support file downloads on iOS through data: uris

assets/download-sandbox.html

@@ -7,16 +7,40 @@
         <a id="link" href="#">Download</a>
         <script type="text/javascript">
             var link = document.getElementById("link");
-            function download(blob, filename) {
+
+            function downloadBlob(blob, filename) {
                 var url = URL.createObjectURL(blob);
                 link.href = url;
                 link.download = filename;
+                link.innerText = url;
                 link.click();
                 URL.revokeObjectURL(url);
             }
-            window.addEventListener("message", function(event) {
+
-                if (event.origin === window.location.origin && event.data.type === "download") {
+            function toBase64(buffer) {
-                    download(event.data.blob, event.data.filename);
+                const bytes = new Uint8Array(buffer);
+                let binaryStr = "";
+                for (let i = 0; i < bytes.byteLength; i++) {
+                    binaryStr += String.fromCharCode(bytes[i]);
+                }
+                return btoa(binaryStr);
+            }
+
+            function downloadBuffer(buffer, mimeType, filename) {
+                var url = "data:" + mimeType + ";base64," + toBase64(buffer);
+                link.href = url;
+                link.download = filename;
+                link.innerText = url;
+                link.click();
+            }
+
+            window.addEventListener("message", async function(event) {
+                if (event.origin === window.location.origin) {
+                    if (event.data.type === "downloadBuffer") {
+                        await downloadBuffer(event.data.buffer, event.data.mimeType, event.data.filename);
+                    } else if (event.data.type === "downloadBlob") {
+                        await downloadBlob(event.data.blob, event.data.filename);
+                    }
                 }
             });
         </script>

src/platform/web/Platform.js

@@ -150,7 +150,7 @@ export class Platform {
         if (navigator.msSaveBlob) {
             navigator.msSaveBlob(blobHandle.nativeBlob, filename);
         } else {
-            downloadInIframe(this._container, this._paths.downloadSandbox, blobHandle.nativeBlob, filename);
+            downloadInIframe(this._container, this._paths.downloadSandbox, blobHandle, filename);
         }
     }
 

src/platform/web/dom/download.js

@@ -14,7 +14,10 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export async function downloadInIframe(container, iframeSrc, blob, filename) {
+// From https://stackoverflow.com/questions/9038625/detect-if-device-is-ios/9039885
+const isIOS = /iPad|iPhone|iPod/.test(navigator.platform) || (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1) && !window.MSStream;
+
+export async function downloadInIframe(container, iframeSrc, blobHandle, filename) {
     let iframe = container.querySelector("iframe.downloadSandbox");
     if (!iframe) {
         iframe = document.createElement("iframe");
@@ -33,5 +36,21 @@ export async function downloadInIframe(container, iframeSrc, blob, filename) {
         });
         detach();
     }
-    iframe.contentWindow.postMessage({type: "download", blob: blob, filename: filename}, "*");
+    if (isIOS) {
+        // iOS can't read a blob in a sandboxed iframe,
+        // see https://github.com/vector-im/hydrogen-web/issues/244
+        const buffer = await blobHandle.readAsBuffer();
+        iframe.contentWindow.postMessage({
+            type: "downloadBuffer",
+            buffer,
+            mimeType: blobHandle.mimeType,
+            filename: filename
+        }, "*");
+    } else {
+        iframe.contentWindow.postMessage({
+            type: "downloadBlob",
+            blob: blobHandle.nativeBlob,
+            filename: filename
+        }, "*");
+    }
 }