1# h2 long poll in lws 2 3lws server and client can support "immortal" streams that are 4not subject to normal timeouts under a special condition. These 5are read-only (to the client). 6 7Network connections that contain at least one immortal stream 8are themselves not subject to timeouts until the last immortal 9stream they are carrying closes. 10 11Because of this, it's recommended there is some other way of 12confirming that the client is still active. 13 14## Setting up lws server for h2 long poll 15 16Vhosts that wish to allow clients to serve these immortal 17streams need to set the info.options flag `LWS_SERVER_OPTION_VH_H2_HALF_CLOSED_LONG_POLL` 18at vhost creation time. The JSON config equivalent is to set 19 20``` 21"h2-half-closed-long-poll": "1" 22``` 23 24on the vhost. That's all that is needed. 25 26Streams continue to act normally for timeout with the exception 27client streams are allowed to signal they are half-closing by 28sending a zero-length DATA frame with END_STREAM set. These 29streams are allowed to exist outside of any timeout and data 30can be sent on them at will in the server -> client direction. 31 32## Setting client streams for long poll 33 34An API is provided to allow established h2 client streams to 35transition to immortal mode and send the END_STREAM to the server 36to indicate it. 37 38``` 39int 40lws_h2_client_stream_long_poll_rxonly(struct lws *wsi); 41``` 42 43## Example applications 44 45You can confirm the long poll flow simply using example applications. 46Build and run `http-server/minimal-http-server-h2-long-poll` in one 47terminal. 48 49In another, build the usual `http-client/minimal-http-client` example 50and run it with the flags `-l --long-poll` 51 52The client will connect to the server and transition to the immortal mode. 53The server sends a timestamp every minute to the client, and that will 54stay up without timeouts. 55 56