[Libwebsockets] regarding publish -subscribe using libwebsockets

Suman.Patro-TRN Suman.Patro-TRN at lntebg.com
Sun Apr 24 08:02:55 CEST 2016


Hello,

            I am trying to achieve publish -subscribe mechanism using libwebsockets.  I have a backend server (tcp) which has pub-sub logic.I have integrated my websocket server based on libwebsockets into the  backend server on different port to that of the tcp one. My goal is whenever a web client subscribes to a specific topic , it should fetch data that the tcp client (publisher) pushes based on the same  topic. This works fine for a single  web client. But I am stuck for a multiple clients scenario. The issue is as follows: Since publishing of data is not from the web client but from tcp client , so LWS SERVER WRITABLE could not be used to publish data. Hence I have written my own method in the websocket server to publish data using LWS_WRITE  for each  connection based on unique wsi pointer. But the problem that arises is whenever a new client comes in, I get a new wsi pointer and soon after LWS_CONNECTION _ESTABLISHED , the new client starts getting data without even subscribing for a topic and the older one stops getting data. My question is: how can I allow publishing of data only after LWS_RECEIVE(after subscription), Can there be any validation that can be done between LWS_CONNECTION_ESTABLISHED  and LWS_RECEIVE? Other design solutions are also welcome.

Please reply. Awaiting response.

Thanks and regards,

Suman

Larsen & Toubro Limited

www.larsentoubro.com

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