Auto merge of servo#24401 - gterzian:ensure_done_chan_is_none_when_revalidating, r=jdm

Fetch: ensure consistency between response, done-chan, and cache state.

This ensures that when a cached response is not used because it requires revalidation, the done chan is set back to `None`(since the cache might have set it to `Some` when constructing the response requiring revalidation).

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- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix servo#24399 (GitHub issue number if applicable)

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Author: bors-servo

components/net/http_loader.rs

@@ -1092,20 +1092,6 @@ fn http_network_or_cache_fetch(
                             response_from_cache.needs_validation,
                         ),
                     };
-                if cached_response.is_none() {
-                    // Ensure the done chan is not set if we're not using the cached response,
-                    // as the cache might have set it to Some if it constructed a pending response.
-                    *done_chan = None;
-
-                    // Update the cache state, incrementing the pending store count,
-                    // or starting the count.
-                    if let HttpCacheEntryState::PendingStore(i) = *state {
-                        let new = i + 1;
-                        *state = HttpCacheEntryState::PendingStore(new);
-                    } else {
-                        *state = HttpCacheEntryState::PendingStore(1);
-                    }
-                }
                 if needs_revalidation {
                     revalidating_flag = true;
                     // Substep 5
@@ -1124,6 +1110,20 @@ fn http_network_or_cache_fetch(
                     // Substep 6
                     response = cached_response;
                 }
+                if response.is_none() {
+                    // Ensure the done chan is not set if we're not using the cached response,
+                    // as the cache might have set it to Some if it constructed a pending response.
+                    *done_chan = None;
+
+                    // Update the cache state, incrementing the pending store count,
+                    // or starting the count.
+                    if let HttpCacheEntryState::PendingStore(i) = *state {
+                        let new = i + 1;
+                        *state = HttpCacheEntryState::PendingStore(new);
+                    } else {
+                        *state = HttpCacheEntryState::PendingStore(1);
+                    }
+                }
             }
         }
         // Notify the next thread waiting in line, if there is any.
@@ -1223,6 +1223,9 @@ fn http_network_or_cache_fetch(
                 .map_or(false, |s| s.0 == StatusCode::NOT_MODIFIED)
         {
             if let Ok(mut http_cache) = context.state.http_cache.write() {
+                // Ensure done_chan is None,
+                // since the network response will be replaced by the revalidated stored one.
+                *done_chan = None;
                 response = http_cache.refresh(&http_request, forward_response.clone(), done_chan);
                 wait_for_cached_response(done_chan, &mut response);
             }