Bug 517119 - Preallocate image source data buffer based on Content-Length.r=jrmuizel,sr=vlad.

modules/libpr0n/public/imgIContainer.idl

@@ -71,7 +71,7 @@ native gfxGraphicsFilter(gfxPattern::GraphicsFilter);
  *
  * Internally, imgIContainer also manages animation of images.
  */
-[scriptable, uuid(74c63935-b54f-43a4-9449-2e9c815e3bef)]
+[scriptable, uuid(e80ec20d-8e9c-405f-a673-cea00aa95b4d)]
 interface imgIContainer : nsISupports
 {
   /**
@@ -359,4 +359,16 @@ interface imgIContainer : nsISupports
   /* Called for multipart images when there's a new source image to add. */
   [noscript] void newSourceData();
 
+  /**
+   * A hint of the number of bytes of source data that the image contains. If
+   * called early on, this can help reduce copying and reallocations by
+   * appropriately preallocating the source data buffer.
+   *
+   * We take this approach rather than having the source data management code do
+   * something more complicated (like chunklisting) because HTTP is by far the
+   * dominant source of images, and the Content-Length header is quite reliable.
+   * Thus, pre-allocation simplifies code and reduces the total number of
+   * allocations.
+   */
+  void setSourceSizeHint(in unsigned long sizeHint);
 };

modules/libpr0n/src/imgContainer.cpp

@@ -1396,6 +1396,15 @@ NS_IMETHODIMP imgContainer::NewSourceData()
   return NS_OK;
 }
 
+//******************************************************************************
+/* void setSourceSizeHint(in unsigned long sizeHint); */
+NS_IMETHODIMP imgContainer::SetSourceSizeHint(PRUint32 sizeHint)
+{
+  if (sizeHint && StoringSourceData())
+    mSourceData.SetCapacity(sizeHint);
+  return NS_OK;
+}
+
 //******************************************************************************
 /* void notify(in nsITimer timer); */
 NS_IMETHODIMP imgContainer::Notify(nsITimer *timer)

modules/libpr0n/src/imgRequest.cpp

@@ -1173,6 +1173,25 @@ NS_IMETHODIMP imgRequest::OnDataAvailable(nsIRequest *aRequest, nsISupports *ctx
       return NS_BINDING_ABORTED;
     }
 
+    /* Use content-length as a size hint for http channels. */
+    if (httpChannel) {
+      nsCAutoString contentLength;
+      rv = httpChannel->GetResponseHeader(NS_LITERAL_CSTRING("content-length"),
+                                          contentLength);
+      if (NS_SUCCEEDED(rv)) {
+        PRInt32 len = contentLength.ToInteger(&rv);
+
+        // Pass anything usable on so that the imgContainer can preallocate its
+        // source buffer
+        if (len > 0) {
+          PRUint32 sizeHint = (PRUint32) len;
+          sizeHint = PR_MIN(sizeHint, 20000000); /* Bound by something reasonable */
+          mImage->SetSourceSizeHint(sizeHint);
+        }
+      }
+    }
+
+
     // If we were waiting on the image to do something, now's our chance.
     if (mDecodeRequested) {
       mImage->RequestDecode();