Fix: Images no longer reserve their space in the timeline correctly

src/components/views/messages/MImageBody.tsx

@@ -385,22 +385,24 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
     }
 
     protected messageContent(
-        contentUrl: string,
+        contentUrl: string | null,
         thumbUrl: string | null,
         content: IMediaEventContent,
         forcedHeight?: number,
     ): JSX.Element {
         if (!thumbUrl) thumbUrl = contentUrl; // fallback
 
-        let infoWidth: number;
-        let infoHeight: number;
+        // magic number
+        // edge case for this not to be set by conditions below
+        let infoWidth = 500;
+        let infoHeight = 500;
         let infoSvg = false;
 
         if (content.info?.w && content.info?.h) {
             infoWidth = content.info.w;
             infoHeight = content.info.h;
             infoSvg = content.info.mimetype === "image/svg+xml";
-        } else {
+        } else if (thumbUrl && contentUrl) {
             // Whilst the image loads, display nothing. We also don't display a blurhash image
             // because we don't really know what size of image we'll end up with.
             //
@@ -522,7 +524,7 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
             </div>
         );
 
-        return this.wrapImage(contentUrl, thumbnail);
+        return contentUrl ? this.wrapImage(contentUrl, thumbnail) : thumbnail;
     }
 
     // Overridden by MStickerBody
@@ -596,7 +598,7 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
             thumbUrl = this.state.thumbUrl ?? this.state.contentUrl;
         }
 
-        const thumbnail = contentUrl ? this.messageContent(contentUrl, thumbUrl, content) : undefined;
+        const thumbnail = this.messageContent(contentUrl, thumbUrl, content);
         const fileBody = this.getFileBody();
 
         return (

test/components/views/messages/MImageBody-test.tsx

@@ -61,6 +61,10 @@ describe("<MImageBody/>", () => {
         sender: userId,
         type: EventType.RoomMessage,
         content: {
+            info: {
+                w: 40,
+                h: 50,
+            },
             file: {
                 url: "mxc://server/encrypted-image",
             },
@@ -72,6 +76,21 @@ describe("<MImageBody/>", () => {
         permalinkCreator: new RoomPermalinkCreator(new Room(encryptedMediaEvent.getRoomId()!, cli, cli.getUserId()!)),
     };
 
+    it("should show a thumbnail while image is being downloaded", async () => {
+        fetchMock.getOnce(url, { status: 200 });
+
+        const { container } = render(
+            <MImageBody
+                {...props}
+                mxEvent={encryptedMediaEvent}
+                mediaEventHelper={new MediaEventHelper(encryptedMediaEvent)}
+            />,
+        );
+
+        // thumbnail with dimensions present
+        expect(container).toMatchSnapshot();
+    });
+
     it("should show error when encrypted media cannot be downloaded", async () => {
         fetchMock.getOnce(url, { status: 500 });
 

test/components/views/messages/__snapshots__/MImageBody-test.tsx.snap

@@ -0,0 +1,36 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`<MImageBody/> should show a thumbnail while image is being downloaded 1`] = `
+<div>
+  <div
+    class="mx_MImageBody"
+  >
+    <div
+      class="mx_MImageBody_thumbnail_container"
+      style="max-height: 50px; max-width: 40px;"
+    >
+      <div
+        class="mx_MImageBody_placeholder"
+      >
+        <div
+          class="mx_Spinner"
+        >
+          <div
+            aria-label="Loading…"
+            class="mx_Spinner_icon"
+            data-testid="spinner"
+            role="progressbar"
+            style="width: 32px; height: 32px;"
+          />
+        </div>
+      </div>
+      <div
+        style="max-height: 50px; max-width: 40px;"
+      />
+      <div
+        style="height: 50px; width: 40px;"
+      />
+    </div>
+  </div>
+</div>
+`;