Reject with error when invalid fetch() body

src/bun.js/webcore/response.zig

@@ -495,6 +495,7 @@ pub const Fetch = struct {
 
     pub const fetch_error_no_args = "fetch() expects a string but received no arguments.";
     pub const fetch_error_blank_url = "fetch() URL must not be a blank string.";
+    pub const fetch_error_unexpected_body = "fetch() request with GET/HEAD/OPTIONS method cannot have body.";
     const JSTypeErrorEnum = std.enums.EnumArray(JSType, string);
     pub const fetch_type_error_names: JSTypeErrorEnum = brk: {
         var errors = JSTypeErrorEnum.initUndefined();
@@ -1102,6 +1103,11 @@ pub const Fetch = struct {
 
         var deferred_promise = JSC.C.JSObjectMakeDeferredPromise(globalThis, null, null, null);
 
+        if (!method.hasRequestBody() and body.size() > 0) {
+            const fetch_error = fetch_error_unexpected_body;
+            return JSPromise.rejectedPromiseValue(globalThis, ZigString.init(fetch_error).toErrorInstance(globalThis)).asRef();
+        }
+
         // var resolve = FetchTasklet.FetchResolver.Class.make(ctx: js.JSContextRef, ptr: *ZigType)
         _ = FetchTasklet.queue(
             default_allocator,

test/bun.js/fetch.test.js

@@ -172,6 +172,31 @@ describe("fetch", () => {
     expect(response.redirected).toBe(true);
     server.stop();
   });
+
+  it("provide body", async () => {
+    const server = Bun.serve({
+      port: 4084,
+      fetch(req) {
+        return new Response(req.body);
+      },
+    });
+
+    // POST with body
+    const url = `http://${server.hostname}:${server.port}`;
+    const response = await fetch(url, { method: "POST", body: "buntastic" });
+    expect(response.status).toBe(200);
+    expect(await response.text()).toBe("buntastic");
+
+    // GET cannot have body
+    try {
+      await fetch(url, { body: "buntastic" });
+      expect(false).toBe(true);
+    } catch (exception) {
+      expect(exception instanceof TypeError);
+    }
+
+    server.stop();
+  });
 });
 
 it("simultaneous HTTPS fetch", async () => {