Fix #1788 incorrect url_for for routes with hosts, added tests.

sanic/app.py

@@ -830,6 +830,14 @@ def url_for(self, view_name: str, **kwargs):
                 "Endpoint with name `{}` was not found".format(view_name)
             )
 
+        # If the route has host defined, split that off
+        # TODO: Retain netloc and path separately in Route objects
+        host = uri.find("/")
+        if host > 0:
+            host, uri = uri[:host], uri[host:]
+        else:
+            host = None
+
         if view_name == "static" or view_name.endswith(".static"):
             filename = kwargs.pop("filename", None)
             # it's static folder
@@ -862,7 +870,7 @@ def url_for(self, view_name: str, **kwargs):
 
         netloc = kwargs.pop("_server", None)
         if netloc is None and external:
-            netloc = self.config.get("SERVER_NAME", "")
+            netloc = host or self.config.get("SERVER_NAME", "")
 
         if external:
             if not scheme:

tests/test_url_for.py

@@ -0,0 +1,12 @@
+def test_routes_with_host(app):
+    @app.route("/")
+    @app.route("/", name="hostindex", host="example.com")
+    @app.route("/path", name="hostpath", host="path.example.com")
+    def index(request):
+        pass
+
+    assert app.url_for("index") == "/"
+    assert app.url_for("hostindex") == "/"
+    assert app.url_for("hostpath") == "/path"
+    assert app.url_for("hostindex", _external=True) == "http://example.com/"
+    assert app.url_for("hostpath", _external=True) == "http://path.example.com/path"