Connection reset socket error occurs when the opponent is forcibly terminated without calling close(). This simply means that a TCP RST was received. TCP RST packet is that the remote side telling you the connection on which the previous TCP packet is sent is not recognized, maybe the connection has closed, maybe the port is not open, and something like these. A reset packet is simply one with no payload and with the RST bit set in the TCP header flags. There are several possible causes.
The other end has deliberately reset the connection, in a way which I will not document here. It is rare, and generally incorrect, for application software to do this, but it is not unknown for commercial software.
More commonly, it is caused by writing to a connection that the other end has already closed normally. In other words an application protocol error.
It can also be caused by closing a socket when there is unread data in the socket receive buffer.
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