shackle

High-Performance Erlang Network Client Framework

Requirements

• Erlang/OTP 25+

Features

• Backpressure via backlog (OOM protection)
• Fast pool implementation (random, round_robin)
• Managed timeouts
• Multi-protocol support (SSL / TCP / UDP)
• Performance-optimized
• Request pipelining
• Smart reconnect mechanism (exponential backoff)

Framework goals

• Reusability
• Speed
• Concurrency
• Safety

How-to

Implementing a client

-behavior(shackle_client).
-export([
    init/0,
    setup/2,
    handle_request/2,
    handle_data/2,
    terminate/1
]).

-record(state, {
    buffer =       <<>> :: binary(),
    request_counter = 0 :: non_neg_integer()
}).

-spec init(Options :: term()) ->
    {ok, State :: term()} |
    {error, Reason :: term()}.

init(_Options) ->
    {ok, #state {}}.

-spec setup(Socket :: inet:socket(), State :: term()) ->
    {ok, State :: term()} |
    {error, Reason :: term(), State :: term()}.

setup(Socket, State) ->
    case gen_tcp:send(Socket, <<"INIT">>) of
        ok ->
            case gen_tcp:recv(Socket, 0) of
                {ok, <<"OK">>} ->
                    {ok, State};
                {error, Reason} ->
                    {error, Reason, State}
            end;
        {error, Reason} ->
            {error, Reason, State}
    end.

-spec handle_request(Request :: term(), State :: term()) ->
    {ok, RequestId :: external_request_id(), Data :: iodata(), State :: term()}.

handle_request(noop,  State) ->
    Data = arithmetic_protocol:request(0, noop, 0, 0),

    {ok, undefined, Data, State};
handle_request({Operation, A, B}, #state {
        request_counter = RequestCounter
    } = State) ->

    RequestId = request_id(RequestCounter),
    Data = request(RequestId, Operation, A, B),

    {ok, RequestId, Data, State#state {
        request_counter = RequestCounter + 1
    }}.

-spec handle_data(Data :: binary(), State :: term()) ->
    {ok, [{RequestId :: external_request_id(), Reply :: term()}], State :: term()}.

handle_data(Data, #state {
        buffer = Buffer
    } = State) ->

    Data2 = <<Buffer/binary, Data/binary>>,
    {Replies, Buffer2} = parse_replies(Data2, []),

    {ok, Replies, State#state {
        buffer = Buffer2
    }}.

-spec terminate(State :: term()) -> ok.

terminate(_State) -> ok.

Starting client pool

shackle_pool:start(shackle_pool:name(), client(), client_options(), pool_options())

client_options:

pool_options:

Calling / Casting client

1> shackle:call(pool_name, {get, <<"test">>}).
{ok, <<"bar">>}

2> {ok, ReqId} = shackle:cast(pool_name, {get, <<"foo">>}, 500).
{ok, {anchor, anchor_client, #Ref<0.0.0.2407>}}

3> shackle:receive_response(ReqId).
{ok, <<"bar">>}

Telemetry

Shackle integrates with the backend-agnostic telemetry library. All events carry #{client => Client} as metadata, where Client is the client module name.

Tests

make dialyzer
make eunit
make xref

Performance testing

To run performance testing targets you must first start the server:

./bin/server.sh

Then you can run the bench or profile target:

make bench
make profile

Clients

License

The MIT License (MIT)

Copyright (c) 2015-2026 Louis-Philippe Gauthier

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.