Gracefully fail when freshness cannot be calculated

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Fix issue where freshness cannot be calculated to re-send request. (#104)
+
 ## 0.0.17 (6/11/2023) 
 
 - Fix `Last-Modified` validation.

hishel/_controller.py

@@ -316,8 +316,10 @@ def construct_response_from_cache(
                 freshness_lifetime = get_heuristic_freshness(
                     response=response, clock=self._clock
                 )
-            else:  # pragma: no cover
-                raise RuntimeError("The lifespan of freshness cannot be calculated.")
+            else:
+                # If Freshness cannot be calculated, then send the request
+                self._make_request_conditional(request=request, response=response)
+                return request
 
         age = get_age(response, self._clock)
         is_fresh = freshness_lifetime > age

tests/test_controller.py

@@ -773,3 +773,16 @@ def test_must_understand_response_directive():
     controller = Controller()
 
     assert controller.is_cachable(request=request, response=response)
+
+
+def test_freshness_lifetime_invalid_information():
+    controller = Controller()
+    response = Response(
+        status=400,
+    )
+    original_request = Request("GET", "https://example.com")
+    request = Request("GET", "https://example.com")
+    conditional_request = controller.construct_response_from_cache(
+        request=request, response=response, original_request=original_request
+    )
+    assert isinstance(conditional_request, Request)