62 lines
2.2 KiB
Go
62 lines
2.2 KiB
Go
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package copy
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import (
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"bytes"
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"compress/bzip2"
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"compress/gzip"
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"errors"
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"io"
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"github.com/Sirupsen/logrus"
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)
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// decompressorFunc, given a compressed stream, returns the decompressed stream.
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type decompressorFunc func(io.Reader) (io.Reader, error)
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func gzipDecompressor(r io.Reader) (io.Reader, error) {
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return gzip.NewReader(r)
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}
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func bzip2Decompressor(r io.Reader) (io.Reader, error) {
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return bzip2.NewReader(r), nil
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}
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func xzDecompressor(r io.Reader) (io.Reader, error) {
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return nil, errors.New("Decompressing xz streams is not supported")
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}
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// compressionAlgos is an internal implementation detail of detectCompression
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var compressionAlgos = map[string]struct {
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prefix []byte
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decompressor decompressorFunc
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}{
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"gzip": {[]byte{0x1F, 0x8B, 0x08}, gzipDecompressor}, // gzip (RFC 1952)
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"bzip2": {[]byte{0x42, 0x5A, 0x68}, bzip2Decompressor}, // bzip2 (decompress.c:BZ2_decompress)
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"xz": {[]byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}, xzDecompressor}, // xz (/usr/share/doc/xz/xz-file-format.txt)
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}
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// detectCompression returns a decompressorFunc if the input is recognized as a compressed format, nil otherwise.
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// Because it consumes the start of input, other consumers must use the returned io.Reader instead to also read from the beginning.
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func detectCompression(input io.Reader) (decompressorFunc, io.Reader, error) {
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buffer := [8]byte{}
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n, err := io.ReadAtLeast(input, buffer[:], len(buffer))
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if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
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// This is a “real” error. We could just ignore it this time, process the data we have, and hope that the source will report the same error again.
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// Instead, fail immediately with the original error cause instead of a possibly secondary/misleading error returned later.
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return nil, nil, err
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}
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var decompressor decompressorFunc
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for name, algo := range compressionAlgos {
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if bytes.HasPrefix(buffer[:n], algo.prefix) {
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logrus.Debugf("Detected compression format %s", name)
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decompressor = algo.decompressor
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break
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}
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}
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if decompressor == nil {
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logrus.Debugf("No compression detected")
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}
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return decompressor, io.MultiReader(bytes.NewReader(buffer[:n]), input), nil
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}
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