Add helpers for authenticated media, and associated documentation (#4185)

* Add helpers for authenticated media, and associated documentation

* Appease the linter

README.md

@@ -21,6 +21,10 @@ endpoints from before Matrix 1.1, for example.
 
 # Quickstart
 
+> [!IMPORTANT]
+> Servers may require or use authenticated endpoints for media (images, files, avatars, etc). See the
+> [Authenticated Media](#authenticated-media) section for information on how to enable support for this.
+
 Using `yarn` instead of `npm` is recommended. Please see the Yarn [install guide](https://classic.yarnpkg.com/en/docs/install)
 if you do not have it already.
 
@@ -89,6 +93,34 @@ Object.keys(client.store.rooms).forEach((roomId) => {
 });
 ```
 
+## Authenticated media
+
+Servers supporting [MSC3916](https://github.com/matrix-org/matrix-spec-proposals/pull/3916) will require clients, like
+yours, to include an `Authorization` header when `/download`ing or `/thumbnail`ing media. For NodeJS environments this
+may be as easy as the following code snippet, though web browsers may need to use [Service Workers](https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API)
+to append the header when using the endpoints in `<img />` elements and similar.
+
+```javascript
+const downloadUrl = client.mxcUrlToHttp(
+    /*mxcUrl=*/ "mxc://example.org/abc123", // the MXC URI to download/thumbnail, typically from an event or profile
+    /*width=*/ undefined, // part of the thumbnail API. Use as required.
+    /*height=*/ undefined, // part of the thumbnail API. Use as required.
+    /*resizeMethod=*/ undefined, // part of the thumbnail API. Use as required.
+    /*allowDirectLinks=*/ false, // should generally be left `false`.
+    /*allowRedirects=*/ true, // implied supported with authentication
+    /*useAuthentication=*/ true, // the flag we're after in this example
+);
+const img = await fetch(downloadUrl, {
+    headers: {
+        Authorization: `Bearer ${client.getAccessToken()}`,
+    },
+});
+// Do something with `img`.
+```
+
+> [!WARNING]
+> In future the js-sdk will _only_ return authentication-required URLs, mandating population of the `Authorization` header.
+
 ## What does this SDK do?
 
 This SDK provides a full object model around the Matrix Client-Server API and emits

spec/unit/content-repo.spec.ts

@@ -76,5 +76,29 @@ describe("ContentRepo", function () {
                 baseUrl + "/_matrix/media/v3/download/server.name/resourceid#automade",
             );
         });
+
+        it("should return an authenticated URL when requested", function () {
+            const mxcUri = "mxc://server.name/resourceid";
+            expect(getHttpUriForMxc(baseUrl, mxcUri, undefined, undefined, undefined, undefined, true, true)).toEqual(
+                baseUrl +
+                    "/_matrix/client/unstable/org.matrix.msc3916/media/download/server.name/resourceid?allow_redirect=true",
+            );
+            expect(getHttpUriForMxc(baseUrl, mxcUri, 64, 64, "scale", undefined, true, true)).toEqual(
+                baseUrl +
+                    "/_matrix/client/unstable/org.matrix.msc3916/media/thumbnail/server.name/resourceid?width=64&height=64&method=scale&allow_redirect=true",
+            );
+        });
+
+        it("should force-enable allow_redirects when useAuthentication is set true", function () {
+            const mxcUri = "mxc://server.name/resourceid";
+            expect(getHttpUriForMxc(baseUrl, mxcUri, undefined, undefined, undefined, undefined, false, true)).toEqual(
+                baseUrl +
+                    "/_matrix/client/unstable/org.matrix.msc3916/media/download/server.name/resourceid?allow_redirect=true",
+            );
+            expect(getHttpUriForMxc(baseUrl, mxcUri, 64, 64, "scale", undefined, false, true)).toEqual(
+                baseUrl +
+                    "/_matrix/client/unstable/org.matrix.msc3916/media/thumbnail/server.name/resourceid?width=64&height=64&method=scale&allow_redirect=true",
+            );
+        });
     });
 });

spec/unit/matrix-client.spec.ts

@@ -386,6 +386,9 @@ describe("MatrixClient", function () {
             expect(client.mxcUrlToHttp(mxc, 32, 46, "scale", false, true)).toBe(
                 getHttpUriForMxc(client.baseUrl, mxc, 32, 46, "scale", false, true),
