CODEWITHSUNDEEP
socketstcp
Leon .Leon
Leon .Leon

Reputation: 21

Using "send" to tcp socket/Windows/c

For c send function(blocking way) it's specified what function returns with size of sent bytes when it's received on destinations. I'm not sure that I understand all nuances, also after writing "demo" app with WSAIoctl and WSARecv on server side.

  1. When send returns with less bytes number than asked in buffer-length parameter?
  2. What is considered as "received on destinations"? My first guess it's when it sit on server's OS buffer and server application is notified. My second one it's when server application recv call have read it fully?

Upvotes: 0

Views: 753

Answers (1)

C. Gonzalez
C. Gonzalez

Reputation: 724

Unless you are using a (somewhat exotic) library, a send on a socket will return the number of bytes passed to the TCP buffer successfully, not the number of bytes received by the peer (see Microsoft´s docs for example).

When you are streaming data via a socket, you need to check the bytes effectively accepted into the TCP send buffer. That´s why usually a send command is inside a loop that will issue several sends if needed.

Errors in send are local: for example if the socket is closed by the peer during a sending operation (making your socket invalid) or if the operation times out (TCP buffer not emptying, i. e. peer not receiving data fast enough or some other trouble).

After all send is completed you have no easy way of knowing if the peer received all the bytes you sent. You´ll usually just issue closesocket and make sure that your socket has a proper linger option set (i. e. only close after timeout or sucessfully finishing the send). Alternatively you wait for a confirmation by the peer (for example via a recv that returns zero bytes, indicating that the connection was gracefully closed).

Edit: typo

Upvotes: 1

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