cross os socket example

client.c

#include "socket.h"

// win32
// -lws2_32

int main() {
    void* sock = socket_bind("127.0.0.1", 6063, 1);
    socket_free(sock);

    return 0;
}

server.c

#include "socket.h"

// win32
// -lws2_32

int main () {
    void* sock = socket_bind("127.0.0.1", 6063, 0);
    void* c_sock = socket_accept(sock);

    socket_free(c_sock);
    socket_free(sock);

    return 0;
}

socket.h

#include <stdio.h>

void* socket_bind (char* ip_addr, int port, int is_client);
void* socket_accept (void* sock_);
void socket_free(void* sock_);

struct sockaddr_in;
int socket_set (char* ip_addr, int port, struct sockaddr_in *sam);

#ifdef _WIN32
#include <winsock2.h>
#include <ws2tcpip.h>

int sock_num = 0;
int sock_init = 0;
WSADATA wsa;

int socket_init (SOCKET *sock) {
    if (!sock_init) {
        if (WSAStartup(MAKEWORD(2,2), &wsa) != 0) {
            fprintf(stderr, "ERROR cannot load dll winsock: %d\n", WSAGetLastError()); 
            return 0;
        }
    }

    *sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (*sock == INVALID_SOCKET) {
        fprintf(stderr, "ERROR cannot create socket: %d\n", WSAGetLastError()); 
        return 0;
    }

    sock_num ++;
    return 1;
}


void socket_free(void* sock_) {
    SOCKET sock = (SOCKET) sock_;
    closesocket(sock);
    sock_num --;

    if (sock_num < 1) {
        WSACleanup();
        sock_init = 0;
    }
}

void* socket_bind (char* ip_addr, int port, int is_client) {
    SOCKET sock = INVALID_SOCKET;
    socket_init(&sock);

    struct sockaddr_in sam;
    socket_set(ip_addr, port, &sam);

    int r;
    if (!is_client) {
        r = bind(sock, (struct sockaddr *) &sam, sizeof(sam));
        if (r == SOCKET_ERROR) {
            fprintf(stderr, "ERROR cannot bind: %d\n", WSAGetLastError()); 
            return NULL;
        }

        listen(sock, SOMAXCONN);
    }
    else {
        r = connect(sock, (struct sockaddr *) &sam, sizeof(sam));
        if (r == SOCKET_ERROR) {
            fprintf(stderr, "ERROR cannot connect: %d\n", WSAGetLastError()); 
            return NULL;
        }
    }

    return (void*) sock;
}

// blocking, accepts client sockets
void* socket_accept (void* sock_) {
    SOCKET sock = (SOCKET) sock_;

    struct sockaddr_in csam;
    SOCKET c_sock = INVALID_SOCKET;
    int c_sock_len = sizeof(struct sockaddr_in);
    c_sock = accept(sock , (struct sockaddr *)&csam, &c_sock_len);
    if (c_sock == INVALID_SOCKET) {
        printf("accept failed with error code : %d" , WSAGetLastError());
        return NULL;
    }
        
    sock_num++;
    return (void*) c_sock;
}

#else
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>

void* socket_bind (char* ip_addr, int port, int is_client) {
    int sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock < 0) {
        fprintf(stderr, "ERROR cannot create socket\n"); 
        return NULL;
    }

    struct sockaddr_in sam;
    socket_set(ip_addr, port, &sam);

    int r;
    if (!is_client) {
        r = bind(sock, (struct sockaddr *) &sam, sizeof(sam));
        if (r < 0) {
            fprintf(stderr, "ERROR cannot bind\n"); 
            return NULL;
        }

        listen(sock, SOMAXCONN);
    }
    else {
        r = connect(sock, (struct sockaddr *) &sam, sizeof(sam));
        if (r < 0) {
            fprintf(stderr, "ERROR cannot connect\n"); 
            return NULL;
        }
    }

    void* sock_ = malloc(sizeof(int));
    *((int*)sock_) = sock;
    return sock_;
}

void* socket_accept (void* sock_) {
    int* sock = (int*) sock_;
    int c_sock;
    unsigned int c_sock_len;
    struct sockaddr_in csam;

    c_sock_len = sizeof(csam);
    c_sock = accept(*sock, (struct sockaddr *) &csam, &c_sock_len);
    if (c_sock < 0) {
        printf("Accept failed\n");
        return NULL;
    }

    void* c_sock_ = malloc(sizeof(int));
    *((int*)c_sock_) = c_sock;
    return c_sock_;
}

void socket_free(void* sock_) {
    if (sock_ == NULL) return;
    
    int* sock = (int*)sock_;
    close(*sock);
    free(sock);
    sock = NULL;
}

#endif

int socket_set (char* ip_addr, int port, struct sockaddr_in *sam) {
    memset(sam, 0, sizeof(*sam));
    sam->sin_family = AF_INET;
    sam->sin_addr.s_addr = ip_addr ? inet_addr(ip_addr) : INADDR_ANY;
    sam->sin_port = htons((u_short) port);

    return 1;
}