app/internal/window: macOS clipboard support

Updates gio#31

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/window/os_darwin.go

@@ -3,9 +3,17 @@
 package window
 
 /*
+#include <Foundation/Foundation.h>
+
 __attribute__ ((visibility ("hidden"))) void gio_wakeupMainThread(void);
+__attribute__ ((visibility ("hidden"))) NSUInteger gio_nsstringLength(CFTypeRef str);
+__attribute__ ((visibility ("hidden"))) void gio_nsstringGetCharacters(CFTypeRef str, unichar *chars, NSUInteger loc, NSUInteger length);
 */
 import "C"
+import (
+	"unicode/utf16"
+	"unsafe"
+)
 
 var mainFuncs = make(chan func(), 1)
 
@@ -28,3 +36,14 @@ func gio_dispatchMainFuncs() {
 		}
 	}
 }
+
+// nsstringToString converts a NSString to a Go string, and
+// releases the original string.
+func nsstringToString(str C.CFTypeRef) string {
+	defer C.CFRelease(str)
+	n := C.gio_nsstringLength(str)
+	chars := make([]uint16, n)
+	C.gio_nsstringGetCharacters(str, (*C.unichar)(unsafe.Pointer(&chars[0])), 0, n)
+	utf8 := utf16.Decode(chars)
+	return string(utf8)
+}