/* block.h -- block transfer
 *
 * Copyright (C) 2010--2012,2014 Olaf Bergmann <bergmann@tzi.org>
 *
 * This file is part of the CoAP library libcoap. Please see
 * README for terms of use.
 */

#ifndef _COAP_BLOCK_H_
#define _COAP_BLOCK_H_

#include "option.h"
#include "encode.h"
#include "pdu.h"

/**
 * @defgroup block Block Transfer
 * @{
 */

#ifndef COAP_MAX_BLOCK_SZX
/**
 * The largest value for the SZX component in a Block option. Note
 * that 1 << (COAP_MAX_BLOCK_SZX + 4) should not exceed
 * COAP_MAX_PDU_SIZE.
 */
#define COAP_MAX_BLOCK_SZX      4
#endif /* COAP_MAX_BLOCK_SZX */

#if (COAP_MAX_PDU_SIZE - 6) < (1 << (COAP_MAX_BLOCK_SZX + 4))
#error "COAP_MAX_BLOCK_SZX too large"
#endif

/**
 * Structure of Block options.
 */
typedef struct {
    unsigned int num: 20;		/**< block number */
    unsigned int m: 1;		/**< 1 if more blocks follow, 0 otherwise */
    unsigned int szx: 3;		/**< block size */
} coap_block_t;

/**
 * Returns the value of the least significant byte of a Block option @p opt.
 * For zero-length options (i.e. num == m == szx == 0), COAP_OPT_BLOCK_LAST
 * returns @c NULL.
 */
#define COAP_OPT_BLOCK_LAST(opt) \
  (COAP_OPT_LENGTH(opt) ? (COAP_OPT_VALUE(opt) + (COAP_OPT_LENGTH(opt)-1)) : 0)

/** Returns the value of the More-bit of a Block option @p opt. */
#define COAP_OPT_BLOCK_MORE(opt) \
  (COAP_OPT_LENGTH(opt) ? (*COAP_OPT_BLOCK_LAST(opt) & 0x08) : 0)

/** Returns the value of the SZX-field of a Block option @p opt. */
#define COAP_OPT_BLOCK_SZX(opt)  \
  (COAP_OPT_LENGTH(opt) ? (*COAP_OPT_BLOCK_LAST(opt) & 0x07) : 0)

/**
 * Returns the value of field @c num in the given block option @p
 * block_opt.
 */
unsigned int coap_opt_block_num(const coap_opt_t *block_opt);

/**
 * Checks if more than @p num blocks are required to deliver @p data_len
 * bytes of data for a block size of 1 << (@p szx + 4).
 */
static inline int
coap_more_blocks(size_t data_len, unsigned int num, unsigned short szx)
{
    return ((num + 1) << (szx + 4)) < data_len;
}

/** Sets the More-bit in @p block_opt */
static inline void
coap_opt_block_set_m(coap_opt_t *block_opt, int m)
{
    if (m) {
        *(COAP_OPT_VALUE(block_opt) + (COAP_OPT_LENGTH(block_opt) - 1)) |= 0x08;
    } else {
        *(COAP_OPT_VALUE(block_opt) + (COAP_OPT_LENGTH(block_opt) - 1)) &= ~0x08;
    }
}

/**
 * Initializes @p block from @p pdu. @p type must be either COAP_OPTION_BLOCK1
 * or COAP_OPTION_BLOCK2. When option @p type was found in @p pdu, @p block
 * is initialized with values from this option and the function returns the
 * value @c 1. Otherwise, @c 0 is returned.
 *
 * @param pdu   The pdu to search for option @p type.
 * @param type  The option to search for (must be COAP_OPTION_BLOCK1 or
 *              COAP_OPTION_BLOCK2)
 * @param block The block structure to initilize.
 * @return @c 1 on success, @c 0 otherwise.
 */
int coap_get_block(coap_pdu_t *pdu, unsigned short type, coap_block_t *block);

/**
 * Writes a block option of type @p type to message @p pdu. If the
 * requested block size is too large to fit in @p pdu, it is reduced
 * accordingly. An exception is made for the final block when less
 * space is required. The actual length of the resource is specified
 * in @p data_length.
 *
 * This function may change *block to reflect the values written to
 * @p pdu. As the function takes into consideration the remaining space
 * @p pdu, no more options should be added after coap_write_block_opt()
 * has returned.
 *
 * @param block      The block structure to use. On return, this object
 *                   is updated according to the values that have been
 *                   written to @p pdu.
 * @param type       COAP_OPTION_BLOCK1 or COAP_OPTION_BLOCK2
 * @param pdu        The message where the block option should be
 *                   written.
 * @param data_length The length of the actual data that will be added
 *                   the @p pdu by calling coap_add_block().
 * @return @c 1 on success, or a negative value on error.
 */
int coap_write_block_opt(coap_block_t *block, unsigned short type,
                         coap_pdu_t *pdu, size_t data_length);

/**
 * Adds the @p block_num block of size 1 << (@p block_szx + 4) from
 * source @p data to @p pdu.
 *
 * @param pdu    The message to add the block
 * @param len    The length of @p data.
 * @param data   The source data to fill the block with
 * @param block_num The actual block number
 * @param block_szx Encoded size of block @p block_number
 * @return @c 1 on success, @c 0 otherwise.
 */
int coap_add_block(coap_pdu_t *pdu, unsigned int len, const unsigned char *data,
                   unsigned int block_num, unsigned char block_szx);
/**@}*/

#endif /* _COAP_BLOCK_H_ */