Configuration

Application Environment

Configure estun in your sys.config or application environment:

[
    {estun, [
        %% Pre-configured STUN servers loaded at startup
        {default_servers, [
            #{host => "stun.l.google.com", port => 19302},
            #{host => "stun1.l.google.com", port => 19302}
        ]},

        %% Default timeout for STUN requests (milliseconds)
        {default_timeout, 5000},

        %% Maximum retransmission attempts (RFC 5389 recommends 7)
        {default_retries, 7}
    ]}
].

Server Configuration

When adding a server, you can specify various options:

estun:add_server(#{
    %% Required: hostname or IP address
    host => "stun.example.com",

    %% Port (default: 3478)
    port => 3478,

    %% Transport protocol (default: udp)
    transport => udp,  %% udp | tcp | tls

    %% Address family (default: inet)
    family => inet,    %% inet | inet6

    %% Authentication (default: none)
    auth => none,      %% none | short_term | long_term

    %% Credentials (for authenticated servers)
    username => <<"user">>,
    password => <<"pass">>,
    realm => <<"example.com">>
}).

Socket Options

When opening a socket for hole punching:

estun:open_socket(#{
    %% Address family
    family => inet,         %% inet | inet6

    %% Local address to bind (default: any)
    local_addr => {0,0,0,0},

    %% Local port (default: 0 = system assigned)
    local_port => 0,

    %% Enable port reuse for hole punching (default: true)
    reuse_port => true
}).

Timeout Configuration

Per-Request Timeout

%% Bind with custom timeout
{ok, Addr} = estun:bind_socket(SocketRef, ServerId, 10000).  %% 10 seconds

Hole Punching Options

estun:punch(SocketRef, PeerIP, PeerPort, #{
    timeout => 5000,    %% Total timeout in ms
    attempts => 10,     %% Number of punch attempts
    interval => 50      %% Interval between attempts in ms
}).

Public STUN Servers

Here are some reliable public STUN servers:

Provider	Host	Port
Google	stun.l.google.com	19302
Google	stun1.l.google.com	19302
Google	stun2.l.google.com	19302
Twilio	global.stun.twilio.com	3478
Cloudflare	stun.cloudflare.com	3478

Production Use

For production applications, consider running your own STUN server or using a paid service for reliability and SLA guarantees.

IPv6 Configuration

To use IPv6:

%% Add IPv6 server
estun:add_server(#{
    host => "stun.example.com",
    port => 3478,
    family => inet6
}).

%% Open IPv6 socket
{ok, SocketRef} = estun:open_socket(#{family => inet6}).

Logging

estun uses the standard Erlang logger for logging. Configure log levels:

logger:set_module_level(estun_client, debug).
logger:set_module_level(estun_codec, warning).