test: allow write empty data

Author: changkun

Dockerfile

@@ -4,7 +4,7 @@
 #
 # Written by Changkun Ou <changkun.de>
 
-FROM golang:1.16rc1
+FROM golang:1.16
 RUN apt-get update && apt-get install -y \
       xvfb libx11-dev \
     && apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

clipboard_darwin.go

@@ -54,11 +54,19 @@ func write(t Format, buf []byte) (bool, <-chan struct{}) {
 	var ok C.int
 	switch t {
 	case FmtText:
-		ok = C.clipboard_write_string(unsafe.Pointer(&buf[0]),
-			C.NSInteger(len(buf)))
+		if len(buf) == 0 {
+			ok = C.clipboard_write_string(unsafe.Pointer(nil), 0)
+		} else {
+			ok = C.clipboard_write_string(unsafe.Pointer(&buf[0]),
+				C.NSInteger(len(buf)))
+		}
 	case FmtImage:
-		ok = C.clipboard_write_image(unsafe.Pointer(&buf[0]),
-			C.NSInteger(len(buf)))
+		if len(buf) == 0 {
+			ok = C.clipboard_write_image(unsafe.Pointer(nil), 0)
+		} else {
+			ok = C.clipboard_write_image(unsafe.Pointer(&buf[0]),
+				C.NSInteger(len(buf)))
+		}
 	}
 	if ok != 0 {
 		return false, nil

clipboard_linux.go

@@ -91,7 +91,12 @@ func write(t Format, buf []byte) (bool, <-chan struct{}) {
 		cs := C.CString(s)
 		defer C.free(unsafe.Pointer(cs))
 
-		ok := C.clipboard_write(cs, (*C.uchar)(unsafe.Pointer(&buf[0])), C.size_t(len(buf)), &start)
+		var ok C.int
+		if len(buf) == 0 {
+			ok = C.clipboard_write(cs, nil, 0, &start)
+		} else {
+			ok = C.clipboard_write(cs, (*C.uchar)(unsafe.Pointer(&(buf[0]))), C.size_t(len(buf)), &start)
+		}
 		if ok != C.int(0) {
 			fmt.Fprintf(os.Stderr, "write failed with status: %d\n", int(ok))
 		}

clipboard_test.go

@@ -119,6 +119,18 @@ func TestClipboardConcurrentRead(t *testing.T) {
 	<-done
 }
 
+func TestClipboardWriteEmpty(t *testing.T) {
+	chg1 := clipboard.Write(clipboard.FmtText, nil)
+	if got := clipboard.Read(clipboard.FmtText); got != nil {
+		t.Fatalf("write nil to clipboard should read nil, got: %v", string(got))
+	}
+	clipboard.Write(clipboard.FmtText, []byte(""))
+	<-chg1
+
+	if got := clipboard.Read(clipboard.FmtText); string(got) != "" {
+		t.Fatalf("write empty string to clipboard should read empty string, got: `%v`", string(got))
+	}
+}
 func BenchmarkClipboard(b *testing.B) {
 
 	b.Run("text", func(b *testing.B) {