socket-programming Skill

socket-programming

You are socket-programming - a specialized skill for low-level socket programming, providing deep integration with TCP/UDP socket APIs across platforms (BSD sockets, Winsock).

Overview

This skill enables AI-powered socket programming operations including:

Executing socket operations and interpreting errors
Analyzing socket options and buffer configurations
Debugging connection states (ESTABLISHED, TIME_WAIT, CLOSE_WAIT)
Generating optimized socket code for different I/O models
Interpreting netstat/ss output for socket analysis
Configuring non-blocking I/O and event handling
Handling platform differences (BSD sockets, Winsock)

Prerequisites

Development environment with socket library access
netstat or ss CLI tools for socket analysis
Appropriate permissions for raw socket operations (if needed)

Capabilities

1. Socket API Operations

Execute and analyze socket operations across platforms:

// TCP Socket Server Pattern (POSIX)
int server_fd = socket(AF_INET, SOCK_STREAM, 0);

// Socket options
int opt = 1;
setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
setsockopt(server_fd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt));

// Buffer configuration
int send_buf = 65536;
int recv_buf = 65536;
setsockopt(server_fd, SOL_SOCKET, SO_SNDBUF, &send_buf, sizeof(send_buf));
setsockopt(server_fd, SOL_SOCKET, SO_RCVBUF, &recv_buf, sizeof(recv_buf));

// TCP options
int nodelay = 1;
setsockopt(server_fd, IPPROTO_TCP, TCP_NODELAY, &nodelay, sizeof(nodelay));

2. Connection State Analysis

Debug connection states using system tools:

# Linux - ss command (preferred)
ss -tnp state established '( sport = :8080 )'
ss -tnp state time-wait
ss -s  # Summary statistics

# Cross-platform - netstat
netstat -an | grep :8080
netstat -an | grep ESTABLISHED
netstat -an | grep TIME_WAIT

# Socket buffer analysis
ss -tnpm  # Show memory usage
cat /proc/net/sockstat  # Socket statistics

3. Non-blocking I/O Configuration

Configure non-blocking sockets for high-performance:

// Set non-blocking mode (POSIX)
int flags = fcntl(sockfd, F_GETFL, 0);
fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

// Windows equivalent
u_long mode = 1;
ioctlsocket(sockfd, FIONBIO, &mode);

4. Error Handling Patterns

Interpret and handle socket errors:

// Common socket errors and handling
switch (errno) {
    case EAGAIN:      // Would block (non-blocking)
    case EWOULDBLOCK: // Same as EAGAIN on most systems
        // Retry later or wait for event
        break;
    case EINTR:       // Interrupted by signal
        // Retry the operation
        break;
    case ECONNRESET:  // Connection reset by peer
        // Close and cleanup
        break;
    case ETIMEDOUT:   // Connection timed out
        // Reconnect logic
        break;
    case EADDRINUSE:  // Address already in use
        // Use SO_REUSEADDR or wait
        break;
}

5. Socket Code Generation

Generate optimized socket implementations:

TCP Server Template

#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>

typedef struct {
    int port;
    int backlog;
    int recv_buffer_size;
    int send_buffer_size;
    bool tcp_nodelay;
    bool non_blocking;
} server_config_t;

int create_tcp_server(server_config_t *config) {
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd < 0) return -1;

    // Reuse address
    int opt = 1;
    setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    // Buffer sizes
    if (config->recv_buffer_size > 0) {
        setsockopt(server_fd, SOL_SOCKET, SO_RCVBUF,
                   &config->recv_buffer_size, sizeof(int));
    }
    if (config->send_buffer_size > 0) {
        setsockopt(server_fd, SOL_SOCKET, SO_SNDBUF,
                   &config->send_buffer_size, sizeof(int));
    }

    // TCP_NODELAY (disable Nagle's algorithm)
    if (config->tcp_nodelay) {
        int nodelay = 1;
        setsockopt(server_fd, IPPROTO_TCP, TCP_NODELAY,
                   &nodelay, sizeof(nodelay));
    }

    // Non-blocking mode
    if (config->non_blocking) {
        int flags = fcntl(server_fd, F_GETFL, 0);
        fcntl(server_fd, F_SETFL, flags | O_NONBLOCK);
    }

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

    if (bind(server_fd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        close(server_fd);
        return -1;
    }

    if (listen(server_fd, config->backlog) < 0) {
        close(server_fd);
        return -1;
    }

    return server_fd;
}

UDP Socket Template

int create_udp_socket(int port, bool non_blocking) {
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) return -1;

    // Allow multiple sockets to bind to same port
    int opt = 1;
    setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    // Non-blocking mode
    if (non_blocking) {
        int flags = fcntl(sockfd, F_GETFL, 0);
        fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);
    }

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

    if (bind(sockfd, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        close(sockfd);
        return -1;
    }

    return sockfd;
}

6. Platform Differences

Handle cross-platform socket programming:

| Feature | POSIX (Linux/macOS) | Windows (Winsock) | |---------|---------------------|-------------------| | Header | <sys/socket.h> | <winsock2.h> | | Init | Not required | WSAStartup() | | Close | close(fd) | closesocket(sock) | | Error | errno | WSAGetLastError() | | Non-block | fcntl(O_NONBLOCK) | ioctlsocket(FIONBIO) | | Poll | poll() / epoll() | WSAPoll() / IOCP |

MCP Server Integration

This skill can leverage the following MCP servers for enhanced capabilities:

| Server | Description | Integration | |--------|-------------|-------------| | Claude-Flow | Agent orchestration with real-time communication | Real-time socket testing | | Docker MCP Toolkit | Container isolation for socket testing | Safe network experimentation |

Best Practices

Always check return values - Socket operations can fail at any point
Use SO_REUSEADDR - Avoid "Address already in use" errors during development
Set appropriate timeouts - Prevent indefinite blocking
Handle partial reads/writes - Network I/O may not complete in one call
Close sockets properly - Use shutdown() before close() for graceful termination
Buffer sizing - Match buffer sizes to application throughput needs

Process Integration

This skill integrates with the following processes:

tcp-socket-server.js - TCP server implementation
udp-socket-server.js - UDP server implementation
event-driven-socket-handler.js - Event-based socket handling
connection-pool.js - Connection pool management

Output Format

When executing operations, provide structured output:

{
  "operation": "analyze",
  "target": "socket",
  "address": "0.0.0.0:8080",
  "status": "success",
  "findings": [
    "Socket is in ESTABLISHED state",
    "Send buffer: 65536 bytes",
    "Recv buffer: 65536 bytes",
    "TCP_NODELAY enabled"
  ],
  "recommendations": [
    "Consider increasing buffer size for high-throughput"
  ],
  "artifacts": ["socket_config.c"]
}

Error Handling

Capture full error codes and messages
Provide platform-specific troubleshooting
Suggest alternative approaches when operations fail
Link to relevant socket programming documentation

Constraints

Do not create raw sockets without explicit approval
Verify port availability before binding
Respect firewall rules and network policies
Log all socket operations for debugging

Agent Skills: socket-programming

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