1 files changed, 57 insertions, 0 deletions
diff --git a/xpcom/io/InputStreamLengthHelper.h b/xpcom/io/InputStreamLengthHelper.h
new file mode 100644
index 0000000000..1f44c70fe3
--- /dev/null
+++ b/xpcom/io/InputStreamLengthHelper.h
@@ -0,0 +1,57 @@
+/* -*- 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_InputStreamLengthHelper_h
+#define mozilla_InputStreamLengthHelper_h
+
+#include <functional>
+
+#include "nsISupportsImpl.h"
+#include "nsIInputStreamLength.h"
+#include "nsThreadUtils.h"
+
+class nsIInputStream;
+
+namespace mozilla {
+
+// This class helps to retrieve the stream's length.
+
+class InputStreamLengthHelper final : public Runnable,
+                                      public nsIInputStreamLengthCallback {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  // This is one of the 2 entry points of this class. It returns false if the
+  // length cannot be taken synchronously.
+  static bool GetSyncLength(nsIInputStream* aStream, int64_t* aLength);
+
+  // This is one of the 2 entry points of this class. The callback is executed
+  // asynchronously when the length is known.
+  static void GetAsyncLength(
+      nsIInputStream* aStream,
+      const std::function<void(int64_t aLength)>& aCallback);
+
+ private:
+  NS_DECL_NSIINPUTSTREAMLENGTHCALLBACK
+
+  InputStreamLengthHelper(
+      nsIInputStream* aStream,
+      const std::function<void(int64_t aLength)>& aCallback);
+
+  ~InputStreamLengthHelper();
+
+  NS_IMETHOD
+  Run() override;
+
+  void ExecCallback(int64_t aLength);
+
+  nsCOMPtr<nsIInputStream> mStream;
+  std::function<void(int64_t aLength)> mCallback;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_InputStreamLengthHelper_h