linux网络编程系列-网络连接的建立

一个比较实用的连接函数，支持host为域名。

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

#include <iostream>
using namespace std;
int my_connect(const char *host, int port)
{
    char buf[1024];
    struct hostent he, *p; 
    struct sockaddr_in sin;
    socklen_t len = 0;
    int sock = -1, ret = 0, err = 0, flags = 0, on = 1;
    struct timeval t;

    assert(host != NULL);

    // invalid server
    if (host[0] == 0 || port <= 0 || port > 65535) {
        cout << "find invalid host " << host << " or port " << port << endl;
        return -1; 
    }
    //socket
    if ((sock = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
        cout << "cannot create socket while connecting to "
            << host << ":" << port << endl;
        return -1;
    }

    //connect
    bzero(&sin, sizeof(sin));
    sin.sin_addr.s_addr = inet_addr(host);
    if ((sin.sin_addr.s_addr) == INADDR_NONE) { /* host is not numbers-and-dots ip address */
        ret = gethostbyname_r(host, &he, buf, sizeof(buf), &p, &err);
        if (ret < 0 || err != 0 || p == NULL) {
                    cout << "cannot resolve hostname while connecting to "
                        << host << ":" << port << endl;
            close(sock);
            return -1;
        }
        memcpy(&sin.sin_addr.s_addr, he.h_addr, sizeof(sin.sin_addr.s_addr));
    }
    sin.sin_family = AF_INET;
    sin.sin_port = htons(port);

    flags = fcntl(sock, F_GETFL, 0);
    fcntl(sock, F_SETFL, flags | O_NONBLOCK);
    setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, &on, sizeof(on));
    ret = connect(sock, (struct sockaddr *) &sin, sizeof(sin));
    if (ret == 0) {
        fcntl(sock, F_SETFL, flags);
        cout << "connect to " << host << ":" << port << "OK" << endl;
        return sock;
    }
    close(sock);
    return -1;
}