101 lines
2.3 KiB
Go
101 lines
2.3 KiB
Go
package unsnap
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import (
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"encoding/binary"
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// no c lib dependency
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snappy "github.com/golang/snappy"
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// or, use the C wrapper for speed
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//snappy "github.com/dgryski/go-csnappy"
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)
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// add Write() method for SnappyFile (see unsnap.go)
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// reference for snappy framing/streaming format:
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// http://code.google.com/p/snappy/source/browse/trunk/framing_format.txt
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// ?spec=svn68&r=71
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//
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// Write writes len(p) bytes from p to the underlying data stream.
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// It returns the number of bytes written from p (0 <= n <= len(p)) and
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// any error encountered that caused the write to stop early. Write
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// must return a non-nil error if it returns n < len(p).
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//
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func (sf *SnappyFile) Write(p []byte) (n int, err error) {
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if sf.SnappyEncodeDecodeOff {
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return sf.Writer.Write(p)
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}
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if !sf.Writing {
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panic("Writing on a read-only SnappyFile")
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}
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// encoding in snappy can apparently go beyond the original size, beware.
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// so our buffers must be sized 2*max snappy chunk => 2 * CHUNK_MAX(65536)
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sf.DecBuf.Reset()
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sf.EncBuf.Reset()
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if !sf.HeaderChunkWritten {
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sf.HeaderChunkWritten = true
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_, err = sf.Writer.Write(SnappyStreamHeaderMagic)
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if err != nil {
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return
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}
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}
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var chunk []byte
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var chunk_type byte
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var crc uint32
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for len(p) > 0 {
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// chunk points to input p by default, unencoded input.
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chunk = p[:IntMin(len(p), CHUNK_MAX)]
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crc = masked_crc32c(chunk)
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writeme := chunk[:]
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// first write to EncBuf, as a temp, in case we want
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// to discard and send uncompressed instead.
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compressed_chunk := snappy.Encode(sf.EncBuf.GetEndmostWritableSlice(), chunk)
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if len(compressed_chunk) <= int((1-_COMPRESSION_THRESHOLD)*float64(len(chunk))) {
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writeme = compressed_chunk
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chunk_type = _COMPRESSED_CHUNK
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} else {
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// keep writeme pointing at original chunk (uncompressed)
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chunk_type = _UNCOMPRESSED_CHUNK
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}
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const crc32Sz = 4
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var tag32 uint32 = uint32(chunk_type) + (uint32(len(writeme)+crc32Sz) << 8)
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err = binary.Write(sf.Writer, binary.LittleEndian, tag32)
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if err != nil {
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return
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}
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err = binary.Write(sf.Writer, binary.LittleEndian, crc)
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if err != nil {
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return
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}
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_, err = sf.Writer.Write(writeme)
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if err != nil {
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return
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}
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n += len(chunk)
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p = p[len(chunk):]
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}
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return n, nil
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}
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func IntMin(a int, b int) int {
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if a < b {
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return a
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}
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return b
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}
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