Only perform range requests for identity Content-Encoding

extensions/firefox/components/PdfStreamConverter.js

@@ -692,17 +692,34 @@ PdfStreamConverter.prototype = {
   // nsIRequestObserver::onStartRequest
   onStartRequest: function(aRequest, aContext) {
     // Setup the request so we can use it below.
-    var acceptRanges = false;
+    var isHttpRequest = false;
     try {
       aRequest.QueryInterface(Ci.nsIHttpChannel);
-      if (aRequest.getResponseHeader('Accept-Ranges') === 'bytes') {
+      isHttpRequest = true;
+    } catch (e) {}
+
+    var rangeRequest = false;
+    if (isHttpRequest) {
+      var contentEncoding = 'identity';
+      try {
+        contentEncoding = aRequest.getResponseHeader('Content-Encoding');
+      } catch (e) {}
+
+      var acceptRanges;
+      try {
+        acceptRanges = aRequest.getResponseHeader('Accept-Ranges');
+      } catch (e) {}
+
       var hash = aRequest.URI.ref;
-        acceptRanges = hash.indexOf('disableRange=true') < 0;
+      rangeRequest = contentEncoding === 'identity' &&
+                     acceptRanges === 'bytes' &&
+                     hash.indexOf('disableRange=true') < 0;
     }
-    } catch (e) {}
+
     aRequest.QueryInterface(Ci.nsIChannel);
 
     aRequest.QueryInterface(Ci.nsIWritablePropertyBag);
+
     var contentDispositionFilename;
     try {
       contentDispositionFilename = aRequest.contentDispositionFilename;
@@ -712,7 +729,7 @@ PdfStreamConverter.prototype = {
     aRequest.setProperty('contentType', aRequest.contentType);
     aRequest.contentType = 'text/html';
 
-    if (!acceptRanges) {
+    if (!rangeRequest) {
       // Creating storage for PDF data
       var contentLength = aRequest.contentLength;
       this.dataListener = new PdfDataListener(contentLength);
@@ -750,7 +767,7 @@ PdfStreamConverter.prototype = {
         // Double check the url is still the correct one.
         if (domWindow.document.documentURIObject.equals(aRequest.URI)) {
           var actions;
-          if (acceptRanges) {
+          if (rangeRequest) {
             // We are going to be issuing range requests, so cancel the
             // original request
             aRequest.resume();

src/worker.js

@@ -183,6 +183,12 @@ var WorkerMessageHandler = {
             return;
           }
 
+          var contentEncoding =
+            fullRequestXhr.getResponseHeader('Content-Encoding') || 'identity';
+          if (contentEncoding !== 'identity') {
+            return;
+          }
+
           var length = fullRequestXhr.getResponseHeader('Content-Length');
           length = parseInt(length, 10);
           if (!isInt(length)) {