Stun

Functions
struct	__attribute__ ((packed))
	STUN server configuration.

Variables
	stun_server_t

STUN Protocol Constants
#define	STUN_DEFAULT_PORT   3478
	Standard STUN port (RFC 5389)
#define	STUN_TLS_DEFAULT_PORT   5349
	STUN over TLS port (RFC 5389)
#define	STUN_MAX_URL_LEN   64
	Maximum STUN URL length.

Detailed Description

This module defines STUN server configuration structures for WebRTC connectivity. STUN servers help clients discover their public IP addresses and port mappings when behind NAT.

RFC 5389: Session Traversal Utilities for NAT (STUN) RFC 8489: Session Traversal Utilities for NAT (STUN) - updated

STUN SERVER ROLE:

• Helps clients discover their public-facing IP address and port
• Essential for WebRTC peer-to-peer connection establishment
• No relay (unlike TURN) - only provides connectivity information

USAGE IN ACDS:

• Discovery server provides STUN server list in SESSION_CREATED response
• Clients use STUN servers for ICE candidate gathering
• Multiple STUN servers can be provided for redundancy

Note

All structures are packed with attribute((packed)) for wire format

Author

Zachary Fogg me@zf.nosp@m.o.gg

Date

January 2026

Version

1.0

Macro Definition Documentation

STUN_DEFAULT_PORT

#define STUN_DEFAULT_PORT   3478

#include <stun.h>

Standard STUN port (RFC 5389)

Definition at line 84 of file stun.h.

STUN_MAX_URL_LEN

#define STUN_MAX_URL_LEN   64

#include <stun.h>

Maximum STUN URL length.

Definition at line 90 of file stun.h.

STUN_TLS_DEFAULT_PORT

#define STUN_TLS_DEFAULT_PORT   5349

#include <stun.h>

STUN over TLS port (RFC 5389)

Definition at line 87 of file stun.h.

Function Documentation

__attribute__()

struct __attribute__

(

(packed)

)

#include <stun.h>

STUN server configuration.

Used in ACDS SESSION_CREATED response to provide WebRTC connectivity information.

Protocol Format:

• host_len: 1 byte (length of host string)
• host: 64 bytes (null-terminated STUN URL)

URL Format Examples:

• stun:discovery.ascii.chat:3478 (standard port)
• stun:stun.l.google.com:19302 (Google public STUN)
• stun:stun.example.com:5349 (custom port)

Wire Format (65 bytes total):

+----------+----------------------------------------+
| host_len |              host[64]                  |
+----------+----------------------------------------+
| 1 byte   |              64 bytes                  |
+----------+----------------------------------------+

< Length of host string (actual URL length)

< STUN server URL (e.g., "stun:discovery.ascii.chat:3478")

Definition at line 1 of file stun.h.

                                       {
  uint8_t host_len; 
  char host[64];    
} stun_server_t;

Variable Documentation

stun_server_t

stun_server_t

#include <stun.h>

Definition at line 75 of file stun.h.

Referenced by server_main().