static int ssl_scan_clienthello_tlsext(SSL *s, unsigned char **p,
                                       unsigned char *limit, int *al)
{
    unsigned short type;
    unsigned short size;
    unsigned short len;
    unsigned char *data = *p;
    int renegotiate_seen = 0;

    s->servername_done = 0;
    s->tlsext_status_type = -1;
# ifndef OPENSSL_NO_NEXTPROTONEG
    s->s3->next_proto_neg_seen = 0;
# endif

    if (s->s3->alpn_selected) {
        OPENSSL_free(s->s3->alpn_selected);
        s->s3->alpn_selected = NULL;
    }
    s->s3->alpn_selected_len = 0;
    if (s->cert->alpn_proposed) {
        OPENSSL_free(s->cert->alpn_proposed);
        s->cert->alpn_proposed = NULL;
    }
    s->cert->alpn_proposed_len = 0;
# ifndef OPENSSL_NO_HEARTBEATS
    s->tlsext_heartbeat &= ~(SSL_TLSEXT_HB_ENABLED |
                             SSL_TLSEXT_HB_DONT_SEND_REQUESTS);
# endif

# ifndef OPENSSL_NO_EC
    if (s->options & SSL_OP_SAFARI_ECDHE_ECDSA_BUG)
        ssl_check_for_safari(s, data, limit);
# endif                         /* !OPENSSL_NO_EC */

    /* Clear any signature algorithms extension received */
    if (s->cert->peer_sigalgs) {
        OPENSSL_free(s->cert->peer_sigalgs);
        s->cert->peer_sigalgs = NULL;
    }
# ifndef OPENSSL_NO_SRP
    if (s->srp_ctx.login != NULL) {
        OPENSSL_free(s->srp_ctx.login);
        s->srp_ctx.login = NULL;
    }
# endif

    s->srtp_profile = NULL;

    if (data == limit)
        goto ri_check;

    if (limit - data < 2)
        goto err;

    n2s(data, len);

    if (limit - data != len)
        goto err;

    while (limit - data >= 4) {
        n2s(data, type);
        n2s(data, size);

        if (limit - data < size)
            goto err;
# if 0
        fprintf(stderr, "Received extension type %d size %d\n", type, size);
# endif
        if (s->tlsext_debug_cb)
            s->tlsext_debug_cb(s, 0, type, data, size, s->tlsext_debug_arg);
/*-
 * The servername extension is treated as follows:
 *
 * - Only the hostname type is supported with a maximum length of 255.
 * - The servername is rejected if too long or if it contains zeros,
 *   in which case an fatal alert is generated.
 * - The servername field is maintained together with the session cache.
 * - When a session is resumed, the servername call back invoked in order
 *   to allow the application to position itself to the right context.
 * - The servername is acknowledged if it is new for a session or when
 *   it is identical to a previously used for the same session.
 *   Applications can control the behaviour.  They can at any time
 *   set a 'desirable' servername for a new SSL object. This can be the
 *   case for example with HTTPS when a Host: header field is received and
 *   a renegotiation is requested. In this case, a possible servername
 *   presented in the new client hello is only acknowledged if it matches
 *   the value of the Host: field.
 * - Applications must  use SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
 *   if they provide for changing an explicit servername context for the
 *   session, i.e. when the session has been established with a servername
 *   extension.
 * - On session reconnect, the servername extension may be absent.
 *
 */

        if (type == TLSEXT_TYPE_server_name) {
            unsigned char *sdata;
            int servname_type;
            int dsize;

            if (size < 2)
                goto err;
            n2s(data, dsize);
            size -= 2;
            if (dsize > size)
                goto err;

            sdata = data;
            while (dsize > 3) {
                servname_type = *(sdata++);
                n2s(sdata, len);
                dsize -= 3;

                if (len > dsize)
                    goto err;

                if (s->servername_done == 0)
                    switch (servname_type) {
                    case TLSEXT_NAMETYPE_host_name:
                        if (!s->hit) {
                            if (s->session->tlsext_hostname)
                                goto err;

