fed-sx-m1: Step 2a — envelope:validate_shape/1 + get_field/2 + 15 shape tests

next/kernel/envelope.erl

@@ -0,0 +1,53 @@
+-module(envelope).
+-export([validate_shape/1, get_field/2]).
+
+%% Activity envelope per design §3.1.
+%%
+%% Erlang maps (#{...}) are not supported by this port, so envelopes
+%% are represented as property lists of {atom_key, value} pairs. This
+%% port's binary syntax also can't carry string literals; values that
+%% would naturally be binaries in real Erlang are kept as atoms or
+%% integer-segment binaries in the test corpus.
+%%
+%% Required fields: id, type, actor, published, signature.
+%% The signature value is itself a property list with key_id,
+%% algorithm, value.
+%%
+%% validate_shape/1 returns ok | {error, Reason}. Reasons:
+%%   not_a_proplist
+%%   {missing_field, FieldName}
+%%   {bad_signature, BadSigReason}
+%%
+%% get_field/2 returns {ok, Value} | not_found.
+
+validate_shape(Env) when is_list(Env) ->
+    case check_required([id, type, actor, published, signature], Env) of
+        ok -> validate_signature_shape(Env);
+        Err -> Err
+    end;
+validate_shape(_) ->
+    {error, not_a_proplist}.
+
+get_field(_, []) -> not_found;
+get_field(K, [{K, V} | _]) -> {ok, V};
+get_field(K, [_ | Rest]) -> get_field(K, Rest).
+
+check_required([], _) -> ok;
+check_required([F | Rest], Env) ->
+    case get_field(F, Env) of
+        {ok, _} -> check_required(Rest, Env);
+        not_found -> {error, {missing_field, F}}
+    end.
+
+validate_signature_shape(Env) ->
+    {ok, Sig} = get_field(signature, Env),
+    case is_list(Sig) of
+        true ->
+            case check_required([key_id, algorithm, value], Sig) of
+                ok -> ok;
+                {error, {missing_field, F}} ->
+                    {error, {bad_signature, {missing_field, F}}}
+            end;
+        false ->
+            {error, {bad_signature, not_a_proplist}}
+    end.