Factor acme bits out to a separate file (#5521)

This makes some of the conditional-import hoop-jumping easier.

changelog.d/5521.misc

@@ -0,0 +1 @@
+Factor acme bits out to a separate file.

synapse/handlers/acme.py

@@ -15,14 +15,9 @@
 
 import logging
 
-import attr
-from zope.interface import implementer
-
 import twisted
 import twisted.internet.error
 from twisted.internet import defer
-from twisted.python.filepath import FilePath
-from twisted.python.url import URL
 from twisted.web import server, static
 from twisted.web.resource import Resource
 
@@ -30,27 +25,6 @@ from synapse.app import check_bind_error
 
 logger = logging.getLogger(__name__)
 
-try:
-    from txacme.interfaces import ICertificateStore
-
-    @attr.s
-    @implementer(ICertificateStore)
-    class ErsatzStore(object):
-        """
-        A store that only stores in memory.
-        """
-
-        certs = attr.ib(default=attr.Factory(dict))
-
-        def store(self, server_name, pem_objects):
-            self.certs[server_name] = [o.as_bytes() for o in pem_objects]
-            return defer.succeed(None)
-
-
-except ImportError:
-    # txacme is missing
-    pass
-
 
 class AcmeHandler(object):
     def __init__(self, hs):
@@ -60,6 +34,7 @@ class AcmeHandler(object):
 
     @defer.inlineCallbacks
     def start_listening(self):
+        from synapse.handlers import acme_issuing_service
 
         # Configure logging for txacme, if you need to debug
         # from eliot import add_destinations
@@ -67,37 +42,18 @@ class AcmeHandler(object):
         #
         # add_destinations(TwistedDestination())
 
-        from txacme.challenges import HTTP01Responder
-        from txacme.service import AcmeIssuingService
-        from txacme.endpoint import load_or_create_client_key
-        from txacme.client import Client
-        from josepy.jwa import RS256
+        well_known = Resource()
 
-        self._store = ErsatzStore()
-        responder = HTTP01Responder()
-
-        self._issuer = AcmeIssuingService(
-            cert_store=self._store,
-            client_creator=(
-                lambda: Client.from_url(
-                    reactor=self.reactor,
-                    url=URL.from_text(self.hs.config.acme_url),
-                    key=load_or_create_client_key(
-                        FilePath(self.hs.config.config_dir_path)
-                    ),
-                    alg=RS256,
-                )
-            ),
-            clock=self.reactor,
-            responders=[responder],
+        self._issuer = acme_issuing_service.create_issuing_service(
+            self.reactor,
+            acme_url=self.hs.config.acme_url,
+            pem_path=self.hs.config.config_dir_path,
+            well_known_resource=well_known,
         )
 
-        well_known = Resource()
-        well_known.putChild(b"acme-challenge", responder.resource)
         responder_resource = Resource()
         responder_resource.putChild(b".well-known", well_known)
         responder_resource.putChild(b"check", static.Data(b"OK", b"text/plain"))
-
         srv = server.Site(responder_resource)
 
         bind_addresses = self.hs.config.acme_bind_addresses
@@ -128,7 +84,7 @@ class AcmeHandler(object):
             logger.exception("Fail!")
             raise
         logger.warning("Reprovisioned %s, saving.", self._acme_domain)
-        cert_chain = self._store.certs[self._acme_domain]
+        cert_chain = self._issuer.cert_store.certs[self._acme_domain]
 
         try:
             with open(self.hs.config.tls_private_key_file, "wb") as private_key_file:

synapse/handlers/acme_issuing_service.py

@@ -0,0 +1,84 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 New Vector Ltd
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Utility function to create an ACME issuing service.
+
+This file contains the unconditional imports on the acme and cryptography bits that we
+only need (and may only have available) if we are doing ACME, so is designed to be
+imported conditionally.
+"""
+
+import attr
+from josepy.jwa import RS256
+from txacme.challenges import HTTP01Responder
+from txacme.client import Client
+from txacme.endpoint import load_or_create_client_key
+from txacme.interfaces import ICertificateStore
+from txacme.service import AcmeIssuingService
+from zope.interface import implementer
+
+from twisted.internet import defer
+from twisted.python.filepath import FilePath
+from twisted.python.url import URL
+
+
+def create_issuing_service(reactor, acme_url, pem_path, well_known_resource):
+    """Create an ACME issuing service, and attach it to a web Resource
+
+    Args:
+        reactor: twisted reactor
+        acme_url (str): URL to use to request certificates
+        pem_path (str): where to store the client key
+        well_known_resource (twisted.web.IResource): web resource for .well-known.
+            we will attach a child resource for "acme-challenge".
+
+    Returns:
+        AcmeIssuingService
+    """
+    responder = HTTP01Responder()
+
+    well_known_resource.putChild(b"acme-challenge", responder.resource)
+
+    store = ErsatzStore()
+
+    return AcmeIssuingService(
+        cert_store=store,
+        client_creator=(
+            lambda: Client.from_url(
+                reactor=reactor,
+                url=URL.from_text(acme_url),
+                key=load_or_create_client_key(FilePath(pem_path)),
+                alg=RS256,
+            )
+        ),
+        clock=reactor,
+        responders=[responder],
+    )
+
+
+@attr.s
+@implementer(ICertificateStore)
+class ErsatzStore(object):
+    """
+    A store that only stores in memory.
+    """
+
+    certs = attr.ib(default=attr.Factory(dict))
+
+    def store(self, server_name, pem_objects):
+        self.certs[server_name] = [o.as_bytes() for o in pem_objects]
+        return defer.succeed(None)