[thirdparty/openssl.git] / ssl / d1_both.c

/* ssl/d1_both.c */
/*
 * DTLS implementation written by Nagendra Modadugu
 * (nagendra@cs.stanford.edu) for the OpenSSL project 2005.
 */
/* ====================================================================
 * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    openssl-core@openssl.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <limits.h>
#include <string.h>
#include <stdio.h>
#include "ssl_locl.h"
#include <openssl/buffer.h>
#include <openssl/rand.h>
#include <openssl/objects.h>
#include <openssl/evp.h>
#include <openssl/x509.h>

#define RSMBLY_BITMASK_SIZE(msg_len) (((msg_len) + 7) / 8)

#define RSMBLY_BITMASK_MARK(bitmask, start, end) { \
                        if ((end) - (start) <= 8) { \
                                long ii; \
                                for (ii = (start); ii < (end); ii++) bitmask[((ii) >> 3)] |= (1 << ((ii) & 7)); \
                        } else { \
                                long ii; \
                                bitmask[((start) >> 3)] |= bitmask_start_values[((start) & 7)]; \
                                for (ii = (((start) >> 3) + 1); ii < ((((end) - 1)) >> 3); ii++) bitmask[ii] = 0xff; \
                                bitmask[(((end) - 1) >> 3)] |= bitmask_end_values[((end) & 7)]; \
                        } }

#define RSMBLY_BITMASK_IS_COMPLETE(bitmask, msg_len, is_complete) { \
                        long ii; \
                        OPENSSL_assert((msg_len) > 0); \
                        is_complete = 1; \
                        if (bitmask[(((msg_len) - 1) >> 3)] != bitmask_end_values[((msg_len) & 7)]) is_complete = 0; \
                        if (is_complete) for (ii = (((msg_len) - 1) >> 3) - 1; ii >= 0 ; ii--) \
                                if (bitmask[ii] != 0xff) { is_complete = 0; break; } }

static unsigned char bitmask_start_values[] =
    { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 };
static unsigned char bitmask_end_values[] =
    { 0xff, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f };

/* XDTLS:  figure out the right values */
static const unsigned int g_probable_mtu[] = { 1500, 512, 256 };

static void dtls1_fix_message_header(SSL *s, unsigned long frag_off,
                                     unsigned long frag_len);
static unsigned char *dtls1_write_message_header(SSL *s, unsigned char *p);
static void dtls1_set_message_header_int(SSL *s, unsigned char mt,
                                         unsigned long len,
                                         unsigned short seq_num,
                                         unsigned long frag_off,
                                         unsigned long frag_len);
static long dtls1_get_message_fragment(SSL *s, int st1, int stn, long max,
                                       int *ok);

static hm_fragment *dtls1_hm_fragment_new(unsigned long frag_len,
                                          int reassembly)
{
    hm_fragment *frag = NULL;
    unsigned char *buf = NULL;
    unsigned char *bitmask = NULL;

    frag = OPENSSL_malloc(sizeof(hm_fragment));
    if (frag == NULL)
        return NULL;

    if (frag_len) {
        buf = OPENSSL_malloc(frag_len);
        if (buf == NULL) {
            OPENSSL_free(frag);
            return NULL;
        }
    }

    /* zero length fragment gets zero frag->fragment */
    frag->fragment = buf;

    /* Initialize reassembly bitmask if necessary */
    if (reassembly) {
        bitmask = OPENSSL_malloc(RSMBLY_BITMASK_SIZE(frag_len));
        if (bitmask == NULL) {
            if (buf != NULL)
                OPENSSL_free(buf);
            OPENSSL_free(frag);
            return NULL;
        }
        memset(bitmask, 0, RSMBLY_BITMASK_SIZE(frag_len));
    }

    frag->reassembly = bitmask;

    return frag;
}

void dtls1_hm_fragment_free(hm_fragment *frag)
{

    if (frag->msg_header.is_ccs) {
        EVP_CIPHER_CTX_free(frag->msg_header.
                            saved_retransmit_state.enc_write_ctx);
        EVP_MD_CTX_destroy(frag->msg_header.
                           saved_retransmit_state.write_hash);
    }
    if (frag->fragment)
        OPENSSL_free(frag->fragment);
    if (frag->reassembly)
        OPENSSL_free(frag->reassembly);
    OPENSSL_free(frag);
}

static int dtls1_query_mtu(SSL *s)
{
    if (s->d1->link_mtu) {
        s->d1->mtu =
            s->d1->link_mtu - BIO_dgram_get_mtu_overhead(SSL_get_wbio(s));
        s->d1->link_mtu = 0;
    }

    /* AHA!  Figure out the MTU, and stick to the right size */
    if (s->d1->mtu < dtls1_min_mtu(s)) {
        if (!(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) {
            s->d1->mtu =
                BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_QUERY_MTU, 0, NULL);

            /*
             * I've seen the kernel return bogus numbers when it doesn't know
             * (initial write), so just make sure we have a reasonable number
             */
            if (s->d1->mtu < dtls1_min_mtu(s)) {
                /* Set to min mtu */
                s->d1->mtu = dtls1_min_mtu(s);
                BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SET_MTU,
                         s->d1->mtu, NULL);
            }
        } else
            return 0;
    }
    return 1;
}

/*
 * send s->init_buf in records of type 'type' (SSL3_RT_HANDSHAKE or
 * SSL3_RT_CHANGE_CIPHER_SPEC)
 */
int dtls1_do_write(SSL *s, int type)
{
    int ret;
    unsigned int curr_mtu;
    int retry = 1;
    unsigned int len, frag_off, mac_size, blocksize, used_len;

    if (!dtls1_query_mtu(s))
        return -1;

