IRC

Sources

• RFC 1459 of 1993 - original
• RFC 2813 of 2000 - update for Server protocol
• Beej's guide to network programming
• Chirc - Similar project from Chicago university

OSI model

Level	Layer	Protocols	Description
7	application	HTTP, SMTP, FTP	closest to end user
6	presentation		configures data into a format suitable for next layer by means of translation, encryption / decryption, compression
5	session		manages connections and sessions between devices
4	transport	UDP, TCP	handles data transmission between devices
3	network	IP, ICMP	determines most efficient path for routing between networks
2	data link	Ethernet	handles node to node data transfer within the same network. Divided into logical link control and MAC sublayers
1	physical		converts data <-> bits across physical network

sockets

• socket can be in passive (listening) or active (sending) mode

ports

• network byte order is big-endian

// create a TCP socket with IPv4
int server_fd = socket(AF_INET, SOCK_STREAM, 0);

// configure address
sockaddr_in addr;
std::memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(6667);
addr.sin_addr.s_addr = INADDR_ANY;

// bind socket with address/port and put it in passive mode
bind(server_fd, (sockaddr*)&addr, sizeof(addr));

signal handling

https://en.cppreference.com/w/c/program/signal

More info

https://man7.org/linux/man-pages/man3/sockaddr.3type.html

Design patterns

Singleton

• Rationale : ensure the same instance of server is returned

Observer

• Rationale : notify observers (connected clients to a channel)

Strategy

• Rationale : handle messages accordingly to their nature

Command

• Rationale : encapsulate a request
• Cons : overhead for small commands

State

• Rationale : tracking connection state : unauthenticated -> registered -> in channel -> disconnected

Inter-process communication with epoll()

Advantages

• complexity of O(1) over the number of watched fds vs O(n) for select() and poll()
• no need to resubmit fd seets at each loop

Usage

• uses a watch list

// create an instance
int epfd = epoll_create1(0);

// add, modify or remove monitored fds
// when we look for read available fds, we subscribe to EPOLLIN
epoll_event ev;
ev.events = EPOLLIN;
ev.data.fd = client_fd;
epoll_ctl(epfd, EPOLL_CTL_ADD, client_fd, &ev);

// wait for events
epoll_event events[64];
int n = epoll_wait(epfd, events, 64, -1);

// handle a connection
int client_fd = accept(server_fd, NULL, NULL);
set_non_blocking(client_fd);
ev.events = EPOLLIN | EPOLLET;
ev.data.fd = client_fd;
epoll_ctl(epfd, EPOLL_CTL_ADD, client_fd, &ev);

• level-triggered mode is the default mode, we get notified as long as data is ready
• edge-triggered is more efficient but requires non-blocking sockets

Testing

Using netcat

nc localhost <port>

Using telnet

telnet localhost 6667

Debugging

lsof -i :6667
netstat -tnp | grep 6667

Checking an existing server output

/raw DEBUG ON
/quote PROTOCTL 
/quote MONITOR + *

Using an irc client

• once IRC protocol responses are implemented

irsssi weechat