Client TCP

/* 1. Tao socket */
Sock s = socket(AF_INET, SOCK_STREAM, 0);

/* 2. Dien dia chi CUA SERVER */
struct sockaddr_in sv;
memset(&sv, 0, sizeof sv);
sv.sin_family = AF_INET;
sv.sin_port   = htons(18080);
inet_pton(AF_INET, "127.0.0.1", &sv.sin_addr);

/* 3. Ket noi */
connect(s, (struct sockaddr *)&sv, sizeof sv);

/* Xong. Tu day tro di s dung duoc voi send va recv. */

/* Client echo TCP.
   Windows:  gcc echo_kh.c -o echo_kh.exe -D_WIN32_WINNT=0x0600 -lws2_32
   Linux:    gcc echo_kh.c -o echo_kh                              */

#include <stdio.h>
#include <string.h>

#if defined(_WIN32)
  #include <winsock2.h>
  #include <ws2tcpip.h>
  typedef SOCKET Sock;
  #define DONG(s)   closesocket(s)
  #define LOI()     WSAGetLastError()
  #define SOCK_XAU  INVALID_SOCKET
#else
  #include <unistd.h>
  #include <errno.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <arpa/inet.h>
  typedef int Sock;
  #define DONG(s)   close(s)
  #define LOI()     errno
  #define SOCK_XAU  (-1)
#endif

#define CONG 18080

int main(int argc, char **argv) {
    setvbuf(stdout, NULL, _IONBF, 0);

    const char *tin = (argc > 1) ? argv[1] : "xin chao server";

#if defined(_WIN32)
    WSADATA d;
    if (WSAStartup(MAKEWORD(2, 2), &d) != 0) return 1;
#endif

    Sock s = socket(AF_INET, SOCK_STREAM, 0);
    if (s == SOCK_XAU) {
        fprintf(stderr, "socket: %d\n", LOI());
        return 1;
    }

    struct sockaddr_in sv;
    memset(&sv, 0, sizeof sv);
    sv.sin_family = AF_INET;
    sv.sin_port   = htons(CONG);

    if (inet_pton(AF_INET, "127.0.0.1", &sv.sin_addr) <= 0) {
        fprintf(stderr, "dia chi khong hop le\n");
        DONG(s);
        return 1;
    }

    if (connect(s, (struct sockaddr *)&sv, sizeof sv) < 0) {
        fprintf(stderr, "connect: %d\n", LOI());
        DONG(s);
        return 1;
    }

    send(s, tin, (int)strlen(tin), 0);

    char bo_dem[1024];
    int n = recv(s, bo_dem, (int)sizeof bo_dem - 1, 0);
    if (n > 0) {
        bo_dem[n] = '\0';
        printf("server tra loi: %s\n", bo_dem);
    }

    DONG(s);
#if defined(_WIN32)
    WSACleanup();
#endif
    return 0;
}

static void thu(const char *ip, int cong, const char *ghi_chu) {
    SOCKET s = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in a;
    memset(&a, 0, sizeof a);
    a.sin_family = AF_INET;
    a.sin_port   = htons((unsigned short)cong);
    inet_pton(AF_INET, ip, &a.sin_addr);

    printf("%-28s %s:%d -> ", ghi_chu, ip, cong);
    fflush(stdout);
    if (connect(s, (struct sockaddr *)&a, sizeof a) == 0) {
        printf("thanh cong\n");
    } else {
        int e = WSAGetLastError();
        const char *ten = "?";
        switch (e) {
            case WSAECONNREFUSED: ten = "WSAECONNREFUSED"; break;
            case WSAETIMEDOUT:    ten = "WSAETIMEDOUT";    break;
            case WSAEHOSTUNREACH: ten = "WSAEHOSTUNREACH"; break;
            case WSAENETUNREACH:  ten = "WSAENETUNREACH";  break;
        }
        printf("loi %d (%s)\n", e, ten);
    }
    closesocket(s);
}

/* Tra ve 0 thanh cong, -1 loi, -2 het gio. */
static int ket_noi_cho(SOCKET s, const struct sockaddr *dc, int dc_co, int giay) {
    /* 1. Chuyen socket sang che do KHONG CHAN */
    u_long khong_chan = 1;
    ioctlsocket(s, FIONBIO, &khong_chan);

    /* 2. connect tra ve ngay lap tuc voi WSAEWOULDBLOCK */
    int r = connect(s, dc, dc_co);
    if (r == 0) goto xong;                          /* xong ngay, loopback */
    if (WSAGetLastError() != WSAEWOULDBLOCK) return -1;

    /* 3. Cho socket san sang GHI, hoac co ngoai le, hoac het gio */
    fd_set ghi, ngoai;
    FD_ZERO(&ghi);   FD_SET(s, &ghi);
    FD_ZERO(&ngoai); FD_SET(s, &ngoai);

    struct timeval tv;
    tv.tv_sec  = giay;
    tv.tv_usec = 0;

    r = select(0, NULL, &ghi, &ngoai, &tv);
    if (r == 0) return -2;                          /* HET GIO */
    if (r <  0) return -1;

    /* 4. San sang ghi KHONG co nghia la thanh cong.
          Phai hoi SO_ERROR de biet ket qua that. */
    int err = 0; int err_co = sizeof err;
    getsockopt(s, SOL_SOCKET, SO_ERROR, (char *)&err, &err_co);
    if (err != 0) { WSASetLastError(err); return -1; }

xong: ;
    /* 5. Tra socket ve che do chan cho de dung tiep */
    u_long chan = 0;
    ioctlsocket(s, FIONBIO, &chan);
    return 0;
}

#include <stdio.h>
#include <string.h>

struct addrinfo goi_y, *kq, *p;
memset(&goi_y, 0, sizeof goi_y);
goi_y.ai_family   = AF_UNSPEC;      /* AF_INET, AF_INET6, hay ca hai */
goi_y.ai_socktype = SOCK_STREAM;    /* TCP */

int r = getaddrinfo("example.com", "80", &goi_y, &kq);
if (r != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(r));
    return 1;
}

/* getaddrinfo tra ve mot DANH SACH. Thu tung cai cho toi khi
   mot cai thanh cong. Do la cach chuong trinh that lam viec. */
Sock s = SOCK_XAU;
for (p = kq; p != NULL; p = p->ai_next) {
    s = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
    if (s == SOCK_XAU) continue;
    if (connect(s, p->ai_addr, (int)p->ai_addrlen) == 0) break;   /* xong */
    DONG(s);
    s = SOCK_XAU;
}

freeaddrinfo(kq);                   /* BAT BUOC, neu khong thi ro ri */

if (s == SOCK_XAU) {
    fprintf(stderr, "khong ket noi duoc toi may nao\n");
    return 1;
}