refactor: change how headers are represented (#22)

* refactor: change how headers are represented

* chore: formatting

examples/fetch_native_lwt_get.re

@@ -2,9 +2,10 @@ Fetch.(
   fetch("https://httpbin.org/get")
   |> Lwt.map(
        fun
-       | Ok({Response.body, status, url, _}) => {
+       | Ok({Response.body, status, url, headers}) => {
            Printf.printf(
-             "Status-Code: %d\nBody: %s\nUrl: %s",
+             "Headers: \n%sStatus-Code: %d\nBody: %s\nUrl: %s",
+             Response.Headers.toString(headers),
              Response.Status.toCode(status),
              Response.Body.toString(body),
              url,

src/fetch-core/src/Headers.re

@@ -1,4 +1,18 @@
-type name = string;
-type value = string;
+type t = (string, string);
 
-type t = (name, value);
+let toString = headers => {
+  let buffer = Buffer.create(128);
+
+  List.iter(
+    ((name, value)) => {
+      Buffer.add_string(buffer, name);
+      Buffer.add_string(buffer, ": ");
+      Buffer.add_string(buffer, value);
+      Buffer.add_string(buffer, "\r\n");
+    },
+    headers,
+  );
+
+  Buffer.add_string(buffer, "\r\n");
+  Buffer.contents(buffer);
+};

src/fetch-core/src/Headers.rei

@@ -1,4 +1,3 @@
-type name = string;
-type value = string;
+type t = (string, string);
 
-type t = (name, value);
+let toString: list(t) => string;

src/fetch-core/src/S.re

@@ -8,6 +8,7 @@ module type Body = {
 module type Response = {
   module Status: (module type of Status);
   module Body: Body;
+  module Headers: (module type of Headers);
 
   type t = {
     body: Body.t,