "" {
 			z.buf[3] |= 0x10
 		}
 		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
 		} else {
 			z.buf[8] = 0
 		}
 		z.buf[9] = z.OS
 		n, z.err = z.w.Write(z.buf[:10])
 		if z.err != nil {
 			return n, z.err
 		}
 		if z.Extra != nil {
 			z.err = z.writeBytes(z.Extra)
 			if z.err != nil {
 				return n, z.err
 			}
 		}
 		if z.Name != "" {
 			z.err = z.writeString(z.Name)
 			if z.err != nil {
 				return n, z.err
 			}
 		}
 		if z.Comment != "" {
 			z.err = z.writeString(z.Comment)
 			if z.err != nil {
 				return n, z.err
 			}
 		}
 
 		if z.compressor == nil && z.level != StatelessCompression {
 			z.compressor, _ = flate.NewWriter(z.w, z.level)
 		}
 	}
 	z.size += uint32(len(p))
 	z.digest = crc32.Update(z.digest, crc32.IEEETable, p)
 	if z.level == StatelessCompression {
 		return len(p), flate.StatelessDeflate(z.w, p, false, nil)
 	}
 	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 || z.level == StatelessCompression {
 		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, flushing any unwritten data to the underlying
 // io.Writer, but 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
 		}
 	}
 	if z.level == StatelessCompression {
 		z.err = flate.StatelessDeflate(z.w, nil, true, nil)
 	} else {
 		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
 }