Socket API và thứ tự byte

struct sockaddr_in {
    short          sin_family;   /* luon la AF_INET */
    unsigned short sin_port;     /* CONG, thu tu byte MANG */
    struct in_addr sin_addr;     /* DIA CHI IP, thu tu byte MANG */
    char           sin_zero[8];  /* dem cho bang sizeof sockaddr */
};

struct in_addr {
    uint32_t s_addr;             /* IPv4 dong goi thanh 32 bit */
};

/* Dien day du: */
struct sockaddr_in a;
memset(&a, 0, sizeof a);                    /* BAT BUOC, xem ben duoi */
a.sin_family      = AF_INET;
a.sin_port        = htons(18080);           /* htons, khong duoc quen */
a.sin_addr.s_addr = htonl(INADDR_ANY);      /* 0.0.0.0 */

#include <stdio.h>
#include <stdint.h>
#include <winsock2.h>

static void in_byte(const char *ten, const void *p, size_t n) {
    const unsigned char *b = (const unsigned char *)p;
    printf("%-22s", ten);
    for (size_t i = 0; i < n; ++i) printf("%02X ", b[i]);
    printf("\n");
}

int main(void) {
    WSADATA d; WSAStartup(MAKEWORD(2,2), &d);

    uint16_t cong      = 18080;          /* 0x46A0 */
    uint16_t cong_mang = htons(cong);
    uint32_t ip        = 0x7F000001u;    /* 127.0.0.1 */
    uint32_t ip_mang   = htonl(ip);

    printf("cong = %u  (0x%04X)\n", cong, cong);
    in_byte("trong bo nho:", &cong, sizeof cong);
    in_byte("sau htons:",    &cong_mang, sizeof cong_mang);

    printf("\nip   = 0x%08X\n", ip);
    in_byte("trong bo nho:", &ip, sizeof ip);
    in_byte("sau htonl:",    &ip_mang, sizeof ip_mang);

    uint32_t thu = 1;
    printf("\nmay nay la %s-endian\n",
           (*(unsigned char *)&thu == 1) ? "little" : "big");
    printf("htons(18080) = %u\n", (unsigned)htons(18080));

    WSACleanup();
    return 0;
}

struct sockaddr_in kh;
socklen_t kh_co = sizeof kh;

Sock c = accept(sv, (struct sockaddr *)&kh, &kh_co);
if (c == SOCK_XAU) { /* xu ly loi */ }

char ip[INET_ADDRSTRLEN];
inet_ntop(AF_INET, &kh.sin_addr, ip, sizeof ip);
printf("ket noi tu %s:%d\n", ip, ntohs(kh.sin_port));
/*                                ^^^^^ ntohs, khong duoc quen */

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

#if defined(_WIN32)
  #include <winsock2.h>
  #include <ws2tcpip.h>
  typedef SOCKET Sock;
  typedef int    socklen_t;
  #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

static int khoi_tao_mang(void) {
#if defined(_WIN32)
    WSADATA d;
    return WSAStartup(MAKEWORD(2, 2), &d) == 0 ? 0 : -1;
#else
    return 0;
#endif
}

static void don_mang(void) {
#if defined(_WIN32)
    WSACleanup();
#endif
}