[fetch] Add Response.json static method

This commit adds support for the `Response.json` static method as
specified in whatwg/fetch#1392.

All WPTs from web-platform-tests/wpt#32825 pass.

Bug: 1305358
Change-Id: Iaafdd514ed12644b6433c02e7d076ce43f51b9ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3639064
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1019479}

third_party/blink/renderer/core/fetch/response.cc

@@ -374,6 +374,40 @@ Response* Response::redirect(ScriptState* script_state,
   return r;
 }
 
+Response* Response::staticJson(ScriptState* script_state,
+                               ScriptValue data,
+                               const ResponseInit* init,
+                               ExceptionState& exception_state) {
+  // "1. Let bytes the result of running serialize a JavaScript value to JSON
+  // bytes on data."
+  v8::Local<v8::String> v8_string;
+  v8::TryCatch try_catch(script_state->GetIsolate());
+  if (!v8::JSON::Stringify(script_state->GetContext(), data.V8Value())
+           .ToLocal(&v8_string)) {
+    exception_state.RethrowV8Exception(try_catch.Exception());
+    return nullptr;
+  }
+
+  String string = ToBlinkString<String>(v8_string, kDoNotExternalize);
+
+  // JSON.stringify can fail to produce a string value in one of two ways: it
+  // can throw an exception (as with unserializable objects), or it can return
+  // `undefined` (as with e.g. passing a function). If JSON.stringify returns
+  // `undefined`, the v8 API then coerces it to the string value "undefined".
+  // Check for this, and consider it a failure.
+  if (string == "undefined") {
+    exception_state.ThrowTypeError("The data is not JSON serializable");
+    return nullptr;
+  }
+
+  BodyStreamBuffer* body_buffer = BodyStreamBuffer::Create(
+      script_state, MakeGarbageCollected<FormDataBytesConsumer>(string),
+      /*abort_signal=*/nullptr, /*cached_metadata_handler=*/nullptr);
+  String content_type = "application/json";
+
+  return Create(script_state, body_buffer, content_type, init, exception_state);
+}
+
 FetchResponseData* Response::CreateUnfilteredFetchResponseDataWithoutBody(
     ScriptState* script_state,
     mojom::blink::FetchAPIResponse& fetch_api_response) {

third_party/blink/renderer/core/fetch/response.h

@@ -56,6 +56,10 @@ class CORE_EXPORT Response final : public ScriptWrappable,
                             const String& url,
                             uint16_t status,
                             ExceptionState&);
+  static Response* staticJson(ScriptState*,
+                              ScriptValue data,
+                              const ResponseInit*,
+                              ExceptionState&);
 
   static FetchResponseData* CreateUnfilteredFetchResponseDataWithoutBody(
       ScriptState*,

third_party/blink/renderer/core/fetch/response.idl

@@ -15,6 +15,7 @@ enum ResponseType { "basic", "cors", "default", "error", "opaque", "opaqueredire
     [CallWith=ScriptState, RaisesException] constructor(optional any body, optional ResponseInit init = {});
     [CallWith=ScriptState, NewObject] static Response error();
     [CallWith=ScriptState, NewObject, RaisesException] static Response redirect(USVString url, optional unsigned short status = 302);
+    [CallWith=ScriptState, NewObject, RaisesException, ImplementedAs=staticJson] static Response json(any data, optional ResponseInit init = {});
     readonly attribute ResponseType type;
     readonly attribute USVString url;
     readonly attribute boolean redirected;