Refactor endpoint parsing for better extensibility

daphne/endpoints.py

@@ -1,22 +1,42 @@
-def build_endpoint_description_strings(
-    host=None, port=None, unix_socket=None, file_descriptor=None
-):
+from abc import ABC, abstractmethod
+
+class Endpoint(ABC):
+    @abstractmethod
+    def parse(self, options):
+        pass
+
+class TCPEndpoint(Endpoint):
+    def parse(self, options):
+        if options.get("port") and options.get("host"):
+            host = options["host"].strip("[]").replace(":", r"\:")
+            return f"tcp:port={int(options['port'])}:interface={host}"
+        elif options.get("port") or options.get("host"):
+            raise ValueError("TCP binding requires both port and host kwargs.")
+        return None
+
+class UNIXEndpoint(Endpoint):
+    def parse(self, options):
+        if options.get("unix_socket"):
+            return f"unix:{options['unix_socket']}"
+        return None
+
+class FileDescriptorEndpoint(Endpoint):
+    def parse(self, options):
+        if options.get("file_descriptor") is not None:
+            return f"fd:fileno={int(options['file_descriptor'])}"
+        return None
+
+endpoint_parsers = [TCPEndpoint(), UNIXEndpoint(), FileDescriptorEndpoint()]
+
+def build_endpoint_description_strings(**kwargs):
     """
     Build a list of twisted endpoint description strings that the server will listen on.
     This is to streamline the generation of twisted endpoint description strings from easier
     to use command line args such as host, port, unix sockets etc.
     """
     socket_descriptions = []
-    if host and port is not None:
-        host = host.strip("[]").replace(":", r"\:")
-        socket_descriptions.append("tcp:port=%d:interface=%s" % (int(port), host))
-    elif any([host, port]):
-        raise ValueError("TCP binding requires both port and host kwargs.")
-
-    if unix_socket:
-        socket_descriptions.append("unix:%s" % unix_socket)
-
-    if file_descriptor is not None:
-        socket_descriptions.append("fd:fileno=%d" % int(file_descriptor))
-
+    for parser in endpoint_parsers:
+        description = parser.parse(kwargs)
+        if description:
+            socket_descriptions.append(description)
     return socket_descriptions

tests/test_cli.py

@@ -4,7 +4,11 @@ from argparse import ArgumentError
 from unittest import TestCase, skipUnless
 
 from daphne.cli import CommandLineInterface
-from daphne.endpoints import build_endpoint_description_strings as build
+from daphne.endpoints import (
+    build_endpoint_description_strings as build,
+    endpoint_parsers,
+    Endpoint,
+)
 
 
 class TestEndpointDescriptions(TestCase):
@@ -64,6 +68,23 @@ class TestEndpointDescriptions(TestCase):
             ),
         )
 
+    def test_custom_endpoint(self):
+        class CustomEndpoint(Endpoint):
+            def parse(self, options):
+                if options.get("custom"):
+                    return f"custom:{options['custom']}"
+                return None
+
+        endpoint_parsers.append(CustomEndpoint())
+
+        self.assertEqual(
+            build(custom="myprotocol"),
+            ["custom:myprotocol"],
+        )
+
+        # Cleanup custom endpoint parser
+        endpoint_parsers.pop()
+
 
 class TestCLIInterface(TestCase):
     """