v811_spc009/external/libwebsockets/minimal-examples/raw/minimal-raw-adopt-udp

lws minimal ws server raw adopt udp

This example demonstrates echoing packets on a UDP socket in lws.

A "foreign" UDP socket is created, bound (so it can "listen"), and adopted into lws event loop. It acts like a tcp RAW mode connection in lws and uses the same callbacks.

Writing is a bit different for UDP. By default, the system has no idea about the receiver state and so asking for a callback_on_writable() always believes that the socket is writeable... the callback will happen next time around the event loop if there are no pending partials.

With UDP, there is no "connection". You need to write with sendto() and direct the packets to a specific destination. You can learn the source of the last packet that arrived at the LWS_CALLBACK_RAW_RX callback by getting a struct lws_udp * from lws_get_udp(wsi). To be able to send back to that guy, you should take a copy of the struct lws_udp * and use the .sa and .salen members in your sendto().

However the kernel may not accept to buffer / write everything you wanted to send. So you are responsible to watch the result of sendto() and resend the unsent part next time.

build

 $ cmake . && make

usage

 $ ./lws-minimal-raw-adopt-udp
$ ./lws-minimal-raw-adopt-udp 
[2018/03/24 08:12:37:8869] USER: LWS minimal raw adopt udp | nc -u 127.0.0.1 7681
[2018/03/24 08:12:37:8870] NOTICE: Creating Vhost 'default' (no listener), 1 protocols, IPv6 off
[2018/03/24 08:12:37:8878] USER: LWS_CALLBACK_RAW_ADOPT
[2018/03/24 08:12:41:5656] USER: LWS_CALLBACK_RAW_RX (6)
[2018/03/24 08:12:41:5656] NOTICE: 
[2018/03/24 08:12:41:5656] NOTICE: 0000: 68 65 6C 6C 6F 0A                                  hello.          
[2018/03/24 08:12:41:5656] NOTICE: 

 $ nc -u 127.0.0.1 7681
hello
hello