I have a udp server in python that i'm testing out by sending packets with netcat -u server_ip server_port

on the udp server, I can receive the packets with data,addrport = socket.recvfrom(some_number) — I can read the data received and see the other socket's address port with addrport.

But if I try to use socket.getpeername() on the same variable instead it gives the OSError: [Errno 107] Transport endpoint is not connected error.

What causes this? I'm confused as my netcat terminal doesn't close after sending, which I assume means its already connected to my UDP socket.

CodePudding user response：

I can receive the packets with data,addrport = socket.recvfrom(some_number)

recvfrom means that you are working with an unconnected UDP socket, i.e. the case where a single socket could receive packets from various sources and also send data to various sources using sendto. getpeername instead expects a connected socket, i.e. one which will only receive data from a single source (using recv not recvfrom) and only send to a single source (using send not sendto). This is the case with TCP established sockets (the ones returned by accept) but also with UDP socket which are explicitly connected by calling connect.