fixed wrong servers 200 ok (#16126)

* fixed wrong servers 200 ok

* Update conans/client/rest/rest_client_common.py

Co-authored-by: Rubén Rincón Blanco <git@rinconblanco.es>

* wip

---------

Co-authored-by: Rubén Rincón Blanco <git@rinconblanco.es>

conans/client/rest/rest_client_common.py

@@ -142,11 +142,14 @@ def server_capabilities(self, user=None, password=None):
             auth = self.auth
         ret = self.requester.get(url, auth=auth, headers=self.custom_headers, verify=self.verify_ssl)
 
-        server_capabilities = ret.headers.get('X-Conan-Server-Capabilities', "")
+        server_capabilities = ret.headers.get('X-Conan-Server-Capabilities')
         if not server_capabilities and not ret.ok:
             # Old Artifactory might return 401/403 without capabilities, we don't want
             # to cache them #5687, so raise the exception and force authentication
             raise get_exception_from_error(ret.status_code)(response_to_str(ret))
+        if server_capabilities is None:
+            # Some servers returning 200-ok, even if not valid repo
+            raise ConanException(f"Remote {self.remote_url} doesn't seem like a valid Conan remote")
 
         return [cap.strip() for cap in server_capabilities.split(",") if cap]
 

conans/test/integration/command/upload/upload_test.py

@@ -8,6 +8,7 @@
 import pytest
 import requests
 from mock import patch
+from requests import Response
 
 from conans.errors import ConanException
 from conans.model.package_ref import PkgReference
@@ -485,6 +486,21 @@ def get(self, url, **kwargs):
         client.run("upload hello0/1.2.1@user/testing -r default")
         assert "Uploading recipe 'hello0/1.2.1@user/testing" in client.out
 
+    def test_server_returns_200_ok(self):
+        # https://github.com/conan-io/conan/issues/16104
+        # If server returns 200 ok, without headers, it raises an error
+        class MyHttpRequester(TestRequester):
+            def get(self, _, **kwargs):
+                resp = Response()
+                resp.status_code = 200
+                return resp
+
+        client = TestClient(requester_class=MyHttpRequester, servers={"default": TestServer()})
+        client.save({"conanfile.py": GenConanfile("hello0", "1.2.1")})
+        client.run("create . ")
+        client.run("upload * -c -r default", assert_error=True)
+        assert "doesn't seem like a valid Conan remote" in client.out
+
 
 def test_upload_only_without_user_channel():
     """