Add read_bytes_body for downloading images, etc

src/ffi.mjs

@@ -1,4 +1,4 @@
-import { Ok, Error, List } from "./gleam.mjs";
+import { Ok, Error, List, toBitArray } from "./gleam.mjs";
 import { to_string as uri_to_string } from "../gleam_stdlib/gleam/uri.mjs";
 import { method_to_string } from "../gleam_http/gleam/http.mjs";
 import { to_uri } from "../gleam_http/gleam/http/request.mjs";
@@ -42,6 +42,16 @@ function make_headers(headersList) {
   return headers;
 }
 
+export async function read_bytes_body(response) {
+  let body;
+  try {
+    body = await response.body.arrayBuffer()
+  } catch (error) {
+    return new Error(new UnableToReadBody());
+  }
+  return new Ok(response.withFields({ body: toBitArray(new Uint8Array(body)) }));
+}
+
 export async function read_text_body(response) {
   let body;
   try {

src/gleam/fetch.gleam

@@ -35,6 +35,11 @@ pub fn to_fetch_request(a: Request(String)) -> FetchRequest
 @external(javascript, "../ffi.mjs", "from_fetch_response")
 pub fn from_fetch_response(a: FetchResponse) -> Response(FetchBody)
 
+@external(javascript, "../ffi.mjs", "read_bytes_body")
+pub fn read_bytes_body(
+  a: Response(FetchBody),
+) -> Promise(Result(Response(BitArray), FetchError))
+
 @external(javascript, "../ffi.mjs", "read_text_body")
 pub fn read_text_body(
   a: Response(FetchBody),

test/gleam_fetch_test.gleam

@@ -17,6 +17,26 @@ pub fn request_test() {
     |> request.set_path("/hello/world")
     |> request.prepend_header("accept", "application/vnd.hmrc.1.0+json")
 
+  fetch.send(req)
+  |> promise.try_await(fetch.read_bytes_body)
+  |> promise.await(fn(resp: Result(Response(BitArray), FetchError)) {
+    let assert Ok(resp) = resp
+    let assert 200 = resp.status
+    let assert Ok("application/json") =
+      response.get_header(resp, "content-type")
+    let assert <<123, 34, 109, 101, 115, 115, 97, 103, 101, 34, 58, 34, 72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 34, 125>> = resp.body
+    promise.resolve(Ok(Nil))
+  })
+}
+
+pub fn text_request_test() {
+  let req =
+    request.new()
+    |> request.set_method(Get)
+    |> request.set_host("test-api.service.hmrc.gov.uk")
+    |> request.set_path("/hello/world")
+    |> request.prepend_header("accept", "application/vnd.hmrc.1.0+json")
+
   fetch.send(req)
   |> promise.try_await(fetch.read_text_body)
   |> promise.await(fn(resp: Result(Response(String), FetchError)) {