[browser] fix server initiated full close (#97320)

src/libraries/System.Net.WebSockets.Client/tests/CloseTest.cs

@@ -266,7 +266,6 @@ public async Task CloseOutputAsync_ClientInitiated_CanReceive_CanClose(Uri serve
         [ConditionalTheory(nameof(WebSocketsSupported)), MemberData(nameof(EchoServers))]
         public async Task CloseOutputAsync_ServerInitiated_CanReceive(Uri server)
         {
-            string message = "Hello WebSockets!";
             var expectedCloseStatus = WebSocketCloseStatus.NormalClosure;
             var expectedCloseDescription = ".shutdownafter";
 
@@ -303,9 +302,6 @@ await cws.SendAsync(
 
                 Assert.Equal(WebSocketState.CloseReceived, cws.State);
 
-                // Should be able to send.
-                await cws.SendAsync(WebSocketData.GetBufferFromText(message), WebSocketMessageType.Text, true, cts.Token);
-
                 // Cannot change the close status/description with the final close.
                 var closeStatus = PlatformDetection.IsNotBrowser ? WebSocketCloseStatus.InvalidPayloadData : (WebSocketCloseStatus)3210;
                 var closeDescription = "CloseOutputAsync_Client_Description";

src/mono/browser/runtime/web-socket.ts

@@ -131,6 +131,11 @@ export function ws_wasm_send(ws: WebSocketExtension, buffer_ptr: VoidPtr, buffer
     if (ws[wasm_ws_is_aborted] || ws[wasm_ws_close_sent]) {
         return rejectedPromise("InvalidState: The WebSocket is not connected.");
     }
+    if (ws.readyState == WebSocket.CLOSED) {
+        // this is server initiated close but not partial close
+        // because CloseOutputAsync_ServerInitiated_CanSend expectations, we don't fail here
+        return resolvedPromise();
+    }
 
     const buffer_view = new Uint8Array(localHeapViewU8().buffer, <any>buffer_ptr, buffer_length);
     const whole_buffer = _mono_wasm_web_socket_send_buffering(ws, buffer_view, message_type, end_of_message);