lwip - what's the reason tcp socket blocked in send()?

Question

I am make a application base on lwip,the applcation just send data to the server; When my app works for some times (about 5 hours),I found that the send thread hung in send() function,and after about 30min send() return 0,and my thread run agin; In the server side ,have make a keepalive,its time is 5min,when my app hungs,5min later the server close the sockect,but my app have not get this,still hungs in send() until 30min get 0 return; why this happen? 1: the up speed is not enough to send data,it will hungs in send? 2: maybe the server have not read data on time,and it make send buff full and hungs?

how can i avoid these peoblems in my code ? I have try to set TCP_NODELAY,SO_SNDTIMEO and select before send,but also have this problem.

Answer 1

send() blocks when the receiver is too far behind the sender. recv() returns zero when the peer has closed the connection, which means you must close the socket and stop reading.