int dtls1_process_record(SSL *s, DTLS1_BITMAP *bitmap)
{
    int i, al;
    int enc_err;
    SSL_SESSION *sess;
    SSL3_RECORD *rr;
    unsigned int mac_size;
    unsigned char md[EVP_MAX_MD_SIZE];

    rr = RECORD_LAYER_get_rrec(&s->rlayer);
    sess = s->session;

    /*
     * At this point, s->packet_length == SSL3_RT_HEADER_LNGTH + rr->length,
     * and we have that many bytes in s->packet
     */
    rr->input = &(RECORD_LAYER_get_packet(&s->rlayer)[DTLS1_RT_HEADER_LENGTH]);

    /*
     * ok, we can now read from 's->packet' data into 'rr' rr->input points
     * at rr->length bytes, which need to be copied into rr->data by either
     * the decryption or by the decompression When the data is 'copied' into
     * the rr->data buffer, rr->input will be pointed at the new buffer
     */

    /*
     * We now have - encrypted [ MAC [ compressed [ plain ] ] ] rr->length
     * bytes of encrypted compressed stuff.
     */

    /* check is not needed I believe */
    if (rr->length > SSL3_RT_MAX_ENCRYPTED_LENGTH) {
        al = SSL_AD_RECORD_OVERFLOW;
        SSLerr(SSL_F_DTLS1_PROCESS_RECORD, SSL_R_ENCRYPTED_LENGTH_TOO_LONG);
        goto f_err;
    }

    /* decrypt in place in 'rr->input' */
    rr->data = rr->input;
    rr->orig_len = rr->length;

    enc_err = s->method->ssl3_enc->enc(s, rr, 1, 0);
    /*-
     * enc_err is:
     *    0: (in non-constant time) if the record is publically invalid.
     *    1: if the padding is valid
     *   -1: if the padding is invalid
     */
    if (enc_err == 0) {
        /* For DTLS we simply ignore bad packets. */
        rr->length = 0;
        RECORD_LAYER_reset_packet_length(&s->rlayer);
        goto err;
    }
#ifdef SSL_DEBUG
    printf("dec %d\n", rr->length);
    {
        unsigned int z;
        for (z = 0; z < rr->length; z++)
            printf("%02X%c", rr->data[z], ((z + 1) % 16) ? ' ' : '\n');
    }
    printf("\n");
#endif

    /* r->length is now the compressed data plus mac */
    if ((sess != NULL) &&
        (s->enc_read_ctx != NULL) && (EVP_MD_CTX_md(s->read_hash) != NULL)) {
        /* s->read_hash != NULL => mac_size != -1 */
        unsigned char *mac = NULL;
        unsigned char mac_tmp[EVP_MAX_MD_SIZE];
        mac_size = EVP_MD_CTX_size(s->read_hash);
        OPENSSL_assert(mac_size <= EVP_MAX_MD_SIZE);

        /*
         * orig_len is the length of the record before any padding was
         * removed. This is public information, as is the MAC in use,
         * therefore we can safely process the record in a different amount
         * of time if it's too short to possibly contain a MAC.
         */
        if (rr->orig_len < mac_size ||
            /* CBC records must have a padding length byte too. */
            (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
             rr->orig_len < mac_size + 1)) {
            al = SSL_AD_DECODE_ERROR;
            SSLerr(SSL_F_DTLS1_PROCESS_RECORD, SSL_R_LENGTH_TOO_SHORT);
            goto f_err;
        }

        if (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE) {
            /*
             * We update the length so that the TLS header bytes can be
             * constructed correctly but we need to extract the MAC in
             * constant time from within the record, without leaking the
             * contents of the padding bytes.
             */
            mac = mac_tmp;
            ssl3_cbc_copy_mac(mac_tmp, rr, mac_size);
            rr->length -= mac_size;
        } else {
            /*
             * In this case there's no padding, so |rec->orig_len| equals
             * |rec->length| and we checked that there's enough bytes for
             * |mac_size| above.
             */
            rr->length -= mac_size;
            mac = &rr->data[rr->length];
        }

        i = s->method->ssl3_enc->mac(s, rr, md, 0 /* not send */ );
        if (i < 0 || mac == NULL
            || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
            enc_err = -1;
        if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH + mac_size)
            enc_err = -1;
    }

    if (enc_err < 0) {
        /* decryption failed, silently discard message */
        rr->length = 0;
        RECORD_LAYER_reset_packet_length(&s->rlayer);
        goto err;
    }

    /* r->length is now just compressed */
    if (s->expand != NULL) {
        if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH) {
            al = SSL_AD_RECORD_OVERFLOW;
            SSLerr(SSL_F_DTLS1_PROCESS_RECORD,
                   SSL_R_COMPRESSED_LENGTH_TOO_LONG);
            goto f_err;
        }
        if (!ssl3_do_uncompress(s, rr)) {
            al = SSL_AD_DECOMPRESSION_FAILURE;
            SSLerr(SSL_F_DTLS1_PROCESS_RECORD, SSL_R_BAD_DECOMPRESSION);
            goto f_err;
        }
    }

    if (rr->length > SSL3_RT_MAX_PLAIN_LENGTH) {
        al = SSL_AD_RECORD_OVERFLOW;
        SSLerr(SSL_F_DTLS1_PROCESS_RECORD, SSL_R_DATA_LENGTH_TOO_LONG);
        goto f_err;
    }

    rr->off = 0;
    /*-
     * So at this point the following is true
     * ssl->s3->rrec.type   is the type of record
     * ssl->s3->rrec.length == number of bytes in record
     * ssl->s3->rrec.off    == offset to first valid byte
     * ssl->s3->rrec.data   == where to take bytes from, increment
     *                         after use :-).
     */

    /* we have pulled in a full packet so zero things */
    RECORD_LAYER_reset_packet_length(&s->rlayer);

    /* Mark receipt of record. */
    dtls1_record_bitmap_update(s, bitmap);

    return (1);

 f_err:
    ssl3_send_alert(s, SSL3_AL_FATAL, al);
 err:
    return (0);
}