             );
+            expect(client.mxcUrlToHttp(mxc, 32, 46, "scale", false, true, true)).toBe(
+                getHttpUriForMxc(client.baseUrl, mxc, 32, 46, "scale", false, true, true),
+            );
         });
     });
 

src/client.ts

@@ -5775,7 +5775,12 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * anyone they share a room with. If false, will return null for such URLs.
      * @param allowRedirects - If true, the caller supports the URL being 307 or
      * 308 redirected to another resource upon request. If false, redirects
-     * are not expected.
+     * are not expected. Implied `true` when `useAuthentication` is `true`.
+     * @param useAuthentication - If true, the caller supports authenticated
+     * media and wants an authentication-required URL. Note that server support
+     * for authenticated media will *not* be checked - it is the caller's responsibility
+     * to do so before calling this function. Note also that `useAuthentication`
+     * implies `allowRedirects`. Defaults to false (unauthenticated endpoints).
      * @returns the avatar URL or null.
      */
     public mxcUrlToHttp(
@@ -5785,8 +5790,18 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         resizeMethod?: string,
         allowDirectLinks?: boolean,
         allowRedirects?: boolean,
+        useAuthentication?: boolean,
     ): string | null {
-        return getHttpUriForMxc(this.baseUrl, mxcUrl, width, height, resizeMethod, allowDirectLinks, allowRedirects);
+        return getHttpUriForMxc(
+            this.baseUrl,
+            mxcUrl,
+            width,
+            height,
+            resizeMethod,
+            allowDirectLinks,
+            allowRedirects,
+            useAuthentication,
+        );
     }
 
     /**

src/content-repo.ts

@@ -30,7 +30,12 @@ import { encodeParams } from "./utils";
  * for such URLs.
  * @param allowRedirects - If true, the caller supports the URL being 307 or
  * 308 redirected to another resource upon request. If false, redirects
- * are not expected.
+ * are not expected. Implied `true` when `useAuthentication` is `true`.
+ * @param useAuthentication - If true, the caller supports authenticated
+ * media and wants an authentication-required URL. Note that server support
+ * for authenticated media will *not* be checked - it is the caller's responsibility
+ * to do so before calling this function. Note also that `useAuthentication`
+ * implies `allowRedirects`. Defaults to false (unauthenticated endpoints).
  * @returns The complete URL to the content.
  */
 export function getHttpUriForMxc(
@@ -41,6 +46,7 @@ export function getHttpUriForMxc(
     resizeMethod?: string,
     allowDirectLinks = false,
     allowRedirects?: boolean,
+    useAuthentication?: boolean,
 ): string {
     if (typeof mxc !== "string" || !mxc) {
         return "";
@@ -52,8 +58,23 @@ export function getHttpUriForMxc(
             return "";
         }
     }
+
+    if (useAuthentication) {
+        allowRedirects = true; // per docs (MSC3916 always expects redirects)
+
+        // Dev note: MSC3916 (as of writing) removes `allow_redirect` entirely, but
+        // for explicitness we set it here. This makes it slightly more obvious to
+        // callers, hopefully.
+    }
+
     let serverAndMediaId = mxc.slice(6); // strips mxc://
-    let prefix = "/_matrix/media/v3/download/";
+    let prefix: string;
+    if (useAuthentication) {
+        // TODO: Use stable once available (requires FCP on MSC3916).
+        prefix = "/_matrix/client/unstable/org.matrix.msc3916/media/download/";
+    } else {
+        prefix = "/_matrix/media/v3/download/";
+    }
     const params: Record<string, string> = {};
 
     if (width) {
@@ -68,7 +89,12 @@ export function getHttpUriForMxc(
     if (Object.keys(params).length > 0) {
         // these are thumbnailing params so they probably want the
         // thumbnailing API...
-        prefix = "/_matrix/media/v3/thumbnail/";
+        if (useAuthentication) {
+            // TODO: Use stable once available (requires FCP on MSC3916).
+            prefix = "/_matrix/client/unstable/org.matrix.msc3916/media/thumbnail/";
+        } else {
+            prefix = "/_matrix/media/v3/thumbnail/";
+        }
     }
 
     if (typeof allowRedirects === "boolean") {