[strongswan.git] / src / charon / encoding / generator.c

/**
 * @file generator.c
 *
 * @brief Implementation of generator_t.
 *
 */

/*
 * Copyright (C) 2005-2006 Martin Willi
 * Copyright (C) 2005 Jan Hutter
 * Hochschule fuer Technik Rapperswil
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 */

#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <stdio.h>


#include "generator.h"

#include <library.h>
#include <daemon.h>
#include <utils/linked_list.h>
#include <encoding/payloads/payload.h>
#include <encoding/payloads/proposal_substructure.h>
#include <encoding/payloads/transform_substructure.h>
#include <encoding/payloads/sa_payload.h>
#include <encoding/payloads/ke_payload.h>
#include <encoding/payloads/notify_payload.h>
#include <encoding/payloads/nonce_payload.h>
#include <encoding/payloads/id_payload.h>
#include <encoding/payloads/auth_payload.h>
#include <encoding/payloads/cert_payload.h>
#include <encoding/payloads/certreq_payload.h>
#include <encoding/payloads/ts_payload.h>
#include <encoding/payloads/delete_payload.h>
#include <encoding/payloads/vendor_id_payload.h>
#include <encoding/payloads/cp_payload.h>
#include <encoding/payloads/configuration_attribute.h>
#include <encoding/payloads/eap_payload.h>


typedef struct private_generator_t private_generator_t;

/**
 * Private part of a generator_t object.
 */
struct private_generator_t {
        /**
         * Public part of a generator_t object.
         */
         generator_t public;
         
        /**
         * Generates a U_INT-Field type and writes it to buffer.
         *
         * @param this                                  private_generator_t object
         * @param int_type                              type of U_INT field (U_INT_4, U_INT_8, etc.)
         *                                                              ATTRIBUTE_TYPE is also generated in this function
         * @param offset                                offset of value in data struct
         * @param generator_contexts    generator_contexts_t object where the context is written or read from
         * @return
         *                                                      - SUCCESS
         *                                                              - FAILED if allignment is wrong
         */
        void (*generate_u_int_type) (private_generator_t *this,encoding_type_t int_type,u_int32_t offset);

        /**
         * Get size of current buffer in bytes.
         *
         * @param this                                  private_generator_t object
         * @return                                              Size of buffer in bytes
         */
        size_t (*get_current_buffer_size) (private_generator_t *this);
        
        /**
         * Get free space of current buffer in bytes.
         *
         * @param this                                  private_generator_t object
         * @return                                              space in buffer in bytes
         */
        size_t (*get_current_buffer_space) (private_generator_t *this);

        /**
         * Get length of data in buffer (in bytes).
         *
         * @param this                                  private_generator_t object
         * @return                                              length of data in bytes
         */     
        size_t (*get_current_data_length) (private_generator_t *this);

        /**
         * Get current offset in buffer (in bytes).
         *
         * @param this                                  private_generator_t object
         * @return                                              offset in bytes
         */     
        u_int32_t (*get_current_buffer_offset) (private_generator_t *this);
        
        /**
         * Generates a RESERVED BIT field or a RESERVED BYTE field and writes 
         * it to the buffer.
         *
         * @param this                                  private_generator_t object
         * @param generator_contexts    generator_contexts_t object where the context is written or read from
         * @param bits                                  number of bits to generate
         */
        void (*generate_reserved_field) (private_generator_t *this,int bits);
        
        /**
         * Generates a FLAG field.
         *
         * @param this                                  private_generator_t object
         * @param generator_contexts    generator_contexts_t object where the context is written or read from
         * @param offset                                offset of flag value in data struct
         */
        void (*generate_flag) (private_generator_t *this,u_int32_t offset);
        
        /**
         * Writes the current buffer content into a chunk_t.
         * 
         * Memory of specific chunk_t gets allocated.
         *
         * @param this                          calling private_generator_t object
         * @param data                          pointer of chunk_t to write to
         */
        void (*write_chunk) (private_generator_t *this,chunk_t *data);
        
        /**
         * Generates a bytestream from a chunk_t.
         *
         * @param this                          private_generator_t object
         * @param offset                        offset of chunk_t value in data struct
         */
        void (*generate_from_chunk) (private_generator_t *this,u_int32_t offset);       

        /**
         * Makes sure enough space is available in buffer to store amount of bits.
     *
         * If buffer is to small to hold the specific amount of bits it 
         * is increased using reallocation function of allocator.
         *
         * @param this                          calling private_generator_t object
         * @param bits                          number of bits to make available in buffer
         */
        void (*make_space_available) (private_generator_t *this,size_t bits);

