Why does TCP socket.recvfrom() not return the sender address as it does with UDP?
When does TCP socket.recv() an empty string?
Thanks!
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Maxim Egorushkin
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Which programming language or library are you talking about? – gpgekko Feb 25 '14 at 15:15
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Why does TCP
socket.recvfrom()not return the sender address as it does with UDP?
Because once a TCP connection is established that address does not change. That is the address that was passed to connect or received from accept calls. You can also find out the peer's address (if you lost it somehow) with getpeername.
When does TCP socket.recv() an empty string?
When the peer has closed the connection and no more data will be coming in. You can still send data though because TCP connections can be half-closed.
Maxim Egorushkin
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@user3109117 I know that you are using Python. Learn how to use this web-site though. – Maxim Egorushkin Feb 25 '14 at 16:11
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You *may* be still able to send data, *if* the peer has half-closed the connection. – user207421 Feb 25 '14 at 22:48
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@EJP If there was an `RST` segment `recv()` returns an error. That means if `recv()` returns an empty string that was a `FIN` and the connection is half-open. – Maxim Egorushkin Feb 25 '14 at 23:21
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@EJP You are right that the peer could have `close`d the connection though. There is no way to tell that from `FIN` alone. – Maxim Egorushkin Feb 25 '14 at 23:26