    OPENSSL_assert(s->d1->mtu >= dtls1_min_mtu(s)); /* should have something
                                                     * reasonable now */

    if (s->init_off == 0 && type == SSL3_RT_HANDSHAKE)
        OPENSSL_assert(s->init_num ==
                       (int)s->d1->w_msg_hdr.msg_len +
                       DTLS1_HM_HEADER_LENGTH);

    if (s->write_hash) {
        if (s->enc_write_ctx
            && EVP_CIPHER_CTX_mode(s->enc_write_ctx) == EVP_CIPH_GCM_MODE)
            mac_size = 0;
        else
            mac_size = EVP_MD_CTX_size(s->write_hash);
    } else
        mac_size = 0;

    if (s->enc_write_ctx &&
        (EVP_CIPHER_CTX_mode(s->enc_write_ctx) == EVP_CIPH_CBC_MODE))
        blocksize = 2 * EVP_CIPHER_block_size(s->enc_write_ctx->cipher);
    else
        blocksize = 0;

    frag_off = 0;
    /* s->init_num shouldn't ever be < 0...but just in case */
    while (s->init_num > 0) {
        used_len = BIO_wpending(SSL_get_wbio(s)) + DTLS1_RT_HEADER_LENGTH
            + mac_size + blocksize;
        if (s->d1->mtu > used_len)
            curr_mtu = s->d1->mtu - used_len;
        else
            curr_mtu = 0;

        if (curr_mtu <= DTLS1_HM_HEADER_LENGTH) {
            /*
             * grr.. we could get an error if MTU picked was wrong
             */
            ret = BIO_flush(SSL_get_wbio(s));
            if (ret <= 0)
                return ret;
            used_len = DTLS1_RT_HEADER_LENGTH + mac_size + blocksize;
            if (s->d1->mtu > used_len + DTLS1_HM_HEADER_LENGTH) {
                curr_mtu = s->d1->mtu - used_len;
            } else {
                /* Shouldn't happen */
                return -1;
            }
        }

        /*
         * We just checked that s->init_num > 0 so this cast should be safe
         */
        if (((unsigned int)s->init_num) > curr_mtu)
            len = curr_mtu;
        else
            len = s->init_num;

        /* Shouldn't ever happen */
        if (len > INT_MAX)
            len = INT_MAX;

        /*
         * XDTLS: this function is too long.  split out the CCS part
         */
        if (type == SSL3_RT_HANDSHAKE) {
            if (s->init_off != 0) {
                OPENSSL_assert(s->init_off > DTLS1_HM_HEADER_LENGTH);
                s->init_off -= DTLS1_HM_HEADER_LENGTH;
                s->init_num += DTLS1_HM_HEADER_LENGTH;

                /*
                 * We just checked that s->init_num > 0 so this cast should
                 * be safe
                 */
                if (((unsigned int)s->init_num) > curr_mtu)
                    len = curr_mtu;
                else
                    len = s->init_num;
            }

            /* Shouldn't ever happen */
            if (len > INT_MAX)
                len = INT_MAX;

            if (len < DTLS1_HM_HEADER_LENGTH) {
                /*
                 * len is so small that we really can't do anything sensible
                 * so fail
                 */
                return -1;
            }
            dtls1_fix_message_header(s, frag_off,
                                     len - DTLS1_HM_HEADER_LENGTH);

            dtls1_write_message_header(s,
                                       (unsigned char *)&s->init_buf->
                                       data[s->init_off]);
        }

        ret = dtls1_write_bytes(s, type, &s->init_buf->data[s->init_off],
                                len);
        if (ret < 0) {
            /*
             * might need to update MTU here, but we don't know which
             * previous packet caused the failure -- so can't really
             * retransmit anything.  continue as if everything is fine and
             * wait for an alert to handle the retransmit
             */
            if (retry && BIO_ctrl(SSL_get_wbio(s),
                                  BIO_CTRL_DGRAM_MTU_EXCEEDED, 0, NULL) > 0) {
                if (!(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) {
                    if (!dtls1_query_mtu(s))
                        return -1;
                    /* Have one more go */
                    retry = 0;
                } else
                    return -1;
            } else {
                return (-1);
            }
        } else {

            /*
             * bad if this assert fails, only part of the handshake message
             * got sent.  but why would this happen?
             */
            OPENSSL_assert(len == (unsigned int)ret);

            if (type == SSL3_RT_HANDSHAKE && !s->d1->retransmitting) {
                /*
                 * should not be done for 'Hello Request's, but in that case
                 * we'll ignore the result anyway
                 */
                unsigned char *p =
                    (unsigned char *)&s->init_buf->data[s->init_off];
                const struct hm_header_st *msg_hdr = &s->d1->w_msg_hdr;
                int xlen;

                if (frag_off == 0 && s->version != DTLS1_BAD_VER) {
                    /*
                     * reconstruct message header is if it is being sent in
                     * single fragment
                     */
                    *p++ = msg_hdr->type;
                    l2n3(msg_hdr->msg_len, p);
                    s2n(msg_hdr->seq, p);
                    l2n3(0, p);
                    l2n3(msg_hdr->msg_len, p);
                    p -= DTLS1_HM_HEADER_LENGTH;
                    xlen = ret;
                } else {
                    p += DTLS1_HM_HEADER_LENGTH;
                    xlen = ret - DTLS1_HM_HEADER_LENGTH;
                }

                ssl3_finish_mac(s, p, xlen);
            }

            if (ret == s->init_num) {
                if (s->msg_callback)
                    s->msg_callback(1, s->version, type, s->init_buf->data,
                                    (size_t)(s->init_off + s->init_num), s,
                                    s->msg_callback_arg);

                s->init_off = 0; /* done writing this message */
                s->init_num = 0;

                return (1);
            }
            s->init_off += ret;
            s->init_num -= ret;
            frag_off += (ret -= DTLS1_HM_HEADER_LENGTH);
        }
    }
    return (0);
}

/*
 * Obtain handshake message of message type 'mt' (any if mt == -1), maximum
 * acceptable body length 'max'. Read an entire handshake message.  Handshake
 * messages arrive in fragments.
 */
long dtls1_get_message(SSL *s, int st1, int stn, int mt, long max, int *ok)
{
    int i, al;
    struct hm_header_st *msg_hdr;
    unsigned char *p;
    unsigned long msg_len;

