Add native fetch() polyfill

CMakeLists.txt

@@ -80,6 +80,7 @@ option(JSRUNTIMEHOST_CORE_SCRIPTLOADER "Include JsRuntimeHost Core ScriptLoader"
 option(JSRUNTIMEHOST_POLYFILL_CONSOLE "Include JsRuntimeHost Polyfill Console." ON)
 option(JSRUNTIMEHOST_POLYFILL_SCHEDULING "Include JsRuntimeHost Polyfill Scheduling." ON)
 option(JSRUNTIMEHOST_POLYFILL_XMLHTTPREQUEST "Include JsRuntimeHost Polyfill XMLHttpRequest." ON)
+option(JSRUNTIMEHOST_POLYFILL_FETCH "Include JsRuntimeHost Polyfill fetch." ON)
 option(JSRUNTIMEHOST_POLYFILL_URL "Include JsRuntimeHost Polyfill URL and URLSearchParams." ON)
 option(JSRUNTIMEHOST_POLYFILL_ABORT_CONTROLLER "Include JsRuntimeHost Polyfills AbortController and AbortSignal." ON)
 option(JSRUNTIMEHOST_POLYFILL_WEBSOCKET "Include JsRuntimeHost Polyfill WebSocket." ON)
@@ -140,7 +141,7 @@ endif()
 FetchContent_MakeAvailable_With_Message(arcana.cpp)
 set_property(TARGET arcana PROPERTY FOLDER Dependencies)
 
-if(JSRUNTIMEHOST_POLYFILL_XMLHTTPREQUEST)
+if(JSRUNTIMEHOST_POLYFILL_XMLHTTPREQUEST OR JSRUNTIMEHOST_POLYFILL_FETCH)
     FetchContent_MakeAvailable_With_Message(UrlLib)
     set_property(TARGET UrlLib PROPERTY FOLDER Dependencies)
 endif()

Polyfills/CMakeLists.txt

@@ -10,6 +10,10 @@ if(JSRUNTIMEHOST_POLYFILL_XMLHTTPREQUEST)
     add_subdirectory(XMLHttpRequest)
 endif()
 
+if(JSRUNTIMEHOST_POLYFILL_FETCH)
+    add_subdirectory(Fetch)
+endif()
+
 if(JSRUNTIMEHOST_POLYFILL_URL)
     add_subdirectory(URL)
 endif()

Polyfills/Fetch/CMakeLists.txt

@@ -0,0 +1,17 @@
+set(SOURCES
+    "Include/Babylon/Polyfills/Fetch.h"
+    "Source/Fetch.h"
+    "Source/Fetch.cpp")
+
+add_library(Fetch ${SOURCES})
+warnings_as_errors(Fetch)
+
+target_include_directories(Fetch PUBLIC "Include")
+
+target_link_libraries(Fetch
+    PUBLIC JsRuntime
+    PRIVATE arcana
+    PRIVATE UrlLib)
+
+set_property(TARGET Fetch PROPERTY FOLDER Polyfills)
+source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR} FILES ${SOURCES})

Polyfills/Fetch/Include/Babylon/Polyfills/Fetch.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <napi/env.h>
+#include <Babylon/Api.h>
+
+namespace Babylon::Polyfills::Fetch
+{
+    void BABYLON_API Initialize(Napi::Env env);
+}

Polyfills/Fetch/Readme.md

@@ -0,0 +1,30 @@
+# Fetch
+Minimal implementation of the [WHATWG `fetch()`](https://fetch.spec.whatwg.org/) API. Like `XMLHttpRequest`, it is implemented on top of the platform-specific transports in the `UrlLib` dependency, so network behavior (libcurl / WinHTTP / etc.) is identical between the two polyfills.
+
+```js
+const response = await fetch("https://example.com/data.json");
+if (response.ok) {
+    const data = await response.json();
+}
+```
+
+## Response
+`fetch()` returns a `Promise` that resolves to a `Response`-like object exposing:
+* `ok`, `status`, `statusText`, `url`, `redirected`, `type`, `bodyUsed`
+* `headers` with `get(name)`, `has(name)`, and `forEach(callback)` (header names are matched case-insensitively)
+* `text()`, `arrayBuffer()`, `json()`, `blob()` (each returns a `Promise`)
+* `clone()`
+
+The response body is fully buffered before the promise resolves. The body accessors may therefore be called more than once (`bodyUsed` is always reported as `false`), which is a deliberate, lenient deviation from the spec's single-use semantics.
+
+`blob()` requires the `Blob` polyfill to be initialized; otherwise the returned promise rejects.
+
+## Local files
+Like `XMLHttpRequest`, `fetch()` supports loading local resources:
+* `file:///` loads from an absolute path
+* `app:///` loads from a path relative to the current program or package depending on platform
+
+## Other things to be aware of
+* Only `GET` and `POST` methods are supported (a `UrlLib` limitation shared with `XMLHttpRequest`).
+* Only string request bodies are supported.
+* Consistent with the fetch spec, the promise rejects only on transport-level failures. A completed request with a non-`2xx` status (e.g. `404`) still resolves, with `response.ok === false`.