Simple TCP/IP echo server
This program demonstrates a simple TCP/IP server. It will accept a connection from a client application, receive one line of text, echo that line back to the client and close the connection.
Programming Issues
This program illustrates the classic process for a TCP/IP server program. Summarised, it is as follows:
- Create a socket with a call to
socket() - Create and initialize a socket address strucure
with the IP address set to
INADDR_ANY(the server will listen on any IP address) and the port to whichever one you wish to use. - Call
bind()to bind the socket address to the socket. - Call
listen()to indicate that this is a passive socket, that we want to accept incoming requests rather than make outgoing ones. - Enter a loop in which we:
- Call
accept()to wait for an incoming connection - Service the request on our new connection
close()our connection, and continue the loop to wait for a new one
- Call
Note that it's present form, the server enters an infinite loop and
has no mechanism for closing itself. We have to use a command such as
kill to terminate it.
Usage
Once launched in the background, the server can be used either with a dedicated echo client, or simply by telnetting to it. For the latter approach, the following is a sample session using Linux:
[paul@localhost paul]$ ./echoserv 3357 & [paul@localhost paul]$ telnet localhost 3357 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. Echo this line for me, please. Echo this line for me, please. Connection closed by foreign host. [paul@localhost paul]$
After executing telnet and receiving some initialisation output, we enter the words "Echo this line for me, please.", and we see the server process echoing them back to us, then closing the connection.
You can specify the port number to listen to as a command line argument. The program will default to ECHO_PORT (#defined as 2002) if one is not supplied.