forked from TrueCloudLab/restic
81 lines
1.5 KiB
Go
81 lines
1.5 KiB
Go
package restic
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import (
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"io"
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"math/rand"
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"github.com/restic/restic/internal/errors"
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)
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// RandReader allows reading from a rand.Rand.
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type RandReader struct {
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rnd *rand.Rand
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buf []byte
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}
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// NewRandReader creates a new Reader from a random source.
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func NewRandReader(rnd *rand.Rand) io.Reader {
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return &RandReader{rnd: rnd, buf: make([]byte, 0, 7)}
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}
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func (rd *RandReader) read(p []byte) (n int, err error) {
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if len(p)%7 != 0 {
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panic("invalid buffer length, not multiple of 7")
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}
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rnd := rd.rnd
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for i := 0; i < len(p); i += 7 {
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val := rnd.Int63()
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p[i+0] = byte(val >> 0)
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p[i+1] = byte(val >> 8)
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p[i+2] = byte(val >> 16)
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p[i+3] = byte(val >> 24)
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p[i+4] = byte(val >> 32)
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p[i+5] = byte(val >> 40)
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p[i+6] = byte(val >> 48)
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}
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return len(p), nil
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}
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func (rd *RandReader) Read(p []byte) (int, error) {
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// first, copy buffer to p
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pos := copy(p, rd.buf)
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copy(rd.buf, rd.buf[pos:])
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// shorten buf and p accordingly
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rd.buf = rd.buf[:len(rd.buf)-pos]
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p = p[pos:]
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// if this is enough to fill p, return
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if len(p) == 0 {
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return pos, nil
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}
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// load multiple of 7 byte
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l := (len(p) / 7) * 7
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n, err := rd.read(p[:l])
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pos += n
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if err != nil {
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return pos, errors.Wrap(err, "Read")
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}
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p = p[n:]
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// load 7 byte to temp buffer
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rd.buf = rd.buf[:7]
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n, err = rd.read(rd.buf)
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if err != nil {
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return pos, errors.Wrap(err, "Read")
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}
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// copy the remaining bytes from the buffer to p
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n = copy(p, rd.buf)
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pos += n
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// save the remaining bytes in rd.buf
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n = copy(rd.buf, rd.buf[n:])
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rd.buf = rd.buf[:n]
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return pos, nil
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}
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