Remove various bits of compatibility code for Python <3.6 (#9879)

I went through and removed a bunch of cruft that was lying around for compatibility with old Python versions. This PR also will now prevent Synapse from starting unless you're running Python 3.6+.

10 files changed, 16 insertions, 80 deletions

diff --git a/synapse/__init__.py b/synapse/__init__.py
index 837e938f56..fbd49a93e1 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -21,8 +21,8 @@ import os
 import sys
 
 # Check that we're not running on an unsupported Python version.
-if sys.version_info < (3, 5):
-    print("Synapse requires Python 3.5 or above.")
+if sys.version_info < (3, 6):
+    print("Synapse requires Python 3.6 or above.")
     sys.exit(1)
 
 # Twisted and canonicaljson will fail to import when this file is executed to
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 2a1c925ee8..2de946f464 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -85,7 +85,7 @@ REQUIREMENTS = [
     "typing-extensions>=3.7.4",
     # We enforce that we have a `cryptography` version that bundles an `openssl`
     # with the latest security patches.
-    "cryptography>=3.4.7;python_version>='3.6'",
+    "cryptography>=3.4.7",
 ]
 
 CONDITIONAL_REQUIREMENTS = {
@@ -100,14 +100,9 @@ CONDITIONAL_REQUIREMENTS = {
     # that use the protocol, such as Let's Encrypt.
     "acme": [
         "txacme>=0.9.2",
-        # txacme depends on eliot. Eliot 1.8.0 is incompatible with
-        # python 3.5.2, as per https://github.com/itamarst/eliot/issues/418
-        "eliot<1.8.0;python_version<'3.5.3'",
     ],
     "saml2": [
-        # pysaml2 6.4.0 is incompatible with Python 3.5 (see https://github.com/IdentityPython/pysaml2/issues/749)
-        "pysaml2>=4.5.0,<6.4.0;python_version<'3.6'",
-        "pysaml2>=4.5.0;python_version>='3.6'",
+        "pysaml2>=4.5.0",
     ],
     "oidc": ["authlib>=0.14.0"],
     # systemd-python is necessary for logging to the systemd journal via
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index edda7861fa..8c9d21d3ea 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -14,6 +14,7 @@
 import hashlib
 import hmac
 import logging
+import secrets
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Dict, List, Optional, Tuple
 
@@ -375,7 +376,7 @@ class UserRegisterServlet(RestServlet):
         """
         self._clear_old_nonces()
 
-        nonce = self.hs.get_secrets().token_hex(64)
+        nonce = secrets.token_hex(64)
         self.nonces[nonce] = int(self.reactor.seconds())
         return 200, {"nonce": nonce}
 
diff --git a/synapse/rest/consent/consent_resource.py b/synapse/rest/consent/consent_resource.py
index c4550d3cf0..b19cd8afc5 100644
--- a/synapse/rest/consent/consent_resource.py
+++ b/synapse/rest/consent/consent_resource.py
@@ -32,14 +32,6 @@ TEMPLATE_LANGUAGE = "en"
 
 logger = logging.getLogger(__name__)
 
-# use hmac.compare_digest if we have it (python 2.7.7), else just use equality
-if hasattr(hmac, "compare_digest"):
-    compare_digest = hmac.compare_digest
-else:
-
-    def compare_digest(a, b):
-        return a == b
-
 
 class ConsentResource(DirectServeHtmlResource):
     """A twisted Resource to display a privacy policy and gather consent to it
@@ -209,5 +201,5 @@ class ConsentResource(DirectServeHtmlResource):
             .encode("ascii")
         )
 
-        if not compare_digest(want_mac, userhmac):
+        if not hmac.compare_digest(want_mac, userhmac):
             raise SynapseError(HTTPStatus.FORBIDDEN, "HMAC incorrect")
diff --git a/synapse/rest/media/v1/filepath.py b/synapse/rest/media/v1/filepath.py
index 4088e7a059..09531ebf54 100644
--- a/synapse/rest/media/v1/filepath.py
+++ b/synapse/rest/media/v1/filepath.py
@@ -21,7 +21,7 @@ from typing import Callable, List
 NEW_FORMAT_ID_RE = re.compile(r"^\d\d\d\d-\d\d-\d\d")
 