    /*
     * s3->tmp is used to store messages that are unexpected, caused by the
     * absence of an optional handshake message
     */
    if (s->s3->tmp.reuse_message) {
        s->s3->tmp.reuse_message = 0;
        if ((mt >= 0) && (s->s3->tmp.message_type != mt)) {
            al = SSL_AD_UNEXPECTED_MESSAGE;
            SSLerr(SSL_F_DTLS1_GET_MESSAGE, SSL_R_UNEXPECTED_MESSAGE);
            goto f_err;
        }
        *ok = 1;
        s->init_msg = s->init_buf->data + DTLS1_HM_HEADER_LENGTH;
        s->init_num = (int)s->s3->tmp.message_size;
        return s->init_num;
    }

    msg_hdr = &s->d1->r_msg_hdr;
    memset(msg_hdr, 0x00, sizeof(struct hm_header_st));

 again:
    i = dtls1_get_message_fragment(s, st1, stn, max, ok);
    if (i == DTLS1_HM_BAD_FRAGMENT || i == DTLS1_HM_FRAGMENT_RETRY) {
        /* bad fragment received */
        goto again;
    } else if (i <= 0 && !*ok) {
        return i;
    }

    p = (unsigned char *)s->init_buf->data;
    msg_len = msg_hdr->msg_len;

    /* reconstruct message header */
    *(p++) = msg_hdr->type;
    l2n3(msg_len, p);
    s2n(msg_hdr->seq, p);
    l2n3(0, p);
    l2n3(msg_len, p);
    if (s->version != DTLS1_BAD_VER) {
        p -= DTLS1_HM_HEADER_LENGTH;
        msg_len += DTLS1_HM_HEADER_LENGTH;
    }

    ssl3_finish_mac(s, p, msg_len);
    if (s->msg_callback)
        s->msg_callback(0, s->version, SSL3_RT_HANDSHAKE,
                        p, msg_len, s, s->msg_callback_arg);

    memset(msg_hdr, 0x00, sizeof(struct hm_header_st));

    /* Don't change sequence numbers while listening */
    if (!s->d1->listen)
        s->d1->handshake_read_seq++;

    s->init_msg = s->init_buf->data + DTLS1_HM_HEADER_LENGTH;
    return s->init_num;

 f_err:
    ssl3_send_alert(s, SSL3_AL_FATAL, al);
    *ok = 0;
    return -1;
}

static int dtls1_preprocess_fragment(SSL *s, struct hm_header_st *msg_hdr,
                                     int max)
{
    size_t frag_off, frag_len, msg_len;

    msg_len = msg_hdr->msg_len;
    frag_off = msg_hdr->frag_off;
    frag_len = msg_hdr->frag_len;

    /* sanity checking */
    if ((frag_off + frag_len) > msg_len) {
        SSLerr(SSL_F_DTLS1_PREPROCESS_FRAGMENT, SSL_R_EXCESSIVE_MESSAGE_SIZE);
        return SSL_AD_ILLEGAL_PARAMETER;
    }

    if ((frag_off + frag_len) > (unsigned long)max) {
        SSLerr(SSL_F_DTLS1_PREPROCESS_FRAGMENT, SSL_R_EXCESSIVE_MESSAGE_SIZE);
        return SSL_AD_ILLEGAL_PARAMETER;
    }

    if (s->d1->r_msg_hdr.frag_off == 0) { /* first fragment */
        /*
         * msg_len is limited to 2^24, but is effectively checked against max
         * above
         */
        if (!BUF_MEM_grow_clean
            (s->init_buf, msg_len + DTLS1_HM_HEADER_LENGTH)) {
            SSLerr(SSL_F_DTLS1_PREPROCESS_FRAGMENT, ERR_R_BUF_LIB);
            return SSL_AD_INTERNAL_ERROR;
        }

        s->s3->tmp.message_size = msg_len;
        s->d1->r_msg_hdr.msg_len = msg_len;
        s->s3->tmp.message_type = msg_hdr->type;
        s->d1->r_msg_hdr.type = msg_hdr->type;
        s->d1->r_msg_hdr.seq = msg_hdr->seq;
    } else if (msg_len != s->d1->r_msg_hdr.msg_len) {
        /*
         * They must be playing with us! BTW, failure to enforce upper limit
         * would open possibility for buffer overrun.
         */
        SSLerr(SSL_F_DTLS1_PREPROCESS_FRAGMENT, SSL_R_EXCESSIVE_MESSAGE_SIZE);
        return SSL_AD_ILLEGAL_PARAMETER;
    }

    return 0;                   /* no error */
}

static int dtls1_retrieve_buffered_fragment(SSL *s, long max, int *ok)
{
    /*-
     * (0) check whether the desired fragment is available
     * if so:
     * (1) copy over the fragment to s->init_buf->data[]
     * (2) update s->init_num
     */
    pitem *item;
    hm_fragment *frag;
    int al;

    *ok = 0;
    item = pqueue_peek(s->d1->buffered_messages);
    if (item == NULL)
        return 0;

    frag = (hm_fragment *)item->data;

    /* Don't return if reassembly still in progress */
    if (frag->reassembly != NULL)
        return 0;

    if (s->d1->handshake_read_seq == frag->msg_header.seq) {
        unsigned long frag_len = frag->msg_header.frag_len;
        pqueue_pop(s->d1->buffered_messages);

        al = dtls1_preprocess_fragment(s, &frag->msg_header, max);

        if (al == 0) {          /* no alert */
            unsigned char *p =
                (unsigned char *)s->init_buf->data + DTLS1_HM_HEADER_LENGTH;
            memcpy(&p[frag->msg_header.frag_off], frag->fragment,
                   frag->msg_header.frag_len);
        }

        dtls1_hm_fragment_free(frag);
        pitem_free(item);

        if (al == 0) {
            *ok = 1;
            return frag_len;
        }

        ssl3_send_alert(s, SSL3_AL_FATAL, al);
        s->init_num = 0;
        *ok = 0;
        return -1;
    } else
        return 0;
}

