all: return signal to indicate last write has changed

Author: changkun

clipboard.go

@@ -34,13 +34,19 @@ func Read(t MIMEType) []byte {
 	return read(t)
 }
 
-// Write writes the given buffer to the clipboard.
+// Write writes a given buffer to the clipboard.
+// The returned channel can receive an empty struct as signal that
+// indicates the clipboard has been overwritten from this write.
 //
 // If the MIME type indicates an image, then the given buf assumes
 // the image data is PNG encoded.
-func Write(t MIMEType, buf []byte) {
+func Write(t MIMEType, buf []byte) <-chan struct{} {
 	lock.Lock()
 	defer lock.Unlock()
 
-	write(t, buf)
+	ok, changed := write(t, buf)
+	if !ok {
+		return nil
+	}
+	return changed
 }

clipboard_darwin.go

@@ -19,9 +19,13 @@ unsigned int clipboard_read_string(void **out);
 unsigned int clipboard_read_image(void **out);
 int clipboard_write_string(const void *bytes, NSInteger n);
 int clipboard_write_image(const void *bytes, NSInteger n);
+NSInteger clipboard_change_count();
 */
 import "C"
-import "unsafe"
+import (
+	"time"
+	"unsafe"
+)
 
 func read(t MIMEType) (buf []byte) {
 	var (
@@ -46,9 +50,8 @@ func read(t MIMEType) (buf []byte) {
 
 // write writes the given data to clipboard and
 // returns true if success or false if failed.
-func write(t MIMEType, buf []byte) bool {
+func write(t MIMEType, buf []byte) (bool, <-chan struct{}) {
 	var ok C.int
-
 	switch t {
 	case MIMEText:
 		ok = C.clipboard_write_string(unsafe.Pointer(&buf[0]),
@@ -58,7 +61,22 @@ func write(t MIMEType, buf []byte) bool {
 			C.NSInteger(len(buf)))
 	}
 	if ok != 0 {
-		return false
+		return false, nil
 	}
-	return true
+
+	// use unbuffered data to prevent goroutine leak
+	changed := make(chan struct{}, 1)
+	cnt := C.long(C.clipboard_change_count())
+	go func() {
+		for {
+			time.Sleep(time.Second)
+			cur := C.long(C.clipboard_change_count())
+			if cnt != cur {
+				changed <- struct{}{}
+				close(changed)
+				return
+			}
+		}
+	}()
+	return true, changed
 }

clipboard_darwin.m

@@ -53,4 +53,8 @@ int clipboard_write_image(const void *bytes, NSInteger n) {
 		return -1;
 	}
 	return 0;
+}
+
+NSInteger clipboard_change_count() {
+	return [[NSPasteboard generalPasteboard] changeCount];
 }

clipboard_linux.go

@@ -74,7 +74,7 @@ func readc(t string) []byte {
 
 // write writes the given data to clipboard and
 // returns true if success or false if failed.
-func write(t MIMEType, buf []byte) bool {
+func write(t MIMEType, buf []byte) (bool, <-chan struct{}) {
 	var s string
 	switch t {
 	case MIMEText:
@@ -84,6 +84,7 @@ func write(t MIMEType, buf []byte) bool {
 	}
 
 	var start C.int
+	done := make(chan struct{}, 1)
 
 	go func() { // surve as a daemon until the ownership is terminated.
 		runtime.LockOSThread()
@@ -94,6 +95,8 @@ func write(t MIMEType, buf []byte) bool {
 		if ok != C.int(0) {
 			fmt.Fprintf(os.Stderr, "write failed with status: %d\n", int(ok))
 		}
+		done <- struct{}{}
+		close(done)
 	}()
 
 	// FIXME: this should race with the code on the C side, start
@@ -102,8 +105,8 @@ func write(t MIMEType, buf []byte) bool {
 	}
 
 	if start < 0 {
-		return false
+		return false, nil
 	}
 	// wait until enter event loop
-	return true
+	return true, done
 }

clipboard_test.go

@@ -7,9 +7,11 @@
 package clipboard_test
 
 import (
+	"context"
 	"os"
 	"reflect"
 	"testing"
+	"time"
 
 	"golang.design/x/clipboard"
 )
@@ -61,11 +63,27 @@ func TestClipboardMultipleWrites(t *testing.T) {
 	if err != nil {
 		t.Fatalf("failed to read gold file: %v", err)
 	}
-	clipboard.Write(clipboard.MIMEImage, data)
+	chg := clipboard.Write(clipboard.MIMEImage, data)
 
 	data = []byte("golang.design/x/clipboard")
 	clipboard.Write(clipboard.MIMEText, data)
 
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
+	defer cancel()
+
+	select {
+	case <-ctx.Done():
+		t.Fatalf("failed to receive clipboard change notification")
+	case _, ok := <-chg:
+		if !ok {
+			t.Fatalf("change channel is closed before receiving the changed clipboard data")
+		}
+	}
+	_, ok := <-chg
+	if ok {
+		t.Fatalf("changed channel should be closed after receiving the notification")
+	}
+
 	b := clipboard.Read(clipboard.MIMEImage)
 	if b != nil {
 		t.Fatalf("read clipboard that should store text data as image should fail, but got: %d", len(b))

cmd/gclip/main.go

@@ -97,7 +97,8 @@ func cpy() error {
 		}
 	}
 
-	clipboard.Write(t, b)
+	// Wait until clipboard content has been changed.
+	<-clipboard.Write(t, b)
 	return nil
 }