mcp: SSETransport discovers messages POST endpoint from /sse and uses it for POSTs

pentestagent/mcp/transport.py

@@ -174,6 +174,7 @@ class SSETransport(MCPTransport):
         self.url = url
         self.session: Optional[Any] = None  # aiohttp.ClientSession
         self._connected = False
+        self._post_url: Optional[str] = None
 
     @property
     def is_connected(self) -> bool:
@@ -186,6 +187,48 @@ class SSETransport(MCPTransport):
             import aiohttp
 
             self.session = aiohttp.ClientSession()
+
+            # Try to discover the POST endpoint for sending messages.
+            # Many MCP SSE servers (including MetasploitMCP) expose an SSE
+            # endpoint (e.g. /sse) which returns an initial `endpoint` event
+            # with a `data: /messages/?session_id=...` value. We perform a
+            # short GET to read that event and extract the messages POST URL.
+            try:
+                async with self.session.get(self.url, timeout=5) as resp:
+                    if resp.status != 200:
+                        # Still consider connected (we may only need POST),
+                        # but leave discovery to send() which will give clearer
+                        # errors if the server isn't compatible.
+                        self._connected = True
+                        return
+
+                    # Read a few lines to find `data:`
+                    for _ in range(20):
+                        line = await resp.content.readline()
+                        if not line:
+                            break
+                        try:
+                            text = line.decode(errors="ignore").strip()
+                        except Exception:
+                            continue
+                        if text.startswith("data:"):
+                            endpoint = text.split("data:", 1)[1].strip()
+                            # Build absolute POST URL from the discovered endpoint
+                            from urllib.parse import urlparse
+
+                            p = urlparse(self.url)
+                            if endpoint.startswith("http"):
+                                self._post_url = endpoint
+                            elif endpoint.startswith("/"):
+                                self._post_url = f"{p.scheme}://{p.netloc}{endpoint}"
+                            else:
+                                self._post_url = f"{p.scheme}://{p.netloc}/{endpoint.lstrip('/') }"
+                            break
+
+            except Exception:
+                # Discovery failed — still create session and let send() report errors.
+                pass
+
             self._connected = True
         except ImportError as e:
             raise RuntimeError(
@@ -206,8 +249,9 @@ class SSETransport(MCPTransport):
             raise RuntimeError("Transport not connected")
 
         try:
+            post_target = self._post_url or self.url
             async with self.session.post(
-                self.url, json=message, headers={"Content-Type": "application/json"}
+                post_target, json=message, headers={"Content-Type": "application/json"}
             ) as response:
                 if response.status != 200:
                     raise RuntimeError(f"HTTP error: {response.status}")