Simple socket example in OSX

socket.cpp

// Compile with: 
// c++ -std=c++11 socket.cpp -o socket

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

#include <vector>
#include <iostream>


template <typename Condition>
void check_syscall(Condition cond, const std::string& errmsg) {
    if (!cond) {
        throw std::runtime_error(errmsg + ": " + strerror(errno));
    }
}


void server() {
    int server_fd = socket(PF_INET, SOCK_STREAM, 0);
    check_syscall(server_fd != -1, "cannot create socket");

    struct sockaddr_in server_addr = {
        sizeof(struct sockaddr_in), AF_INET, htons(8080), {INADDR_ANY}};
    check_syscall(
        bind(server_fd, (struct sockaddr*) &server_addr,sizeof(server_addr))
            != -1,
        "cannot assign an address");

    check_syscall(listen(server_fd, 16) != -1, "cannot listen on socket");

    struct sockaddr_in client_addr;
    socklen_t client_addr_len = sizeof(client_addr);
    int client_fd = accept(
        server_fd, (struct sockaddr*) &client_addr, &client_addr_len);
    check_syscall(client_fd != -1, "cannot accept new connections");

    std::vector<char> buffer(1024, 0);
    char* pos = buffer.data();
    while (auto bytes = read(client_fd, pos, 1024)) {
        check_syscall(bytes != -1, "cannot read from client");
        if (bytes == 1024) {
            buffer.resize(buffer.size() + 1024);
            pos += 1024;
        } else {
            buffer.resize(pos + bytes - buffer.data());
        }
    }

    std::string message(buffer.begin(), buffer.end());
    std::cerr << "Received message: " << message.c_str() << std::endl;

    close(client_fd);
    close(server_fd);
}


void client() {
    int fd = socket(AF_INET, SOCK_STREAM, 0);
    check_syscall(fd != -1, "cannot create socket");

    struct sockaddr_in server_addr = {
        sizeof(struct sockaddr_in), AF_INET, htons(8080), {INADDR_ANY}};
    check_syscall(
        connect(fd, (struct sockaddr*) &server_addr, sizeof(server_addr))
        != -1,
        "cannot connect to server");

    std::string message = "Hello from the client!";
    int bytes = write(fd, message.data(), message.size());
    check_syscall(bytes, "cannot write data to socket");

    close(fd);
}


void usage(const char* program) {
    std::cerr << "Usage: " << program << " <server|client>" << std::endl;
}


int main(int argc, char const *argv[])
{
    if (argc != 2) {
        usage(argv[0]);
        return 1;
    }

    std::string mode{argv[1]};
    if (mode == "server") {
        server();
    } else if (mode == "client") {
        client();
    } else {
        usage(argv[0]);
        return 1;
    }

    return 0;
}