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87 lines
1.4 KiB
Go
87 lines
1.4 KiB
Go
package filex
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import (
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"io"
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"os"
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)
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const bufSize = 1024
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// FirstLine returns the first line of the file.
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func FirstLine(filename string) (string, error) {
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file, err := os.Open(filename)
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if err != nil {
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return "", err
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}
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defer file.Close()
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return firstLine(file)
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}
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// LastLine returns the last line of the file.
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func LastLine(filename string) (string, error) {
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file, err := os.Open(filename)
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if err != nil {
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return "", err
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}
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defer file.Close()
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return lastLine(filename, file)
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}
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func firstLine(file *os.File) (string, error) {
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var first []byte
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var offset int64
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for {
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buf := make([]byte, bufSize)
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n, err := file.ReadAt(buf, offset)
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if err != nil && err != io.EOF {
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return "", err
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}
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for i := 0; i < n; i++ {
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if buf[i] == '\n' {
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return string(append(first, buf[:i]...)), nil
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}
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}
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first = append(first, buf[:n]...)
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offset += bufSize
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}
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}
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func lastLine(filename string, file *os.File) (string, error) {
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info, err := os.Stat(filename)
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if err != nil {
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return "", err
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}
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var last []byte
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offset := info.Size()
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for {
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offset -= bufSize
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if offset < 0 {
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offset = 0
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}
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buf := make([]byte, bufSize)
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n, err := file.ReadAt(buf, offset)
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if err != nil && err != io.EOF {
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return "", err
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}
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if buf[n-1] == '\n' {
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buf = buf[:n-1]
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n--
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} else {
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buf = buf[:n]
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}
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for n--; n >= 0; n-- {
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if buf[n] == '\n' {
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return string(append(buf[n+1:], last...)), nil
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}
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}
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last = append(buf, last...)
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}
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}
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