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// SPDX-License-Identifier: GPL-3.0-or-later
package logs
import (
"errors"
"os"
"github.com/clbanning/rfile/v2"
)
const DefaultMaxLineWidth = 4 * 1024 // assume disk block size is 4K
var ErrTooLongLine = errors.New("too long line")
// ReadLastLine returns the last line of the file and any read error encountered.
// It expects last line width <= maxLineWidth.
// If maxLineWidth <= 0, it defaults to DefaultMaxLineWidth.
func ReadLastLine(filename string, maxLineWidth int64) ([]byte, error) {
if maxLineWidth <= 0 {
maxLineWidth = DefaultMaxLineWidth
}
f, err := os.Open(filename)
if err != nil {
return nil, err
}
defer func() { _ = f.Close() }()
stat, _ := f.Stat()
endPos := stat.Size()
if endPos == 0 {
return []byte{}, nil
}
startPos := endPos - maxLineWidth
if startPos < 0 {
startPos = 0
}
buf := make([]byte, endPos-startPos)
n, err := f.ReadAt(buf, startPos)
if err != nil {
return nil, err
}
lnPos := 0
foundLn := false
for i := n - 2; i >= 0; i-- {
ch := buf[i]
if ch == '\n' {
foundLn = true
lnPos = i
break
}
}
if foundLn {
return buf[lnPos+1 : n], nil
}
if startPos == 0 {
return buf[0:n], nil
}
return nil, ErrTooLongLine
}
func ReadLastLines(filename string, n uint) ([]string, error) {
return rfile.Tail(filename, int(n))
}
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