62 lines
1.2 KiB
Go
62 lines
1.2 KiB
Go
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package tailfile
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import (
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"bytes"
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"errors"
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"os"
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)
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const blockSize = 1024
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var eol = []byte("\n")
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var ErrNonPositiveLinesNumber = errors.New("Lines number must be positive")
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//TailFile returns last n lines of file f
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func TailFile(f *os.File, n int) ([][]byte, error) {
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if n <= 0 {
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return nil, ErrNonPositiveLinesNumber
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}
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size, err := f.Seek(0, os.SEEK_END)
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if err != nil {
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return nil, err
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}
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block := -1
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var data []byte
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var cnt int
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for {
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var b []byte
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step := int64(block * blockSize)
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left := size + step // how many bytes to beginning
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if left < 0 {
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if _, err := f.Seek(0, os.SEEK_SET); err != nil {
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return nil, err
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}
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b = make([]byte, blockSize+left)
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if _, err := f.Read(b); err != nil {
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return nil, err
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}
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data = append(b, data...)
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break
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} else {
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b = make([]byte, blockSize)
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if _, err := f.Seek(step, os.SEEK_END); err != nil {
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return nil, err
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}
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if _, err := f.Read(b); err != nil {
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return nil, err
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}
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data = append(b, data...)
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}
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cnt += bytes.Count(b, eol)
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if cnt > n {
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break
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}
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block--
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}
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lines := bytes.Split(data, eol)
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if n < len(lines) {
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return lines[len(lines)-n-1 : len(lines)-1], nil
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}
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return lines[:len(lines)-1], nil
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}
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