Issue #2258 - Part 2: Move XCTO:nosniff check into sniffers.

This fixes a regression for the JSON viewer from part 1 as it relies on
sniffing to prettify (and should carve out the exception even if `nosniff`
headers are sent).
No real functional changes otherwise. Just catering to a corner case.

image/imgLoader.cpp

@@ -2489,6 +2489,13 @@ imgLoader::GetMIMETypeFromContent(nsIRequest* aRequest,
                                   uint32_t aLength,
                                   nsACString& aContentType)
 {
+  nsCOMPtr<nsIChannel> channel(do_QueryInterface(aRequest));
+  if (channel) {
+    nsCOMPtr<nsILoadInfo> loadInfo = channel->GetLoadInfo();
+    if (loadInfo->GetSkipContentSniffing()) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+  }
   return GetMimeTypeFromContent((const char*)aContents, aLength, aContentType);
 }
 

netwerk/base/nsNetUtil.cpp

@@ -2129,16 +2129,6 @@ NS_SniffContent(const char *aSnifferType, nsIRequest *aRequest,
                 const uint8_t *aData, uint32_t aLength,
                 nsACString &aSniffedType)
 {
-  // In case XCTO nosniff was present, we could just skip sniffing here
-  nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
-  if (channel) {
-    nsCOMPtr<nsILoadInfo> loadInfo = channel->GetLoadInfo();
-    if (loadInfo->GetSkipContentSniffing()) {
-      aSniffedType.Truncate();
-      return;
-    }
-  }
-
   typedef nsCategoryCache<nsIContentSniffer> ContentSnifferCache;
   extern ContentSnifferCache* gNetSniffers;
   extern ContentSnifferCache* gDataSniffers;

netwerk/protocol/http/nsHttpChannel.cpp

@@ -1106,7 +1106,7 @@ ProcessXCTO(nsIURI* aURI, nsHttpResponseHead* aResponseHead, nsILoadInfo* aLoadI
         policyType == nsIContentPolicy::TYPE_SUBDOCUMENT) {
       // If the header XCTO nosniff is set for any browsing context, then
       // we set the skipContentSniffing flag on the Loadinfo. Within
-      // NS_SniffContent we then bail early and do not do any sniffing.
+      // GetMIMETypeFromContent we then bail early and do not do any sniffing.
       aLoadInfo->SetSkipContentSniffing(true);
       return NS_OK;
     }

netwerk/streamconv/converters/nsUnknownDecoder.cpp

@@ -317,9 +317,11 @@ nsUnknownDecoder::GetMIMETypeFromContent(nsIRequest* aRequest,
 {
   // Note: This is only used by sniffer, therefore we do not need to lock anything here.
   nsCOMPtr<nsIChannel> channel(do_QueryInterface(aRequest));
-  nsCOMPtr<nsILoadInfo> loadInfo = channel->GetLoadInfo();
+  if (channel) {
-  if (loadInfo->GetSkipContentSniffing()) {
+    nsCOMPtr<nsILoadInfo> loadInfo = channel->GetLoadInfo();
-    return NS_OK;
+    if (loadInfo->GetSkipContentSniffing()) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
   }
   mBuffer = const_cast<char*>(reinterpret_cast<const char*>(aData));
   mBufferLen = aLength;

toolkit/components/mediasniffer/nsMediaSniffer.cpp

@@ -138,6 +138,10 @@ nsMediaSniffer::GetMIMETypeFromContent(nsIRequest* aRequest,
                                        nsACString& aSniffedType) {
   nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
   if (channel) {
+    nsCOMPtr<nsILoadInfo> loadInfo = channel->GetLoadInfo();
+    if (loadInfo->GetSkipContentSniffing()) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
     nsLoadFlags loadFlags = 0;
     channel->GetLoadFlags(&loadFlags);
     if (!(loadFlags & nsIChannel::LOAD_MEDIA_SNIFFER_OVERRIDES_CONTENT_TYPE)) {