        /**
         * Writes a specific amount of byte into the buffer.
         * 
         * If buffer is to small to hold the specific amount of bytes it 
         * is increased.
         *
         * @param this                          calling private_generator_t object
         * @param bytes                         pointer to bytes to write
         * @param number_of_bytes       number of bytes to write into buffer
         */
        void (*write_bytes_to_buffer) (private_generator_t *this,void * bytes,size_t number_of_bytes);
        
        
        /**
         * Writes a specific amount of byte into the buffer at a specific offset.
         * 
         * @warning buffer size is not check to hold the data if offset is to large.
         *
         * @param this                          calling private_generator_t object
         * @param bytes                         pointer to bytes to write
         * @param number_of_bytes       number of bytes to write into buffer
         * @param offset                        offset to write the data into
         */
        void (*write_bytes_to_buffer_at_offset) (private_generator_t *this,void * bytes,size_t number_of_bytes,u_int32_t offset);
        
        /**
         * Buffer used to generate the data into.
         */
        u_int8_t *buffer;

        /**
         * Current write position in buffer (one byte aligned).
         */
        u_int8_t *out_position;

        /**
         * Position of last byte in buffer.
         */
        u_int8_t *roof_position;

        /**
         * Current bit writing to in current byte (between 0 and 7).
         */
        size_t current_bit;

        /**
         * Associated data struct to read informations from.
         */
        void * data_struct;
        
        /*
         * Last payload length position offset in the buffer.
         */
        u_int32_t last_payload_length_position_offset;
        
        /**
         * Offset of the header length field in the buffer.
         */
        u_int32_t header_length_position_offset;
        
        /**
         * Last SPI size.
         */
        u_int8_t last_spi_size;
        
        /**
         * Attribute format of the last generated transform attribute.
         *
         * Used to check if a variable value field is used or not for 
         * the transform attribute value.
         */
        bool attribute_format;
        
        /**
         * Depending on the value of attribute_format this field is used
         * to hold the length of the transform attribute in bytes.
         */
        u_int16_t attribute_length;
};

/**
 * Implementation of private_generator_t.get_current_buffer_size.
 */
static size_t get_current_buffer_size (private_generator_t *this)
{
        return ((this->roof_position) - (this->buffer));
}

/**
 * Implementation of private_generator_t.get_current_buffer_space.
 */
static size_t get_current_buffer_space (private_generator_t *this)
{
        /* we know, one byte more */
        size_t space = (this->roof_position) - (this->out_position);
        return (space);
}

/**
 * Implementation of private_generator_t.get_current_data_length.
 */
static size_t get_current_data_length (private_generator_t *this)
{
        return (this->out_position - this->buffer);
}

/**
 * Implementation of private_generator_t.get_current_buffer_offset.
 */
static u_int32_t get_current_buffer_offset (private_generator_t *this)
{
        return (this->out_position - this->buffer);
}

/**
 * Implementation of private_generator_t.generate_u_int_type.
 */
static void generate_u_int_type (private_generator_t *this,encoding_type_t int_type,u_int32_t offset)
{
        size_t number_of_bits = 0;

        /* find out number of bits of each U_INT type to check for enough space 
           in buffer */
        switch (int_type)
        {
                        case U_INT_4:
                                number_of_bits = 4;
                                break;
                        case TS_TYPE:
                        case U_INT_8:
                                number_of_bits = 8;
                                break;
                        case U_INT_16:
                        case CONFIGURATION_ATTRIBUTE_LENGTH:
                                number_of_bits = 16;
                                break;
                        case U_INT_32:
                                number_of_bits = 32;
                                break;
                        case U_INT_64:
                                number_of_bits = 64;
                                break;
                        case ATTRIBUTE_TYPE:
                                number_of_bits = 15;
                                break;
                        case IKE_SPI:
                                number_of_bits = 64;
                                break;

                        default:
                        DBG1(DBG_ENC, "U_INT Type %N is not supported",
                                 encoding_type_names, int_type);

                        return;
        }
        /* U_INT Types of multiple then 8 bits must be aligned */
        if (((number_of_bits % 8) == 0) && (this->current_bit != 0))
        {
                DBG1(DBG_ENC, "U_INT Type %N is not 8 Bit aligned",
                         encoding_type_names, int_type);
                /* current bit has to be zero for values multiple of 8 bits */
                return;
        }
        
