Add option to automatically retry refresh with /v1 prefix on error

src/client.ts

@@ -476,6 +476,15 @@ export interface IRefreshTokenOpts {
      * @defaultValue false
      */
     forcePrefixV1?: boolean;
+
+    /**
+     * If true, automatically retries the refresh request using a `/v1` prefix
+     * if request fails with an `M_UNRECOGNIZED` error. This is a workaround to
+     * target Synapse before and after v1.72.
+     * This has no effect if `forcePrefixV1` is true.
+     * @defaultValue false
+     */
+    retryWithPrefixV1OnUnrecognizedRequest?: boolean;
 }
 
 export enum RoomVersionStability {
@@ -7527,17 +7536,36 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * @returns Promise which resolves to the new token.
      * @returns Rejects with an error response.
      */
-    public refreshToken(refreshToken: string, options: IRefreshTokenOpts = {}): Promise<IRefreshTokenResponse> {
-        return this.http.authedRequest(
-            Method.Post,
-            "/refresh",
-            undefined,
-            { refresh_token: refreshToken },
-            {
-                prefix: options.forcePrefixV1 ? ClientPrefix.V1 : ClientPrefix.V3,
-                inhibitLogoutEmit: true, // we don't want to cause logout loops
-            },
-        );
+    public async refreshToken(refreshToken: string, options: IRefreshTokenOpts = {}): Promise<IRefreshTokenResponse> {
+        try {
+            return await this.http.authedRequest(
+                Method.Post,
+                "/refresh",
+                undefined,
+                { refresh_token: refreshToken },
+                {
+                    prefix: options.forcePrefixV1 ? ClientPrefix.V1 : ClientPrefix.V3,
+                    inhibitLogoutEmit: true, // we don't want to cause logout loops
+                },
+            );
+        } catch (err) {
+            // If caller wants to `retryWithPrefixV1OnUnrecognizedRequest`, try
+            // again with `forcePrefixV1: true`.
+            if (
+                err instanceof MatrixError &&
+                err.errcode === "M_UNRECOGNIZED" &&
+                options.retryWithPrefixV1OnUnrecognizedRequest &&
+                !options.forcePrefixV1
+            ) {
+                return this.refreshToken(refreshToken, {
+                    ...options,
+                    forcePrefixV1: true,
+                });
+            }
+
+            // Otherwise, pass along the caught error.
+            throw err;
+        }
     }
 
     /**