Socket Programming for Games Skill

Socket Programming for Games

Master low-level socket programming for custom game networking.

Socket Types

| Type | Protocol | Use Case | |------|----------|----------| | SOCK_STREAM | TCP | Reliable data | | SOCK_DGRAM | UDP | Real-time | | SOCK_RAW | Raw IP | Custom protocols |

BSD Socket (C)

#include <sys/socket.h>
#include <netinet/in.h>

int create_game_server(int port) {
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    struct sockaddr_in addr = {
        .sin_family = AF_INET,
        .sin_port = htons(port),
        .sin_addr.s_addr = INADDR_ANY
    };

    bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
    fcntl(sockfd, F_SETFL, O_NONBLOCK);

    return sockfd;
}

Socket Options

// Disable Nagle (reduce latency)
int flag = 1;
setsockopt(sockfd, IPPROTO_TCP, TCP_NODELAY, &flag, sizeof(flag));

// Enable address reuse
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag));

// Set buffer size
int bufsize = 65536;
setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &bufsize, sizeof(bufsize));

Byte Order

// Network byte order
uint16_t port_net = htons(8080);
uint32_t ip_net = htonl(ip_host);

// Host byte order
uint16_t port_host = ntohs(port_net);

Platform Differences

| Feature | BSD | Winsock | |---------|-----|---------| | Init | None | WSAStartup() | | Close | close() | closesocket() | | Error | errno | WSAGetLastError() | | Non-block | fcntl() | ioctlsocket() |

Troubleshooting

Common Failure Modes

| Error | Root Cause | Solution | |-------|------------|----------| | EADDRINUSE | Port in use | SO_REUSEADDR | | ECONNRESET | Peer closed | Handle gracefully | | EMFILE | Too many fds | Increase ulimit | | High latency | Nagle | TCP_NODELAY |

Debug Checklist

# Check listening sockets
netstat -tlnp | grep game-server

# Trace syscalls
strace -e socket,bind,connect ./game-server

# Monitor traffic
tcpdump -i lo port 8080

Unit Test Template

void test_socket_creation() {
    int fd = create_game_server(8080);
    assert(fd >= 0);

    struct sockaddr_in addr;
    socklen_t len = sizeof(addr);
    getsockname(fd, (struct sockaddr*)&addr, &len);
    assert(ntohs(addr.sin_port) == 8080);

    close(fd);
}

Resources

assets/ - Socket templates
references/ - Platform guides

Agent Skills: Socket Programming for Games

Skill Files