Bug 1947431 - Add "zstd" as a CompressionFormat r=saschanaz,webidl

This patch adds a new variant for "zstd" to the CompressionFormat
enum in WebIDL. It also adds a couple Mozilla-specific WPTs to ensure
that the construction of CompressionStream and DecompressionStream
objects with this format are restricted to the correct contexts.

Differential Revision: https://phabricator.services.mozilla.com/D238135

dom/base/CompressionStream.cpp

@@ -228,6 +228,13 @@ JSObject* CompressionStream::WrapObject(JSContext* aCx,
 // https://wicg.github.io/compression/#dom-compressionstream-compressionstream
 already_AddRefed<CompressionStream> CompressionStream::Constructor(
     const GlobalObject& aGlobal, CompressionFormat aFormat, ErrorResult& aRv) {
+  if (aFormat == CompressionFormat::Zstd) {
+    aRv.ThrowTypeError(
+        "'zstd' (value of argument 1) is not a valid value for enumeration "
+        "CompressionFormat.");
+    return nullptr;
+  }
+
   // Step 1: If format is unsupported in CompressionStream, then throw a
   // TypeError.
   // XXX: Skipped as we are using enum for this

dom/base/DecompressionStream.cpp

@@ -270,6 +270,14 @@ JSObject* DecompressionStream::WrapObject(JSContext* aCx,
 // https://wicg.github.io/compression/#dom-decompressionstream-decompressionstream
 already_AddRefed<DecompressionStream> DecompressionStream::Constructor(
     const GlobalObject& aGlobal, CompressionFormat aFormat, ErrorResult& aRv) {
+  if (aFormat == CompressionFormat::Zstd &&
+      aGlobal.CallerType() != CallerType::System) {
+    aRv.ThrowTypeError(
+        "'zstd' (value of argument 1) is not a valid value for enumeration "
+        "CompressionFormat.");
+    return nullptr;
+  }
+
   // Step 1: If format is unsupported in DecompressionStream, then throw a
   // TypeError.
   // XXX: Skipped as we are using enum for this

dom/webidl/CompressionStream.webidl

@@ -11,6 +11,7 @@ enum CompressionFormat {
   "deflate",
   "deflate-raw",
   "gzip",
+  "zstd",
 };
 
 [Exposed=*]

testing/web-platform/mozilla/tests/compression/zstd/compression-constructor.tentative.any.js

@@ -0,0 +1,34 @@
+// META: global=window
+
+"use strict";
+
+test(t => {
+  assert_throws_js(
+    TypeError,
+    () => new CompressionStream("zstd"),
+    'Constructor given "zstd" should throw'
+  );
+}, '"zstd" should be an invalid CompressionStream option');
+
+promise_test(async t => {
+  const constructorFailed = await SpecialPowers.spawnChrome([], () => {
+    let cs;
+
+    try {
+      cs = new this.browsingContext.topChromeWindow.CompressionStream("zstd");
+    } catch {
+      return true;
+    }
+
+    if (cs) {
+      throw new Error(
+        'Constructed a CompressionStream with "zstd" format, when that should be disallowed'
+      );
+    }
+  });
+
+  assert_true(
+    constructorFailed,
+    'Constructor given "zstd" should throw, even in a privileged context'
+  );
+}, '"zstd" should be an invalid CompressionStream format, even in a privileged context');

testing/web-platform/mozilla/tests/compression/zstd/decompression-constructor.tentative.any.js

@@ -0,0 +1,35 @@
+// META: global=window
+
+"use strict";
+
+test(t => {
+  assert_throws_js(
+    TypeError,
+    () => new DecompressionStream("zstd"),
+    'Constructor given "zstd" should throw.'
+  );
+}, '"zstd" should be an invalid DecompressionStream format in an unprivileged context.');
+
+promise_test(async t => {
+  const constructorSucceeded = await SpecialPowers.spawnChrome(
+    [],
+    function create_decompression_stream_in_chrome_context() {
+      const ds = new this.browsingContext.topChromeWindow.DecompressionStream(
+        "zstd"
+      );
+
+      if (!ds) {
+        throw new Error(
+          'Failed to construct DecompressionStream with "zstd" format in privileged context.'
+        );
+      }
+
+      return true;
+    }
+  );
+
+  assert_true(
+    constructorSucceeded,
+    'Constructor given "zstd" should succeed in a privileged context'
+  );
+}, '"zstd" should be a valid DecompressionStream format in a privileged context.');