fix(extensions/fetch): Filter out custom HOST headers (#11020)

This commit updates "fetch" API to ignore custom "Host" headers
and return value provided by "reqwest".

cli/tests/unit/fetch_test.ts

@@ -1149,3 +1149,49 @@ unitTest({}, function fetchWritableRespProps(): void {
   assertEquals(original.status, new_.status);
   assertEquals(new_.headers.get("x-deno"), "foo");
 });
+
+function returnHostHeaderServer(addr: string): Deno.Listener {
+  const [hostname, port] = addr.split(":");
+  const listener = Deno.listen({
+    hostname,
+    port: Number(port),
+  }) as Deno.Listener;
+
+  listener.accept().then(async (conn: Deno.Conn) => {
+    const httpConn = Deno.serveHttp(conn);
+
+    await httpConn.nextRequest()
+      .then(async (requestEvent: Deno.RequestEvent | null) => {
+        const hostHeader = requestEvent?.request.headers.get("Host");
+        const headersToReturn = hostHeader ? { "Host": hostHeader } : undefined;
+
+        await requestEvent?.respondWith(
+          new Response("", {
+            status: 200,
+            headers: headersToReturn,
+          }),
+        );
+      });
+
+    httpConn.close();
+  });
+
+  return listener;
+}
+
+unitTest(
+  { perms: { net: true } },
+  async function fetchFilterOutCustomHostHeader(): Promise<
+    void
+  > {
+    const addr = "127.0.0.1:4502";
+    const listener = returnHostHeaderServer(addr);
+    const response = await fetch(`http://${addr}/`, {
+      headers: { "Host": "example.com" },
+    });
+    await response.text();
+    listener.close();
+
+    assertEquals(response.headers.get("Host"), addr);
+  },
+);

extensions/fetch/lib.rs

@@ -29,6 +29,7 @@ use deno_web::BlobUrlStore;
 use reqwest::header::HeaderMap;
 use reqwest::header::HeaderName;
 use reqwest::header::HeaderValue;
+use reqwest::header::HOST;
 use reqwest::header::USER_AGENT;
 use reqwest::redirect::Policy;
 use reqwest::Body;
@@ -197,7 +198,9 @@ where
       for (key, value) in args.headers {
         let name = HeaderName::from_bytes(key.as_bytes()).unwrap();
         let v = HeaderValue::from_str(&value).unwrap();
-        request = request.header(name, v);
+        if name != HOST {
+          request = request.header(name, v);
+        }
       }
 
       let cancel_handle = CancelHandle::new_rc();