Provided by: libcoap3_4.3.1-2_amd64 
NAME
coap_recovery, coap_session_set_ack_random_factor, coap_session_get_ack_random_factor,
coap_session_set_ack_timeout, coap_session_get_ack_timeout,
coap_session_set_default_leisure, coap_session_get_default_leisure,
coap_session_set_max_retransmit, coap_session_get_max_retransmit, coap_session_set_nstart,
coap_session_get_nstart, coap_session_set_probing_wait, coap_session_get_probing_wait,
coap_debug_set_packet_loss - Work with CoAP packet transmissions
SYNOPSIS
#include <coap3/coap.h>
void coap_session_set_ack_random_factor(coap_session_t *session, coap_fixed_point_t
value);
coap_fixed_point_t coap_session_get_ack_random_factor( const coap_session_t *session);
void coap_session_set_ack_timeout(coap_session_t *session, coap_fixed_point_t value);
coap_fixed_point_t coap_session_get_ack_timeout( const coap_session_t *session);
void coap_session_set_default_leisure(coap_session_t *session, coap_fixed_point_t value);
coap_fixed_point_t coap_session_get_default_leisure( const coap_session_t *session);
void coap_session_set_max_retransmit(coap_session_t *session, uint16_t value);
uint16_t coap_session_get_max_retransmit(const coap_session_t *session);
void coap_session_set_nstart(coap_session_t *session, uint16_t value);
uint16_t coap_session_get_nstart(const coap_session_t *session);
void coap_session_set_probing_rate(coap_session_t *session, uint32_t value);
uint32_t coap_session_get_probing_rate(const coap_session_t *session);
int coap_debug_set_packet_loss(const char *loss_level);
For specific (D)TLS library support, link with -lcoap-3-notls, -lcoap-3-gnutls,
-lcoap-3-openssl, -lcoap-3-mbedtls or -lcoap-3-tinydtls. Otherwise, link with -lcoap-3 to
get the default (D)TLS library support.
DESCRIPTION
For CoAP Confirmable messages, it is possible to define the retry counts, repeat rate etc.
for error recovery. Further information can be found in "RFC7272: 4.2. Messages
Transmitted Reliably", with the default values defined in "RFC7272: 4.8 Transmission
Parameters".
It is not recommended that the suggested default setting are changed, but there may be
some special requirements that need different values and the consequences of changing
these values is fully understood.
Some of the parameters or return values are in fixed point format as defined by the
coap_fixed_point_t structure as below
typedef struct coap_fixed_point_t {
uint16_t integer_part; /* Integer part of fixed point variable */
uint16_t fractional_part; /* Fractional part of fixed point variable
1/1000 (3 points) precision */
} coap_fixed_point_t;
The CoAP message retry rules are (with the default values to compute the time)
1st retransmit after 1 * ack_timeout * ack_random factor (3 seconds)
2nd retransmit after 2 * ack_timeout * ack_random factor (6 seconds)
3rd retransmit after 3 * ack_timeout * ack_random factor (12 seconds)
4th retransmit after 4 * ack_timeout * ack_random factor (24 seconds)
5th retransmit after 5 * ack_timeout * ack_random factor (48 seconds)
As max_retransmit (by default) is 4, then the 5th retransmit does not get sent,
but at that point COAP_NACK_TOO_MANY_RETRIES gets raised in the nack_handler
(if defined). Note that the sum of the seconds is 93 matching RFC7252.
It should be noted that these retries are separate from the DTLS or TLS encrypted session
setup retry timeouts. For DTLS, the initial requesting packet will get sent max_retransmit
times before reporting failure. For TLS the initial TCP connection will timeout before
reporting failure.
It is also possible to set up packet losses, for both confirmable, and non-confirmable
messages. This can be used for stress testing packet transmission recovery as well as
application handling of lossy networks.
The following functions reflect the RFC7252 uppercase names in lowercase following the
coap_session[sg]_ function prefix.
The coap_session_set_ack_random_factor() function updates the session ack random wait
factor, used to randomize re-transmissions, with the new value. The default value is 1.5.
The coap_session_get_ack_random_factor() function returns the current session ack random
wait factor.
The coap_session_set_ack_timeout() function updates the session initial ack or response
timeout with the new value. The default value is 2.0.
The coap_session_get_ack_timeout() function returns the current session initial ack or
response timeout.
The coap_session_set_default_leisure() function updates the session default leisure time
with the new value. The initial default value is 5.0.
The coap_session_get_default_leisure() function returns the current session default
leisure time.
The coap_session_set_max_retransmit() function updates the session maximum retransmit
count with the new value. The default value is 4.
The coap_session_get_max_retransmit() function returns the current session maximum
retransmit count.
The coap_session_set_nstart() function updates the session nstart with the new value. The
default value is 1.
The coap_session_get_nstart() function returns the current session nstart value.
The coap_session_set_probing_rate() function updates the session probing rate with the new
value. The default value is 1 byte per second.
The coap_session_get_probing_rate() function returns the current session probing rate
value.
The coap_debug_set_packet_loss() function is uses to set the packet loss levels as defined
in loss_level. loss_level can be set as a percentage from "0%" to "100%". Alternatively,
it is possible to specify which packets of a packet sequence are dropped. A definition of
"1,5-9,11-20,101" means that packets 1, 5 through 9, 11 through 20 and 101 will get
dropped. A maximum of 10 different packet sets is supported. The packet count is reset to
0 when coap_debug_set_packet_loss() is called. To remove any packet losses, set the
loss_level to "0%".
RETURN VALUES
coap_session_get_ack_random_factor(), coap_session_get_ack_timeout(),
coap_session_get_default_leisure(), coap_session_get_max_retransmit(),
coap_session_get_nstart() and coap_session_get_probing_rate() return their respective
current values.
coap_debug_set_packet_loss() returns 0 if loss_level does not parse correctly, otherwise 1
if successful.
TESTING
The libcoap recovery/re-transmit logic will only work for confirmable requests.
To see what is happening (other than by sniffing the network traffic), the logging level
needs to be set to LOG_DEBUG in the client by using coap_set_log_level(LOG_DEBUG) and
coap_dtls_set_log_level(LOG_DEBUG).
The client needs to be sending confirmable requests during the test.
The server can either be stopped, or if packet loss levels are set to 100% by using
coap_debug_set_packet_loss("100%") when receiving the client requests.
NOTE: If the server end of the connection is returning ICMP unreachable packets after
being turned off, you will get a debug message of the form "coap_network_read:
unreachable", so libcoap will stop doing the retries. If this is the case, then you need
to make use of (on the server) coap_debug_set_packet_loss("100%") or put in some packet
filtering to drop the packets.
The client should then restart transmitting the requests based on the ack_timeout,
ack_random_factor and max_retransmit values. The client’s nack_handler will get called
with COAP_NACK_TOO_MANY_RETRIES when the confirmable request cannot be successfully
transmitted.
FURTHER INFORMATION
See "RFC7252: The Constrained Application Protocol (CoAP)" for further information.
BUGS
Please report bugs on the mailing list for libcoap:
libcoap-developers@lists.sourceforge.net or raise an issue on GitHub at
https://github.com/obgm/libcoap/issues
AUTHORS
The libcoap project <libcoap-developers@lists.sourceforge.net>