issue two purges for fastly surrogate keys (#12771)

* issue two purges for fastly surrogate keys

https://developer.fastly.com/learning/concepts/purging/#race-conditions states there are some race conditions we may be running into with shielding enabled.

ref: #12214

* 🖤

* test for second purge failure

tests/unit/cache/origin/test_fastly.py

@@ -10,6 +10,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import itertools
+
 import celery.exceptions
 import pretend
 import pytest
@@ -188,9 +190,17 @@ def test_purge_key_ok(self, monkeypatch):
                     "Fastly-Key": "an api key",
                     "Fastly-Soft-Purge": "1",
                 },
-            )
+            ),
+            pretend.call(
+                "https://api.fastly.com/service/the-service-id/purge/one",
+                headers={
+                    "Accept": "application/json",
+                    "Fastly-Key": "an api key",
+                    "Fastly-Soft-Purge": "1",
+                },
+            ),
         ]
-        assert response.raise_for_status.calls == [pretend.call()]
+        assert response.raise_for_status.calls == [pretend.call(), pretend.call()]
 
     @pytest.mark.parametrize("result", [{"status": "fail"}, {}])
     def test_purge_key_unsuccessful(self, monkeypatch, result):
@@ -218,3 +228,42 @@ def test_purge_key_unsuccessful(self, monkeypatch, result):
             )
         ]
         assert response.raise_for_status.calls == [pretend.call()]
+
+    @pytest.mark.parametrize(
+        "result", [[{"status": "ok"}, {"status": "fail"}], [{"status": "ok"}, {}]]
+    )
+    def test_purge_key_second_unsuccessful(self, monkeypatch, result):
+        cacher = fastly.FastlyCache(
+            api_key="an api key", service_id="the-service-id", purger=None
+        )
+
+        _result = itertools.cycle(result)
+        response = pretend.stub(
+            raise_for_status=pretend.call_recorder(lambda: None),
+            json=lambda: next(_result),
+        )
+        requests_post = pretend.call_recorder(lambda *a, **kw: response)
+        monkeypatch.setattr(requests, "post", requests_post)
+
+        with pytest.raises(fastly.UnsuccessfulPurgeError):
+            cacher.purge_key("one")
+
+        assert requests_post.calls == [
+            pretend.call(
+                "https://api.fastly.com/service/the-service-id/purge/one",
+                headers={
+                    "Accept": "application/json",
+                    "Fastly-Key": "an api key",
+                    "Fastly-Soft-Purge": "1",
+                },
+            ),
+            pretend.call(
+                "https://api.fastly.com/service/the-service-id/purge/one",
+                headers={
+                    "Accept": "application/json",
+                    "Fastly-Key": "an api key",
+                    "Fastly-Soft-Purge": "1",
+                },
+            ),
+        ]
+        assert response.raise_for_status.calls == [pretend.call(), pretend.call()]

warehouse/cache/origin/fastly.py

@@ -10,6 +10,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import time
 import urllib.parse
 
 import requests
@@ -106,3 +107,11 @@ def purge_key(self, key):
 
         if resp.json().get("status") != "ok":
             raise UnsuccessfulPurgeError(f"Could not purge {key!r}")
+
+        time.sleep(2)
+
+        resp = requests.post(url, headers=headers)
+        resp.raise_for_status()
+
+        if resp.json().get("status") != "ok":
+            raise UnsuccessfulPurgeError(f"Could not double purge {key!r}")