cjson2cbor.c

/*
 * Contributed by Jacob Teplitsky <[email protected]>
 *
 * libcbor is free software; you can redistribute it and/or modify
 * it under the terms of the MIT license. See LICENSE for details.
 */

/**
 * This code demonstrates how cJSON (https://github.com/DaveGamble/cJSON)
 * callbacks can be used in conjunction with the streaming parser to translate
 * JSON to CBOR. Please note that cbor_builder_* APIs are internal and thus
 * subject to change.
 *
 * The example will only be compiled when cJSON is available
 */

#include <cjson/cJSON.h>
#include <float.h>
#include <math.h>
#include <string.h>
#include "cbor.h"
#include "cbor/internal/builder_callbacks.h"
#include "cbor/internal/loaders.h"

typedef void (*cbor_load_callback_t)(cJSON *, const struct cbor_callbacks *,
                                     void *);

cbor_item_t *cjson_cbor_load(void *source,
                             cbor_load_callback_t cbor_load_callback) {
  static struct cbor_callbacks callbacks = {
      .uint64 = &cbor_builder_uint64_callback,
      .negint64 = &cbor_builder_negint64_callback,
      .string = &cbor_builder_string_callback,
      .array_start = &cbor_builder_array_start_callback,
      .map_start = &cbor_builder_map_start_callback,
      .null = &cbor_builder_null_callback,
      .boolean = &cbor_builder_boolean_callback,
      .float4 = &cbor_builder_float4_callback,
  };

  /* Context stack */
  struct _cbor_stack stack = _cbor_stack_init();

  /* Target for callbacks */
  struct _cbor_decoder_context context = (struct _cbor_decoder_context){
      .stack = &stack,
  };

  cbor_load_callback(source, &callbacks, &context);

  return context.root;
}

void cjson_cbor_stream_decode(cJSON *source,
                              const struct cbor_callbacks *callbacks,
                              void *context) {
  switch (source->type) {
    case cJSON_False: {
      callbacks->boolean(context, false);
      return;
    }
    case cJSON_True: {
      callbacks->boolean(context, true);
      return;
    }
    case cJSON_NULL: {
      callbacks->null(context);
      return;
    }
    case cJSON_Number: {
      // This is stupid -- ints and doubles cannot are not distinguished
      if (fabs(source->valuedouble - source->valueint) > DBL_EPSILON) {
        callbacks->float4(context, source->valuedouble);
      } else {
        // XXX: This is not portable
        if (source->valueint >= 0) {
          callbacks->uint64(context, source->valueint);
        } else {
          callbacks->negint64(context, source->valueint + 1);
        }
      }
      return;
    }
    case cJSON_String: {
      // XXX: Assume cJSON handled unicode correctly
      callbacks->string(context, (unsigned char *)source->valuestring,
                        strlen(source->valuestring));
      return;
    }
    case cJSON_Array: {
      callbacks->array_start(context, cJSON_GetArraySize(source));
      cJSON *item = source->child;
      while (item != NULL) {
        cjson_cbor_stream_decode(item, callbacks, context);
        item = item->next;
      }
      return;
    }
    case cJSON_Object: {
      callbacks->map_start(context, cJSON_GetArraySize(source));
      cJSON *item = source->child;
      while (item != NULL) {
        callbacks->string(context, (unsigned char *)item->string,
                          strlen(item->string));
        cjson_cbor_stream_decode(item, callbacks, context);
        item = item->next;
      }
      return;
    }
  }
}

void usage(void) {
  printf("Usage: cjson2cbor [input JSON file]\n");
  exit(1);
}

int main(int argc, char *argv[]) {
  if (argc != 2) usage();
  FILE *f = fopen(argv[1], "rb");
  if (f == NULL) usage();
  /* Read input file into a buffer (cJSON doesn't work with streams) */
  fseek(f, 0, SEEK_END);
  size_t length = (size_t)ftell(f);
  fseek(f, 0, SEEK_SET);
  char *json_buffer = malloc(length + 1);
  fread(json_buffer, length, 1, f);
  json_buffer[length] = '\0';

  /* Convert between JSON and CBOR */
  cJSON *json = cJSON_Parse(json_buffer);
  cbor_item_t *cbor = cjson_cbor_load(json, cjson_cbor_stream_decode);

  /* Print out CBOR bytes */
  unsigned char *buffer;
  size_t buffer_size;
  cbor_serialize_alloc(cbor, &buffer, &buffer_size);

  fwrite(buffer, 1, buffer_size, stdout);

  free(buffer);
  fflush(stdout);
  cJSON_Delete(json);
  cbor_decref(&cbor);
}