initial import

core/iox/textfile.go

@@ -0,0 +1,39 @@
+package iox
+
+import (
+	"bytes"
+	"io"
+	"os"
+)
+
+const bufSize = 32 * 1024
+
+func CountLines(file string) (int, error) {
+	f, err := os.Open(file)
+	if err != nil {
+		return 0, err
+	}
+	defer f.Close()
+
+	var noEol bool
+	buf := make([]byte, bufSize)
+	count := 0
+	lineSep := []byte{'\n'}
+
+	for {
+		c, err := f.Read(buf)
+		count += bytes.Count(buf[:c], lineSep)
+
+		switch {
+		case err == io.EOF:
+			if noEol {
+				count++
+			}
+			return count, nil
+		case err != nil:
+			return count, err
+		}
+
+		noEol = c > 0 && buf[c-1] != '\n'
+	}
+}