Support none-blocking DNS resolve.

[JalySN]

srs_tcp_connect is a modification I made, what do you think, esteemed author?

#include "res.c"
srs_error_t srs_tcp_connect(string server, int port, srs_utime_t tm, srs_netfd_t* pstfd)
{
    st_utime_t timeout = ST_UTIME_NO_TIMEOUT;
    if (tm != SRS_UTIME_NO_TIMEOUT) {
        timeout = tm;
    }
    
    *pstfd = NULL;
    srs_netfd_t stfd = NULL;
/*
    char sport[8];
    snprintf(sport, sizeof(sport), "%d", port);
    
    addrinfo hints;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family   = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    
    addrinfo* r  = NULL;
    SrsAutoFree(addrinfo, r);
    if(getaddrinfo(server.c_str(), sport, (const addrinfo*)&hints, &r)) {
        return srs_error_new(ERROR_SYSTEM_IP_INVALID, "get address info");
    }
    int sock = socket(r->ai_family, r->ai_socktype, r->ai_protocol);
    if(sock == -1){
        return srs_error_new(ERROR_SOCKET_CREATE, "create socket");
    }
*/
    struct in_addr addr;
    if (dns_getaddr(server.c_str(), &addr, timeout) < 0) {
        return srs_error_new(ERROR_SYSTEM_IP_INVALID, "get address info");
    }
    uint32_t uiIP;
    memcpy(&uiIP, &addr, 4);
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    if(sock == -1) {
        return srs_error_new(ERROR_SOCKET_CREATE, "create socket");
    }
    stfd = st_netfd_open_socket(sock);
    if(stfd == NULL){
        ::close(sock);
        return srs_error_new(ERROR_ST_OPEN_SOCKET, "open socket");
    }
    struct sockaddr_in address;
    memset(&address, 0, sizeof(address));
    address.sin_family      = AF_INET;
    address.sin_addr.s_addr = uiIP;
    address.sin_port        = htons(port);
    if (st_connect((st_netfd_t)stfd, (struct sockaddr*)&address, sizeof(address), timeout) == -1){
        srs_close_stfd(stfd);
        return srs_error_new(ERROR_ST_CONNECT, "connect to %s:%d", server.c_str(), port);
    }
    
    *pstfd = stfd;
    return srs_success;
}

[winlinvip]

Yes, you're right, would you like to submit a patch?

[winlinvip]

It would be best if it could equivalently replace the system's getaddrinfo function, as it would be more convenient to use and is used in many places.

[winlinvip]

It's time to improve the DNS resolution process using ST, allowing it to resolve names and cache the results. This is crucial because WebRTC relies on DNS resolution to parse candidate IP addresses from the API host, which could potentially be blocked.

The key point in WebRTC is that if the API server and media server are the same, we can obtain the external IP of the server by resolving the domain name of the API, thus avoiding the use of candidates.