        /* make sure enough space is available in buffer */
        this->make_space_available(this,number_of_bits);
        /* now handle each u int type differently */
        switch (int_type)
        {
                case U_INT_4:
                {
                        if (this->current_bit == 0)
                        {
                                /* highval of current byte in buffer has to be set to the new value*/
                                u_int8_t high_val = *((u_int8_t *)(this->data_struct + offset)) << 4;
                                /* lowval in buffer is not changed */
                                u_int8_t low_val = *(this->out_position) & 0x0F;
                                /* highval is set, low_val is not changed */
                                *(this->out_position) = high_val | low_val;
                                DBG3(DBG_ENC, "   => %d", *(this->out_position));
                                /* write position is not changed, just bit position is moved */
                                this->current_bit = 4;
                        }
                        else if (this->current_bit == 4)
                        {
                                /* highval in buffer is not changed */
                                u_int high_val = *(this->out_position) & 0xF0;
                                /* lowval of current byte in buffer has to be set to the new value*/
                                u_int low_val = *((u_int8_t *)(this->data_struct + offset)) & 0x0F;
                                *(this->out_position) = high_val | low_val;
                                DBG3(DBG_ENC, "   => %d", *(this->out_position));
                                this->out_position++;
                                this->current_bit = 0;

                        }
                        else
                        {
                                DBG1(DBG_ENC, "U_INT_4 Type is not 4 Bit aligned");
                                /* 4 Bit integers must have a 4 bit alignment */
                                return;
                        };
                        break;
                }
                case TS_TYPE:
                case U_INT_8:
                {
                        /* 8 bit values are written as they are */
                        *this->out_position = *((u_int8_t *)(this->data_struct + offset));
                        DBG3(DBG_ENC, "   => %d", *(this->out_position));
                        this->out_position++;
                        break;

                }
                case ATTRIBUTE_TYPE:
                {
                        /* attribute type must not change first bit uf current byte ! */
                        if (this->current_bit != 1)
                        {
                                DBG1(DBG_ENC, "ATTRIBUTE FORMAT flag is not set");
                                /* first bit has to be set! */
                                return;
                        }
                        /* get value of attribute format flag */
                        u_int8_t attribute_format_flag = *(this->out_position) & 0x80;
                        /* get attribute type value as 16 bit integer*/
                        u_int16_t int16_val = htons(*((u_int16_t*)(this->data_struct + offset)));
                        /* last bit must be unset */
                        int16_val = int16_val & 0xFF7F;
                        
                        int16_val = int16_val | attribute_format_flag;
                        DBG3(DBG_ENC, "   => %d", int16_val);
                        /* write bytes to buffer (set bit is overwritten)*/                             
                        this->write_bytes_to_buffer(this,&int16_val,sizeof(u_int16_t));
                        this->current_bit = 0;
                        break;
                        
                }
                case U_INT_16:
                case CONFIGURATION_ATTRIBUTE_LENGTH:
                {
                        u_int16_t int16_val = htons(*((u_int16_t*)(this->data_struct + offset)));
                        DBG3(DBG_ENC, "   => %b", (void*)&int16_val, sizeof(int16_val));
                        this->write_bytes_to_buffer(this,&int16_val,sizeof(u_int16_t));
                        break;
                }
                case U_INT_32:
                {
                        u_int32_t int32_val = htonl(*((u_int32_t*)(this->data_struct + offset)));
                        DBG3(DBG_ENC, "   => %b", (void*)&int32_val, sizeof(int32_val));
                        this->write_bytes_to_buffer(this,&int32_val,sizeof(u_int32_t));
                        break;
                }
                case U_INT_64:
                {
                        /* 64 bit integers are written as two 32 bit integers */
                        u_int32_t int32_val_low = htonl(*((u_int32_t*)(this->data_struct + offset)));
                        u_int32_t int32_val_high = htonl(*((u_int32_t*)(this->data_struct + offset) + 1));
                        DBG3(DBG_ENC, "   => %b %b",
                                 (void*)&int32_val_low, sizeof(int32_val_low),
                                 (void*)&int32_val_high, sizeof(int32_val_high));
                        /* TODO add support for big endian machines */
                        this->write_bytes_to_buffer(this,&int32_val_high,sizeof(u_int32_t));
                        this->write_bytes_to_buffer(this,&int32_val_low,sizeof(u_int32_t));
                        break;
                }
                
                case IKE_SPI:
                {
                        /* 64 bit are written as they come :-) */
                        this->write_bytes_to_buffer(this,(this->data_struct + offset),sizeof(u_int64_t));
                        DBG3(DBG_ENC, "   => %b", (void*)(this->data_struct + offset), sizeof(u_int64_t));
                        break;
                }
                default:
                {
                        DBG1(DBG_ENC, "U_INT Type %N is not supported",
                                 encoding_type_names, int_type);
                        return;
                }
        }
}

