Handle slow loading of images

Internet Explorer seems to flag images as loaded prematurely, which
can result in rendering bugs. We can detect this by looking at the
dimensions though.

kasmweb/core/display.js

@@ -360,8 +360,14 @@ export default class Display {
     }
 
     imageRect(x, y, w, h, mime, arr) {
+        /* The internal logic cannot handle empty images, so bail early */
+        if ((width === 0) || (height === 0)) {
+            return;
+        }
+
         const img = new Image();
         img.src = "data: " + mime + ";base64," + Base64.encode(arr);
+
         this._renderQ_push({
             'type': 'img',
             'img': img,
@@ -621,7 +627,8 @@ export default class Display {
                     this.blitRgbxImage(a.x, a.y, a.width, a.height, a.data, 0, true);
                     break;
                 case 'img':
-                    if (a.img.complete) {
+                    /* IE tends to set "complete" prematurely, so check dimensions */
+                    if (a.img.complete && (a.img.width !== 0) && (a.img.height !== 0)) {
                         this.drawImage(a.img, a.x, a.y, a.w, a.h);
                     } else {
                         a.img._noVNC_display = this;

kasmweb/tests/test.display.js

@@ -300,7 +300,7 @@ describe('Display/Canvas Helper', function () {
         });
 
         it('should support drawing images via #imageRect', function (done) {
-            display.imageRect(0, 0, "image/png", make_image_png(checked_data));
+            display.imageRect(0, 0, 4, 4, "image/png", make_image_png(checked_data));
             display.flip();
             display.onflush = () => {
                 expect(display).to.have.displayed(checked_data);
@@ -401,8 +401,8 @@ describe('Display/Canvas Helper', function () {
         });
 
         it('should wait until an image is loaded to attempt to draw it and the rest of the queue', function () {
-            const img = { complete: false, addEventListener: sinon.spy() };
+            const img = { complete: false, width: 4, height: 4, addEventListener: sinon.spy() };
-            display._renderQ = [{ type: 'img', x: 3, y: 4, img: img },
+            display._renderQ = [{ type: 'img', x: 3, y: 4, width: 4, height: 4, img: img },
                                 { type: 'fill', x: 1, y: 2, width: 3, height: 4, color: 5 }];
             display.drawImage = sinon.spy();
             display.fillRect = sinon.spy();
@@ -419,6 +419,27 @@ describe('Display/Canvas Helper', function () {
             expect(img.addEventListener).to.have.been.calledOnce;
         });
 
+        it('should wait if an image is incorrectly loaded', function () {
+            const img = { complete: true, width: 0, height: 0, addEventListener: sinon.spy() };
+            display._renderQ = [{ type: 'img', x: 3, y: 4, width: 4, height: 4, img: img },
+                                { type: 'fill', x: 1, y: 2, width: 3, height: 4, color: 5 }];
+            display.drawImage = sinon.spy();
+            display.fillRect = sinon.spy();
+
+            display._scan_renderQ();
+            expect(display.drawImage).to.not.have.been.called;
+            expect(display.fillRect).to.not.have.been.called;
+            expect(img.addEventListener).to.have.been.calledOnce;
+
+            display._renderQ[0].img.complete = true;
+            display._renderQ[0].img.width = 4;
+            display._renderQ[0].img.height = 4;
+            display._scan_renderQ();
+            expect(display.drawImage).to.have.been.calledOnce;
+            expect(display.fillRect).to.have.been.calledOnce;
+            expect(img.addEventListener).to.have.been.calledOnce;
+        });
+
         it('should call callback when queue is flushed', function () {
             display.onflush = sinon.spy();
             display.fillRect(0, 0, 4, 4, [0, 0xff, 0]);