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100 lines
2.2 KiB
100 lines
2.2 KiB
package solidblock
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import (
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"errors"
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"hash"
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"hash/crc32"
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"io"
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"io/ioutil"
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)
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var (
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// ErrChecksumMismatch is returned when a file's crc check fails.
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ErrChecksumMismatch = errors.New("checksum mismatch")
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)
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// Solidblock provides sequential access to files that have been concatenated
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// into a single compressed data block.
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type Solidblock struct {
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sizes []uint64
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crcs []uint32
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base io.Reader
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file io.Reader
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crc hash.Hash32
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target int
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index int
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}
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// New returns a new solidblock reader.
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func New(r io.Reader, sizes []uint64, crcs []uint32) *Solidblock {
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if len(sizes) != len(crcs) {
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panic("crcs slice needs to be the same length as sizes slice")
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}
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return &Solidblock{
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sizes: sizes,
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crcs: crcs,
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target: -1,
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base: r,
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}
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}
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// Next advances to the next file entry in solid block.
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//
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// Calling Next without reading the current file is supported. Only when Read
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// is called will decompression occur for current file. Any skipped files will
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// still need to be decompressed, but their contents is discarded.
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//
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// io.EOF is returned at the end of the input.
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func (fr *Solidblock) Next() error {
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if fr.target < len(fr.sizes)-1 {
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fr.target++
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return nil
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}
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return io.EOF
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}
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// Read reads from the current file in solid block.
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// It returns (0, io.EOF) when it reaches the end of that file,
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// until Next is called to advance to the next file.
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func (fr *Solidblock) Read(p []byte) (int, error) {
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if fr.file != nil && fr.index != fr.target {
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// drain current fileReader
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_, err := io.Copy(ioutil.Discard, fr.file)
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if err != nil {
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return 0, err
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}
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}
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if fr.file == nil || fr.index != fr.target {
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// discard until we're at the position we want to be at
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for i := fr.index + 1; i < fr.target; i++ {
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_, err := io.CopyN(ioutil.Discard, fr.base, int64(fr.sizes[i]))
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if err != nil {
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return 0, err
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}
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}
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fr.crc = crc32.NewIEEE()
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fr.file = io.TeeReader(io.LimitReader(fr.base, int64(fr.sizes[fr.target])), fr.crc)
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fr.index = fr.target
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}
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n, err := fr.file.Read(p)
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if err == io.EOF {
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if fr.crc.Sum32() != fr.crcs[fr.index] {
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return n, ErrChecksumMismatch
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}
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}
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return n, err
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}
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func (fr *Solidblock) Size() int64 {
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if fr.target < 0 {
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return 0
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}
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return int64(fr.sizes[fr.target])
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} |