static int ssl_parse_client_psk_identity( mbedtls_ssl_context *ssl, unsigned char **p,
                                          const unsigned char *end )
{
    int ret = 0;
    uint16_t n;

    if( ssl_conf_has_psk_or_cb( ssl->conf ) == 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no pre-shared key" ) );
        return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
    }

    /*
     * Receive client pre-shared key identity name
     */
    if( end - *p < 2 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
    }

    n = ( (*p)[0] << 8 ) | (*p)[1];
    *p += 2;

    if( n == 0 || n > end - *p )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
    }

    if( ssl->conf->f_psk != NULL )
    {
        if( ssl->conf->f_psk( ssl->conf->p_psk, ssl, *p, n ) != 0 )
            ret = MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY;
    }
    else
    {
        /* Identity is not a big secret since clients send it in the clear,
         * but treat it carefully anyway, just in case */
        if( n != ssl->conf->psk_identity_len ||
            mbedtls_ct_memcmp( ssl->conf->psk_identity, *p, n ) != 0 )
        {
            ret = MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY;
        }
    }

    if( ret == MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY )
    {
        MBEDTLS_SSL_DEBUG_BUF( 3, "Unknown PSK identity", *p, n );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNKNOWN_PSK_IDENTITY );
        return( MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY );
    }

    *p += n;

    return( 0 );
}
static int ssl_parse_client_psk_identity( mbedtls_ssl_context *ssl, unsigned char **p,
                                          const unsigned char *end )
{
    int ret = 0;
    uint16_t n;

    if( ssl_conf_has_psk_or_cb( ssl->conf ) == 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no pre-shared key" ) );
        return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
    }

     
    if( end - *p < 2 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
    }

    n = ( (*p)[0] << 8 ) | (*p)[1];
    *p += 2;

    if( n == 0 || n > end - *p )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
    }

    if( ssl->conf->f_psk != NULL )
    {
        if( ssl->conf->f_psk( ssl->conf->p_psk, ssl, *p, n ) != 0 )
            ret = MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY;
    }
    else
    {
         
        if( n != ssl->conf->psk_identity_len ||
            mbedtls_ct_memcmp( ssl->conf->psk_identity, *p, n ) != 0 )
        {
            ret = MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY;
        }
    }

    if( ret == MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY )
    {
        MBEDTLS_SSL_DEBUG_BUF( 3, "Unknown PSK identity", *p, n );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNKNOWN_PSK_IDENTITY );
        return( MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY );
    }

    *p += n;

    return( 0 );
}