                            if (len > TLSEXT_MAXLEN_host_name) {
                                *al = TLS1_AD_UNRECOGNIZED_NAME;
                                return 0;
                            }
                            if ((s->session->tlsext_hostname =
                                 OPENSSL_malloc(len + 1)) == NULL) {
                                *al = TLS1_AD_INTERNAL_ERROR;
                                return 0;
                            }
                            memcpy(s->session->tlsext_hostname, sdata, len);
                            s->session->tlsext_hostname[len] = '\0';
                            if (strlen(s->session->tlsext_hostname) != len) {
                                OPENSSL_free(s->session->tlsext_hostname);
                                s->session->tlsext_hostname = NULL;
                                *al = TLS1_AD_UNRECOGNIZED_NAME;
                                return 0;
                            }
                            s->servername_done = 1;

                        } else
                            s->servername_done = s->session->tlsext_hostname
                                && strlen(s->session->tlsext_hostname) == len
                                && strncmp(s->session->tlsext_hostname,
                                           (char *)sdata, len) == 0;

                        break;

                    default:
                        break;
                    }

                dsize -= len;
            }
            if (dsize != 0)
                goto err;

        }
# ifndef OPENSSL_NO_SRP
        else if (type == TLSEXT_TYPE_srp) {
            if (size == 0 || ((len = data[0])) != (size - 1))
                goto err;
            if (s->srp_ctx.login != NULL)
                goto err;
            if ((s->srp_ctx.login = OPENSSL_malloc(len + 1)) == NULL)
                return -1;
            memcpy(s->srp_ctx.login, &data[1], len);
            s->srp_ctx.login[len] = '\0';

            if (strlen(s->srp_ctx.login) != len)
                goto err;
        }
# endif

# ifndef OPENSSL_NO_EC
        else if (type == TLSEXT_TYPE_ec_point_formats) {
            unsigned char *sdata = data;
            int ecpointformatlist_length = *(sdata++);

            if (ecpointformatlist_length != size - 1 ||
                ecpointformatlist_length < 1)
                goto err;
            if (!s->hit) {
                if (s->session->tlsext_ecpointformatlist) {
                    OPENSSL_free(s->session->tlsext_ecpointformatlist);
                    s->session->tlsext_ecpointformatlist = NULL;
                }
                s->session->tlsext_ecpointformatlist_length = 0;
                if ((s->session->tlsext_ecpointformatlist =
                     OPENSSL_malloc(ecpointformatlist_length)) == NULL) {
                    *al = TLS1_AD_INTERNAL_ERROR;
                    return 0;
                }
                s->session->tlsext_ecpointformatlist_length =
                    ecpointformatlist_length;
                memcpy(s->session->tlsext_ecpointformatlist, sdata,
                       ecpointformatlist_length);
            }
#  if 0
            fprintf(stderr,
                    "ssl_parse_clienthello_tlsext s->session->tlsext_ecpointformatlist (length=%i) ",
                    s->session->tlsext_ecpointformatlist_length);
            sdata = s->session->tlsext_ecpointformatlist;
            for (i = 0; i < s->session->tlsext_ecpointformatlist_length; i++)
                fprintf(stderr, "%i ", *(sdata++));
            fprintf(stderr, "\n");
#  endif
        } else if (type == TLSEXT_TYPE_elliptic_curves) {
            unsigned char *sdata = data;
            int ellipticcurvelist_length = (*(sdata++) << 8);
            ellipticcurvelist_length += (*(sdata++));

            if (ellipticcurvelist_length != size - 2 ||
                ellipticcurvelist_length < 1 ||
                /* Each NamedCurve is 2 bytes. */
                ellipticcurvelist_length & 1)
                    goto err;

            if (!s->hit) {
                if (s->session->tlsext_ellipticcurvelist)
                    goto err;

