1 files changed, 100 insertions, 0 deletions
diff --git a/dom/heapsnapshot/ZeroCopyNSIOutputStream.cpp b/dom/heapsnapshot/ZeroCopyNSIOutputStream.cpp
new file mode 100644
index 000000000..0c29db7f9
--- /dev/null
+++ b/dom/heapsnapshot/ZeroCopyNSIOutputStream.cpp
@@ -0,0 +1,100 @@
+/* -*-  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/. */
+
+#include "mozilla/devtools/ZeroCopyNSIOutputStream.h"
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Unused.h"
+
+namespace mozilla {
+namespace devtools {
+
+ZeroCopyNSIOutputStream::ZeroCopyNSIOutputStream(nsCOMPtr<nsIOutputStream>& out)
+  : out(out)
+  , result_(NS_OK)
+  , amountUsed(0)
+  , writtenCount(0)
+{
+  DebugOnly<bool> nonBlocking = false;
+  MOZ_ASSERT(out->IsNonBlocking(&nonBlocking) == NS_OK);
+  MOZ_ASSERT(!nonBlocking);
+}
+
+ZeroCopyNSIOutputStream::~ZeroCopyNSIOutputStream()
+{
+  if (!failed())
+    Unused << NS_WARN_IF(NS_FAILED(writeBuffer()));
+}
+
+nsresult
+ZeroCopyNSIOutputStream::writeBuffer()
+{
+  if (failed())
+    return result_;
+
+  if (amountUsed == 0)
+    return NS_OK;
+
+  int32_t amountWritten = 0;
+  while (amountWritten < amountUsed) {
+    uint32_t justWritten = 0;
+
+    result_ = out->Write(buffer + amountWritten,
+                         amountUsed - amountWritten,
+                         &justWritten);
+    if (NS_WARN_IF(NS_FAILED(result_)))
+      return result_;
+
+    amountWritten += justWritten;
+  }
+
+  writtenCount += amountUsed;
+  amountUsed = 0;
+  return NS_OK;
+}
+
+// ZeroCopyOutputStream Interface
+
+bool
+ZeroCopyNSIOutputStream::Next(void** data, int* size)
+{
+  MOZ_ASSERT(data != nullptr);
+  MOZ_ASSERT(size != nullptr);
+
+  if (failed())
+    return false;
+
+  if (amountUsed == BUFFER_SIZE) {
+    if (NS_FAILED(writeBuffer()))
+      return false;
+  }
+
+  *data = buffer + amountUsed;
+  *size = BUFFER_SIZE - amountUsed;
+  amountUsed = BUFFER_SIZE;
+  return true;
+}
+
+void
+ZeroCopyNSIOutputStream::BackUp(int count)
+{
+  MOZ_ASSERT(count >= 0,
+             "Cannot back up a negative amount of bytes.");
+  MOZ_ASSERT(amountUsed == BUFFER_SIZE,
+             "Can only call BackUp directly after calling Next.");
+  MOZ_ASSERT(count <= amountUsed,
+             "Can't back up further than we've given out.");
+
+  amountUsed -= count;
+}
+
+::google::protobuf::int64
+ZeroCopyNSIOutputStream::ByteCount() const
+{
+  return writtenCount + amountUsed;
+}
+
+} // namespace devtools
+} // namespace mozilla