nes-proj/examples/coap/resources/res-chunks.c

/*
 * Copyright (c) 2013, Institute for Pervasive Computing, ETH Zurich
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * This file is part of the Contiki operating system.
 */

/**
 * \file
 *      Example resource
 * \author
 *      Matthias Kovatsch <kovatsch@inf.ethz.ch>
 */

#include <string.h>
#include "rest-engine.h"

static void res_get_handler(void *request, void *response, uint8_t *buffer, uint16_t preferred_size, int32_t *offset);

/*
 * For data larger than REST_MAX_CHUNK_SIZE (e.g., when stored in flash) resources must be aware of the buffer limitation
 * and split their responses by themselves. To transfer the complete resource through a TCP stream or CoAP's blockwise transfer,
 * the byte offset where to continue is provided to the handler as int32_t pointer.
 * These chunk-wise resources must set the offset value to its new position or -1 of the end is reached.
 * (The offset for CoAP's blockwise transfer can go up to 2'147'481'600 = ~2047 M for block size 2048 (reduced to 1024 in observe-03.)
 */
RESOURCE(res_chunks,
         "title=\"Blockwise demo\";rt=\"Data\"",
         res_get_handler,
         NULL,
         NULL,
         NULL);

#define CHUNKS_TOTAL    2050

static void
res_get_handler(void *request, void *response, uint8_t *buffer, uint16_t preferred_size, int32_t *offset)
{
  int32_t strpos = 0;

  /* Check the offset for boundaries of the resource data. */
  if(*offset >= CHUNKS_TOTAL) {
    REST.set_response_status(response, REST.status.BAD_OPTION);
    /* A block error message should not exceed the minimum block size (16). */

    const char *error_msg = "BlockOutOfScope";
    REST.set_response_payload(response, error_msg, strlen(error_msg));
    return;
  }

  /* Generate data until reaching CHUNKS_TOTAL. */
  while(strpos < preferred_size) {
    strpos += snprintf((char *)buffer + strpos, preferred_size - strpos + 1, "|%ld|", (long) *offset);
  }

  /* snprintf() does not adjust return value if truncated by size. */
  if(strpos > preferred_size) {
    strpos = preferred_size;
    /* Truncate if above CHUNKS_TOTAL bytes. */
  }
  if(*offset + (int32_t)strpos > CHUNKS_TOTAL) {
    strpos = CHUNKS_TOTAL - *offset;
  }
  REST.set_response_payload(response, buffer, strpos);

  /* IMPORTANT for chunk-wise resources: Signal chunk awareness to REST engine. */
  *offset += strpos;

  /* Signal end of resource representation. */
  if(*offset >= CHUNKS_TOTAL) {
    *offset = -1;
  }
}