mirror of
https://github.com/rclone/rclone
synced 2024-12-03 13:14:37 +01:00
e43b5ce5e5
This is possible now that we no longer support go1.12 and brings rclone into line with standard practices in the Go world. This also removes errors.New and errors.Errorf from lib/errors and prefers the stdlib errors package over lib/errors.
59 lines
1.2 KiB
Go
59 lines
1.2 KiB
Go
package readers
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import (
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"errors"
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"io"
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)
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// This is the smallest prime less than 256
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//
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// Using a prime here means we are less likely to hit repeating patterns
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const patternReaderModulo = 251
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// NewPatternReader creates a reader, that returns a deterministic byte pattern.
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// After length bytes are read
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func NewPatternReader(length int64) io.ReadSeeker {
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return &patternReader{
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length: length,
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}
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}
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type patternReader struct {
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offset int64
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length int64
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c byte
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}
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func (r *patternReader) Read(p []byte) (n int, err error) {
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for i := range p {
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if r.offset >= r.length {
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return n, io.EOF
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}
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p[i] = r.c
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r.c = (r.c + 1) % patternReaderModulo
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r.offset++
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n++
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}
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return
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}
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// Seek implements the io.Seeker interface.
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func (r *patternReader) Seek(offset int64, whence int) (abs int64, err error) {
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switch whence {
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case io.SeekStart:
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abs = offset
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case io.SeekCurrent:
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abs = r.offset + offset
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case io.SeekEnd:
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abs = r.length + offset
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default:
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return 0, errors.New("patternReader: invalid whence")
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}
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if abs < 0 {
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return 0, errors.New("patternReader: negative position")
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}
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r.offset = abs
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r.c = byte(abs % patternReaderModulo)
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return abs, nil
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}
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