1 files changed, 34 insertions, 0 deletions
diff --git a/dom/streams/StreamUtils.cpp b/dom/streams/StreamUtils.cpp
new file mode 100644
index 0000000000..15ad80867d
--- /dev/null
+++ b/dom/streams/StreamUtils.cpp
@@ -0,0 +1,34 @@
+/* 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 "StreamUtils.h"
+
+#include <cmath>
+#include "mozilla/dom/QueuingStrategyBinding.h"
+
+namespace mozilla::dom {
+
+// Streams Spec: 7.4
+// https://streams.spec.whatwg.org/#validate-and-normalize-high-water-mark
+double ExtractHighWaterMark(const QueuingStrategy& aStrategy,
+                            double aDefaultHWM, mozilla::ErrorResult& aRv) {
+  // Step 1.
+  if (!aStrategy.mHighWaterMark.WasPassed()) {
+    return aDefaultHWM;
+  }
+
+  // Step 2.
+  double highWaterMark = aStrategy.mHighWaterMark.Value();
+
+  // Step 3.
+  if (std::isnan(highWaterMark) || highWaterMark < 0) {
+    aRv.ThrowRangeError("Invalid highWaterMark");
+    return 0.0;
+  }
+
+  // Step 4.
+  return highWaterMark;
+}
+
+}  // namespace mozilla::dom