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New next/kernel/discovery.erl with the local-side webfinger
primitives per design §13.7:
parse_acct/1(Bin) -> {ok, User, Host} | {error, _}
Accepts <<acct:user@host>> (with prefix) or <<user@host>>
(bare). Host preserves an optional :port suffix. Rejects
empty user/host and missing @.
parse_resource/1 alias for the webfinger ?resource= shape
actor_url_for/2(User, Host)
Synthesises <<http://<host>/actors/<user>>>. TLS / https
is v3, gated on a TLS substrate Blocker.
webfinger_body/3(User, Host, ActorUrl)
Builds the RFC 7033 JSON body:
{"subject":"acct:<user>@<host>",
"links":[{"rel":"self",
"type":"application/activity+json",
"href":"<actor_url>"}]}
Hand-rolled byte concatenation — no JSON BIF on this port.
Substrate gotcha re-confirmed: <<"acct:">> string literals
truncate to one byte on this port. "acct:" is spelled as
<<97,99,99,116,58>> in the implementation.
12/12 in next/tests/discovery.sh covering:
- parse_acct prefixed + bare forms
- host with :port preserved
- reject empty user / missing @ / empty host
- parse_resource alias
- actor_url_for synthesis + port preservation
- webfinger_body prefix shape + byte_size sanity
Step 10b (http_server route GET /.well-known/webfinger) and
Step 10c (peer-actor fetch via Step 5's lookup_or_fetch slot)
layer on top. 10c gates on Blockers #2 (native http-request
primitive missing).
99 lines
4.1 KiB
Erlang
99 lines
4.1 KiB
Erlang
-module(discovery).
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-export([parse_acct/1, parse_resource/1,
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actor_url_for/2, webfinger_body/3]).
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%% Discovery primitives per design §13.7. Step 10a covers the
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%% local-side webfinger endpoint (responding when a peer asks
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%% "where does acct:alice@here live?"); the peer-fetch direction
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%% (loading a peer's actor doc lazily on first inbound) is Step 10b
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%% and gates on Blockers #2 (native http-request primitive).
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%%
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%% parse_acct/1 — accept a binary in either form:
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%% <<"acct:alice@host:port">> (full prefixed URI)
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%% <<"alice@host:port">> (bare account, prefix optional)
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%% Returns {ok, User, Host} | {error, Reason}.
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%%
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%% parse_resource/1 — the resource= query parameter from
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%% /.well-known/webfinger. Same shape as parse_acct.
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%%
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%% actor_url_for/2(User, Host) — synthesises the canonical
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%% per-actor URL `<scheme>://<host>/actors/<user>`. v2 hardcodes
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%% http://; TLS / https is v3 (Blockers gate).
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%%
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%% webfinger_body/3 — builds the JSON response body.
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%% ── parse_acct / parse_resource ─────────────────────────────────
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%% "acct:" -> 5 bytes: 97 99 99 116 58
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parse_acct(Bin) when is_binary(Bin) ->
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AcctPrefix = <<97,99,99,116,58>>,
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case strip_prefix(AcctPrefix, Bin) of
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{ok, Rest} -> split_user_host(Rest);
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nomatch -> split_user_host(Bin)
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end;
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parse_acct(_) -> {error, bad_input}.
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parse_resource(Bin) -> parse_acct(Bin).
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%% strip_prefix/2 — return {ok, Rest} when Bin starts with Prefix,
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%% else nomatch. Substrate has no proper prefix-match BIF; this
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%% byte-walks.
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strip_prefix(<<>>, Rest) -> {ok, Rest};
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strip_prefix(<<B, PRest/binary>>, <<B, RRest/binary>>) ->
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strip_prefix(PRest, RRest);
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strip_prefix(_, _) -> nomatch.
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%% split_user_host/1 — split a `user@host[:port]` binary at the
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%% first `@`. Returns {ok, User, Host} where Host may include the
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%% optional port suffix.
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split_user_host(Bin) ->
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case split_at(64, Bin) of % 64 = '@'
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{Before, After} when byte_size(Before) > 0, byte_size(After) > 0 ->
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{ok, Before, After};
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_ ->
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{error, bad_acct}
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end.
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split_at(Byte, Bin) ->
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split_at(Byte, Bin, <<>>).
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split_at(_, <<>>, Acc) ->
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{Acc, <<>>};
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split_at(Byte, <<Byte, Rest/binary>>, Acc) ->
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{Acc, Rest};
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split_at(Byte, <<B, Rest/binary>>, Acc) ->
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split_at(Byte, Rest, <<Acc/binary, B>>).
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%% ── URL synthesis ──────────────────────────────────────────────
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%% "http://" -> 7 bytes | "/actors/" -> 8 bytes
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actor_url_for(User, Host) ->
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Pre = <<104,116,116,112,58,47,47>>, % "http://"
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Mid = <<47,97,99,116,111,114,115,47>>, % "/actors/"
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<<Pre/binary, Host/binary, Mid/binary, User/binary>>.
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%% ── webfinger JSON body ────────────────────────────────────────
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%%
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%% Mastodon-shape per RFC 7033:
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%% {"subject":"acct:<user>@<host>",
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%% "links":[{"rel":"self",
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%% "type":"application/activity+json",
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%% "href":"<actor_url>"}]}
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%%
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%% Hand-rolled byte concatenation — no JSON BIF on this port. The
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%% caller has already validated User + Host; we don't need to
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%% re-escape (Mastodon's webfinger inputs are alphanumeric +
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%% .-_ in practice).
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webfinger_body(User, Host, ActorUrl) ->
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AcctPre = <<123,34,115,117,98,106,101,99,116,34,58,34,97,99,99,116,58>>, % '{"subject":"acct:'
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AcctAt = <<64>>, % '@'
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LinksHd = <<34,44,34,108,105,110,107,115,34,58,91,123,34,114,101,108,34,58,34,115,101,108,102,34,44,
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34,116,121,112,101,34,58,34,97,112,112,108,105,99,97,116,105,111,110,47,97,99,116,
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105,118,105,116,121,43,106,115,111,110,34,44,34,104,114,101,102,34,58,34>>, % '","links":[{"rel":"self","type":"application/activity+json","href":"'
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LinksTl = <<34,125,93,125,10>>, % '"}]}\n'
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<<AcctPre/binary, User/binary, AcctAt/binary, Host/binary,
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LinksHd/binary, ActorUrl/binary, LinksTl/binary>>.
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