Extism Erlang SDK

A native Extism host SDK for Erlang/OTP. Plugins run on erlang_wasm. This library implements the Extism kernel, host env, manifests, host functions and WASI on that engine.

Requires OTP 29+.

Use it

The default handle lives in your process. No gen_server, no mailbox hop.

{ok, P} = extism:open("priv/plugins/count_vowels.wasm"),
{ok, Out} = extism:call(P, count_vowels, <<"Hello, World!">>),
ok = extism:close(P).
%% Out = <<"{\"count\":3,\"total\":3,\"vowels\":\"aeiouAEIOU\"}">>

new/1 is the same as open/1. A path, raw bytes, WAT, a bundled name, or a manifest are all fine:

{ok, P} = extism:open(#{
    wasm => [#{path => "plugin.wasm"}],
    config => #{<<"vowels">> => <<"aeiou">>},
    allowed_hosts => [<<"example.com">>]
}).

Host functions

A map of funs. Arity is the number of Extism memory handles; values are binaries. That is the usual PDK shape (String / Vec<u8>).

{ok, P} = extism:open(count_vowels_kvstore, #{
    functions => #{
        kv_read => fun(Key) -> {ok, maps:get(Key, Store, <<0,0,0,0>>)} end,
        kv_write => fun(Key, Val) -> ets:insert(T, {Key, Val}), ok end
    }
}).

When you need the handle (or raw i64 offsets):

#{host_reflect => {raw, [i64], [i64], fun(P, [Off]) ->
    {ok, In} = extism:read(P, Off),
    extism:write(P, In)
end}}

OTP

Own the instance from a worker when you want a name, a supervisor, or to kill a runaway call by stopping the process.

{ok, Pid} = extism:start_link(Source, #{name => {local, vowels}}),
{ok, Out} = extism:call(Pid, count_vowels, <<"hi">>),

%% in your supervisor:
extism:child_spec(Source, Opts, #{id => vowels}).

call/3 accepts either the inline handle or the pid.

Errors

Every failure is one map:

{error, #{class := plugin | link | trap | host | timeout | manifest,
          reason := atom(),
          message := binary()}}

Bundled plugins

priv/plugins/ has real guests from Extism PDK and SDK repos. See priv/plugins/SOURCES.md.

extism:bundled_plugins().

Develop

rebar3 compile
rebar3 ct
rebar3 shell