server: Parse port numbers from MCP server URLs in CORS proxy (#20208)

* Parse port numbers from MCP server URLs

* Pass scheme to http proxy for determining whether to use SSL

* Fix download on non-standard port and re-add port to logging

* add test

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

common/http.h

@@ -7,6 +7,7 @@ struct common_http_url {
     std::string user;
     std::string password;
     std::string host;
+    int port;
     std::string path;
 };
 
@@ -47,6 +48,20 @@ static common_http_url common_http_parse_url(const std::string & url) {
         parts.host = rest;
         parts.path = "/";
     }
+
+    auto colon_pos = parts.host.find(':');
+
+    if (colon_pos != std::string::npos) {
+        parts.port = std::stoi(parts.host.substr(colon_pos + 1));
+        parts.host = parts.host.substr(0, colon_pos);
+    } else if (parts.scheme == "http") {
+        parts.port = 80;
+    } else if (parts.scheme == "https") {
+        parts.port = 443;
+    } else {
+        throw std::runtime_error("unsupported URL scheme: " + parts.scheme);
+    }
+
     return parts;
 }
 
@@ -68,7 +83,7 @@ static std::pair<httplib::Client, common_http_url> common_http_client(const std:
     }
 #endif
 
-    httplib::Client cli(parts.scheme + "://" + parts.host);
+    httplib::Client cli(parts.scheme + "://" + parts.host + ":" + std::to_string(parts.port));
 
     if (!parts.user.empty()) {
         cli.set_basic_auth(parts.user, parts.password);

tools/server/server-cors-proxy.h

@@ -30,12 +30,13 @@ static server_http_res_ptr proxy_request(const server_http_req & req, std::strin
         throw std::runtime_error("unsupported URL scheme in target URL: " + parsed_url.scheme);
     }
 
-    SRV_INF("proxying %s request to %s://%s%s\n", method.c_str(), parsed_url.scheme.c_str(), parsed_url.host.c_str(), parsed_url.path.c_str());
+    SRV_INF("proxying %s request to %s://%s:%i%s\n", method.c_str(), parsed_url.scheme.c_str(), parsed_url.host.c_str(), parsed_url.port, parsed_url.path.c_str());
 
     auto proxy = std::make_unique<server_http_proxy>(
             method,
+            parsed_url.scheme,
             parsed_url.host,
-            parsed_url.scheme == "http" ? 80 : 443,
+            parsed_url.port,
             parsed_url.path,
             req.headers,
             req.body,

tools/server/server-models.cpp

@@ -783,6 +783,7 @@ server_http_res_ptr server_models::proxy_request(const server_http_req & req, co
     }
     auto proxy = std::make_unique<server_http_proxy>(
             method,
+            "http",
             CHILD_ADDR,
             meta->port,
             proxy_path,
@@ -1079,6 +1080,7 @@ static bool should_strip_proxy_header(const std::string & header_name) {
 
 server_http_proxy::server_http_proxy(
         const std::string & method,
+        const std::string & scheme,
         const std::string & host,
         int port,
         const std::string & path,
@@ -1092,7 +1094,7 @@ server_http_proxy::server_http_proxy(
     auto cli  = std::make_shared<httplib::ClientImpl>(host, port);
     auto pipe = std::make_shared<pipe_t<msg_t>>();
 
-    if (port == 443) {
+    if (scheme == "https") {
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
         cli.reset(new httplib::SSLClient(host, port));
 #else

tools/server/server-models.h

@@ -180,6 +180,7 @@ struct server_http_proxy : server_http_res {
     std::function<void()> cleanup = nullptr;
 public:
     server_http_proxy(const std::string & method,
+                      const std::string & scheme,
                       const std::string & host,
                       int port,
                       const std::string & path,

tools/server/tests/unit/test_proxy.py

@@ -0,0 +1,41 @@
+import pytest
+from utils import *
+
+server = ServerPreset.tinyllama2()
+
+
+@pytest.fixture(autouse=True)
+def create_server():
+    global server
+    server = ServerPreset.tinyllama2()
+
+
+def test_mcp_no_proxy():
+    global server
+    server.webui_mcp_proxy = False
+    server.start()
+
+    res = server.make_request("GET", "/cors-proxy")
+    assert res.status_code == 404
+
+
+def test_mcp_proxy():
+    global server
+    server.webui_mcp_proxy = True
+    server.start()
+
+    url = f"http://{server.server_host}:{server.server_port}/cors-proxy?url=http://example.com"
+    res = requests.get(url)
+    assert res.status_code == 200
+    assert "Example Domain" in res.text
+
+
+def test_mcp_proxy_custom_port():
+    global server
+    server.webui_mcp_proxy = True
+    server.start()
+
+    # try getting the server's models API via the proxy
+    res = server.make_request("GET", f"/cors-proxy?url=http://{server.server_host}:{server.server_port}/models")
+    assert res.status_code == 200
+    assert "data" in res.body

tools/server/tests/utils.py

@@ -102,6 +102,7 @@ class ServerProcess:
     mmproj_url: str | None = None
     media_path: str | None = None
     sleep_idle_seconds: int | None = None
+    webui_mcp_proxy: bool = False
 
     # session variables
     process: subprocess.Popen | None = None
@@ -236,6 +237,8 @@ class ServerProcess:
             server_args.extend(["--media-path", self.media_path])
         if self.sleep_idle_seconds is not None:
             server_args.extend(["--sleep-idle-seconds", self.sleep_idle_seconds])
+        if self.webui_mcp_proxy:
+            server_args.append("--webui-mcp-proxy")
 
         args = [str(arg) for arg in [server_path, *server_args]]
         print(f"tests: starting server with: {' '.join(args)}")