int tls1_process_heartbeat(SSL *s)
{
    unsigned char *p = &s->s3->rrec.data[0], *pl;
    unsigned short hbtype;
    unsigned int payload;
    unsigned int padding = 16;  /* Use minimum padding */

    if (s->msg_callback)
        s->msg_callback(0, s->version, TLS1_RT_HEARTBEAT,
                        &s->s3->rrec.data[0], s->s3->rrec.length,
                        s, s->msg_callback_arg);

    /* Read type and payload length first */
    if (1 + 2 + 16 > s->s3->rrec.length)
        return 0;               /* silently discard */
    hbtype = *p++;
    n2s(p, payload);
    if (1 + 2 + payload + 16 > s->s3->rrec.length)
        return 0;               /* silently discard per RFC 6520 sec. 4 */
    pl = p;

    if (hbtype == TLS1_HB_REQUEST) {
        unsigned char *buffer, *bp;
        int r;

        /*
         * Allocate memory for the response, size is 1 bytes message type,
         * plus 2 bytes payload length, plus payload, plus padding
         */
        buffer = OPENSSL_malloc(1 + 2 + payload + padding);
        bp = buffer;

        /* Enter response type, length and copy payload */
        *bp++ = TLS1_HB_RESPONSE;
        s2n(payload, bp);
        memcpy(bp, pl, payload);
        bp += payload;
        /* Random padding */
        RAND_pseudo_bytes(bp, padding);

        r = ssl3_write_bytes(s, TLS1_RT_HEARTBEAT, buffer,
                             3 + payload + padding);

        if (r >= 0 && s->msg_callback)
            s->msg_callback(1, s->version, TLS1_RT_HEARTBEAT,
                            buffer, 3 + payload + padding,
                            s, s->msg_callback_arg);

        OPENSSL_free(buffer);

        if (r < 0)
            return r;
    } else if (hbtype == TLS1_HB_RESPONSE) {
        unsigned int seq;

        /*
         * We only send sequence numbers (2 bytes unsigned int), and 16
         * random bytes, so we just try to read the sequence number
         */
        n2s(pl, seq);

        if (payload == 18 && seq == s->tlsext_hb_seq) {
            s->tlsext_hb_seq++;
            s->tlsext_hb_pending = 0;
        }
    }

    return 0;
}

Unknown