Bug 1278778 - Show JS stack traces of Fetch requests in Netmonitor r=bkelly

devtools/client/netmonitor/test/browser_net_cause.js

@@ -40,12 +40,19 @@ const EXPECTED_REQUESTS = [
     causeUri: CAUSE_URL,
     hasStack: { fn: "performXhrRequest", file: CAUSE_FILE_NAME, line: 22 }
   },
+  {
+    method: "GET",
+    url: EXAMPLE_URL + "fetch_request",
+    causeType: "fetch",
+    causeUri: CAUSE_URL,
+    hasStack: { fn: "performFetchRequest", file: CAUSE_FILE_NAME, line: 26 }
+  },
   {
     method: "POST",
     url: EXAMPLE_URL + "beacon_request",
     causeType: "beacon",
     causeUri: CAUSE_URL,
-    hasStack: { fn: "performBeaconRequest", file: CAUSE_FILE_NAME, line: 26 }
+    hasStack: { fn: "performBeaconRequest", file: CAUSE_FILE_NAME, line: 30 }
   },
 ];
 

devtools/client/netmonitor/test/html_cause-test-page.html

@@ -22,11 +22,16 @@
         xhr.send();
       }
 
+      function performFetchRequest() {
+        fetch("fetch_request");
+      }
+
       function performBeaconRequest() {
         navigator.sendBeacon("beacon_request");
       }
 
       performXhrRequest();
+      performFetchRequest();
       performBeaconRequest();
     </script>
   </body>

dom/fetch/Fetch.cpp

@@ -124,23 +124,29 @@ public:
   Run()
   {
     AssertIsOnMainThread();
+    RefPtr<FetchDriver> fetch;
     RefPtr<PromiseWorkerProxy> proxy = mResolver->mPromiseProxy;
-    MutexAutoLock lock(proxy->Lock());
-    if (proxy->CleanedUp()) {
-      NS_WARNING("Aborting Fetch because worker already shut down");
-      return NS_OK;
+
+    {
+      // Acquire the proxy mutex while getting data from the WorkerPrivate...
+      MutexAutoLock lock(proxy->Lock());
+      if (proxy->CleanedUp()) {
+        NS_WARNING("Aborting Fetch because worker already shut down");
+        return NS_OK;
+      }
+
+      nsCOMPtr<nsIPrincipal> principal = proxy->GetWorkerPrivate()->GetPrincipal();
+      MOZ_ASSERT(principal);
+      nsCOMPtr<nsILoadGroup> loadGroup = proxy->GetWorkerPrivate()->GetLoadGroup();
+      MOZ_ASSERT(loadGroup);
+      fetch = new FetchDriver(mRequest, principal, loadGroup);
     }
 
-    nsCOMPtr<nsIPrincipal> principal = proxy->GetWorkerPrivate()->GetPrincipal();
-    MOZ_ASSERT(principal);
-    nsCOMPtr<nsILoadGroup> loadGroup = proxy->GetWorkerPrivate()->GetLoadGroup();
-    MOZ_ASSERT(loadGroup);
-    RefPtr<FetchDriver> fetch = new FetchDriver(mRequest, principal, loadGroup);
-    nsresult rv = fetch->Fetch(mResolver);
-    // Right now we only support async fetch, which should never directly fail.
-    if (NS_WARN_IF(NS_FAILED(rv))) {
-      return rv;
-    }
+    // ...but release it before calling Fetch, because mResolver's callback can
+    // be called synchronously and they want the mutex, too.
+    fetch->Fetch(mResolver);
+
+    // FetchDriver::Fetch never directly fails
     return NS_OK;
   }
 };

dom/fetch/FetchDriver.cpp

@@ -83,20 +83,12 @@ FetchDriver::Fetch(FetchDriverObserver* aObserver)
   MOZ_RELEASE_ASSERT(!mRequest->IsSynchronous(),
                      "Synchronous fetch not supported");
 
-  return NS_DispatchToCurrentThread(NewRunnableMethod(this, &FetchDriver::ContinueFetch));
-}
-
-nsresult
-FetchDriver::ContinueFetch()
-{
-  workers::AssertIsOnMainThread();
-
-  nsresult rv = HttpFetch();
-  if (NS_FAILED(rv)) {
+  if (NS_FAILED(HttpFetch())) {
     FailWithNetworkError();
   }
 
-  return rv;
+  // Any failure is handled by FailWithNetworkError notifying the aObserver.
+  return NS_OK;
 }
 
 // This function implements the "HTTP Fetch" algorithm from the Fetch spec.

dom/fetch/FetchDriver.h

@@ -27,6 +27,11 @@ namespace dom {
 class InternalRequest;
 class InternalResponse;
 
+/**
+ * Provides callbacks to be called when response is available or on error.
+ * Implemenations usually resolve or reject the promise returned from fetch().
+ * The callbacks can be called synchronously or asynchronously from FetchDriver::Fetch.
+ */
 class FetchDriverObserver
 {
 public:
@@ -92,7 +97,6 @@ private:
   FetchDriver& operator=(const FetchDriver&) = delete;
   ~FetchDriver();
 
-  nsresult ContinueFetch();
   nsresult HttpFetch();
   // Returns the filtered response sent to the observer.
   already_AddRefed<InternalResponse>