diff --git a/zstd/decodeheader.go b/zstd/decodeheader.go index f6a240970d..6a5a2988b6 100644 --- a/zstd/decodeheader.go +++ b/zstd/decodeheader.go @@ -95,42 +95,54 @@ type Header struct { // If there isn't enough input, io.ErrUnexpectedEOF is returned. // The FirstBlock.OK will indicate if enough information was available to decode the first block header. func (h *Header) Decode(in []byte) error { + _, err := h.DecodeAndStrip(in) + return err +} + +// DecodeAndStrip will decode the header from the beginning of the stream +// and on success return the remaining bytes. +// This will decode the frame header and the first block header if enough bytes are provided. +// It is recommended to provide at least HeaderMaxSize bytes. +// If the frame header cannot be read an error will be returned. +// If there isn't enough input, io.ErrUnexpectedEOF is returned. +// The FirstBlock.OK will indicate if enough information was available to decode the first block header. +func (h *Header) DecodeAndStrip(in []byte) (remain []byte, err error) { *h = Header{} if len(in) < 4 { - return io.ErrUnexpectedEOF + return nil, io.ErrUnexpectedEOF } h.HeaderSize += 4 b, in := in[:4], in[4:] if string(b) != frameMagic { if string(b[1:4]) != skippableFrameMagic || b[0]&0xf0 != 0x50 { - return ErrMagicMismatch + return nil, ErrMagicMismatch } if len(in) < 4 { - return io.ErrUnexpectedEOF + return nil, io.ErrUnexpectedEOF } h.HeaderSize += 4 h.Skippable = true h.SkippableID = int(b[0] & 0xf) h.SkippableSize = binary.LittleEndian.Uint32(in) - return nil + return in[4:], nil } // Read Window_Descriptor // https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor if len(in) < 1 { - return io.ErrUnexpectedEOF + return nil, io.ErrUnexpectedEOF } fhd, in := in[0], in[1:] h.HeaderSize++ h.SingleSegment = fhd&(1<<5) != 0 h.HasCheckSum = fhd&(1<<2) != 0 if fhd&(1<<3) != 0 { - return errors.New("reserved bit set on frame header") + return nil, errors.New("reserved bit set on frame header") } if !h.SingleSegment { if len(in) < 1 { - return io.ErrUnexpectedEOF + return nil, io.ErrUnexpectedEOF } var wd byte wd, in = in[0], in[1:] @@ -148,7 +160,7 @@ func (h *Header) Decode(in []byte) error { size = 4 } if len(in) < int(size) { - return io.ErrUnexpectedEOF + return nil, io.ErrUnexpectedEOF } b, in = in[:size], in[size:] h.HeaderSize += int(size) @@ -178,7 +190,7 @@ func (h *Header) Decode(in []byte) error { if fcsSize > 0 { h.HasFCS = true if len(in) < fcsSize { - return io.ErrUnexpectedEOF + return nil, io.ErrUnexpectedEOF } b, in = in[:fcsSize], in[fcsSize:] h.HeaderSize += int(fcsSize) @@ -199,7 +211,7 @@ func (h *Header) Decode(in []byte) error { // Frame Header done, we will not fail from now on. if len(in) < 3 { - return nil + return in, nil } tmp := in[:3] bh := uint32(tmp[0]) | (uint32(tmp[1]) << 8) | (uint32(tmp[2]) << 16) @@ -209,7 +221,7 @@ func (h *Header) Decode(in []byte) error { cSize := int(bh >> 3) switch blockType { case blockTypeReserved: - return nil + return in, nil case blockTypeRLE: h.FirstBlock.Compressed = true h.FirstBlock.DecompressedSize = cSize @@ -225,5 +237,25 @@ func (h *Header) Decode(in []byte) error { } h.FirstBlock.OK = true - return nil + return in, nil +} + +// AppendTo will append the encoded header to the dst slice. +// There is no error checking performed on the header values. +func (h *Header) AppendTo(dst []byte) ([]byte, error) { + if h.Skippable { + magic := [4]byte{0x50, 0x2a, 0x4d, 0x18} + magic[0] |= byte(h.SkippableID & 0xf) + dst = append(dst, magic[:]...) + f := h.SkippableSize + return append(dst, uint8(f), uint8(f>>8), uint8(f>>16), uint8(f>>24)), nil + } + f := frameHeader{ + ContentSize: h.FrameContentSize, + WindowSize: uint32(h.WindowSize), + SingleSegment: h.SingleSegment, + Checksum: h.HasCheckSum, + DictID: h.DictionaryID, + } + return f.appendTo(dst), nil } diff --git a/zstd/frameenc.go b/zstd/frameenc.go index 2f5d5ed454..667ca06794 100644 --- a/zstd/frameenc.go +++ b/zstd/frameenc.go @@ -76,7 +76,7 @@ func (f frameHeader) appendTo(dst []byte) []byte { if f.SingleSegment { dst = append(dst, uint8(f.ContentSize)) } - // Unless SingleSegment is set, framessizes < 256 are nto stored. + // Unless SingleSegment is set, framessizes < 256 are not stored. case 1: f.ContentSize -= 256 dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8))