65 lines
1.8 KiB
Go
65 lines
1.8 KiB
Go
package fs
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import (
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"io"
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"github.com/pkg/errors"
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)
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// A RepeatableReader implements the io.ReadSeeker it allow to seek cached data
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// back and forth within the reader but will only read data from the internal Reader as necessary
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// and will play nicely with the Account and io.LimitedReader to reflect current speed
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type RepeatableReader struct {
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in io.Reader // Input reader
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i int64 // current reading index
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b []byte // internal cache buffer
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}
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var _ io.ReadSeeker = (*RepeatableReader)(nil)
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// Seek implements the io.Seeker interface.
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// If seek position is passed the cache buffer length the function will return
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// the maximum offset that can be used and "fs.RepeatableReader.Seek: offset is unavailable" Error
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func (r *RepeatableReader) Seek(offset int64, whence int) (int64, error) {
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var abs int64
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cacheLen := int64(len(r.b))
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switch whence {
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case 0: //io.SeekStart
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abs = offset
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case 1: //io.SeekCurrent
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abs = r.i + offset
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case 2: //io.SeekEnd
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abs = cacheLen + offset
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default:
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return 0, errors.New("fs.RepeatableReader.Seek: invalid whence")
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}
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if abs < 0 {
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return 0, errors.New("fs.RepeatableReader.Seek: negative position")
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}
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if abs > cacheLen {
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return offset - (abs - cacheLen), errors.New("fs.RepeatableReader.Seek: offset is unavailable")
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}
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r.i = abs
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return abs, nil
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}
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// Read data from original Reader into bytes
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// Data is either served from the underlying Reader or from cache if was already read
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func (r *RepeatableReader) Read(b []byte) (n int, err error) {
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cacheLen := int64(len(r.b))
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if r.i == cacheLen {
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n, err = r.in.Read(b)
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if n > 0 {
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r.b = append(r.b, b[:n]...)
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}
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} else {
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n = copy(b, r.b[r.i:])
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}
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r.i += int64(n)
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return n, err
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}
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// NewRepeatableReader create new repeatable reader from Reader r
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func NewRepeatableReader(r io.Reader) *RepeatableReader {
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return &RepeatableReader{in: r}
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}
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