/*
 * dtls1_max_handshake_message_len returns the maximum number of bytes
 * permitted in a DTLS handshake message for |s|. The minimum is 16KB, but
 * may be greater if the maximum certificate list size requires it.
 */
static unsigned long dtls1_max_handshake_message_len(const SSL *s)
{
    unsigned long max_len =
        DTLS1_HM_HEADER_LENGTH + SSL3_RT_MAX_ENCRYPTED_LENGTH;
    if (max_len < (unsigned long)s->max_cert_list)
        return s->max_cert_list;
    return max_len;
}

static int
dtls1_reassemble_fragment(SSL *s, const struct hm_header_st *msg_hdr, int *ok)
{
    hm_fragment *frag = NULL;
    pitem *item = NULL;
    int i = -1, is_complete;
    unsigned char seq64be[8];
    unsigned long frag_len = msg_hdr->frag_len;

    if ((msg_hdr->frag_off + frag_len) > msg_hdr->msg_len ||
        msg_hdr->msg_len > dtls1_max_handshake_message_len(s))
        goto err;

    if (frag_len == 0)
        return DTLS1_HM_FRAGMENT_RETRY;

    /* Try to find item in queue */
    memset(seq64be, 0, sizeof(seq64be));
    seq64be[6] = (unsigned char)(msg_hdr->seq >> 8);
    seq64be[7] = (unsigned char)msg_hdr->seq;
    item = pqueue_find(s->d1->buffered_messages, seq64be);

    if (item == NULL) {
        frag = dtls1_hm_fragment_new(msg_hdr->msg_len, 1);
        if (frag == NULL)
            goto err;
        memcpy(&(frag->msg_header), msg_hdr, sizeof(*msg_hdr));
        frag->msg_header.frag_len = frag->msg_header.msg_len;
        frag->msg_header.frag_off = 0;
    } else {
        frag = (hm_fragment *)item->data;
        if (frag->msg_header.msg_len != msg_hdr->msg_len) {
            item = NULL;
            frag = NULL;
            goto err;
        }
    }

    /*
     * If message is already reassembled, this must be a retransmit and can
     * be dropped. In this case item != NULL and so frag does not need to be
     * freed.
     */
    if (frag->reassembly == NULL) {
        unsigned char devnull[256];

        while (frag_len) {
            i = s->method->ssl_read_bytes(s, SSL3_RT_HANDSHAKE,
                                          devnull,
                                          frag_len >
                                          sizeof(devnull) ? sizeof(devnull) :
                                          frag_len, 0);
            if (i <= 0)
                goto err;
            frag_len -= i;
        }
        return DTLS1_HM_FRAGMENT_RETRY;
    }

    /* read the body of the fragment (header has already been read */
    i = s->method->ssl_read_bytes(s, SSL3_RT_HANDSHAKE,
                                  frag->fragment + msg_hdr->frag_off,
                                  frag_len, 0);
    if ((unsigned long)i != frag_len)
        i = -1;
    if (i <= 0)
        goto err;

    RSMBLY_BITMASK_MARK(frag->reassembly, (long)msg_hdr->frag_off,
                        (long)(msg_hdr->frag_off + frag_len));

    RSMBLY_BITMASK_IS_COMPLETE(frag->reassembly, (long)msg_hdr->msg_len,
                               is_complete);

    if (is_complete) {
        OPENSSL_free(frag->reassembly);
        frag->reassembly = NULL;
    }

    if (item == NULL) {
        item = pitem_new(seq64be, frag);
        if (item == NULL) {
            i = -1;
            goto err;
        }

        item = pqueue_insert(s->d1->buffered_messages, item);
        /*
         * pqueue_insert fails iff a duplicate item is inserted. However,
         * |item| cannot be a duplicate. If it were, |pqueue_find|, above,
         * would have returned it and control would never have reached this
         * branch.
         */
        OPENSSL_assert(item != NULL);
    }

    return DTLS1_HM_FRAGMENT_RETRY;

 err:
    if (frag != NULL && item == NULL)
        dtls1_hm_fragment_free(frag);
    *ok = 0;
    return i;
}

static int
dtls1_process_out_of_seq_message(SSL *s, const struct hm_header_st *msg_hdr,
                                 int *ok)
{
    int i = -1;
    hm_fragment *frag = NULL;
    pitem *item = NULL;
    unsigned char seq64be[8];
    unsigned long frag_len = msg_hdr->frag_len;

    if ((msg_hdr->frag_off + frag_len) > msg_hdr->msg_len)
        goto err;

    /* Try to find item in queue, to prevent duplicate entries */
    memset(seq64be, 0, sizeof(seq64be));
    seq64be[6] = (unsigned char)(msg_hdr->seq >> 8);
    seq64be[7] = (unsigned char)msg_hdr->seq;
    item = pqueue_find(s->d1->buffered_messages, seq64be);

    /*
     * If we already have an entry and this one is a fragment, don't discard
     * it and rather try to reassemble it.
     */
    if (item != NULL && frag_len != msg_hdr->msg_len)
        item = NULL;

    /*
     * Discard the message if sequence number was already there, is too far
     * in the future, already in the queue or if we received a FINISHED
     * before the SERVER_HELLO, which then must be a stale retransmit.
     */
    if (msg_hdr->seq <= s->d1->handshake_read_seq ||
        msg_hdr->seq > s->d1->handshake_read_seq + 10 || item != NULL ||
        (s->d1->handshake_read_seq == 0 && msg_hdr->type == SSL3_MT_FINISHED))
    {
        unsigned char devnull[256];

        while (frag_len) {
            i = s->method->ssl_read_bytes(s, SSL3_RT_HANDSHAKE,
                                          devnull,
                                          frag_len >
                                          sizeof(devnull) ? sizeof(devnull) :
                                          frag_len, 0);
            if (i <= 0)
                goto err;
            frag_len -= i;
        }
    } else {
        if (frag_len != msg_hdr->msg_len)
            return dtls1_reassemble_fragment(s, msg_hdr, ok);

        if (frag_len > dtls1_max_handshake_message_len(s))
            goto err;

        frag = dtls1_hm_fragment_new(frag_len, 0);
        if (frag == NULL)
            goto err;

