Source: compressed.go in package golang.org/x/crypto/openpgp/packet


package packet

import (
	"compress/bzip2"
	"compress/flate"
	"compress/zlib"
	"golang.org/x/crypto/openpgp/errors"
	"io"
	"strconv"
)

Compressed represents a compressed OpenPGP packet. The decompressed contents will contain more OpenPGP packets. See RFC 4880, section 5.6.

type Compressed struct {
	Body io.Reader
}

const (
	NoCompression      = flate.NoCompression
	BestSpeed          = flate.BestSpeed
	BestCompression    = flate.BestCompression
	DefaultCompression = flate.DefaultCompression
)

CompressionConfig contains compressor configuration settings.

Level is the compression level to use. It must be set to between -1 and 9, with -1 causing the compressor to use the default compression level, 0 causing the compressor to use no compression and 1 to 9 representing increasing (better, slower) compression levels. If Level is less than -1 or more then 9, a non-nil error will be returned during encryption. See the constants above for convenient common settings for Level.

	Level int
}

func (c *Compressed) parse(r io.Reader) error {
	var buf [1]byte
	_, err := readFull(r, buf[:])
	if err != nil {
		return err
	}

	switch buf[0] {
	case 1:
		c.Body = flate.NewReader(r)
	case 2:
		c.Body, err = zlib.NewReader(r)
	case 3:
		c.Body = bzip2.NewReader(r)
	default:
		err = errors.UnsupportedError("unknown compression algorithm: " + strconv.Itoa(int(buf[0])))
	}

	return err
}

compressedWriterCloser represents the serialized compression stream header and the compressor. Its Close() method ensures that both the compressor and serialized stream header are closed. Its Write() method writes to the compressor.

type compressedWriteCloser struct {
	sh io.Closer      // Stream Header
	c  io.WriteCloser // Compressor
}

func (cwc compressedWriteCloser) Write(p []byte) (int, error) {
	return cwc.c.Write(p)
}

func (cwc compressedWriteCloser) Close() (err error) {
	err = cwc.c.Close()
	if err != nil {
		return err
	}

	return cwc.sh.Close()
}

SerializeCompressed serializes a compressed data packet to w and returns a WriteCloser to which the literal data packets themselves can be written and which MUST be closed on completion. If cc is nil, sensible defaults will be used to configure the compression algorithm.

func SerializeCompressed(w io.WriteCloser, algo CompressionAlgo, cc *CompressionConfig) (literaldata io.WriteCloser, err error) {
	compressed, err := serializeStreamHeader(w, packetTypeCompressed)
	if err != nil {
		return
	}

	_, err = compressed.Write([]byte{uint8(algo)})
	if err != nil {
		return
	}

	level := DefaultCompression
	if cc != nil {
		level = cc.Level
	}

	var compressor io.WriteCloser
	switch algo {
	case CompressionZIP:
		compressor, err = flate.NewWriter(compressed, level)
	case CompressionZLIB:
		compressor, err = zlib.NewWriterLevel(compressed, level)
	default:
		s := strconv.Itoa(int(algo))
		err = errors.UnsupportedError("Unsupported compression algorithm: " + s)
	}
	if err != nil {
		return
	}

	literaldata = compressedWriteCloser{compressed, compressor}

	return