Allow room moderators to view redacted event content

Implements MSC2815

Signed-off-by: Tulir Asokan <[email protected]>

Author: tulir

src/client.ts

@@ -7226,6 +7226,32 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return this.http.authedRequest(callback, Method.Get, path);
     }
 
+    /**
+     * Get the content of a redacted event event in a room by its event id.
+     * @param {string} roomId
+     * @param {string} eventId
+     * @param {module:client.callback} callback Optional.
+     *
+     * @return {Promise} Resolves to an object containing the event.
+     * @return {module:http-api.MatrixError} Rejects: with an error response.
+     */
+    public unstableFetchRedactedRoomEventContent(
+        roomId: string,
+        eventId: string,
+        callback?: Callback,
+    ): Promise<IMinimalEvent> {
+        const path = utils.encodeUri(
+            "/rooms/$roomId/event/$eventId", {
+                $roomId: roomId,
+                $eventId: eventId,
+            },
+        );
+        const query = {
+            "fi.mau.msc2815.include_unredacted_content": "true",
+        }
+        return this.http.authedRequest(callback, Method.Get, path, query);
+    }
+
     /**
      * @param {string} roomId
      * @param {string} includeMembership the membership type to include in the response

src/models/event.ts

@@ -284,6 +284,11 @@ export class MatrixEvent extends TypedEventEmitter<EmittedEvents, MatrixEventHan
     public error: MatrixError = null;
     public forwardLooking = true; // only state events may be backwards looking
 
+    /* flag to indicate that the event was redacted, but we fetched the
+     * unredacted content from the server using room moderator powers.
+     */
+    public viewingRedactedContent = false;
+
     /* If the event is a `m.key.verification.request` (or to_device `m.key.verification.start`) event,
      * `Crypto` will set this the `VerificationRequest` for the event
      * so it can be easily accessed from the timeline.
@@ -1142,7 +1147,7 @@ export class MatrixEvent extends TypedEventEmitter<EmittedEvents, MatrixEventHan
      * @return {boolean} True if this event has been redacted
      */
     public isRedacted(): boolean {
-        return Boolean(this.getUnsigned().redacted_because);
+        return Boolean(this.getUnsigned().redacted_because && !this.viewingRedactedContent);
     }
 
     /**
@@ -1267,6 +1272,19 @@ export class MatrixEvent extends TypedEventEmitter<EmittedEvents, MatrixEventHan
         this.localTimestamp = Date.now() - this.getAge();
     }
 
+    public showRedactedContent(event: object): void {
+        const oldUnsigned = this.getUnsigned();
+        this.event = event;
+        this.clearEvent = undefined;
+        if (!this.event.unsigned) {
+            this.event.unsigned = {};
+        }
+        this.event.unsigned.redacted_because = oldUnsigned.redacted_because;
+        this.viewingRedactedContent = true;
+        this.setStatus(null);
+        this.localTimestamp = Date.now() - this.getAge();
+    }
+
     /**
      * Whether the event is in any phase of sending, send failure, waiting for
      * remote echo, etc.