                s->session->tlsext_ellipticcurvelist_length = 0;
                if ((s->session->tlsext_ellipticcurvelist =
                     OPENSSL_malloc(ellipticcurvelist_length)) == NULL) {
                    *al = TLS1_AD_INTERNAL_ERROR;
                    return 0;
                }
                s->session->tlsext_ellipticcurvelist_length =
                    ellipticcurvelist_length;
                memcpy(s->session->tlsext_ellipticcurvelist, sdata,
                       ellipticcurvelist_length);
            }
#  if 0
            fprintf(stderr,
                    "ssl_parse_clienthello_tlsext s->session->tlsext_ellipticcurvelist (length=%i) ",
                    s->session->tlsext_ellipticcurvelist_length);
            sdata = s->session->tlsext_ellipticcurvelist;
            for (i = 0; i < s->session->tlsext_ellipticcurvelist_length; i++)
                fprintf(stderr, "%i ", *(sdata++));
            fprintf(stderr, "\n");
#  endif
        }
# endif                         /* OPENSSL_NO_EC */
# ifdef TLSEXT_TYPE_opaque_prf_input
        else if (type == TLSEXT_TYPE_opaque_prf_input) {
            unsigned char *sdata = data;

            if (size < 2) {
                *al = SSL_AD_DECODE_ERROR;
                return 0;
            }
            n2s(sdata, s->s3->client_opaque_prf_input_len);
            if (s->s3->client_opaque_prf_input_len != size - 2) {
                *al = SSL_AD_DECODE_ERROR;
                return 0;
            }

            if (s->s3->client_opaque_prf_input != NULL) {
                /* shouldn't really happen */
                OPENSSL_free(s->s3->client_opaque_prf_input);
            }

            /* dummy byte just to get non-NULL */
            if (s->s3->client_opaque_prf_input_len == 0)
                s->s3->client_opaque_prf_input = OPENSSL_malloc(1);
            else
                s->s3->client_opaque_prf_input =
                    BUF_memdup(sdata, s->s3->client_opaque_prf_input_len);
            if (s->s3->client_opaque_prf_input == NULL) {
                *al = TLS1_AD_INTERNAL_ERROR;
                return 0;
            }
        }
# endif
        else if (type == TLSEXT_TYPE_session_ticket) {
            if (s->tls_session_ticket_ext_cb &&
                !s->tls_session_ticket_ext_cb(s, data, size,
                                              s->tls_session_ticket_ext_cb_arg))
            {
                *al = TLS1_AD_INTERNAL_ERROR;
                return 0;
            }
        } else if (type == TLSEXT_TYPE_renegotiate) {
            if (!ssl_parse_clienthello_renegotiate_ext(s, data, size, al))
                return 0;
            renegotiate_seen = 1;
        } else if (type == TLSEXT_TYPE_signature_algorithms) {
            int dsize;
            if (s->cert->peer_sigalgs || size < 2)
                goto err;
            n2s(data, dsize);
            size -= 2;
            if (dsize != size || dsize & 1 || !dsize)
                goto err;
            if (!tls1_save_sigalgs(s, data, dsize))
                goto err;
        } else if (type == TLSEXT_TYPE_status_request) {

            if (size < 5)
                goto err;

            s->tlsext_status_type = *data++;
            size--;
            if (s->tlsext_status_type == TLSEXT_STATUSTYPE_ocsp) {
                const unsigned char *sdata;
                int dsize;
                /* Read in responder_id_list */
                n2s(data, dsize);
                size -= 2;
                if (dsize > size)
                    goto err;
                while (dsize > 0) {
                    OCSP_RESPID *id;
                    int idsize;
                    if (dsize < 4)
                        goto err;
                    n2s(data, idsize);
                    dsize -= 2 + idsize;
                    size -= 2 + idsize;
                    if (dsize < 0)
                        goto err;
                    sdata = data;
                    data += idsize;
                    id = d2i_OCSP_RESPID(NULL, &sdata, idsize);
                    if (!id)
                        goto err;
                    if (data != sdata) {
                        OCSP_RESPID_free(id);
                        goto err;
                    }
                    if (!s->tlsext_ocsp_ids
                        && !(s->tlsext_ocsp_ids =
                             sk_OCSP_RESPID_new_null())) {
                        OCSP_RESPID_free(id);
                        *al = SSL_AD_INTERNAL_ERROR;
                        return 0;
                    }
                    if (!sk_OCSP_RESPID_push(s->tlsext_ocsp_ids, id)) {
                        OCSP_RESPID_free(id);
                        *al = SSL_AD_INTERNAL_ERROR;
                        return 0;
                    }
                }