/**
 * Implementation of private_generator_t.generate_reserved_field.
 */
static void generate_reserved_field(private_generator_t *this,int bits)
{
        /* only one bit or 8 bit fields are supported */
        if ((bits != 1) && (bits != 8))
        {
                DBG1(DBG_ENC, "reserved field of %d bits cannot be generated", bits);
                return ;
        }
        /* make sure enough space is available in buffer */
        this->make_space_available(this,bits);
        
        if (bits == 1)
        {       
                /* one bit processing */
                u_int8_t reserved_bit = ~(1 << (7 - this->current_bit));
                *(this->out_position) = *(this->out_position) & reserved_bit;
                if (this->current_bit == 0)
                {
                        /* memory must be zero */
                        *(this->out_position) = 0x00;
                }


                this->current_bit++;
                if (this->current_bit >= 8)
                {
                        this->current_bit = this->current_bit % 8;
                        this->out_position++;
                }
        }
        else
        {
                /* one byte processing*/
                if (this->current_bit > 0)
                {
                        DBG1(DBG_ENC, "reserved field cannot be written cause "
                                 "alignement of current bit is %d", this->current_bit);
                        return;
                }
                *(this->out_position) = 0x00;
                this->out_position++;
        }
}

/**
 * Implementation of private_generator_t.generate_flag.
 */
static void generate_flag (private_generator_t *this,u_int32_t offset)
{
        /* value of current flag */
        u_int8_t flag_value;
        /* position of flag in current byte */
        u_int8_t flag;
        
        /* if the value in the data_struct is TRUE, flag_value is set to 1, 0 otherwise */
        flag_value = (*((bool *) (this->data_struct + offset))) ? 1 : 0;
        /* get flag position */
        flag = (flag_value << (7 - this->current_bit));
        
        /* make sure one bit is available in buffer */
        this->make_space_available(this,1);
        if (this->current_bit == 0)
        {
                /* memory must be zero */
                *(this->out_position) = 0x00;
        }

        *(this->out_position) = *(this->out_position) | flag;
        
        
        DBG3(DBG_ENC, "   => %d", *(this->out_position));

        this->current_bit++;
        if (this->current_bit >= 8)
        {
                this->current_bit = this->current_bit % 8;
                this->out_position++;
        }
}

/**
 * Implementation of private_generator_t.generate_from_chunk.
 */
static void generate_from_chunk (private_generator_t *this,u_int32_t offset)
{
        if (this->current_bit != 0)
        {
                DBG1(DBG_ENC, "can not generate a chunk at Bitpos %d", this->current_bit);
                return ;
        }
        
        /* position in buffer */
        chunk_t *attribute_value = (chunk_t *)(this->data_struct + offset);
        
        DBG3(DBG_ENC, "   => %B", attribute_value);
        
        /* use write_bytes_to_buffer function to do the job */
        this->write_bytes_to_buffer(this,attribute_value->ptr,attribute_value->len);
}

/**
 * Implementation of private_generator_t.make_space_available.
 */
static void make_space_available (private_generator_t *this, size_t bits)
{
        while (((this->get_current_buffer_space(this) * 8) - this->current_bit) < bits)
        {
                /* must increase buffer */
                size_t old_buffer_size = this->get_current_buffer_size(this);
                size_t new_buffer_size = old_buffer_size + GENERATOR_DATA_BUFFER_INCREASE_VALUE;
                size_t out_position_offset = ((this->out_position) - (this->buffer));

                DBG2(DBG_ENC, "increased gen buffer from %d to %d byte", 
                         old_buffer_size, new_buffer_size);
                
                /* Reallocate space for new buffer */
                this->buffer = realloc(this->buffer,new_buffer_size);

                this->out_position = (this->buffer + out_position_offset);
                this->roof_position = (this->buffer + new_buffer_size);
        }
}

/**
 * Implementation of private_generator_t.write_bytes_to_buffer.
 */
static void write_bytes_to_buffer (private_generator_t *this,void * bytes, size_t number_of_bytes)
{
        int i;
        u_int8_t *read_position = (u_int8_t *) bytes;
        
        this->make_space_available(this,number_of_bytes * 8);

        for (i = 0; i < number_of_bytes; i++)
        {
                *(this->out_position) = *(read_position);
                read_position++;
                this->out_position++;
        }
}

