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.
In Windows, ‘software caused connection abort’, which is not the same as ‘connection reset’, is caused by network problems sending from your end. There’s a Microsoft knowledge base article about this.
More about….Socket Programming
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