Timer

Timer — STUN timer Usage

Stability Level

Stable, unless otherwise indicated

Functions

Types and Values

Includes

#include <stun/usages/timer.h>

Description

The STUN timer usage is a set of helpful utility functions that allows you to easily track when a STUN message should be retransmitted or considered as timed out.

Example 3. Simple example on how to use the timer usage

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StunTimer timer;
unsigned remainder;
StunUsageTimerReturn ret;

// Build the message, etc..
...

// Send the message and start the timer
send(socket, request, sizeof(request));
stun_timer_start(&timer, STUN_TIMER_DEFAULT_TIMEOUT,
                 STUN_TIMER_DEFAULT_MAX_RETRANSMISSIONS);

// Loop until we get the response
for (;;) {
  remainder = stun_timer_remainder(&timer);

  // Poll the socket until data is received or the timer expires
  if (poll (&pollfd, 1, delay) <= 0) {
    // Time out and no response was received
    ret = stun_timer_refresh (&timer);
    if (ret == STUN_USAGE_TIMER_RETURN_TIMEOUT) {
      // Transaction timed out
      break;
    } else if (ret == STUN_USAGE_TIMER_RETURN_RETRANSMIT) {
      // A retransmission is necessary
      send(socket, request, sizeof(request));
      continue;
    } else if (ret == STUN_USAGE_TIMER_RETURN_SUCCESS) {
      // The refresh succeeded and nothing has to be done, continue polling
      continue;
    }
  } else {
    // We received a response, read it
    recv(socket, response, sizeof(response));
    break;
  }
}

// Check if the transaction timed out or not
if (ret == STUN_USAGE_TIMER_RETURN_TIMEOUT) {
  // do whatever needs to be done in that case
} else {
  // Parse the response
}

Functions

stun_timer_start ()

void
stun_timer_start (StunTimer *timer,
                  unsigned int initial_timeout,
                  unsigned int max_retransmissions);

Starts a STUN transaction retransmission timer. This should be called as soon as you send the message for the first time on a UDP socket. The timeout before the next retransmission is set to initial_timeout , then each time a packet is retransmited, that timeout will be doubled, until the max_retransmissions retransmissions limit is reached.

To determine the total timeout value, one can use the following equation :

 total_timeout =  initial_timeout * (2^(max_retransmissions + 1) - 1);
 

See also: STUN_TIMER_DEFAULT_TIMEOUT

See also: STUN_TIMER_DEFAULT_MAX_RETRANSMISSIONS

Parameters

timer

The StunTimer to start

 

initial_timeout

The initial timeout to use before the first retransmission

 

max_retransmissions

The maximum number of transmissions before the StunTimer times out

 

stun_timer_start_reliable ()

void
stun_timer_start_reliable (StunTimer *timer,
                           unsigned int initial_timeout);

Starts a STUN transaction retransmission timer for a reliable transport. This should be called as soon as you send the message for the first time on a TCP socket

Parameters

timer

The StunTimer to start

 

initial_timeout

The initial timeout to use before the first retransmission

 

stun_timer_refresh ()

StunUsageTimerReturn
stun_timer_refresh (StunTimer *timer);

Updates a STUN transaction retransmission timer.

Parameters

timer

The StunTimer to refresh

 

Returns

A StunUsageTimerReturn telling you what to do next


stun_timer_remainder ()

unsigned
stun_timer_remainder (const StunTimer *timer);

Query the timer on the time left before the next refresh should be done

Parameters

timer

The StunTimer to query

 

Returns

The time remaining for the timer to expire in milliseconds

Types and Values

StunTimer

typedef struct stun_timer_s StunTimer;

An opaque structure representing a STUN transaction retransmission timer


enum StunUsageTimerReturn

Return value of stun_usage_timer_refresh() which provides you with status information on the timer.

Members

STUN_USAGE_TIMER_RETURN_SUCCESS

The timer was refreshed successfully and there is nothing to be done

 

STUN_USAGE_TIMER_RETURN_RETRANSMIT

The timer expired and the message should be retransmitted now.

 

STUN_USAGE_TIMER_RETURN_TIMEOUT

The timer expired as well as all the retransmissions, the transaction timed out

 

STUN_TIMER_DEFAULT_MAX_RETRANSMISSIONS

#define STUN_TIMER_DEFAULT_MAX_RETRANSMISSIONS 3

The default maximum retransmissions allowed before a timer decides to timeout


STUN_TIMER_DEFAULT_RELIABLE_TIMEOUT

#define STUN_TIMER_DEFAULT_RELIABLE_TIMEOUT 7900

The default intial timeout to use for a reliable timer


STUN_TIMER_DEFAULT_TIMEOUT

#define STUN_TIMER_DEFAULT_TIMEOUT 600

The default intial timeout to use for the timer