1.7 KiB
Using UDP in lws
UDP is supported in lws... the quickest way is to use the api
lws_create_adopt_udp() which returns a wsi bound to the provided
vhost, protocol, lws_retry struct, dns address and port.
The wsi can be treated normally and lws_write() used to write on
it.
Implementing UDP retries
Retries are important in udp but there's no standardized ack method
unlike tcp. Lws allows you to bind an lws_retry struct describing
the policy to the udp wsi, but since one UDP socket may have many
transactions in flight, the lws_sul and uint16_t to count the
retries must live in the user's transaction object like this
...
lws_sorted_usec_list_t sul;
uint16_t retry;
...
in the LWS_CALLBACK_RAW_WRITEABLE callback, before doing the write,
set up the retry like this
if (lws_dll2_is_detached(&transaction->sul_write.list) &&
lws_retry_sul_schedule_retry_wsi(wsi, &transaction->sul_write,
transaction_retry_write_cb,
&transaction->retry_count_write)) {
/* we have reached the end of our concealed retries */
lwsl_warn("%s: concealed retries done, failing\n", __func__);
goto retry_conn;
}
This manages the retry counter in the transaction object, guards against it wrapping,
selects the timeout using the policy bound to the wsi, and sets the lws_sul in the
transaction object to call the given callback if the sul time expires.
In the callback, it should simply call lws_callback_on_writable() for the udp wsi.
Simulating packetloss
lws now allows you to set the amount of simulated packetloss on udp rx and tx in
the context creation info struct, using .udp_loss_sim_tx_pc and .udp_loss_sim_rx_pc,
the values are percentages between 0 and 100. 0, the default, means no packetloss.