/**
 * Implementation of private_generator_t.write_bytes_to_buffer_at_offset.
 */
static void write_bytes_to_buffer_at_offset (private_generator_t *this,void * bytes,size_t number_of_bytes,u_int32_t offset)
{
        int i;
        u_int8_t *read_position = (u_int8_t *) bytes;
        u_int8_t *write_position;
        u_int32_t free_space_after_offset = (this->get_current_buffer_size(this) - offset);

        /* check first if enough space for new data is available */     
        if (number_of_bytes > free_space_after_offset)
        {
                this->make_space_available(this,(number_of_bytes - free_space_after_offset) * 8);
        }
        
        write_position = this->buffer + offset;
        for (i = 0; i < number_of_bytes; i++)
        {
                *(write_position) = *(read_position);
                read_position++;
                write_position++;
        }
}

/**
 * Implementation of private_generator_t.write_to_chunk.
 */
static void write_to_chunk (private_generator_t *this,chunk_t *data)
{
        size_t data_length = this->get_current_data_length(this);
        u_int32_t header_length_field = data_length;
        
        /* write length into header length field */
        if (this->header_length_position_offset > 0)
        {
                u_int32_t int32_val = htonl(header_length_field);
                this->write_bytes_to_buffer_at_offset(this,&int32_val,sizeof(u_int32_t),this->header_length_position_offset);
        }

        if (this->current_bit > 0)
        data_length++;
        data->ptr = malloc(data_length);
        memcpy(data->ptr,this->buffer,data_length);
        data->len = data_length;
        
        DBG3(DBG_ENC, "generated data of this generator %B", data);
}

/**
 * Implementation of private_generator_t.generate_payload.
 */
static void generate_payload (private_generator_t *this,payload_t *payload)
{
        int i;
        this->data_struct = payload;
        size_t rule_count;
        encoding_rule_t *rules;
        payload_type_t payload_type;
        u_int8_t *payload_start;
        
        /* get payload type */
        payload_type = payload->get_type(payload);
        /* spi size has to get reseted */
        this->last_spi_size = 0;
        
        payload_start = this->out_position;
        
        DBG2(DBG_ENC, "generating payload of type %N",
                 payload_type_names, payload_type);
        
        /* each payload has its own encoding rules */
        payload->get_encoding_rules(payload,&rules,&rule_count);

        for (i = 0; i < rule_count;i++)
        {
                DBG2(DBG_ENC, "  generating rule %d %N",
                         i, encoding_type_names, rules[i].type);
                switch (rules[i].type)
                {
                        /* all u int values, IKE_SPI,TS_TYPE and ATTRIBUTE_TYPE are generated in generate_u_int_type */
                        case U_INT_4:
                        case U_INT_8:
                        case U_INT_16:
                        case U_INT_32:
                        case U_INT_64:
                        case IKE_SPI:
                        case TS_TYPE:
                        case ATTRIBUTE_TYPE:
                        case CONFIGURATION_ATTRIBUTE_LENGTH:
                        {
                                this->generate_u_int_type(this,rules[i].type,rules[i].offset);
                                break;
                        }
                        case RESERVED_BIT:
                        {
                                this->generate_reserved_field(this,1);
                                break;
                        }
                        case RESERVED_BYTE:
                        {
                                this->generate_reserved_field(this,8);
                                break;
                        } 
                        case FLAG:
                        {
                                this->generate_flag(this,rules[i].offset);
                                break;
                        }
                        case PAYLOAD_LENGTH:
                        {
                                /* position of payload lenght field is temporary stored */
                                this->last_payload_length_position_offset = this->get_current_buffer_offset(this);
                                /* payload length is generated like an U_INT_16 */
                                this->generate_u_int_type(this,U_INT_16,rules[i].offset);
                                break;
                        }
                        case HEADER_LENGTH:
                        {
                                /* position of header length field is temporary stored */                       
                                this->header_length_position_offset = this->get_current_buffer_offset(this);    
                                /* header length is generated like an U_INT_32 */
                                this->generate_u_int_type(this,U_INT_32,rules[i].offset);
                                break;
                        }
                        case SPI_SIZE:
                                /* spi size is handled as 8 bit unsigned integer */
                                this->generate_u_int_type(this,U_INT_8,rules[i].offset);
                                /* last spi size is temporary stored */
                                this->last_spi_size = *((u_int8_t *)(this->data_struct + rules[i].offset));
                                break;
                        case ADDRESS:
                        {
                                /* the Address value is generated from chunk */
                                this->generate_from_chunk(this,rules[i].offset);
                                break;
                        }
                        case SPI:
                        {
                                /* the SPI value is generated from chunk */
                                this->generate_from_chunk(this,rules[i].offset);
                                break;
                        }
                        case KEY_EXCHANGE_DATA:
                        case NOTIFICATION_DATA:
                        case NONCE_DATA:
                        case ID_DATA:
                        case AUTH_DATA:
                        case CERT_DATA:
                        case CERTREQ_DATA:
                        case SPIS:
                        case CONFIGURATION_ATTRIBUTE_VALUE:
                        case VID_DATA:
                        case EAP_MESSAGE:
                        {
                                u_int32_t payload_length_position_offset;
                                u_int16_t length_of_payload;
                                u_int16_t header_length = 0;
                                u_int16_t length_in_network_order;

