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Buffer last 2048 bytes of a file for unpack
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parent
3c3a180417
commit
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@ -241,32 +241,55 @@ type Unpacker struct {
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k *crypto.Key
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}
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const preloadHeaderSize = 2048
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// NewUnpacker returns a pointer to Unpacker which can be used to read
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// individual Blobs from a pack.
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func NewUnpacker(k *crypto.Key, rd io.ReadSeeker) (*Unpacker, error) {
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var err error
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// read the last 2048 byte, this will mostly be enough for the header, so
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// we do not need another round trip.
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buf := make([]byte, preloadHeaderSize)
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_, err = rd.Seek(-int64(len(buf)), 2)
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if err != nil {
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return nil, fmt.Errorf("seek to -%d failed: %v", len(buf), err)
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}
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_, err = io.ReadFull(rd, buf)
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if err != nil {
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return nil, fmt.Errorf("error reading last %d bytes: %v", len(buf), err)
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}
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hdrRd := io.ReadSeeker(bytes.NewReader(buf))
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ls := binary.Size(uint32(0))
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// reset to the end to read header length
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_, err = rd.Seek(-int64(ls), 2)
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_, err = hdrRd.Seek(-int64(ls), 2)
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if err != nil {
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return nil, fmt.Errorf("seeking to read header length failed: %v", err)
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}
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var length uint32
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err = binary.Read(rd, binary.LittleEndian, &length)
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err = binary.Read(hdrRd, binary.LittleEndian, &length)
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if err != nil {
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return nil, fmt.Errorf("reading header length failed: %v", err)
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}
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// if the header is longer than the preloaded buffer, use the original
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// reader (and do another round trip)
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if int(length) > preloadHeaderSize-ls {
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hdrRd = rd
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}
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// reset to the beginning of the header
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_, err = rd.Seek(-int64(ls)-int64(length), 2)
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_, err = hdrRd.Seek(-int64(ls)-int64(length), 2)
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if err != nil {
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return nil, fmt.Errorf("seeking to read header length failed: %v", err)
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}
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// read header
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hrd, err := crypto.DecryptFrom(k, io.LimitReader(rd, int64(length)))
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hrd, err := crypto.DecryptFrom(k, io.LimitReader(hdrRd, int64(length)))
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if err != nil {
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return nil, err
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}
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