c ++ Winsock发送，recv-他们的工作方式

Question

I'm new in network programming and I'm trying to understand how functions like send and recv work under the hood in a TCP connection.I know that in a connection between a client and a server for example ,when the client manage to send a message to the server ,the message is split in different packages and at it's arrival,the server part checks to see if the sum of the packages is the same as it was before sending,and if is ok it sends a message back to the client as an approval.If a problem appears the client resends the message.

What I don't understand is that if you send a message from the client and you sleep the server for 10 seconds,you can still do what you want in the client,like the send function is executing in another thread ,or if you use multiple times send function in these 10 seconds,the message arrives as a combination of the messages used in that time.

If anyone can explain the situation ,I'll be very grateful !

Answer 1

This is implemented by the TCP/IP networking stack of your operating system.

The TCP/IP stack ...

• provides a send buffer. When your program sends, the OS first fills internal buffers. You app can send immediately until the buffers are full. Then your send will block.
• takes data from the internal buffer and sends it out onto the network in single packets.
• receives data over the network and fills internal receive buffers with that data.
• gives your program the data from the internal buffers when you call receive.
• takes care of the TCP/IP protocol stuff like establishing connections, acknowledging received data, resending data if no receive acknowledge was received.

In the case you wrote the client is filling the sender OS's send buffer and the receiver OS's receive buffer. Your client can send non-blocking until both buffers are full. Then it will block until the server calls recv again.