                                switch(rules[i].type)
                                {
                                        case KEY_EXCHANGE_DATA:
                                                header_length = KE_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case NOTIFICATION_DATA:
                                                header_length = NOTIFY_PAYLOAD_HEADER_LENGTH + this->last_spi_size ;
                                                break;
                                        case NONCE_DATA:
                                                header_length = NONCE_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case ID_DATA:
                                                header_length = ID_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case AUTH_DATA:
                                                header_length = AUTH_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case CERT_DATA:
                                                header_length = CERT_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case CERTREQ_DATA:
                                                header_length = CERTREQ_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case SPIS:
                                                header_length = DELETE_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case VID_DATA:
                                                header_length = VENDOR_ID_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        case CONFIGURATION_ATTRIBUTE_VALUE:
                                                header_length = CONFIGURATION_ATTRIBUTE_HEADER_LENGTH;
                                                break;
                                        case EAP_MESSAGE:
                                                header_length = EAP_PAYLOAD_HEADER_LENGTH;
                                                break;
                                        default:
                                                break;
                                }
                                
                                /* the data value is generated from chunk */
                                this->generate_from_chunk(this,rules[i].offset);

                                payload_length_position_offset = this->last_payload_length_position_offset;
                                
                                
                                /* Length of payload is calculated */
                                length_of_payload = header_length + ((chunk_t *)(this->data_struct + rules[i].offset))->len;

                                length_in_network_order = htons(length_of_payload);                     
                                this->write_bytes_to_buffer_at_offset(this,&length_in_network_order,sizeof(u_int16_t),payload_length_position_offset);
                                break;
                        }
                        case PROPOSALS:
                        {
                                /* before iterative generate the transforms, store the current payload length position */
                                u_int32_t payload_length_position_offset = this->last_payload_length_position_offset;
                                /* Length of SA_PAYLOAD is calculated */
                                u_int16_t length_of_sa_payload = SA_PAYLOAD_HEADER_LENGTH;
                                u_int16_t int16_val;
                                /* proposals are stored in a linked list and so accessed */
                                linked_list_t *proposals = *((linked_list_t **)(this->data_struct + rules[i].offset));
                                iterator_t *iterator;
                                payload_t *current_proposal;
                                
                                /* create forward iterator */
                                iterator = proposals->create_iterator(proposals,TRUE);
                                /* every proposal is processed (iterative call )*/
                                while (iterator->iterate(iterator, (void**)&current_proposal))
                                {
                                        u_int32_t before_generate_position_offset;
                                        u_int32_t after_generate_position_offset;
                                        
                                        before_generate_position_offset = this->get_current_buffer_offset(this);
                                        this->public.generate_payload(&(this->public),current_proposal);
                                        after_generate_position_offset = this->get_current_buffer_offset(this);
                                        
                                        /* increase size of transform */
                                        length_of_sa_payload += (after_generate_position_offset - before_generate_position_offset);
                                }
                                iterator->destroy(iterator);
                                
                                int16_val = htons(length_of_sa_payload);
                                this->write_bytes_to_buffer_at_offset(this,&int16_val,sizeof(u_int16_t),payload_length_position_offset);
                                break;
                        }
                        case TRANSFORMS:
                        {
                                /* before iterative generate the transforms, store the current length position */
                                u_int32_t payload_length_position_offset = this->last_payload_length_position_offset;
                                u_int16_t length_of_proposal = PROPOSAL_SUBSTRUCTURE_HEADER_LENGTH + this->last_spi_size;
                                u_int16_t int16_val;
                                linked_list_t *transforms = *((linked_list_t **)(this->data_struct + rules[i].offset));
                                iterator_t *iterator;
                                payload_t *current_transform;
                                