                /* Read in request_extensions */
                if (size < 2)
                    goto err;
                n2s(data, dsize);
                size -= 2;
                if (dsize != size)
                    goto err;
                sdata = data;
                if (dsize > 0) {
                    if (s->tlsext_ocsp_exts) {
                        sk_X509_EXTENSION_pop_free(s->tlsext_ocsp_exts,
                                                   X509_EXTENSION_free);
                    }

                    s->tlsext_ocsp_exts =
                        d2i_X509_EXTENSIONS(NULL, &sdata, dsize);
                    if (!s->tlsext_ocsp_exts || (data + dsize != sdata))
                        goto err;
                }
            }
            /*
             * We don't know what to do with any other type * so ignore it.
             */
            else
                s->tlsext_status_type = -1;
        }
# ifndef OPENSSL_NO_HEARTBEATS
        else if (type == TLSEXT_TYPE_heartbeat) {
            switch (data[0]) {
            case 0x01:         /* Client allows us to send HB requests */
                s->tlsext_heartbeat |= SSL_TLSEXT_HB_ENABLED;
                break;
            case 0x02:         /* Client doesn't accept HB requests */
                s->tlsext_heartbeat |= SSL_TLSEXT_HB_ENABLED;
                s->tlsext_heartbeat |= SSL_TLSEXT_HB_DONT_SEND_REQUESTS;
                break;
            default:
                *al = SSL_AD_ILLEGAL_PARAMETER;
                return 0;
            }
        }
# endif
# ifndef OPENSSL_NO_NEXTPROTONEG
        else if (type == TLSEXT_TYPE_next_proto_neg &&
                 s->s3->tmp.finish_md_len == 0) {
            /*-
             * We shouldn't accept this extension on a
             * renegotiation.
             *
             * s->new_session will be set on renegotiation, but we
             * probably shouldn't rely that it couldn't be set on
             * the initial renegotation too in certain cases (when
             * there's some other reason to disallow resuming an
             * earlier session -- the current code won't be doing
             * anything like that, but this might change).
             *
             * A valid sign that there's been a previous handshake
             * in this connection is if s->s3->tmp.finish_md_len >
             * 0.  (We are talking about a check that will happen
             * in the Hello protocol round, well before a new
             * Finished message could have been computed.)
             */
            s->s3->next_proto_neg_seen = 1;
        }
# endif

        else if (type == TLSEXT_TYPE_application_layer_protocol_negotiation &&
                 s->s3->tmp.finish_md_len == 0) {
            if (tls1_alpn_handle_client_hello(s, data, size, al) != 0)
                return 0;
        }

        /* session ticket processed earlier */
# ifndef OPENSSL_NO_SRTP
        else if (SSL_IS_DTLS(s) && SSL_get_srtp_profiles(s)
                 && type == TLSEXT_TYPE_use_srtp) {
            if (ssl_parse_clienthello_use_srtp_ext(s, data, size, al))
                return 0;
        }
# endif

        data += size;
    }

    /* Spurious data on the end */
    if (data != limit)
        goto err;

    *p = data;

 ri_check:

    /* Need RI if renegotiating */

    if (!renegotiate_seen && s->renegotiate &&
        !(s->options & SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION)) {
        *al = SSL_AD_HANDSHAKE_FAILURE;
        SSLerr(SSL_F_SSL_SCAN_CLIENTHELLO_TLSEXT,
               SSL_R_UNSAFE_LEGACY_RENEGOTIATION_DISABLED);
        return 0;
    }

    return 1;
err:
    *al = SSL_AD_DECODE_ERROR;
    return 0;
}