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50 lines
961 B
Go
50 lines
961 B
Go
package filex
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import (
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"errors"
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"os"
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)
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// errExceedFileSize indicates that the file size is exceeded.
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var errExceedFileSize = errors.New("exceed file size")
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// A RangeReader is used to read a range of content from a file.
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type RangeReader struct {
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file *os.File
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start int64
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stop int64
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}
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// NewRangeReader returns a RangeReader, which will read the range of content from file.
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func NewRangeReader(file *os.File, start, stop int64) *RangeReader {
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return &RangeReader{
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file: file,
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start: start,
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stop: stop,
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}
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}
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// Read reads the range of content into p.
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func (rr *RangeReader) Read(p []byte) (n int, err error) {
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stat, err := rr.file.Stat()
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if err != nil {
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return 0, err
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}
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if rr.stop < rr.start || rr.start >= stat.Size() {
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return 0, errExceedFileSize
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}
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if rr.stop-rr.start < int64(len(p)) {
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p = p[:rr.stop-rr.start]
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}
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n, err = rr.file.ReadAt(p, rr.start)
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if err != nil {
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return n, err
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}
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rr.start += int64(n)
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return
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}
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