1 files changed, 70 insertions, 0 deletions
diff --git a/dom/heapsnapshot/ZeroCopyNSIOutputStream.h b/dom/heapsnapshot/ZeroCopyNSIOutputStream.h
new file mode 100644
index 000000000..117fc0f87
--- /dev/null
+++ b/dom/heapsnapshot/ZeroCopyNSIOutputStream.h
@@ -0,0 +1,70 @@
+/* -*-  Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_devtools_ZeroCopyNSIOutputStream__
+#define mozilla_devtools_ZeroCopyNSIOutputStream__
+
+#include <google/protobuf/io/zero_copy_stream.h>
+#include <google/protobuf/stubs/common.h>
+
+#include "nsCOMPtr.h"
+#include "nsIOutputStream.h"
+
+namespace mozilla {
+namespace devtools {
+
+// A `google::protobuf::io::ZeroCopyOutputStream` implementation that uses an
+// `nsIOutputStream` under the covers.
+//
+// This class will automatically write and flush its data to the
+// `nsIOutputStream` in its destructor, but if you care whether that call
+// succeeds or fails, then you should call the `flush` method yourself. Errors
+// will be logged, however.
+class MOZ_STACK_CLASS ZeroCopyNSIOutputStream
+  : public ::google::protobuf::io::ZeroCopyOutputStream
+{
+  static const int BUFFER_SIZE = 8192;
+
+  // The nsIOutputStream we are streaming to.
+  nsCOMPtr<nsIOutputStream>& out;
+
+  // The buffer we write data to before passing it to the output stream.
+  char buffer[BUFFER_SIZE];
+
+  // The status of writing to the underlying output stream.
+  nsresult result_;
+
+  // The number of bytes in the buffer that have been used thus far.
+  int amountUsed;
+
+  // Excluding the amount of the buffer currently used (which hasn't been
+  // written and flushed yet), this is the number of bytes written to the output
+  // stream.
+  int64_t writtenCount;
+
+  // Write the internal buffer to the output stream and flush it.
+  nsresult writeBuffer();
+
+public:
+  explicit ZeroCopyNSIOutputStream(nsCOMPtr<nsIOutputStream>& out);
+
+  nsresult flush() { return writeBuffer(); }
+
+  // Return true if writing to the underlying output stream ever failed.
+  bool failed() const { return NS_FAILED(result_); }
+
+  nsresult result() const { return result_; }
+
+  // ZeroCopyOutputStream Interface
+  virtual ~ZeroCopyNSIOutputStream() override;
+  virtual bool Next(void** data, int* size) override;
+  virtual void BackUp(int count) override;
+  virtual ::google::protobuf::int64 ByteCount() const override;
+};
+
+} // namespace devtools
+} // namespace mozilla
+
+#endif // mozilla_devtools_ZeroCopyNSIOutputStream__