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56 lines
2.3 KiB
Erlang
56 lines
2.3 KiB
Erlang
-module(outbox).
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-export([construct/4, sign/2, cid_of/1]).
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%% Outbox envelope construction + signing per design §3.1.
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%%
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%% construct/4 builds an unsigned activity envelope from caller-supplied
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%% (Type, ActorId, Published, Object). The envelope's `:id` field is
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%% derived from the host `cid:to_string` BIF over a skeleton tag, so
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%% recipients can address the activity by its content hash. The
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%% returned property list is the canonical key-sorted form that
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%% `envelope:canonical_bytes/1` operates on.
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%%
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%% sign/2 takes the unsigned envelope plus a KeySpec proplist that
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%% mirrors a `public_keys` entry: `[{key_id, _}, {algorithm, _},
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%% {value, KeyMaterial}]`. It computes the v1 HMAC stand-in
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%% `crypto:hash(sha256, <<KeyMaterial/binary, CanonicalBytes/binary>>)`
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%% — the same scheme `envelope:verify_signature/2` checks — and
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%% appends a `:signature` pair.
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%%
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%% Real Ed25519 / RSA signing arrives in milestone 2 once
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%% `crypto:sign_ed25519/2` BIFs land; the API shape doesn't change.
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%% construct/4 — Type and ActorId are atoms; Published is an
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%% integer timestamp the caller supplies (no clock BIF in this
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%% port; the HTTP layer / outbox:publish caller injects it).
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%% Object can be any term, including a property list of inner
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%% fields.
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construct(Type, ActorId, Published, Object) ->
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Skeleton = [{actor, ActorId},
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{object, Object},
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{published, Published},
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{type, Type}],
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Id = cid:to_string({activity_envelope, Skeleton}),
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[{actor, ActorId},
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{id, Id},
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{object, Object},
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{published, Published},
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{type, Type}].
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%% sign/2 — KeySpec carries key_id, algorithm, value (key material).
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sign(Envelope, KeySpec) ->
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{ok, KeyId} = envelope:get_field(key_id, KeySpec),
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{ok, Alg} = envelope:get_field(algorithm, KeySpec),
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{ok, KM} = envelope:get_field(value, KeySpec),
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CB = envelope:canonical_bytes(Envelope),
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SigValue = crypto:hash(sha256, <<KM/binary, CB/binary>>),
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Sig = [{algorithm, Alg}, {key_id, KeyId}, {value, SigValue}],
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Envelope ++ [{signature, Sig}].
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%% cid_of/1 — extract the :id field from a constructed envelope.
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%% Convenience for callers that don't want to thread the CID
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%% separately when both the envelope and its ID matter.
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cid_of(Envelope) ->
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{ok, Id} = envelope:get_field(id, Envelope),
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Id.
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