From a9e9efb3361df9fca0621cfceb9338ca4274205c Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Mon, 19 Oct 2020 14:26:12 -0400
Subject: [PATCH] direct tests for `@render_exception`

---
 src/allmydata/test/web/test_common.py | 211 ++++++++++++++++++++++++++
 src/allmydata/web/common.py           |   2 +-
 2 files changed, 212 insertions(+), 1 deletion(-)
 create mode 100644 src/allmydata/test/web/test_common.py

diff --git a/src/allmydata/test/web/test_common.py b/src/allmydata/test/web/test_common.py
new file mode 100644
index 000000000..f9152e126
--- /dev/null
+++ b/src/allmydata/test/web/test_common.py
@@ -0,0 +1,211 @@
+"""
+Tests for ``allmydata.web.common``.
+"""
+
+from bs4 import (
+    BeautifulSoup,
+)
+from hyperlink import (
+    DecodedURL,
+)
+
+from testtools.matchers import (
+    Equals,
+    Contains,
+    MatchesPredicate,
+)
+from testtools.twistedsupport import (
+    succeeded,
+    has_no_result,
+)
+
+from twisted.internet.defer import (
+    fail,
+)
+from twisted.web.server import (
+    NOT_DONE_YET,
+)
+from twisted.web.resource import (
+    Resource,
+)
+
+from ...web.common import (
+    render_exception,
+)
+
+from ..common import (
+    SyncTestCase,
+)
+from ..common_web import (
+    render,
+)
+from .common import (
+    assert_soup_has_tag_with_attributes,
+)
+
+class StaticResource(Resource):
+    def __init__(self, response):
+        Resource.__init__(self)
+        self._response = response
+
+    @render_exception
+    def render(self, request):
+        return self._response
+
+
+class RenderExceptionTests(SyncTestCase):
+    """
+    Tests for ``render_exception``.
+    """
+    def test_exception(self):
+        """
+        If the decorated method raises an exception then the exception is rendered
+        into the response.
+        """
+        class R(Resource):
+            @render_exception
+            def render(self, request):
+                raise Exception("synthetic exception")
+
+        self.assertThat(
+            render(R(), {}),
+            succeeded(
+                Contains(b"synthetic exception"),
+            ),
+        )
+
+    def test_failure(self):
+        """
+        If the decorated method returns a ``Deferred`` that fires with a
+        ``Failure`` then the exception the ``Failure`` wraps is rendered into
+        the response.
+        """
+        resource = StaticResource(fail(Exception("synthetic exception")))
+        self.assertThat(
+            render(resource, {}),
+            succeeded(
+                Contains(b"synthetic exception"),
+            ),
+        )
+
+    def test_resource(self):
+        """
+        If the decorated method returns an ``IResource`` provider then that
+        resource is used to render the response.
+        """
+        resource = StaticResource(StaticResource(b"static result"))
+        self.assertThat(
+            render(resource, {}),
+            succeeded(
+                Equals(b"static result"),
+            ),
+        )
+
+    def test_unicode(self):
+        """
+        If the decorated method returns a ``unicode`` string then that string is
+        UTF-8 encoded and rendered into the response.
+        """
+        text = u"\N{SNOWMAN}"
+        resource = StaticResource(text)
+        self.assertThat(
+            render(resource, {}),
+            succeeded(
+                Equals(text.encode("utf-8")),
+            ),
+        )
+
+    def test_bytes(self):
+        """
+        If the decorated method returns a ``bytes`` string then that string is
+        rendered into the response.
+        """
+        data = b"hello world"
+        resource = StaticResource(data)
+        self.assertThat(
+            render(resource, {}),
+            succeeded(
+                Equals(data),
+            ),
+        )
+
+    def test_decodedurl(self):
+        """
+        If the decorated method returns a ``DecodedURL`` then a redirect to that
+        location is rendered into the response.
+        """
+        loc = u"http://example.invalid/foo?bar=baz"
+        resource = StaticResource(DecodedURL.from_text(loc))
+        self.assertThat(
+            render(resource, {}),
+            succeeded(
+                MatchesPredicate(
+                    lambda value: assert_soup_has_tag_with_attributes(
+                        self,
+                        BeautifulSoup(value),
+                        "meta",
+                        {"http-equiv": "refresh",
+                         "content": "0;URL={}".format(loc.encode("ascii")),
+                        },
+                    )
+                    # The assertion will raise if it has a problem, otherwise
+                    # return None.  Turn the None into something
+                    # MatchesPredicate recognizes as success.
+                    or True,
+                    "did not find meta refresh tag in %r",
+                ),
+            ),
+        )
+
+    def test_none(self):
+        """
+        If the decorated method returns ``None`` then the response is finished
+        with no additional content.
+        """
+        self.assertThat(
+            render(StaticResource(None), {}),
+            succeeded(
+                Equals(b""),
+            ),
+        )
+
+    def test_not_done_yet(self):
+        """
+        If the decorated method returns ``NOT_DONE_YET`` then the resource is
+        responsible for finishing the request itself.
+        """
+        the_request = []
+        class R(Resource):
+            @render_exception
+            def render(self, request):
+                the_request.append(request)
+                return NOT_DONE_YET
+
+        d = render(R(), {})
+
+        self.assertThat(
+            d,
+            has_no_result(),
+        )
+
+        the_request[0].write(b"some content")
+        the_request[0].finish()
+
+        self.assertThat(
+            d,
+            succeeded(
+                Equals(b"some content"),
+            ),
+        )
+
+    def test_unknown(self):
+        """
+        If the decorated method returns something which is not explicitly
+        supported, an internal server error is rendered into the response.
+        """
+        self.assertThat(
+            render(StaticResource(object()), {}),
+            succeeded(
+                Equals(b"Internal Server Error"),
+            ),
+        )
diff --git a/src/allmydata/web/common.py b/src/allmydata/web/common.py
index 56bef9dfc..215abb46e 100644
--- a/src/allmydata/web/common.py
+++ b/src/allmydata/web/common.py
@@ -605,7 +605,7 @@ def _finish(result, render, request):
             result,
         ))
         request.setResponseCode(http.INTERNAL_SERVER_ERROR)
-        _finish(b"", render, request)
+        _finish(b"Internal Server Error", render, request)
 
 
 def _renderHTTP_exception(request, failure):