Bug 1176988 - Patch 2 - Remove XHR cache bypass in cast of POST request. r=jdm

--HG--
extra : commitid : H3p5Ob7Kc6K
extra : rebase_source : dc7765152a8ca8302114e130c1de001c811b55bd

dom/base/nsXMLHttpRequest.cpp

@@ -2875,26 +2875,22 @@ nsXMLHttpRequest::Send(nsIVariant* aVariant, const Nullable<RequestBody>& aBody)
   NS_ASSERTION(listener != this,
                "Using an object as a listener that can't be exposed to JS");
 
-  // Bypass the network cache in cases where it makes no sense:
-  // POST responses are always unique, and we provide no API that would
-  // allow our consumers to specify a "cache key" to access old POST
-  // responses, so they are not worth caching.
-  if (method.EqualsLiteral("POST")) {
-    AddLoadFlags(mChannel,
-        nsIRequest::LOAD_BYPASS_CACHE | nsIRequest::INHIBIT_CACHING);
-  } else {
-    // When we are sync loading, we need to bypass the local cache when it would
-    // otherwise block us waiting for exclusive access to the cache.  If we don't
-    // do this, then we could dead lock in some cases (see bug 309424).
-    //
-    // Also don't block on the cache entry on async if it is busy - favoring parallelism
-    // over cache hit rate for xhr. This does not disable the cache everywhere -
-    // only in cases where more than one channel for the same URI is accessed
-    // simultanously.
+  // When we are sync loading, we need to bypass the local cache when it would
+  // otherwise block us waiting for exclusive access to the cache.  If we don't
+  // do this, then we could dead lock in some cases (see bug 309424).
+  //
+  // Also don't block on the cache entry on async if it is busy - favoring parallelism
+  // over cache hit rate for xhr. This does not disable the cache everywhere -
+  // only in cases where more than one channel for the same URI is accessed
+  // simultanously.
 
-    AddLoadFlags(mChannel,
-                 nsICachingChannel::LOAD_BYPASS_LOCAL_CACHE_IF_BUSY);
-  }
+  AddLoadFlags(mChannel,
+               nsICachingChannel::LOAD_BYPASS_LOCAL_CACHE_IF_BUSY);
+
+  // While it would be optimal to bypass the cache in case of POST requests
+  // since they are never cached, our ServiceWorker interception implementation
+  // on single-process systems is implemented via the HTTP cache, so DO NOT
+  // bypass the cache based on method!
 
   // Since we expect XML data, set the type hint accordingly
   // if the channel doesn't know any content type.