Bug 993591: Eagerly free nsStreamLoader data. r=mcmanus

netwerk/base/public/nsIStreamLoader.idl

@@ -27,9 +27,9 @@ interface nsIStreamLoaderObserver : nsISupports
      * If the observer wants to take over responsibility for the
      * data buffer (result), it returns NS_SUCCESS_ADOPTED_DATA
      * in place of NS_OK as its success code. The loader will then
-     * "forget" about the data, and not NS_Free() it in its own
-     * destructor; observer must call NS_Free() when the data is
-     * no longer required.
+     * "forget" about the data and not NS_Free() it after
+     * onStreamComplete() returns; observer must call NS_Free()
+     * when the data is no longer required.
      */
     void onStreamComplete(in nsIStreamLoader loader,
                           in nsISupports ctxt,

netwerk/base/src/nsStreamLoader.cpp

@@ -18,9 +18,7 @@ nsStreamLoader::nsStreamLoader()
 
 nsStreamLoader::~nsStreamLoader()
 {
-  if (mData) {
-    NS_Free(mData);
-  }
+  ReleaseData();
 }
 
 NS_IMETHODIMP
@@ -103,10 +101,9 @@ nsStreamLoader::OnStopRequest(nsIRequest* request, nsISupports *ctxt,
       // the observer now owns the data buffer, and the loader must
       // not deallocate it
       mData = nullptr;
-      mLength = 0;
-      mAllocated = 0;
     }
     // done.. cleanup
+    ReleaseData();
     mRequest = 0;
     mObserver = 0;
     mContext = 0;
@@ -132,8 +129,7 @@ nsStreamLoader::WriteSegmentFun(nsIInputStream *inStr,
     self->mData = static_cast<uint8_t*>(NS_Realloc(self->mData,
                                                    self->mLength + count));
     if (!self->mData) {
-      self->mLength = 0;
-      self->mAllocated = 0;
+      self->ReleaseData();
       return NS_ERROR_OUT_OF_MEMORY;
     }
     self->mAllocated = self->mLength + count;
@@ -155,3 +151,14 @@ nsStreamLoader::OnDataAvailable(nsIRequest* request, nsISupports *ctxt,
   uint32_t countRead;
   return inStr->ReadSegments(WriteSegmentFun, this, count, &countRead);
 }
+
+void
+nsStreamLoader::ReleaseData()
+{
+  if (mData) {
+    NS_Free(mData);
+    mData = nullptr;
+  }
+  mLength = 0;
+  mAllocated = 0;
+}

netwerk/base/src/nsStreamLoader.h

@@ -30,6 +30,10 @@ protected:
   static NS_METHOD WriteSegmentFun(nsIInputStream *, void *, const char *,
                                    uint32_t, uint32_t, uint32_t *);
 
+  // Utility method to free mData, if present, and update other state to
+  // reflect that no data has been allocated.
+  void ReleaseData();
+
   nsCOMPtr<nsIStreamLoaderObserver> mObserver;
   nsCOMPtr<nsISupports>             mContext;  // the observer's context
   nsCOMPtr<nsIRequest>              mRequest;