WriteFile util function

R=rsc
DELTA=41  (41 added, 0 deleted, 0 changed)
OCL=31349
CL=31358

src/pkg/io/utils.go

@@ -28,3 +28,19 @@ func ReadFile(filename string) ([]byte, os.Error) {
 	defer f.Close();
 	return ReadAll(f);
 }
+
+// WriteFile writes data to a file named by filename.
+// If the file does not exist, WriteFile creates it with permissions perm.
+//
+func WriteFile(filename string, data []byte, perm int) os.Error {
+	f, err := os.Open(filename, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, perm);
+	if err != nil {
+		return err;
+	}
+	n, err := f.Write(data);
+	if err == nil && n < len(data) {
+		err = ErrShortWrite;
+	}
+	f.Close();
+	return err;
+}

src/pkg/io/utils_test.go

@@ -7,6 +7,7 @@ package io
 import (
 	"io";
 	"os";
+	"strings";
 	"testing";
 )
 
@@ -35,3 +36,27 @@ func TestReadFile(t *testing.T) {
 
 	checkSize(t, filename, uint64(len(contents)));
 }
+
+func TestWriteFile(t *testing.T) {
+	filename := "_obj/rumpelstilzchen";
+	data :=
+		"Programming today is a race between software engineers striving to "
+		"build bigger and better idiot-proof programs, and the Universe trying "
+		"to produce bigger and better idiots. So far, the Universe is winning.";
+
+	if err := WriteFile(filename, strings.Bytes(data), 0644); err != nil {
+		t.Fatalf("WriteFile %s: %v", filename, err);
+	}
+
+	contents, err := ReadFile(filename);
+	if err != nil {
+		t.Fatalf("ReadFile %s: %v", filename, err);
+	}
+
+	if string(contents) != data {
+		t.Fatalf("contents = %q\nexpected = %q", string(contents), data);
+	}
+
+	// cleanup
+	os.Remove(filename);  // ignore error
+}