        memcpy(&(frag->msg_header), msg_hdr, sizeof(*msg_hdr));

        if (frag_len) {
            /*
             * read the body of the fragment (header has already been read
             */
            i = s->method->ssl_read_bytes(s, SSL3_RT_HANDSHAKE,
                                          frag->fragment, frag_len, 0);
            if ((unsigned long)i != frag_len)
                i = -1;
            if (i <= 0)
                goto err;
        }

        item = pitem_new(seq64be, frag);
        if (item == NULL)
            goto err;

        item = pqueue_insert(s->d1->buffered_messages, item);
        /*
         * pqueue_insert fails iff a duplicate item is inserted. However,
         * |item| cannot be a duplicate. If it were, |pqueue_find|, above,
         * would have returned it. Then, either |frag_len| !=
         * |msg_hdr->msg_len| in which case |item| is set to NULL and it will
         * have been processed with |dtls1_reassemble_fragment|, above, or
         * the record will have been discarded.
         */
        OPENSSL_assert(item != NULL);
    }

    return DTLS1_HM_FRAGMENT_RETRY;

 err:
    if (frag != NULL && item == NULL)
        dtls1_hm_fragment_free(frag);
    *ok = 0;
    return i;
}

static long
dtls1_get_message_fragment(SSL *s, int st1, int stn, long max, int *ok)
{
    unsigned char wire[DTLS1_HM_HEADER_LENGTH];
    unsigned long len, frag_off, frag_len;
    int i, al;
    struct hm_header_st msg_hdr;

 redo:
    /* see if we have the required fragment already */
    if ((frag_len = dtls1_retrieve_buffered_fragment(s, max, ok)) || *ok) {
        if (*ok)
            s->init_num = frag_len;
        return frag_len;
    }

    /* read handshake message header */
    i = s->method->ssl_read_bytes(s, SSL3_RT_HANDSHAKE, wire,
                                  DTLS1_HM_HEADER_LENGTH, 0);
    if (i <= 0) {               /* nbio, or an error */
        s->rwstate = SSL_READING;
        *ok = 0;
        return i;
    }
    /* Handshake fails if message header is incomplete */
    if (i != DTLS1_HM_HEADER_LENGTH) {
        al = SSL_AD_UNEXPECTED_MESSAGE;
        SSLerr(SSL_F_DTLS1_GET_MESSAGE_FRAGMENT, SSL_R_UNEXPECTED_MESSAGE);
        goto f_err;
    }

    /* parse the message fragment header */
    dtls1_get_message_header(wire, &msg_hdr);

    /*
     * if this is a future (or stale) message it gets buffered
     * (or dropped)--no further processing at this time
     * While listening, we accept seq 1 (ClientHello with cookie)
     * although we're still expecting seq 0 (ClientHello)
     */
    if (msg_hdr.seq != s->d1->handshake_read_seq
        && !(s->d1->listen && msg_hdr.seq == 1))
        return dtls1_process_out_of_seq_message(s, &msg_hdr, ok);

    len = msg_hdr.msg_len;
    frag_off = msg_hdr.frag_off;
    frag_len = msg_hdr.frag_len;

    if (frag_len && frag_len < len)
        return dtls1_reassemble_fragment(s, &msg_hdr, ok);

    if (!s->server && s->d1->r_msg_hdr.frag_off == 0 &&
        wire[0] == SSL3_MT_HELLO_REQUEST) {
        /*
         * The server may always send 'Hello Request' messages -- we are
         * doing a handshake anyway now, so ignore them if their format is
         * correct. Does not count for 'Finished' MAC.
         */
        if (wire[1] == 0 && wire[2] == 0 && wire[3] == 0) {
            if (s->msg_callback)
                s->msg_callback(0, s->version, SSL3_RT_HANDSHAKE,
                                wire, DTLS1_HM_HEADER_LENGTH, s,
                                s->msg_callback_arg);

            s->init_num = 0;
            goto redo;
        } else {                /* Incorrectly formated Hello request */

            al = SSL_AD_UNEXPECTED_MESSAGE;
            SSLerr(SSL_F_DTLS1_GET_MESSAGE_FRAGMENT,
                   SSL_R_UNEXPECTED_MESSAGE);
            goto f_err;
        }
    }

    if ((al = dtls1_preprocess_fragment(s, &msg_hdr, max)))
        goto f_err;

    /* XDTLS:  ressurect this when restart is in place */
    s->state = stn;

    if (frag_len > 0) {
        unsigned char *p =
            (unsigned char *)s->init_buf->data + DTLS1_HM_HEADER_LENGTH;

        i = s->method->ssl_read_bytes(s, SSL3_RT_HANDSHAKE,
                                      &p[frag_off], frag_len, 0);
        /*
         * XDTLS: fix this--message fragments cannot span multiple packets
         */
        if (i <= 0) {
            s->rwstate = SSL_READING;
            *ok = 0;
            return i;
        }
    } else
        i = 0;

    /*
     * XDTLS: an incorrectly formatted fragment should cause the handshake
     * to fail
     */
    if (i != (int)frag_len) {
        al = SSL3_AD_ILLEGAL_PARAMETER;
        SSLerr(SSL_F_DTLS1_GET_MESSAGE_FRAGMENT, SSL3_AD_ILLEGAL_PARAMETER);
        goto f_err;
    }

    *ok = 1;

    /*
     * Note that s->init_num is *not* used as current offset in
     * s->init_buf->data, but as a counter summing up fragments' lengths: as
     * soon as they sum up to handshake packet length, we assume we have got
     * all the fragments.
     */
    s->init_num = frag_len;
    return frag_len;

 f_err:
    ssl3_send_alert(s, SSL3_AL_FATAL, al);
    s->init_num = 0;

