1 files changed, 65 insertions, 0 deletions
diff --git a/src/go/collectors/go.d.plugin/pkg/logs/lastline.go b/src/go/collectors/go.d.plugin/pkg/logs/lastline.go
new file mode 100644
index 000000000..911dbf497
--- /dev/null
+++ b/src/go/collectors/go.d.plugin/pkg/logs/lastline.go
@@ -0,0 +1,65 @@
+// 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))
+}