1.8 KiB
h2 long poll in lws
lws server and client can support "immortal" streams that are not subject to normal timeouts under a special condition. These are read-only (to the client).
Network connections that contain at least one immortal stream are themselves not subject to timeouts until the last immortal stream they are carrying closes.
Because of this, it's recommended there is some other way of confirming that the client is still active.
Setting up lws server for h2 long poll
Vhosts that wish to allow clients to serve these immortal
streams need to set the info.options flag LWS_SERVER_OPTION_VH_H2_HALF_CLOSED_LONG_POLL
at vhost creation time. The JSON config equivalent is to set
"h2-half-closed-long-poll": "1"
on the vhost. That's all that is needed.
Streams continue to act normally for timeout with the exception client streams are allowed to signal they are half-closing by sending a zero-length DATA frame with END_STREAM set. These streams are allowed to exist outside of any timeout and data can be sent on them at will in the server -> client direction.
Setting client streams for long poll
An API is provided to allow established h2 client streams to transition to immortal mode and send the END_STREAM to the server to indicate it.
int
lws_h2_client_stream_long_poll_rxonly(struct lws *wsi);
Example applications
You can confirm the long poll flow simply using example applications.
Build and run http-server/minimal-http-server-h2-long-poll in one
terminal.
In another, build the usual http-client/minimal-http-client example
and run it with the flags -l --long-poll
The client will connect to the server and transition to the immortal mode. The server sends a timestamp every minute to the client, and that will stay up without timeouts.