服务器可以从其他进程和套接字发送响应吗？

Question

After server, which is listening on port X, receives a request from the client, can it send response from a different process and a socket with sendto call. Please note that the client also sends request with sendto (server address) call.

Here are the steps:

1. server opens a socket and binds it to IP address (abcd) and port (x)
2. client opens a socket and binds it to IP address (klmn) and port (z) and sends request to server with sendto call.
3. Server (in different process) opens a socket and binds it to IP address (abcd) and port (y)
4. server sends response from above socket to client with sendto

Both client and server knows each other ip addresses and port numbers.

I am noticing that client does not receive response when server sends response from a different process. Otherwise, it does.

Answer 1

This can be done but there are some major caveats.

1. The client must bind the socket and use sendto() and recvfrom() rather than connect() 'ing the socket and using send() and recv() . This allows it to receive incoming packets from anywhere as long as they are directed to the IP/Port that recvfrom() is reading on.

2. If there is a firewall or NAT in the path between client and server, it is likely to block the response since the sending IP/Port does not match the IP/Port that the client originally sent its request to.