Add support for forward and back mouse buttons

This commit implements the extendedMouseButtons pseudo-encoding, which
makes it possible to use the forward and back mouse buttons.

core/encodings.js

@@ -30,6 +30,7 @@ export const encodings = {
     pseudoEncodingXvp: -309,
     pseudoEncodingFence: -312,
     pseudoEncodingContinuousUpdates: -313,
+    pseudoEncodingExtendedMouseButtons: -316,
     pseudoEncodingCompressLevel9: -247,
     pseudoEncodingCompressLevel0: -256,
     pseudoEncodingVMwareCursor: 0x574d5664,

core/rfb.js

@@ -152,6 +152,8 @@ export default class RFB extends EventTargetMixin {
 
         this._qemuExtKeyEventSupported = false;
 
+        this._extendedPointerEventSupported = false;
+
         this._clipboardText = null;
         this._clipboardServerCapabilitiesActions = {};
         this._clipboardServerCapabilitiesFormats = {};
@@ -1051,10 +1053,11 @@ export default class RFB extends EventTargetMixin {
             1: 1 << 2, // Right
             2: 1 << 1, // Middle
             3: 1 << 7, // Back
+            4: 1 << 8, // Forward
         };
 
         let bmask = 0;
-        for (let i = 0; i < 4; i++) {
+        for (let i = 0; i < 5; i++) {
             if (buttons & (1 << i)) {
                 bmask |= buttonMaskMap[i];
             }
@@ -1189,8 +1192,20 @@ export default class RFB extends EventTargetMixin {
         if (this._rfbConnectionState !== 'connected') { return; }
         if (this._viewOnly) { return; } // View only, skip mouse events
 
-        RFB.messages.pointerEvent(this._sock, this._display.absX(x),
-                                  this._display.absY(y), mask);
+        // Highest bit in mask is never sent to the server
+        if (mask & 0x8000) {
+            throw new Error("Illegal mouse button mask (mask: " + mask + ")");
+        }
+
+        let extendedMouseButtons = mask & 0x7f80;
+
+        if (this._extendedPointerEventSupported && extendedMouseButtons) {
+            RFB.messages.extendedPointerEvent(this._sock, this._display.absX(x),
+                                              this._display.absY(y), mask);
+        } else {
+            RFB.messages.pointerEvent(this._sock, this._display.absX(x),
+                                      this._display.absY(y), mask);
+        }
     }
 
     _handleWheel(ev) {
@@ -2229,6 +2244,7 @@ export default class RFB extends EventTargetMixin {
         encs.push(encodings.pseudoEncodingContinuousUpdates);
         encs.push(encodings.pseudoEncodingDesktopName);
         encs.push(encodings.pseudoEncodingExtendedClipboard);
+        encs.push(encodings.pseudoEncodingExtendedMouseButtons);
 
         if (this._fbDepth == 24) {
             encs.push(encodings.pseudoEncodingVMwareCursor);
@@ -2658,6 +2674,10 @@ export default class RFB extends EventTargetMixin {
             case encodings.pseudoEncodingExtendedDesktopSize:
                 return this._handleExtendedDesktopSize();
 
+            case encodings.pseudoEncodingExtendedMouseButtons:
+                this._extendedPointerEventSupported = true;
+                return true;
+
             case encodings.pseudoEncodingQEMULedEvent:
                 return this._handleLedEvent();
 
@@ -3067,6 +3087,10 @@ RFB.messages = {
     pointerEvent(sock, x, y, mask) {
         sock.sQpush8(5); // msg-type
 
+        // Marker bit must be set to 0, otherwise the server might
+        // confuse the marker bit with the highest bit in a normal
+        // PointerEvent message.
+        mask = mask & 0x7f;
         sock.sQpush8(mask);
 
         sock.sQpush16(x);
@@ -3075,6 +3099,27 @@ RFB.messages = {
         sock.flush();
     },
 
+    extendedPointerEvent(sock, x, y, mask) {
+        sock.sQpush8(5); // msg-type
+
+        let higherBits = (mask >> 7) & 0xff;
+
+        // Bits 2-7 are reserved
+        if (higherBits & 0xfc) {
+            throw new Error("Invalid mouse button mask: " + mask);
+        }
+
+        let lowerBits = mask & 0x7f;
+        lowerBits |= 0x80; // Set marker bit to 1
+
+        sock.sQpush8(lowerBits);
+        sock.sQpush16(x);
+        sock.sQpush16(y);
+        sock.sQpush8(higherBits);
+
+        sock.flush();
+    },
+
     // Used to build Notify and Request data.
     _buildExtendedClipboardFlags(actions, formats) {
         let data = new Uint8Array(4);