initial import

core/filex/file.go

@@ -0,0 +1,84 @@
+package filex
+
+import (
+	"io"
+	"os"
+)
+
+const bufSize = 1024
+
+func FirstLine(filename string) (string, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	return firstLine(file)
+}
+
+func LastLine(filename string) (string, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	return lastLine(filename, file)
+}
+
+func firstLine(file *os.File) (string, error) {
+	var first []byte
+	var offset int64
+	for {
+		buf := make([]byte, bufSize)
+		n, err := file.ReadAt(buf, offset)
+		if err != nil && err != io.EOF {
+			return "", err
+		}
+
+		for i := 0; i < n; i++ {
+			if buf[i] == '\n' {
+				return string(append(first, buf[:i]...)), nil
+			}
+		}
+
+		first = append(first, buf[:n]...)
+		offset += bufSize
+	}
+}
+
+func lastLine(filename string, file *os.File) (string, error) {
+	info, err := os.Stat(filename)
+	if err != nil {
+		return "", err
+	}
+
+	var last []byte
+	offset := info.Size()
+	for {
+		offset -= bufSize
+		if offset < 0 {
+			offset = 0
+		}
+		buf := make([]byte, bufSize)
+		n, err := file.ReadAt(buf, offset)
+		if err != nil && err != io.EOF {
+			return "", err
+		}
+
+		if buf[n-1] == '\n' {
+			buf = buf[:n-1]
+			n -= 1
+		} else {
+			buf = buf[:n]
+		}
+		for n -= 1; n >= 0; n-- {
+			if buf[n] == '\n' {
+				return string(append(buf[n+1:], last...)), nil
+			}
+		}
+
+		last = append(buf, last...)
+	}
+}