Add support for FormData

Author: ghivert

src/gleam/fetch.gleam

@@ -1,6 +1,7 @@
+import gleam/dynamic.{type Dynamic}
+import gleam/form_data.{type FormData}
 import gleam/http/request.{type Request}
 import gleam/http/response.{type Response}
-import gleam/dynamic.{type Dynamic}
 import gleam/javascript/promise.{type Promise}
 
 pub type FetchError {
@@ -29,6 +30,17 @@ pub fn send(
   })
 }
 
+pub fn send_form_data(
+  request: Request(FormData),
+) -> Promise(Result(Response(FetchBody), FetchError)) {
+  request
+  |> form_data_to_fetch_request
+  |> raw_send
+  |> promise.try_await(fn(resp) {
+    promise.resolve(Ok(from_fetch_response(resp)))
+  })
+}
+
 pub fn send_bits(
   request: Request(BitArray),
 ) -> Promise(Result(Response(FetchBody), FetchError)) {
@@ -43,6 +55,9 @@ pub fn send_bits(
 @external(javascript, "../gleam_fetch_ffi.mjs", "to_fetch_request")
 pub fn to_fetch_request(a: Request(String)) -> FetchRequest
 
+@external(javascript, "../gleam_fetch_ffi.mjs", "form_data_to_fetch_request")
+pub fn form_data_to_fetch_request(a: Request(FormData)) -> FetchRequest
+
 @external(javascript, "../gleam_fetch_ffi.mjs", "bitarray_request_to_fetch_request")
 pub fn bitarray_request_to_fetch_request(a: Request(BitArray)) -> FetchRequest
 

src/gleam/form_data.gleam

@@ -0,0 +1,20 @@
+pub type FormData
+
+@external(javascript, "../gleam_fetch_ffi.mjs", "newFormData")
+pub fn new() -> FormData
+
+@external(javascript, "../gleam_fetch_ffi.mjs", "appendFormData")
+pub fn append(form_data: FormData, key: String, value: String) -> FormData
+
+@external(javascript, "../gleam_fetch_ffi.mjs", "appendBitsFormData")
+pub fn append_bits(
+  form_data: FormData,
+  key: String,
+  value: BitArray,
+) -> FormData
+
+@external(javascript, "../gleam_fetch_ffi.mjs", "setFormData")
+pub fn set(form_data: FormData, key: String, value: String) -> FormData
+
+@external(javascript, "../gleam_fetch_ffi.mjs", "setBitsFormData")
+pub fn set_bits(form_data: FormData, key: String, value: BitArray) -> FormData

src/gleam_fetch_ffi.mjs

@@ -41,6 +41,14 @@ export function to_fetch_request(request) {
   return new globalThis.Request(url, options);
 }
 
+export function form_data_to_fetch_request(request) {
+  let [url, options] = request_common(request)
+  if (options.method !== "GET" && options.method !== "HEAD") options.body = request.body;
+  // Remove `content-type`, because the browser will add the correct header by itself.
+  delete options.headers['content-type']
+  return new globalThis.Request(url, options);
+}
+
 export function bitarray_request_to_fetch_request(request) {
   let [url, options] = request_common(request)
   if (options.method !== "GET" && options.method !== "HEAD") options.body = request.body.buffer;
@@ -81,3 +89,37 @@ export async function read_json_body(response) {
     return new Error(new InvalidJsonBody());
   }
 }
+
+export function newFormData() {
+  return new FormData()
+}
+
+function cloneFormData(formData) {
+  const f = new FormData()
+  for (const [key, value] of formData.entries()) f.append(key, value)
+  return f
+}
+
+export function appendFormData(formData, key, value) {
+  const f = cloneFormData(formData)
+  f.append(key, value)
+  return f
+}
+
+export function setFormData(formData, key, value) {
+  const f = cloneFormData(formData)
+  f.set(key, value)
+  return f
+}
+
+export function appendBitsFormData(formData, key, value) {
+  const f = cloneFormData(formData)
+  f.append(key, new Blob([value.buffer]))
+  return f
+}
+
+export function setBitsFormData(formData, key, value) {
+  const f = cloneFormData(formData)
+  f.set(key, new Blob([value.buffer]))
+  return f
+}