send_all, recv_all và giao thức tiền tố độ dài

/* Gui DU n byte. Tra ve 0 thanh cong, -1 loi. */
static int send_all(Sock s, const void *dl, size_t n) {
    const char *p = (const char *)dl;
    size_t con = n;

    while (con > 0) {
        int g = send(s, p, (int)con, 0);

        if (g > 0) {                    /* gui duoc mot phan */
            p   += g;
            con -= (size_t)g;
            continue;
        }

        if (g == 0) return -1;          /* khong the xay ra voi n > 0,
                                           nhung phong xa */

#if defined(_WIN32)
        int e = WSAGetLastError();
        if (e == WSAEINTR) continue;    /* bi ngat, thu lai */
#else
        if (errno == EINTR) continue;   /* bi tin hieu ngat, thu lai */
#endif
        return -1;                      /* loi that su */
    }
    return 0;
}

/* Doc DU n byte. Tra ve 0 thanh cong, -1 loi hoac ben kia dong. */
static int recv_all(Sock s, void *dl, size_t n) {
    char  *p   = (char *)dl;
    size_t con = n;

    while (con > 0) {
        int g = recv(s, p, (int)con, 0);

        if (g > 0) {
            p   += g;
            con -= (size_t)g;
            continue;
        }

        if (g == 0) return -1;          /* ben kia dong SACH giua chung */

#if defined(_WIN32)
        if (WSAGetLastError() == WSAEINTR) continue;
#else
        if (errno == EINTR) continue;
#endif
        return -1;
    }
    return 0;
}

#include <stdint.h>

#define TIN_TOI_DA (1024u * 1024u)          /* 1 MB */

/* Khung: [do dai 4 byte, thu tu mang][du lieu N byte] */

static int gui_khung(Sock s, const void *dl, uint32_t n) {
    uint32_t d = htonl(n);
    if (send_all(s, &d, 4) != 0) return -1;
    if (n > 0 && send_all(s, dl, n) != 0) return -1;
    return 0;
}

/* Cap phat bo dem va tra ve qua *ra. Nguoi goi PHAI free. */
static int nhan_khung(Sock s, char **ra, uint32_t *ra_n) {
    uint32_t d;
    if (recv_all(s, &d, 4) != 0) return -1;
    d = ntohl(d);

    if (d > TIN_TOI_DA) {
        fprintf(stderr, "khung qua lon: %u\n", d);
        return -1;                          /* dong ket noi */
    }

    char *dem = malloc((size_t)d + 1);      /* +1 de them NUL */
    if (dem == NULL) return -1;

    if (d > 0 && recv_all(s, dem, d) != 0) { free(dem); return -1; }
    dem[d] = '\0';

    *ra   = dem;
    *ra_n = d;
    return 0;
}

static int send_all(SOCKET s, const void *dl, size_t n) {
    const char *p = (const char *)dl;
    size_t con = n;
    while (con > 0) {
        int g = send(s, p, (int)(con > 1 ? 1 : con), 0);   /* CO Y 1 byte */
        if (g <= 0) return -1;
        p += g; con -= (size_t)g;
    }
    return 0;
}

static const char *TIN[] = {
    "xin chao",
    "day la thong diep thu hai dai hon",
    "a",
    "",                                 /* khung RONG, truong hop bien */
    "ket thuc"
};

/* Khung: [do dai 4][loai 1][du lieu N-1] */

enum Loai {
    LOAI_TIN   = 1,     /* tin nhan van ban */
    LOAI_TEN   = 2,     /* dat ten */
    LOAI_LENH  = 3,     /* lenh dieu khien */
    LOAI_PING  = 4,     /* giu ket noi song */
    LOAI_PONG  = 5,
};

typedef struct {
    uint8_t  loai;
    uint32_t co;
    char    *du_lieu;   /* co the NULL neu co == 0 */
} Khung;

static int gui_khung2(Sock s, uint8_t loai, const void *dl, uint32_t n) {
    uint32_t d = htonl(n + 1);          /* +1 cho byte loai */
    if (send_all(s, &d, 4) != 0)     return -1;
    if (send_all(s, &loai, 1) != 0)  return -1;
    if (n > 0 && send_all(s, dl, n) != 0) return -1;
    return 0;
}

static int nhan_khung2(Sock s, Khung *k) {
    uint32_t d;
    if (recv_all(s, &d, 4) != 0) return -1;
    d = ntohl(d);

    if (d < 1 || d > TIN_TOI_DA) return -1;   /* phai co it nhat byte loai */

    if (recv_all(s, &k->loai, 1) != 0) return -1;

    k->co = d - 1;
    k->du_lieu = malloc((size_t)k->co + 1);
    if (k->du_lieu == NULL) return -1;

    if (k->co > 0 && recv_all(s, k->du_lieu, k->co) != 0) {
        free(k->du_lieu);
        k->du_lieu = NULL;
        return -1;
    }
    k->du_lieu[k->co] = '\0';
    return 0;
}