1 files changed, 54 insertions, 0 deletions
diff --git a/dom/quota/MemoryOutputStream.h b/dom/quota/MemoryOutputStream.h
new file mode 100644
index 0000000000..fb0d73b736
--- /dev/null
+++ b/dom/quota/MemoryOutputStream.h
@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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_dom_quota_MemoryOutputStream_h
+#define mozilla_dom_quota_MemoryOutputStream_h
+
+#include <cstdint>
+#include "mozilla/AlreadyAddRefed.h"
+#include "nsIOutputStream.h"
+#include "nsISupports.h"
+#include "nsString.h"
+
+class nsIInputStream;
+
+namespace mozilla {
+namespace dom {
+namespace quota {
+
+// An output stream so you can read your potentially-async input stream into
+// a contiguous buffer in the form of an nsCString using NS_AsyncCopy.
+// Back when streams were more synchronous and people didn't know blocking I/O
+// was bad, if you wanted to read a stream into a flat buffer, you could use
+// NS_ReadInputStreamToString/NS_ReadInputStreamToBuffer.  But those don't work
+// with async streams. This can be used to replace hand-rolled Read/AsyncWait()
+// loops.  Because you specify the expected size up front, the nsCString buffer
+// is pre-allocated so wasteful reallocations can be avoided.  However,
+// nsCString currently may over-allocate and this can be problematic on 32-bit
+// windows until we're rid of that build configuration.
+class MemoryOutputStream final : public nsIOutputStream {
+  nsCString mData;
+  uint64_t mOffset;
+
+ public:
+  static already_AddRefed<MemoryOutputStream> Create(uint64_t aSize);
+
+  const nsCString& Data() const { return mData; }
+
+ private:
+  MemoryOutputStream() : mOffset(0) {}
+
+  virtual ~MemoryOutputStream() = default;
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOUTPUTSTREAM
+};
+
+}  // namespace quota
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_dom_quota_MemoryOutputStream_h */