From 3f5a994a2489f6714bf50ca4da09a2fc63a9987b Mon Sep 17 00:00:00 2001
From: Johannes Marbach <johannesm@element.io>
Date: Tue, 18 Jun 2024 10:14:48 +0200
Subject: [PATCH] Add via parameter for MSC4156 (#4247)

* Add via parameter for MSC4156

Signed-off-by: Johannes Marbach <n0-0ne+github@mailbox.org>

* Always include both parameters

* Fix tests

---------

Signed-off-by: Johannes Marbach <n0-0ne+github@mailbox.org>
---
 spec/integ/matrix-client-methods.spec.ts |  2 +-
 src/client.ts                            | 16 ++++++++++++----
 src/feature.ts                           |  4 ++++
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/spec/integ/matrix-client-methods.spec.ts b/spec/integ/matrix-client-methods.spec.ts
index 06986652d48..c321403d591 100644
--- a/spec/integ/matrix-client-methods.spec.ts
+++ b/spec/integ/matrix-client-methods.spec.ts
@@ -257,7 +257,7 @@ describe("MatrixClient", function () {
                 .when("POST", "/knock/" + encodeURIComponent(roomId))
                 .check((request) => {
                     expect(request.data).toEqual({ reason: opts.reason });
-                    expect(request.queryParams).toEqual({ server_name: opts.viaServers });
+                    expect(request.queryParams).toEqual({ server_name: opts.viaServers, via: opts.viaServers });
                 })
                 .respond(200, { room_id: roomId });
 
diff --git a/src/client.ts b/src/client.ts
index 1e3c57783cf..40a9e5d89b7 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -4319,9 +4319,13 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             signPromise = this.http.requestOtherUrl<IThirdPartySigned>(Method.Post, url);
         }
 
-        const queryString: Record<string, string | string[]> = {};
+        let queryParams: QueryDict = {};
         if (opts.viaServers) {
-            queryString["server_name"] = opts.viaServers;
+            queryParams.server_name = opts.viaServers;
+            queryParams.via = opts.viaServers;
+            if (this.canSupport.get(Feature.MigrateServerNameToVia) === ServerSupport.Unstable) {
+                queryParams = replaceParam("via", "org.matrix.msc4156.via", queryParams);
+            }
         }
 
         const data: IJoinRequestBody = {};
@@ -4331,7 +4335,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         }
 
         const path = utils.encodeUri("/join/$roomid", { $roomid: roomIdOrAlias });
-        const res = await this.http.authedRequest<{ room_id: string }>(Method.Post, path, queryString, data);
+        const res = await this.http.authedRequest<{ room_id: string }>(Method.Post, path, queryParams, data);
 
         const roomId = res.room_id;
         // In case we were originally given an alias, check the room cache again
@@ -4364,9 +4368,13 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
 
         const path = utils.encodeUri("/knock/$roomIdOrAlias", { $roomIdOrAlias: roomIdOrAlias });
 
-        const queryParams: Record<string, string | string[]> = {};
+        let queryParams: QueryDict = {};
         if (opts.viaServers) {
             queryParams.server_name = opts.viaServers;
+            queryParams.via = opts.viaServers;
+            if (this.canSupport.get(Feature.MigrateServerNameToVia) === ServerSupport.Unstable) {
+                queryParams = replaceParam("via", "org.matrix.msc4156.via", queryParams);
+            }
         }
 
         const body: Record<string, string> = {};
diff --git a/src/feature.ts b/src/feature.ts
index 01cadd8e87c..0657a217cd5 100644
--- a/src/feature.ts
+++ b/src/feature.ts
@@ -33,6 +33,7 @@ export enum Feature {
     AccountDataDeletion = "AccountDataDeletion",
     RelationsRecursion = "RelationsRecursion",
     IntentionalMentions = "IntentionalMentions",
+    MigrateServerNameToVia = "MigrateServerNameToVia",
 }
 
 type FeatureSupportCondition = {
@@ -65,6 +66,9 @@ const featureSupportResolver: Record<string, FeatureSupportCondition> = {
         unstablePrefixes: ["org.matrix.msc3952_intentional_mentions"],
         matrixVersion: "v1.7",
     },
+    [Feature.MigrateServerNameToVia]: {
+        unstablePrefixes: ["org.matrix.msc4156"],
+    },
 };
 
 export async function buildFeatureSupportMap(versions: IServerVersions): Promise<Map<Feature, ServerSupport>> {