 
-def _wrap_in_base_path(func: "Callable[..., str]") -> "Callable[..., str]":
+def _wrap_in_base_path(func: Callable[..., str]) -> Callable[..., str]:
     """Takes a function that returns a relative path and turns it into an
     absolute path based on the location of the primary media store
     """
diff --git a/synapse/secrets.py b/synapse/secrets.py
deleted file mode 100644
index bf829251fd..0000000000
--- a/synapse/secrets.py
+++ /dev/null
@@ -1,44 +0,0 @@
-# Copyright 2018 New Vector Ltd
-#
-# 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.
-
-"""
-Injectable secrets module for Synapse.
-
-See https://docs.python.org/3/library/secrets.html#module-secrets for the API
-used in Python 3.6, and the API emulated in Python 2.7.
-"""
-import sys
-
-# secrets is available since python 3.6
-if sys.version_info[0:2] >= (3, 6):
-    import secrets
-
-    class Secrets:
-        def token_bytes(self, nbytes: int = 32) -> bytes:
-            return secrets.token_bytes(nbytes)
-
-        def token_hex(self, nbytes: int = 32) -> str:
-            return secrets.token_hex(nbytes)
-
-
-else:
-    import binascii
-    import os
-
-    class Secrets:
-        def token_bytes(self, nbytes: int = 32) -> bytes:
-            return os.urandom(nbytes)
-
-        def token_hex(self, nbytes: int = 32) -> str:
-            return binascii.hexlify(self.token_bytes(nbytes)).decode("ascii")
diff --git a/synapse/server.py b/synapse/server.py
index 06570bb1ce..2337d2d9b4 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -126,7 +126,6 @@ from synapse.rest.media.v1.media_repository import (
     MediaRepository,
     MediaRepositoryResource,
 )
-from synapse.secrets import Secrets
 from synapse.server_notices.server_notices_manager import ServerNoticesManager
 from synapse.server_notices.server_notices_sender import ServerNoticesSender
 from synapse.server_notices.worker_server_notices_sender import (
@@ -642,10 +641,6 @@ class HomeServer(metaclass=abc.ABCMeta):
         return GroupAttestionRenewer(self)
 
     @cache_in_self
-    def get_secrets(self) -> Secrets:
-        return Secrets()
-
-    @cache_in_self
     def get_stats_handler(self) -> StatsHandler:
         return StatsHandler(self)
 
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index d472676acf..6b68d8720c 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -114,7 +114,7 @@ def db_to_json(db_content: Union[memoryview, bytes, bytearray, str]) -> Any:
         db_content = db_content.tobytes()
 
     # Decode it to a Unicode string before feeding it to the JSON decoder, since
-    # Python 3.5 does not support deserializing bytes.
+    # it only supports handling strings
     if isinstance(db_content, (bytes, bytearray)):
         db_content = db_content.decode("utf8")
 
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 9452368bf0..bd39c095af 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -171,10 +171,7 @@ class LoggingDatabaseConnection:
 
 
 # The type of entry which goes on our after_callbacks and exception_callbacks lists.
-#
-# Python 3.5.2 doesn't support Callable with an ellipsis, so we wrap it in quotes so
-# that mypy sees the type but the runtime python doesn't.
-_CallbackListEntry = Tuple["Callable[..., None]", Iterable[Any], Dict[str, Any]]
+_CallbackListEntry = Tuple[Callable[..., None], Iterable[Any], Dict[str, Any]]
 
 
 R = TypeVar("R")
@@ -221,7 +218,7 @@ class LoggingTransaction:
         self.after_callbacks = after_callbacks
         self.exception_callbacks = exception_callbacks
 
-    def call_after(self, callback: "Callable[..., None]", *args: Any, **kwargs: Any):
+    def call_after(self, callback: Callable[..., None], *args: Any, **kwargs: Any):
         """Call the given callback on the main twisted thread after the
         transaction has finished. Used to invalidate the caches on the
         correct thread.
@@ -233,7 +230,7 @@ class LoggingTransaction:
         self.after_callbacks.append((callback, args, kwargs))
 
     def call_on_exception(
-        self, callback: "Callable[..., None]", *args: Any, **kwargs: Any
+        self, callback: Callable[..., None], *args: Any, **kwargs: Any
     ):
         # if self.exception_callbacks is None, that means that whatever constructed the
         # LoggingTransaction isn't expecting there to be any callbacks; assert that
@@ -485,7 +482,7 @@ class DatabasePool:
         desc: str,
         after_callbacks: List[_CallbackListEntry],
         exception_callbacks: List[_CallbackListEntry],
-        func: "Callable[..., R]",
+        func: Callable[..., R],
         *args: Any,
         **kwargs: Any,
     ) -> R:
@@ -618,7 +615,7 @@ class DatabasePool:
     async def runInteraction(
         self,
         desc: str,
-        func: "Callable[..., R]",
+        func: Callable[..., R],
         *args: Any,
         db_autocommit: bool = False,
         **kwargs: Any,
@@ -678,7 +675,7 @@ class DatabasePool:
 
     async def runWithConnection(
         self,
-        func: "Callable[..., R]",
+        func: Callable[..., R],
         *args: Any,
         db_autocommit: bool = False,
         **kwargs: Any,
diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py
index 2529845c9e..25ea1bcc91 100644
--- a/synapse/util/caches/response_cache.py
+++ b/synapse/util/caches/response_cache.py
@@ -110,7 +110,7 @@ class ResponseCache(Generic[T]):
         return result.observe()
 
     def wrap(
-        self, key: T, callback: "Callable[..., Any]", *args: Any, **kwargs: Any
+        self, key: T, callback: Callable[..., Any], *args: Any, **kwargs: Any
     ) -> defer.Deferred:
         """Wrap together a *get* and *set* call, taking care of logcontexts