                                /* create forward iterator */
                                iterator = transforms->create_iterator(transforms,TRUE);
                                while (iterator->iterate(iterator, (void**)&current_transform))
                                {
                                        u_int32_t before_generate_position_offset;
                                        u_int32_t after_generate_position_offset;
                                        
                                        before_generate_position_offset = this->get_current_buffer_offset(this);
                                        this->public.generate_payload(&(this->public),current_transform);
                                        after_generate_position_offset = this->get_current_buffer_offset(this);
                                        
                                        /* increase size of transform */
                                        length_of_proposal += (after_generate_position_offset - before_generate_position_offset);
                                }
                                
                                iterator->destroy(iterator);
                                
                                int16_val = htons(length_of_proposal);
                                this->write_bytes_to_buffer_at_offset(this,&int16_val,sizeof(u_int16_t),payload_length_position_offset);
                                
                                break;
                        }       
                        case TRANSFORM_ATTRIBUTES:
                        {
                                /* before iterative generate the transform attributes, store the current length position */
                                u_int32_t transform_length_position_offset = this->last_payload_length_position_offset;
                                u_int16_t length_of_transform = TRANSFORM_SUBSTRUCTURE_HEADER_LENGTH;
                                u_int16_t int16_val;
                                linked_list_t *transform_attributes =*((linked_list_t **)(this->data_struct + rules[i].offset));
                                iterator_t *iterator;
                                payload_t *current_attribute;
                                
                                /* create forward iterator */
                                iterator = transform_attributes->create_iterator(transform_attributes,TRUE);
                                while (iterator->iterate(iterator, (void**)&current_attribute))
                                {
                                        u_int32_t before_generate_position_offset;
                                        u_int32_t after_generate_position_offset;
                                        
                                        before_generate_position_offset = this->get_current_buffer_offset(this);
                                        this->public.generate_payload(&(this->public),current_attribute);
                                        after_generate_position_offset = this->get_current_buffer_offset(this);
                                        
                                        /* increase size of transform */
                                        length_of_transform += (after_generate_position_offset - before_generate_position_offset);
                                }
                                
                                iterator->destroy(iterator);
                                
                                int16_val = htons(length_of_transform);
                                this->write_bytes_to_buffer_at_offset(this,&int16_val,sizeof(u_int16_t),transform_length_position_offset);
                                
                                break;
                        }
                        case CONFIGURATION_ATTRIBUTES:
                        {
                                /* before iterative generate the configuration attributes, store the current length position */
                                u_int32_t configurations_length_position_offset = this->last_payload_length_position_offset;
                                u_int16_t length_of_configurations = CP_PAYLOAD_HEADER_LENGTH;
                                u_int16_t int16_val;
                                linked_list_t *configuration_attributes =*((linked_list_t **)(this->data_struct + rules[i].offset));
                                iterator_t *iterator;
                                payload_t *current_attribute;
                                
                                /* create forward iterator */
                                iterator = configuration_attributes->create_iterator(configuration_attributes,TRUE);
                                while (iterator->iterate(iterator, (void**)&current_attribute))
                                {
                                        u_int32_t before_generate_position_offset;
                                        u_int32_t after_generate_position_offset;
                                        
                                        before_generate_position_offset = this->get_current_buffer_offset(this);
                                        this->public.generate_payload(&(this->public),current_attribute);
                                        after_generate_position_offset = this->get_current_buffer_offset(this);
                                        
                                        /* increase size of transform */
                                        length_of_configurations += (after_generate_position_offset - before_generate_position_offset);
                                }
                                
                                iterator->destroy(iterator);
                                
                                int16_val = htons(length_of_configurations);
                                this->write_bytes_to_buffer_at_offset(this,&int16_val,sizeof(u_int16_t),configurations_length_position_offset);
                                
                                break;
                        }       
                        case ATTRIBUTE_FORMAT:
                        {
                                this->generate_flag(this,rules[i].offset);
                                /* Attribute format is a flag which is stored in context*/
                                this->attribute_format = *((bool *) (this->data_struct + rules[i].offset));
                                break;
                        }       

