Update: Needs Testing - Not Tested

RelayServer/Endpoints/RtcEndpoints.cs

@@ -16,6 +16,14 @@ public static class RtcEndpoints
         app.MapPost("/api/rtc/offer", async (RtcOffer request, RtcCallService rtcCallService) =>
         {
             await rtcCallService.WriteOfferAsync(request.ChannelId, request.Username, request.SessionDescription);
+
+            RtcNotificationService.Broadcast(new RtcNotificationMessage
+            {
+                Type = "rtc_offer_updated",
+                ChannelId = request.ChannelId,
+                Username = request.Username
+            });
+
             return Results.Ok();
         });
 
@@ -31,14 +39,6 @@ public static class RtcEndpoints
             return Results.Ok(await rtcCallService.HasActiveCallAsync(channelId));
         });
 
-        // TODO: You can uncomment me if you'd like to have both. Otherwise delete me - you never know but I made it "call" instead of "active"
-        // Return the active call object for the specified channel.
-        //app.MapGet("/api/rtc/call/{channelId}", async (string channelId, RtcCallService rtcCallService) =>
-        //{
-        //    var call = await rtcCallService.GetActiveCallAsync(channelId);
-        //    return call is null ? Results.NotFound() : Results.Ok(call);
-        //});
-
         // Return the latest stored SDP offer for the specified channel.
         app.MapGet("/api/rtc/offers/{channelId}", async (string channelId, RtcCallService rtcCallService) =>
         {
@@ -47,9 +47,22 @@ public static class RtcEndpoints
         });
 
         // Store a new SDP answer for the specified channel call.
-        app.MapPost("/api/rtc/answer", async (RtcOffer request, RtcCallService rtcCallService) =>
+        app.MapPost("/api/rtc/answer", async (RtcAnswer request, RtcCallService rtcCallService) =>
         {
-            await rtcCallService.WriteAnswerAsync(request.ChannelId, request.SessionDescription);
+            await rtcCallService.WriteAnswerAsync(
+                request.ChannelId,
+                new RtcSessionDescription
+                {
+                    Type = "answer",
+                    Sdp = request.Sdp
+                });
+
+            RtcNotificationService.Broadcast(new RtcNotificationMessage
+            {
+                Type = "rtc_answer_updated",
+                ChannelId = request.ChannelId
+            });
+
             return Results.Ok();
         });
 
@@ -78,6 +91,14 @@ public static class RtcEndpoints
                 request.Direction
             );
 
+            RtcNotificationService.Broadcast(new RtcNotificationMessage
+            {
+                Type = "rtc_candidate_added",
+                ChannelId = request.ChannelId,
+                Username = request.Username,
+                Direction = request.Direction
+            });
+
             return Results.Ok();
         });
 
@@ -102,6 +123,14 @@ public static class RtcEndpoints
         app.MapPost("/api/rtc/leave", async (RtcLeaveRequest request, RtcCallService rtcCallService) =>
         {
             await rtcCallService.LeaveCallAsync(request.ChannelId, request.Username);
+
+            RtcNotificationService.Broadcast(new RtcNotificationMessage
+            {
+                Type = "rtc_call_left",
+                ChannelId = request.ChannelId,
+                Username = request.Username
+            });
+
             return Results.Ok();
         });
     }

RelayServer/Models/Rtc/RtcNotificationMessage.cs

@@ -0,0 +1,9 @@
+namespace RelayServer.Models.Rtc;
+
+public sealed class RtcNotificationMessage
+{
+    public required string Type { get; set; } // rtc_offer_updated / rtc_answer_updated / rtc_candidate_added
+    public required string ChannelId { get; set; }
+    public string? Username { get; set; }
+    public string? Direction { get; set; }
+}

RelayServer/Program.cs

@@ -30,8 +30,10 @@ app.MapRtcEndpoints();
 
 var wssv = new WebSocketServer("ws://localhost:1337");
 wssv.AddWebSocketService<ChatSocketBehavior>("/");
-//TODO: Create WebSocket message system which can alert clients already connected to a channel of changes to offer, answers, and ice candidates
+RtcNotificationService.Server = wssv;
+
 //TODO: Use AnswerCallback as a test on client and use the /rtc/answer endpoint call as a test on server
+
 wssv.Start();
 Console.WriteLine("WebSocket server started");
 

RelayServer/Services/Rtc/RtcNotificationService.cs

@@ -0,0 +1,19 @@
+using System.Text.Json;
+using RelayServer.Models.Rtc;
+using WebSocketSharp.Server;
+
+namespace RelayServer.Services.Rtc;
+
+public static class RtcNotificationService
+{
+    public static WebSocketServer? Server { get; set; }
+
+    public static void Broadcast(RtcNotificationMessage message)
+    {
+        if (Server is null)
+            return;
+
+        var json = JsonSerializer.Serialize(message);
+        Server.WebSocketServices["/"]?.Sessions.Broadcast(json);
+    }
+}