fed-sx-m1: Step 8d-accept — Accept header parsing (accept_format/1 + accept_format_from/1) + 13 tests

next/kernel/http_server.erl

@@ -9,7 +9,8 @@
          activity_path/0, unauthorized_response/0,
          post_activity_response/0,
          validation_failed_response/0,
-         cid_response/1]).
+         cid_response/1,
+         accept_format/1, accept_format_from/1]).
 
 %% HTTP request router per design §16.1.
 %%
@@ -283,3 +284,75 @@ expected_token(Cfg) ->
         nil -> not_found;
         T -> {ok, T}
     end.
+
+%% ── Step 8d: Accept-header parsing ──────────────────────────────
+%%
+%% accept_format/1 — given an Accept header value, return the
+%% content-negotiation atom the route should serialise into. The
+%% first media-type prefix that matches wins, in this priority:
+%%   application/activity+json -> activity_json
+%%   application/json          -> json
+%%   application/sx            -> sx
+%%   application/cbor          -> cbor
+%% Anything else (including unrecognised, empty, or missing header)
+%% returns text — current routes default to text/plain bodies.
+%%
+%% Per-prefix recognition uses `match_prefix`. The header value is
+%% NOT split on `,` here; matching against the leading bytes is
+%% enough for the v1 envelope shapes the kernel currently emits.
+
+%% Media-type prefix byte sequences — hand-spelled because
+%% `<<"...">>` string-segments truncate in this port.
+
+%% "application/activity+json" — 25 bytes
+activity_json_prefix() ->
+    <<97,112,112,108,105,99,97,116,105,111,110,47,
+      97,99,116,105,118,105,116,121,43,106,115,111,110>>.
+
+%% "application/json" — 16 bytes
+json_prefix() ->
+    <<97,112,112,108,105,99,97,116,105,111,110,47,106,115,111,110>>.
+
+%% "application/sx" — 14 bytes
+sx_prefix() ->
+    <<97,112,112,108,105,99,97,116,105,111,110,47,115,120>>.
+
+%% "application/cbor" — 16 bytes
+cbor_prefix() ->
+    <<97,112,112,108,105,99,97,116,105,111,110,47,99,98,111,114>>.
+
+accept_format(nil) -> text;
+accept_format(<<>>) -> text;
+accept_format(V) when is_binary(V) ->
+    case match_prefix(activity_json_prefix(), V) of
+        {ok, _} -> activity_json;
+        _ ->
+            case match_prefix(json_prefix(), V) of
+                {ok, _} -> json;
+                _ ->
+                    case match_prefix(sx_prefix(), V) of
+                        {ok, _} -> sx;
+                        _ ->
+                            case match_prefix(cbor_prefix(), V) of
+                                {ok, _} -> cbor;
+                                _ -> text
+                            end
+                    end
+            end
+    end;
+accept_format(_) -> text.
+
+%% accept_format_from/1 — pull the Accept header out of a request
+%% proplist and run accept_format on its value. Lowercase key name
+%% (matches the BIF wrapper's normalisation).
+accept_format_from(Req) ->
+    case field(headers, Req) of
+        nil -> text;
+        Hs ->
+            %% "accept" — 6 bytes
+            K = <<97,99,99,101,112,116>>,
+            case find_header(K, Hs) of
+                {ok, V} -> accept_format(V);
+                not_found -> text
+            end
+    end.