                        case ATTRIBUTE_LENGTH_OR_VALUE:
                        {
                                if (this->attribute_format == FALSE)
                                {
                                        this->generate_u_int_type(this,U_INT_16,rules[i].offset);
                                        /* this field hold the length of the attribute */
                                        this->attribute_length = *((u_int16_t *)(this->data_struct + rules[i].offset));
                                }
                                else
                                {
                                        this->generate_u_int_type(this,U_INT_16,rules[i].offset);
                                }
                                break;
                        }
                        case ATTRIBUTE_VALUE:
                        {
                                if (this->attribute_format == FALSE)
                                {
                                        DBG2(DBG_ENC, "attribute value has not fixed size");
                                        /* the attribute value is generated */
                                        this->generate_from_chunk(this,rules[i].offset);
                                }
                                break;
                        }
                        case TRAFFIC_SELECTORS:
                        {
                                /* before iterative generate the traffic_selectors, store the current payload length position */
                                u_int32_t payload_length_position_offset = this->last_payload_length_position_offset;
                                /* Length of SA_PAYLOAD is calculated */
                                u_int16_t length_of_ts_payload = TS_PAYLOAD_HEADER_LENGTH;
                                u_int16_t int16_val;
                                /* traffic selectors are stored in a linked list and so accessed */
                                linked_list_t *traffic_selectors = *((linked_list_t **)(this->data_struct + rules[i].offset));
                                iterator_t *iterator;
                                payload_t *current_traffic_selector_substructure;
                                
                                /* create forward iterator */
                                iterator = traffic_selectors->create_iterator(traffic_selectors,TRUE);
                                /* every proposal is processed (iterative call )*/
                                while (iterator->iterate(iterator, (void **)&current_traffic_selector_substructure))
                                {
                                        u_int32_t before_generate_position_offset;
                                        u_int32_t after_generate_position_offset;

                                        before_generate_position_offset = this->get_current_buffer_offset(this);
                                        this->public.generate_payload(&(this->public),current_traffic_selector_substructure);
                                        after_generate_position_offset = this->get_current_buffer_offset(this);
                                        
                                        /* increase size of transform */
                                        length_of_ts_payload += (after_generate_position_offset - before_generate_position_offset);
                                }
                                iterator->destroy(iterator);
                                
                                int16_val = htons(length_of_ts_payload);
                                this->write_bytes_to_buffer_at_offset(this,&int16_val,sizeof(u_int16_t),payload_length_position_offset);
                                break;
                        }       
                        
                        case ENCRYPTED_DATA:
                        {
                                this->generate_from_chunk(this, rules[i].offset);
                                break;
                        }
                        default:
                                DBG1(DBG_ENC, "field type %N is not supported",
                                         encoding_type_names, rules[i].type);
                                return;
                }
        }
        DBG2(DBG_ENC, "generating %N payload finished",
                 payload_type_names, payload_type);
        DBG3(DBG_ENC, "generated data for this payload %b",
                 payload_start, this->out_position-payload_start);
}

/**
 * Implementation of generator_t.destroy.
 */
static status_t destroy(private_generator_t *this)
{
        free(this->buffer);
        free(this);
        return SUCCESS;
}

/*
 * Described in header
 */
generator_t *generator_create()
{
        private_generator_t *this;

        this = malloc_thing(private_generator_t);

        /* initiate public functions */
        this->public.generate_payload = (void(*)(generator_t*, payload_t *)) generate_payload;
        this->public.destroy = (void(*)(generator_t*)) destroy;
        this->public.write_to_chunk = (void (*) (generator_t *,chunk_t *)) write_to_chunk;
        
        
        /* initiate private functions */
        this->get_current_buffer_size = get_current_buffer_size;
        this->get_current_buffer_space = get_current_buffer_space;
        this->get_current_data_length = get_current_data_length;
        this->get_current_buffer_offset = get_current_buffer_offset;
        this->generate_u_int_type = generate_u_int_type;
        this->generate_reserved_field = generate_reserved_field;
        this->generate_flag = generate_flag;
        this->generate_from_chunk = generate_from_chunk;
        this->make_space_available = make_space_available;
        this->write_bytes_to_buffer = write_bytes_to_buffer;
        this->write_bytes_to_buffer_at_offset = write_bytes_to_buffer_at_offset;


        /* allocate memory for buffer */
        this->buffer = malloc(GENERATOR_DATA_BUFFER_SIZE);

        /* initiate private variables */
        this->out_position = this->buffer;
        this->roof_position = this->buffer + GENERATOR_DATA_BUFFER_SIZE;
        this->data_struct = NULL;
        this->current_bit = 0;
        this->last_payload_length_position_offset = 0;
        this->header_length_position_offset = 0;

        return &(this->public);
}