    *ok = 0;
    return (-1);
}

/*-
 * for these 2 messages, we need to
 * ssl->enc_read_ctx                    re-init
 * ssl->rlayer.read_sequence            zero
 * ssl->s3->read_mac_secret             re-init
 * ssl->session->read_sym_enc           assign
 * ssl->session->read_compression       assign
 * ssl->session->read_hash              assign
 */
int dtls1_send_change_cipher_spec(SSL *s, int a, int b)
{
    unsigned char *p;

    if (s->state == a) {
        p = (unsigned char *)s->init_buf->data;
        *p++ = SSL3_MT_CCS;
        s->d1->handshake_write_seq = s->d1->next_handshake_write_seq;
        s->init_num = DTLS1_CCS_HEADER_LENGTH;

        if (s->version == DTLS1_BAD_VER) {
            s->d1->next_handshake_write_seq++;
            s2n(s->d1->handshake_write_seq, p);
            s->init_num += 2;
        }

        s->init_off = 0;

        dtls1_set_message_header_int(s, SSL3_MT_CCS, 0,
                                     s->d1->handshake_write_seq, 0, 0);

        /* buffer the message to handle re-xmits */
        if (!dtls1_buffer_message(s, 1)) {
            SSLerr(SSL_F_DTLS1_SEND_CHANGE_CIPHER_SPEC, ERR_R_INTERNAL_ERROR);
            return -1;
        }

        s->state = b;
    }

    /* SSL3_ST_CW_CHANGE_B */
    return (dtls1_do_write(s, SSL3_RT_CHANGE_CIPHER_SPEC));
}

int dtls1_read_failed(SSL *s, int code)
{
    if (code > 0) {
        fprintf(stderr, "invalid state reached %s:%d", __FILE__, __LINE__);
        return 1;
    }

    if (!dtls1_is_timer_expired(s)) {
        /*
         * not a timeout, none of our business, let higher layers handle
         * this.  in fact it's probably an error
         */
        return code;
    }
#ifndef OPENSSL_NO_HEARTBEATS
    /* done, no need to send a retransmit */
    if (!SSL_in_init(s) && !s->tlsext_hb_pending)
#else
    /* done, no need to send a retransmit */
    if (!SSL_in_init(s))
#endif
    {
        BIO_set_flags(SSL_get_rbio(s), BIO_FLAGS_READ);
        return code;
    }

    return dtls1_handle_timeout(s);
}

int dtls1_get_queue_priority(unsigned short seq, int is_ccs)
{
    /*
     * The index of the retransmission queue actually is the message sequence
     * number, since the queue only contains messages of a single handshake.
     * However, the ChangeCipherSpec has no message sequence number and so
     * using only the sequence will result in the CCS and Finished having the
     * same index. To prevent this, the sequence number is multiplied by 2.
     * In case of a CCS 1 is subtracted. This does not only differ CSS and
     * Finished, it also maintains the order of the index (important for
     * priority queues) and fits in the unsigned short variable.
     */
    return seq * 2 - is_ccs;
}

int dtls1_retransmit_buffered_messages(SSL *s)
{
    pqueue sent = s->d1->sent_messages;
    piterator iter;
    pitem *item;
    hm_fragment *frag;
    int found = 0;

    iter = pqueue_iterator(sent);

    for (item = pqueue_next(&iter); item != NULL; item = pqueue_next(&iter)) {
        frag = (hm_fragment *)item->data;
        if (dtls1_retransmit_message(s, (unsigned short)
                                     dtls1_get_queue_priority
                                     (frag->msg_header.seq,
                                      frag->msg_header.is_ccs), 0,
                                     &found) <= 0 && found) {
            fprintf(stderr, "dtls1_retransmit_message() failed\n");
            return -1;
        }
    }

    return 1;
}

int dtls1_buffer_message(SSL *s, int is_ccs)
{
    pitem *item;
    hm_fragment *frag;
    unsigned char seq64be[8];

    /*
     * this function is called immediately after a message has been
     * serialized
     */
    OPENSSL_assert(s->init_off == 0);

    frag = dtls1_hm_fragment_new(s->init_num, 0);
    if (!frag)
        return 0;

    memcpy(frag->fragment, s->init_buf->data, s->init_num);

    if (is_ccs) {
        /* For DTLS1_BAD_VER the header length is non-standard */
        OPENSSL_assert(s->d1->w_msg_hdr.msg_len +
                       ((s->version==DTLS1_BAD_VER)?3:DTLS1_CCS_HEADER_LENGTH)
                       == (unsigned int)s->init_num);
    } else {
        OPENSSL_assert(s->d1->w_msg_hdr.msg_len +
                       DTLS1_HM_HEADER_LENGTH == (unsigned int)s->init_num);
    }

    frag->msg_header.msg_len = s->d1->w_msg_hdr.msg_len;
    frag->msg_header.seq = s->d1->w_msg_hdr.seq;
    frag->msg_header.type = s->d1->w_msg_hdr.type;
    frag->msg_header.frag_off = 0;
    frag->msg_header.frag_len = s->d1->w_msg_hdr.msg_len;
    frag->msg_header.is_ccs = is_ccs;

    /* save current state */
    frag->msg_header.saved_retransmit_state.enc_write_ctx = s->enc_write_ctx;
    frag->msg_header.saved_retransmit_state.write_hash = s->write_hash;
    frag->msg_header.saved_retransmit_state.compress = s->compress;
    frag->msg_header.saved_retransmit_state.session = s->session;
    frag->msg_header.saved_retransmit_state.epoch =
        DTLS_RECORD_LAYER_get_w_epoch(&s->rlayer);

    memset(seq64be, 0, sizeof(seq64be));
    seq64be[6] =
        (unsigned
         char)(dtls1_get_queue_priority(frag->msg_header.seq,
                                        frag->msg_header.is_ccs) >> 8);
    seq64be[7] =
        (unsigned
         char)(dtls1_get_queue_priority(frag->msg_header.seq,
                                        frag->msg_header.is_ccs));

    item = pitem_new(seq64be, frag);
    if (item == NULL) {
        dtls1_hm_fragment_free(frag);
        return 0;
    }

    pqueue_insert(s->d1->sent_messages, item);
    return 1;
}

int
dtls1_retransmit_message(SSL *s, unsigned short seq, unsigned long frag_off,
                         int *found)
{
    int ret;
    /* XDTLS: for now assuming that read/writes are blocking */
    pitem *item;
    hm_fragment *frag;
    unsigned long header_length;
    unsigned char seq64be[8];
    struct dtls1_retransmit_state saved_state;

