1 files changed, 46 insertions, 0 deletions
diff --git a/dom/base/ZLibHelper.h b/dom/base/ZLibHelper.h
new file mode 100644
index 0000000000..86de8c4086
--- /dev/null
+++ b/dom/base/ZLibHelper.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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 DOM_ZLIBHELPER_H_
+#define DOM_ZLIBHELPER_H_
+
+#include "js/TypeDecls.h"
+#include "zlib.h"
+
+#include "mozilla/dom/CompressionStreamBinding.h"
+
+namespace mozilla::dom {
+
+// From the docs in
+// https://searchfox.org/mozilla-central/source/modules/zlib/src/zlib.h
+inline int8_t ZLibWindowBits(CompressionFormat format) {
+  switch (format) {
+    case CompressionFormat::Deflate:
+      // The windowBits parameter is the base two logarithm of the window size
+      // (the size of the history buffer). It should be in the range 8..15 for
+      // this version of the library. Larger values of this parameter result
+      // in better compression at the expense of memory usage.
+      return 15;
+    case CompressionFormat::Deflate_raw:
+      // windowBits can also be –8..–15 for raw deflate. In this case,
+      // -windowBits determines the window size.
+      return -15;
+    case CompressionFormat::Gzip:
+      // windowBits can also be greater than 15 for optional gzip encoding.
+      // Add 16 to windowBits to write a simple gzip header and trailer around
+      // the compressed data instead of a zlib wrapper.
+      return 31;
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unknown compression format");
+      return 0;
+  }
+}
+
+enum ZLibFlush : uint8_t { No = Z_NO_FLUSH, Yes = Z_FINISH };
+
+}  // namespace mozilla::dom
+
+#endif  // DOM_ZLIBHELPER_H_