all: watch API to watch clipboard changes

Author: changkun

clipboard.go

@@ -7,6 +7,7 @@
 package clipboard // import "golang.design/x/clipboard"
 
 import (
+	"context"
 	"sync"
 )
 
@@ -50,3 +51,9 @@ func Write(t Format, buf []byte) <-chan struct{} {
 	}
 	return changed
 }
+
+// Watch returns a receive-only channel that received the clipboard data
+// if any changes of clipboard data in the desired format happends.
+func Watch(ctx context.Context, t Format) <-chan []byte {
+	return watch(ctx, t)
+}

clipboard_darwin.go

@@ -23,6 +23,7 @@ NSInteger clipboard_change_count();
 */
 import "C"
 import (
+	"context"
 	"time"
 	"unsafe"
 )
@@ -77,6 +78,7 @@ func write(t Format, buf []byte) (bool, <-chan struct{}) {
 	cnt := C.long(C.clipboard_change_count())
 	go func() {
 		for {
+			// not sure if we are too slow or the user too fast :)
 			time.Sleep(time.Second)
 			cur := C.long(C.clipboard_change_count())
 			if cnt != cur {
@@ -88,3 +90,30 @@ func write(t Format, buf []byte) (bool, <-chan struct{}) {
 	}()
 	return true, changed
 }
+
+func watch(ctx context.Context, t Format) <-chan []byte {
+	recv := make(chan []byte, 1)
+	go func() {
+		// not sure if we are too slow or the user too fast :)
+		ti := time.NewTicker(time.Second)
+		lastCount := C.long(C.clipboard_change_count())
+		for {
+			select {
+			case <-ctx.Done():
+				close(recv)
+				return
+			case <-ti.C:
+				this := C.long(C.clipboard_change_count())
+				if lastCount != this {
+					b := Read(t)
+					if b == nil {
+						continue
+					}
+					recv <- b
+					lastCount = this
+				}
+			}
+		}
+	}()
+	return recv
+}

clipboard_linux.go

@@ -29,9 +29,12 @@ unsigned long clipboard_read(char* typ, char **out);
 */
 import "C"
 import (
+	"bytes"
+	"context"
 	"fmt"
 	"os"
 	"runtime"
+	"time"
 	"unsafe"
 )
 
@@ -75,6 +78,7 @@ func readc(t string) []byte {
 // write writes the given data to clipboard and
 // returns true if success or false if failed.
 func write(t Format, buf []byte) (bool, <-chan struct{}) {
+
 	var s string
 	switch t {
 	case FmtText:
@@ -115,3 +119,28 @@ func write(t Format, buf []byte) (bool, <-chan struct{}) {
 	// wait until enter event loop
 	return true, done
 }
+
+func watch(ctx context.Context, t Format) <-chan []byte {
+	recv := make(chan []byte, 1)
+	go func() {
+		ti := time.NewTicker(time.Second)
+		last := read(t)
+		for {
+			select {
+			case <-ctx.Done():
+				close(recv)
+				return
+			case <-ti.C:
+				b := read(t)
+				if b == nil {
+					continue
+				}
+				if bytes.Compare(last, b) != 0 {
+					recv <- b
+					last = b
+				}
+			}
+		}
+	}()
+	return recv
+}

clipboard_test.go

@@ -7,6 +7,7 @@
 package clipboard_test
 
 import (
+	"bytes"
 	"context"
 	"os"
 	"reflect"
@@ -131,6 +132,51 @@ func TestClipboardWriteEmpty(t *testing.T) {
 		t.Fatalf("write empty string to clipboard should read empty string, got: `%v`", string(got))
 	}
 }
+
+func TestClipboardWatch(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
+	defer cancel()
+
+	// clear clipboard
+	clipboard.Write(clipboard.FmtText, []byte(""))
+	lastRead := clipboard.Read(clipboard.FmtText)
+
+	changed := clipboard.Watch(ctx, clipboard.FmtText)
+
+	want := []byte("golang.design/x/clipboard")
+	go func(ctx context.Context) {
+		t := time.NewTicker(time.Millisecond * 500)
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-t.C:
+				clipboard.Write(clipboard.FmtText, want)
+			}
+		}
+	}(ctx)
+	for {
+		select {
+		case <-ctx.Done():
+			if string(lastRead) == "" {
+				t.Fatalf("clipboard watch never receives a notification")
+			}
+			return
+		case data, ok := <-changed:
+			if !ok {
+				if string(lastRead) == "" {
+					t.Fatalf("clipboard watch never receives a notification")
+				}
+				return
+			}
+			if bytes.Compare(data, want) != 0 {
+				t.Fatalf("received data from watch mismatch, want: %v, got %v", string(want), string(data))
+			}
+			lastRead = data
+		}
+	}
+}
+
 func BenchmarkClipboard(b *testing.B) {
 
 	b.Run("text", func(b *testing.B) {