    /*-
      OPENSSL_assert(s->init_num == 0);
      OPENSSL_assert(s->init_off == 0);
     */

    /* XDTLS:  the requested message ought to be found, otherwise error */
    memset(seq64be, 0, sizeof(seq64be));
    seq64be[6] = (unsigned char)(seq >> 8);
    seq64be[7] = (unsigned char)seq;

    item = pqueue_find(s->d1->sent_messages, seq64be);
    if (item == NULL) {
        fprintf(stderr, "retransmit:  message %d non-existant\n", seq);
        *found = 0;
        return 0;
    }

    *found = 1;
    frag = (hm_fragment *)item->data;

    if (frag->msg_header.is_ccs)
        header_length = DTLS1_CCS_HEADER_LENGTH;
    else
        header_length = DTLS1_HM_HEADER_LENGTH;

    memcpy(s->init_buf->data, frag->fragment,
           frag->msg_header.msg_len + header_length);
    s->init_num = frag->msg_header.msg_len + header_length;

    dtls1_set_message_header_int(s, frag->msg_header.type,
                                 frag->msg_header.msg_len,
                                 frag->msg_header.seq, 0,
                                 frag->msg_header.frag_len);

    /* save current state */
    saved_state.enc_write_ctx = s->enc_write_ctx;
    saved_state.write_hash = s->write_hash;
    saved_state.compress = s->compress;
    saved_state.session = s->session;
    saved_state.epoch = DTLS_RECORD_LAYER_get_w_epoch(&s->rlayer);

    s->d1->retransmitting = 1;

    /* restore state in which the message was originally sent */
    s->enc_write_ctx = frag->msg_header.saved_retransmit_state.enc_write_ctx;
    s->write_hash = frag->msg_header.saved_retransmit_state.write_hash;
    s->compress = frag->msg_header.saved_retransmit_state.compress;
    s->session = frag->msg_header.saved_retransmit_state.session;
    DTLS_RECORD_LAYER_set_saved_w_epoch(&s->rlayer,
        frag->msg_header.saved_retransmit_state.epoch);

    ret = dtls1_do_write(s, frag->msg_header.is_ccs ?
                         SSL3_RT_CHANGE_CIPHER_SPEC : SSL3_RT_HANDSHAKE);

    /* restore current state */
    s->enc_write_ctx = saved_state.enc_write_ctx;
    s->write_hash = saved_state.write_hash;
    s->compress = saved_state.compress;
    s->session = saved_state.session;
    DTLS_RECORD_LAYER_set_saved_w_epoch(&s->rlayer, saved_state.epoch);

    s->d1->retransmitting = 0;

    (void)BIO_flush(SSL_get_wbio(s));
    return ret;
}

/* call this function when the buffered messages are no longer needed */
void dtls1_clear_record_buffer(SSL *s)
{
    pitem *item;

    for (item = pqueue_pop(s->d1->sent_messages);
         item != NULL; item = pqueue_pop(s->d1->sent_messages)) {
        dtls1_hm_fragment_free((hm_fragment *)item->data);
        pitem_free(item);
    }
}

void dtls1_set_message_header(SSL *s, unsigned char *p,
                                        unsigned char mt, unsigned long len,
                                        unsigned long frag_off,
                                        unsigned long frag_len)
{
    /* Don't change sequence numbers while listening */
    if (frag_off == 0 && !s->d1->listen) {
        s->d1->handshake_write_seq = s->d1->next_handshake_write_seq;
        s->d1->next_handshake_write_seq++;
    }

    dtls1_set_message_header_int(s, mt, len, s->d1->handshake_write_seq,
                                 frag_off, frag_len);
}

/* don't actually do the writing, wait till the MTU has been retrieved */
static void
dtls1_set_message_header_int(SSL *s, unsigned char mt,
                             unsigned long len, unsigned short seq_num,
                             unsigned long frag_off, unsigned long frag_len)
{
    struct hm_header_st *msg_hdr = &s->d1->w_msg_hdr;

    msg_hdr->type = mt;
    msg_hdr->msg_len = len;
    msg_hdr->seq = seq_num;
    msg_hdr->frag_off = frag_off;
    msg_hdr->frag_len = frag_len;
}

static void
dtls1_fix_message_header(SSL *s, unsigned long frag_off,
                         unsigned long frag_len)
{
    struct hm_header_st *msg_hdr = &s->d1->w_msg_hdr;

    msg_hdr->frag_off = frag_off;
    msg_hdr->frag_len = frag_len;
}

static unsigned char *dtls1_write_message_header(SSL *s, unsigned char *p)
{
    struct hm_header_st *msg_hdr = &s->d1->w_msg_hdr;

    *p++ = msg_hdr->type;
    l2n3(msg_hdr->msg_len, p);

    s2n(msg_hdr->seq, p);
    l2n3(msg_hdr->frag_off, p);
    l2n3(msg_hdr->frag_len, p);

    return p;
}

unsigned int dtls1_link_min_mtu(void)
{
    return (g_probable_mtu[(sizeof(g_probable_mtu) /
                            sizeof(g_probable_mtu[0])) - 1]);
}

unsigned int dtls1_min_mtu(SSL *s)
{
    return dtls1_link_min_mtu() - BIO_dgram_get_mtu_overhead(SSL_get_wbio(s));
}

void
dtls1_get_message_header(unsigned char *data, struct hm_header_st *msg_hdr)
{
    memset(msg_hdr, 0x00, sizeof(struct hm_header_st));
    msg_hdr->type = *(data++);
    n2l3(data, msg_hdr->msg_len);

    n2s(data, msg_hdr->seq);
    n2l3(data, msg_hdr->frag_off);
    n2l3(data, msg_hdr->frag_len);
}

void dtls1_get_ccs_header(unsigned char *data, struct ccs_header_st *ccs_hdr)
{
    memset(ccs_hdr, 0x00, sizeof(struct ccs_header_st));

    ccs_hdr->type = *(data++);
}

int dtls1_shutdown(SSL *s)
{
    int ret;
#ifndef OPENSSL_NO_SCTP
    if (BIO_dgram_is_sctp(SSL_get_wbio(s)) &&
        !(s->shutdown & SSL_SENT_SHUTDOWN)) {
        ret = BIO_dgram_sctp_wait_for_dry(SSL_get_wbio(s));
        if (ret < 0)
            return -1;

        if (ret == 0)
            BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SCTP_SAVE_SHUTDOWN, 1,
                     NULL);
    }
#endif
    ret = ssl3_shutdown(s);
#ifndef OPENSSL_NO_SCTP
    BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SCTP_SAVE_SHUTDOWN, 0, NULL);
#endif
    return ret;
}

