fix: Allow ArrayBuffer as Fetch request body (#5831)

cli/js/web/fetch.ts

@@ -505,6 +505,8 @@ export async function fetch(
           contentType = "text/plain;charset=UTF-8";
         } else if (isTypedArray(init.body)) {
           body = init.body;
+        } else if (init.body instanceof ArrayBuffer) {
+          body = new Uint8Array(init.body);
         } else if (init.body instanceof URLSearchParams) {
           body = new TextEncoder().encode(init.body.toString());
           contentType = "application/x-www-form-urlencoded;charset=UTF-8";

cli/tests/unit/fetch_test.ts

@@ -258,6 +258,19 @@ unitTest(
   }
 );
 
+unitTest(
+  { perms: { net: true } },
+  async function fetchInitArrayBufferBody(): Promise<void> {
+    const data = "Hello World";
+    const response = await fetch("http://localhost:4545/echo_server", {
+      method: "POST",
+      body: new TextEncoder().encode(data).buffer,
+    });
+    const text = await response.text();
+    assertEquals(text, data);
+  }
+);
+
 unitTest(
   { perms: { net: true } },
   async function fetchInitURLSearchParamsBody(): Promise<void> {