Category Archives: Network programming

Multi client chat server in Twisted Python

In a multi client chat server, N clients are connected to a server and send messages. In this program, one of the clients send messages to the server and it will send back the messages to all other clients. I implemented it in Twisted Python also.

Twisted is an event-driven networking engine written in Python and licensed under the open source. Twisted makes it easy to implement custom network applications, both servers and clients.It gives developers a complete set of tools for communicating across networks and the Internet. Twisted includes both high- and low-level tools.

This program also uses TCP.


The twisted event loop is started by starting the reactor. Starting the reactor is easy. Import the reactor object from the twisted.internet module. Then call ) to start the reactor’s event loop. Call the reactor.connectTCP( ) method to start a TCP connection, passing a StdioProxyFactory object as the third parameter. The StdioProxyFactory object waits for the connection to be established, and then creates a Protocol object that manages the flow of data back and forth along that connection. Use a subclass of Protocol to send and receive data. Override the dataReceived method to control what happens when data is received from the connection. Use self.transport.write to send data.

Keyboard input is given by importing stdio from twisted.internet.

This program includes a class called DataForwardingProtocol, which takes any data received and writes it to self.output. This usage makes it possible to create a simple application, similar to the classic utility netcat, that passes any data received on standard input to a server, while printing any data received from the server to standard output.


Twisted server accepts connections from clients and interacts with them by creating a Protocol object defining our server’s behavior. Create a MultiClientEchoFactory object using the Protocol, and pass it to reactor.listenTCP. The list self.clients defined in the factory stores clients connections. Whenever a data is received from one of the clients, the server send back this data to all clients in the clients list.

The complete code of this program is available in


Multi client chat server in C

I implemented a multi client chat server in C using socket programming. In a multi client chat server, N clients are connected to a server and send messages. In this program, one of the clients send messages to the server and it will send back the messages to all other clients. I implemented it using TCP.
A simple Client-Server Interaction


In the server program, first is the establishment of connection to a port. we get the socket file descriptor ,

int socket(int domain, int type, int protocol);

‘setsockopt’ is used for losing the pesky “Address already in use” error message. Once we have a socket, we might have to associate that socket with a port on our local machine. This can be done by using the ‘bind’.

int bind(int sockfd, struct sockaddr *my_addr, int addrlen);

We want to wait for incoming connections, we use ‘listen’ in this situation.

int listen(int sockfd, int backlog);

sockfd is the usual socket file descriptor from the socket() system call. backlog is the number of connections allowed on the incoming queue .

In the case of a server, it wants to listen for incoming connections as well as keep reading from the connections it already have. select() gives the power to monitor several sockets at the same time. It’ll tell you which ones are ready for reading, which are ready for writing, and which sockets have raised exceptions.

int select(int numfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

If we want to see if we can read from standard input and some socket descriptor, sockfd, just add the file descriptors 0 and sockfd to the set readfds. The parameter numfds should be set to the values of the highest file descriptor plus one. When select() returns, readfds will be modified to reflect which of the file descriptors we

selected which is ready for reading. After ‘select’, it run through the existing connections looking for data to read. If we got one, new connections are handled and the new file descriptor is added to the master set by keeping track of the maximum file descriptor. If there is no need to handle new connection, handle data from a client. If there is any data in the recv_buf, it can be received by using recv().Or , the data is send to all other clients by using the function send().


In the client program, first is the establishment of connection to the server and running on the localhost. Connection is established by using connect(). Then select() is used for either reading or writing as in the server program. It sends message to the server from the keyboard input using stdin. If there is data in the recv_buf, it receives data using recv().

The code of this program is available in

The Blog

The latest news on and the WordPress community.