#ifndef OPENSSL_NO_HEARTBEATS
int dtls1_process_heartbeat(SSL *s, unsigned char *p, unsigned int length)
{
    unsigned char *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,
                        p, length, s, s->msg_callback_arg);

    /* Read type and payload length first */
    if (1 + 2 + 16 > length)
        return 0;               /* silently discard */
    if (length > SSL3_RT_MAX_PLAIN_LENGTH)
        return 0;               /* silently discard per RFC 6520 sec. 4 */

    hbtype = *p++;
    n2s(p, payload);
    if (1 + 2 + payload + 16 > length)
        return 0;               /* silently discard per RFC 6520 sec. 4 */
    pl = p;

    if (hbtype == TLS1_HB_REQUEST) {
        unsigned char *buffer, *bp;
        unsigned int write_length = 1 /* heartbeat type */  +
            2 /* heartbeat length */  +
            payload + padding;
        int r;

        if (write_length > SSL3_RT_MAX_PLAIN_LENGTH)
            return 0;

        /*
         * Allocate memory for the response, size is 1 byte message type,
         * plus 2 bytes payload length, plus payload, plus padding
         */
        buffer = OPENSSL_malloc(write_length);
        if (buffer == NULL)
            return -1;
        bp = buffer;

        /* Enter response type, length and copy payload */
        *bp++ = TLS1_HB_RESPONSE;
        s2n(payload, bp);
        memcpy(bp, pl, payload);
        bp += payload;
        /* Random padding */
        if (RAND_bytes(bp, padding) <= 0) {
            OPENSSL_free(buffer);
            return -1;
        }

        r = dtls1_write_bytes(s, TLS1_RT_HEARTBEAT, buffer, write_length);

        if (r >= 0 && s->msg_callback)
            s->msg_callback(1, s->version, TLS1_RT_HEARTBEAT,
                            buffer, write_length, 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) {
            dtls1_stop_timer(s);
            s->tlsext_hb_seq++;
            s->tlsext_hb_pending = 0;
        }
    }

    return 0;
}

int dtls1_heartbeat(SSL *s)
{
    unsigned char *buf, *p;
    int ret = -1;
    unsigned int payload = 18;  /* Sequence number + random bytes */
    unsigned int padding = 16;  /* Use minimum padding */

    /* Only send if peer supports and accepts HB requests... */
    if (!(s->tlsext_heartbeat & SSL_TLSEXT_HB_ENABLED) ||
        s->tlsext_heartbeat & SSL_TLSEXT_HB_DONT_SEND_REQUESTS) {
        SSLerr(SSL_F_DTLS1_HEARTBEAT, SSL_R_TLS_HEARTBEAT_PEER_DOESNT_ACCEPT);
        return -1;
    }

    /* ...and there is none in flight yet... */
    if (s->tlsext_hb_pending) {
        SSLerr(SSL_F_DTLS1_HEARTBEAT, SSL_R_TLS_HEARTBEAT_PENDING);
        return -1;
    }

    /* ...and no handshake in progress. */
    if (SSL_in_init(s) || s->in_handshake) {
        SSLerr(SSL_F_DTLS1_HEARTBEAT, SSL_R_UNEXPECTED_MESSAGE);
        return -1;
    }

    /*
     * Check if padding is too long, payload and padding must not exceed 2^14
     * - 3 = 16381 bytes in total.
     */
    OPENSSL_assert(payload + padding <= 16381);

    /*-
     * Create HeartBeat message, we just use a sequence number
     * as payload to distuingish different messages and add
     * some random stuff.
     *  - Message Type, 1 byte
     *  - Payload Length, 2 bytes (unsigned int)
     *  - Payload, the sequence number (2 bytes uint)
     *  - Payload, random bytes (16 bytes uint)
     *  - Padding
     */
    buf = OPENSSL_malloc(1 + 2 + payload + padding);
    if (buf == NULL) {
        SSLerr(SSL_F_DTLS1_HEARTBEAT, ERR_R_MALLOC_FAILURE);
        return -1;
    }
    p = buf;
    /* Message Type */
    *p++ = TLS1_HB_REQUEST;
    /* Payload length (18 bytes here) */
    s2n(payload, p);
    /* Sequence number */
    s2n(s->tlsext_hb_seq, p);
    /* 16 random bytes */
    if (RAND_bytes(p, 16) <= 0) {
        SSLerr(SSL_F_DTLS1_HEARTBEAT, ERR_R_INTERNAL_ERROR);
        goto err;
    }
    p += 16;
    /* Random padding */
    if (RAND_bytes(p, padding) <= 0) {
        SSLerr(SSL_F_DTLS1_HEARTBEAT, ERR_R_INTERNAL_ERROR);
        goto err;
    }

    ret = dtls1_write_bytes(s, TLS1_RT_HEARTBEAT, buf, 3 + payload + padding);
    if (ret >= 0) {
        if (s->msg_callback)
            s->msg_callback(1, s->version, TLS1_RT_HEARTBEAT,
                            buf, 3 + payload + padding,
                            s, s->msg_callback_arg);

        dtls1_start_timer(s);
        s->tlsext_hb_pending = 1;
    }

 err:
    OPENSSL_free(buf);

    return ret;
}
#endif