Example set of changes to support an optional Endpoint

Author: aaronpowell

samples/aspire/McpSample.Client/Program.cs

@@ -14,9 +14,7 @@
 
     var endpoint = httpClient.BaseAddress?.ToString().Replace("https+", "") ?? throw new InvalidOperationException("No endpoint set for MCP server");
 
-    var transport = new SseClientTransport(new SseClientTransportOptions { 
-        Endpoint = new(endpoint)
-    }, httpClient);
+    var transport = new SseClientTransport(new SseClientTransportOptions(), httpClient);
 
     var t = McpClientFactory.CreateAsync(transport);
     t.Wait();

src/ModelContextProtocol.Core/Client/SseClientSessionTransport.cs

@@ -17,7 +17,6 @@ internal sealed partial class SseClientSessionTransport : TransportBase
 {
     private readonly HttpClient _httpClient;
     private readonly SseClientTransportOptions _options;
-    private readonly Uri _sseEndpoint;
     private Uri? _messageEndpoint;
     private readonly CancellationTokenSource _connectionCts;
     private Task? _receiveTask;
@@ -40,7 +39,6 @@ public SseClientSessionTransport(
         Throw.IfNull(httpClient);
 
         _options = transportOptions;
-        _sseEndpoint = transportOptions.Endpoint;
         _httpClient = httpClient;
         _connectionCts = new CancellationTokenSource();
         _logger = (ILogger?)loggerFactory?.CreateLogger<SseClientTransport>() ?? NullLogger.Instance;
@@ -150,7 +148,7 @@ private async Task ReceiveMessagesAsync(CancellationToken cancellationToken)
     {
         try
         {
-            using var request = new HttpRequestMessage(HttpMethod.Get, _sseEndpoint);
+            using var request = new HttpRequestMessage(HttpMethod.Get, _httpClient.BaseAddress);
             request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/event-stream"));
             StreamableHttpClientSessionTransport.CopyAdditionalHeaders(request.Headers, _options.AdditionalHeaders, sessionId: null, protocolVersion: null);
 
@@ -239,8 +237,8 @@ private void HandleEndpointEvent(string data)
             return;
         }
 
-        // If data is an absolute URL, the Uri will be constructed entirely from it and not the _sseEndpoint.
-        _messageEndpoint = new Uri(_sseEndpoint, data);
+        // If data is an absolute URL, the Uri will be constructed entirely from it and not the _httpClient.BaseAddress.
+        _messageEndpoint = new Uri(_httpClient.BaseAddress!, data);
 
         // Set connected state
         SetConnected();

src/ModelContextProtocol.Core/Client/SseClientTransport.cs

@@ -25,7 +25,7 @@ public sealed class SseClientTransport : IClientTransport, IAsyncDisposable
     /// <param name="transportOptions">Configuration options for the transport.</param>
     /// <param name="loggerFactory">Logger factory for creating loggers used for diagnostic output during transport operations.</param>
     public SseClientTransport(SseClientTransportOptions transportOptions, ILoggerFactory? loggerFactory = null)
-        : this(transportOptions, new HttpClient(), loggerFactory, ownsHttpClient: true)
+        : this(transportOptions, new HttpClient { BaseAddress = transportOptions.Endpoint ?? throw new InvalidOperationException("No Endpoint provided on the transport options.") }, loggerFactory, ownsHttpClient: true)
     {
     }
 
@@ -44,11 +44,16 @@ public SseClientTransport(SseClientTransportOptions transportOptions, HttpClient
         Throw.IfNull(transportOptions);
         Throw.IfNull(httpClient);
 
+        if (httpClient.BaseAddress is null)
+        {
+            throw new InvalidOperationException("No BaseAddress set on the HttpClient. Please set the BaseAddress to the server's endpoint.");
+        }
+
         _options = transportOptions;
         _httpClient = httpClient;
         _loggerFactory = loggerFactory;
         _ownsHttpClient = ownsHttpClient;
-        Name = transportOptions.Name ?? transportOptions.Endpoint.ToString();
+        Name = transportOptions.Name ?? httpClient.BaseAddress.ToString();
     }
 
     /// <inheritdoc />

src/ModelContextProtocol.Core/Client/SseClientTransportOptions.cs

@@ -8,7 +8,7 @@ public sealed class SseClientTransportOptions
     /// <summary>
     /// Gets or sets the base address of the server for SSE connections.
     /// </summary>
-    public required Uri Endpoint
+    public Uri? Endpoint
     {
         get;
         set

tests/ModelContextProtocol.AspNetCore.Tests/HttpServerIntegrationTests.cs

@@ -53,7 +53,7 @@ public async Task Connect_TestServer_ShouldProvideServerFields()
         Assert.NotNull(client.ServerCapabilities);
         Assert.NotNull(client.ServerInfo);
 
-        if (ClientTransportOptions.Endpoint.AbsolutePath.EndsWith("/sse"))
+        if (ClientTransportOptions.Endpoint is not null && ClientTransportOptions.Endpoint.AbsolutePath.EndsWith("/sse"))
         {
             Assert.Null(client.SessionId);
         }