[netwerk] Make nsIncrementalStreamLoader's GetNumBytesRead threadsafe.

This prevents a potential race and simplifies the code a bit by keeping the
bytes read separate instead of using mData, which is modified from another
thread from OnDataAvailable.
Relaxed atomics are fine for these, since they don't guard any memory.

netwerk/base/nsIncrementalStreamLoader.cpp

@@ -11,10 +11,7 @@
 
 #include <limits>
 
-nsIncrementalStreamLoader::nsIncrementalStreamLoader()
-  : mData(), mBytesConsumed(0)
-{
-}
+nsIncrementalStreamLoader::nsIncrementalStreamLoader() = default;
 
 nsIncrementalStreamLoader::~nsIncrementalStreamLoader()
 {
@@ -49,7 +46,7 @@ NS_IMPL_ISUPPORTS(nsIncrementalStreamLoader, nsIIncrementalStreamLoader,
 NS_IMETHODIMP
 nsIncrementalStreamLoader::GetNumBytesRead(uint32_t* aNumBytes)
 {
-  *aNumBytes = mBytesConsumed + mData.length();
+  *aNumBytes = mBytesRead;
   return NS_OK;
 }
 
@@ -180,7 +177,6 @@ nsIncrementalStreamLoader::WriteSegmentFun(nsIInputStream *inStr,
     }
   }
 
-  self->mBytesConsumed += consumedCount;
   *writeCount = count;
 
   return NS_OK;
@@ -198,6 +194,8 @@ nsIncrementalStreamLoader::OnDataAvailable(nsIRequest* request, nsISupports *ctx
   uint32_t countRead;
   nsresult rv = inStr->ReadSegments(WriteSegmentFun, this, count, &countRead);
   mRequest = nullptr;
+  NS_ENSURE_SUCCESS(rv, rv);
+  mBytesRead += countRead;
   return rv;
 }
 

netwerk/base/nsIncrementalStreamLoader.h

@@ -47,8 +47,9 @@ protected:
   // available.
   mozilla::Vector<uint8_t, 0> mData;
 
-  // Number of consumed bytes from the mData.
-  size_t  mBytesConsumed;
+  // Number of bytes read, which may differ from the number of bytes in mData,
+  // since we incrementally remove from there.
+  mozilla::Atomic<uint32_t, mozilla::Relaxed> mBytesRead;
 };
 
 #endif // nsIncrementalStreamLoader_h__

netwerk/base/nsStreamLoader.cpp

@@ -54,7 +54,7 @@ NS_IMPL_ISUPPORTS(nsStreamLoader, nsIStreamLoader,
 NS_IMETHODIMP 
 nsStreamLoader::GetNumBytesRead(uint32_t* aNumBytes)
 {
-  *aNumBytes = mData.length();
+  *aNumBytes = mBytesRead;
   return NS_OK;
 }
 
@@ -150,7 +150,10 @@ nsStreamLoader::OnDataAvailable(nsIRequest* request, nsISupports *ctxt,
                                 uint64_t sourceOffset, uint32_t count)
 {
   uint32_t countRead;
-  return inStr->ReadSegments(WriteSegmentFun, this, count, &countRead);
+  nsresult rv = inStr->ReadSegments(WriteSegmentFun, this, count, &countRead);
+  NS_ENSURE_SUCCESS(rv, rv);
+  mBytesRead += countRead;
+  return NS_OK;
 }
 
 void

netwerk/base/nsStreamLoader.h

@@ -47,6 +47,8 @@ protected:
   nsCOMPtr<nsIRequest>              mRequest;
   nsCOMPtr<nsIRequestObserver>      mRequestObserver;
 
+  mozilla::Atomic<uint32_t, mozilla::Relaxed> mBytesRead;
+
   // Buffer to accumulate incoming data. We preallocate if contentSize is
   // available.
   mozilla::Vector<uint8_t, 0> mData;