io/ioutil: add TempDir

It's a little confusing that os.TempDir and ioutil.TempDir have
different meanings.  I don't know what to change the names to,
if anything.  At least they also have different signatures.

R=golang-dev, bradfitzgo, r, gri
CC=golang-dev
https://golang.org/cl/4247051

src/pkg/io/ioutil/tempfile.go

@@ -46,6 +46,7 @@ func TempFile(dir, prefix string) (f *os.File, err os.Error) {
 
 	nconflict := 0
 	for i := 0; i < 10000; i++ {
+		// TODO(rsc): use filepath.Join
 		name := dir + "/" + prefix + nextSuffix()
 		f, err = os.Open(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
 		if pe, ok := err.(*os.PathError); ok && pe.Error == os.EEXIST {
@@ -58,3 +59,34 @@ func TempFile(dir, prefix string) (f *os.File, err os.Error) {
 	}
 	return
 }
+
+// TempDir creates a new temporary directory in the directory dir
+// with a name beginning with prefix and returns the path of the
+// new directory.  If dir is the empty string, TempDir uses the
+// default directory for temporary files (see os.TempDir).
+// Multiple programs calling TempDir simultaneously
+// will not choose the same directory.  It is the caller's responsibility
+// to remove the directory when no longer needed.
+func TempDir(dir, prefix string) (name string, err os.Error) {
+	if dir == "" {
+		dir = os.TempDir()
+	}
+
+	nconflict := 0
+	for i := 0; i < 10000; i++ {
+		// TODO(rsc): use filepath.Join
+		try := dir + "/" + prefix + nextSuffix()
+		err = os.Mkdir(try, 0700)
+		if pe, ok := err.(*os.PathError); ok && pe.Error == os.EEXIST {
+			if nconflict++; nconflict > 10 {
+				rand = reseed()
+			}
+			continue
+		}
+		if err == nil {
+			name = try
+		}
+		break
+	}
+	return
+}

src/pkg/io/ioutil/tempfile_test.go

@@ -23,11 +23,31 @@ func TestTempFile(t *testing.T) {
 		t.Errorf("TempFile(dir, `ioutil_test`) = %v, %v", f, err)
 	}
 	if f != nil {
+		f.Close()
+		os.Remove(f.Name())
 		re := regexp.MustCompile("^" + regexp.QuoteMeta(dir) + "/ioutil_test[0-9]+$")
 		if !re.MatchString(f.Name()) {
 			t.Errorf("TempFile(`"+dir+"`, `ioutil_test`) created bad name %s", f.Name())
 		}
-		os.Remove(f.Name())
 	}
-	f.Close()
+}
+
+func TestTempDir(t *testing.T) {
+	name, err := TempDir("/_not_exists_", "foo")
+	if name != "" || err == nil {
+		t.Errorf("TempDir(`/_not_exists_`, `foo`) = %v, %v", name, err)
+	}
+
+	dir := os.TempDir()
+	name, err = TempDir(dir, "ioutil_test")
+	if name == "" || err != nil {
+		t.Errorf("TempDir(dir, `ioutil_test`) = %v, %v", name, err)
+	}
+	if name != "" {
+		os.Remove(name)
+		re := regexp.MustCompile("^" + regexp.QuoteMeta(dir) + "/ioutil_test[0-9]+$")
+		if !re.MatchString(name) {
+			t.Errorf("TempDir(`"+dir+"`, `ioutil_test`) created bad name %s", name)
+		}
+	}
 }