From 186aa9abc4715ef42f7d7d1c7ecd95884bdeab45 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Fri, 15 Apr 2022 09:32:15 -0400
Subject: [PATCH] Make the utility reusable.

---
 src/allmydata/test/test_deferredutil.py  | 28 +++++++++++++++++++
 src/allmydata/test/test_storage_https.py | 17 +-----------
 src/allmydata/util/deferredutil.py       | 35 +++++++++++++-----------
 3 files changed, 48 insertions(+), 32 deletions(-)

diff --git a/src/allmydata/test/test_deferredutil.py b/src/allmydata/test/test_deferredutil.py
index 2a155089f..a37dfdd6f 100644
--- a/src/allmydata/test/test_deferredutil.py
+++ b/src/allmydata/test/test_deferredutil.py
@@ -129,3 +129,31 @@ class UntilTests(unittest.TestCase):
         self.assertEqual([1], counter)
         r1.callback(None)
         self.assertEqual([2], counter)
+
+
+class AsyncToDeferred(unittest.TestCase):
+    """Tests for ``deferredutil.async_to_deferred.``"""
+
+    def test_async_to_deferred_success(self):
+        """
+        Normal results from a ``@async_to_deferred``-wrapped function get
+        turned into a ``Deferred`` with that value.
+        """
+        @deferredutil.async_to_deferred
+        async def f(x, y):
+            return x + y
+
+        result = f(1, y=2)
+        self.assertEqual(self.successResultOf(result), 3)
+
+    def test_async_to_deferred_exception(self):
+        """
+        Exceptions from a ``@async_to_deferred``-wrapped function get
+        turned into a ``Deferred`` with that value.
+        """
+        @deferredutil.async_to_deferred
+        async def f(x, y):
+            return x/y
+
+        result = f(1, 0)
+        self.assertIsInstance(self.failureResultOf(result).value, ZeroDivisionError)
diff --git a/src/allmydata/test/test_storage_https.py b/src/allmydata/test/test_storage_https.py
index 73c99725a..3b41e8308 100644
--- a/src/allmydata/test/test_storage_https.py
+++ b/src/allmydata/test/test_storage_https.py
@@ -6,14 +6,12 @@ server authentication logic, which may one day apply outside of HTTP Storage
 Protocol.
 """
 
-from functools import wraps
 from contextlib import asynccontextmanager
 
 from cryptography import x509
 
 from twisted.internet.endpoints import serverFromString
 from twisted.internet import reactor
-from twisted.internet.defer import Deferred
 from twisted.internet.task import deferLater
 from twisted.web.server import Site
 from twisted.web.static import Data
@@ -31,6 +29,7 @@ from .certs import (
 from ..storage.http_common import get_spki_hash
 from ..storage.http_client import _StorageClientHTTPSPolicy
 from ..storage.http_server import _TLSEndpointWrapper
+from ..util.deferredutil import async_to_deferred
 
 
 class HTTPSNurlTests(SyncTestCase):
@@ -73,20 +72,6 @@ ox5zO3LrQmQw11OaIAs2/kviKAoKTFFxeyYcpS5RuKNDZfHQCXlLwt9bySxG
         self.assertEqual(get_spki_hash(certificate), expected_hash)
 
 
-def async_to_deferred(f):
-    """
-    Wrap an async function to return a Deferred instead.
-
-    Maybe solution to https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3886
-    """
-
-    @wraps(f)
-    def not_async(*args, **kwargs):
-        return Deferred.fromCoroutine(f(*args, **kwargs))
-
-    return not_async
-
-
 class PinningHTTPSValidation(AsyncTestCase):
     """
     Test client-side validation logic of HTTPS certificates that uses
diff --git a/src/allmydata/util/deferredutil.py b/src/allmydata/util/deferredutil.py
index ed2a11ee4..782663e8b 100644
--- a/src/allmydata/util/deferredutil.py
+++ b/src/allmydata/util/deferredutil.py
@@ -4,24 +4,13 @@ Utilities for working with Twisted Deferreds.
 Ported to Python 3.
 """
 
-from __future__ import absolute_import
-from __future__ import division
-from __future__ import print_function
-from __future__ import unicode_literals
-
-from future.utils import PY2
-if PY2:
-    from builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401
-
 import time
+from functools import wraps
 
-try:
-    from typing import (
-        Callable,
-        Any,
-    )
-except ImportError:
-    pass
+from typing import (
+    Callable,
+    Any,
+)
 
 from foolscap.api import eventually
 from eliot.twisted import (
@@ -231,3 +220,17 @@ def until(
         yield action()
         if condition():
             break
+
+
+def async_to_deferred(f):
+    """
+    Wrap an async function to return a Deferred instead.
+
+    Maybe solution to https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3886
+    """
+
+    @wraps(f)
+    def not_async(*args, **kwargs):
+        return defer.Deferred.fromCoroutine(f(*args, **kwargs))
+
+    return not_async