path: root/src/json/json.c

/*
  This file is part of TALER
  Copyright (C) 2014, 2015, 2016, 2020 Taler Systems SA

  TALER 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 3, or (at your option) any later version.

  TALER 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.

  You should have received a copy of the GNU General Public License along with
  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file json/json.c
 * @brief helper functions for JSON processing using libjansson
 * @author Sree Harsha Totakura <sreeharsha@totakura.in>
 */
#include "platform.h"
#include <gnunet/gnunet_util_lib.h>
#include "taler_util.h"
#include "taler_json_lib.h"


/**
 * Dump the @a json to a string and hash it.
 *
 * @param json value to hash
 * @param salt salt value to include when using HKDF,
 *        NULL to not use any salt and to use SHA512
 * @param[out] hc where to store the hash
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
 */
static int
dump_and_hash (const json_t *json,
               const char *salt,
               struct GNUNET_HashCode *hc)
{
  char *wire_enc;
  size_t len;

  if (NULL == (wire_enc = json_dumps (json,
                                      JSON_COMPACT | JSON_SORT_KEYS)))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  len = strlen (wire_enc) + 1;
  if (NULL == salt)
  {
    GNUNET_CRYPTO_hash (wire_enc,
                        len,
                        hc);
  }
  else
  {
    if (GNUNET_YES !=
        GNUNET_CRYPTO_kdf (hc,
                           sizeof (*hc),
                           salt,
                           strlen (salt) + 1,
                           wire_enc,
                           len,
                           NULL,
                           0))
    {
      free (wire_enc);
      return GNUNET_SYSERR;
    }
  }
  free (wire_enc);
  return GNUNET_OK;
}


/**
 * Replace "forgettable" parts of a JSON object with its salted hash.
 *
 * @param[in] in some JSON value
 * @return NULL on error
 */
static json_t *
forget (const json_t *in)
{
  if (json_is_array (in))
  {
    /* array is a JSON array */
    size_t index;
    json_t *value;
    json_t *ret;

    ret = json_array ();
    if (NULL == ret)
    {
      GNUNET_break (0);
      return NULL;
    }
    json_array_foreach (in, index, value) {
      json_t *t;

      t = forget (value);
      if (NULL == t)
      {
        GNUNET_break (0);
        json_decref (ret);
        return NULL;
      }
      if (0 != json_array_append_new (ret, t))
      {
        GNUNET_break (0);
        json_decref (ret);
        return NULL;
      }
    }
    return ret;
  }
  if (! json_is_object (in))
  {
    json_t *ret;
    const char *key;
    json_t *value;
    json_t *fg;
    json_t *rx;

    fg = json_object_get (in,
                          "_forgettable");
    rx = json_object_get (in,
                          "_forgotten");
    if (NULL != rx)
      rx = json_deep_copy (rx); /* should be shallow
                                   by structure, but
                                   deep copy is safer */
    ret = json_object ();
    if (NULL == ret)
    {
      GNUNET_break (0);
      return NULL;
    }
    json_object_foreach ((json_t*) in, key, value) {
      json_t *t;
      json_t *salt;

      if (0 == strcmp (key,
                       "_forgettable"))
        continue; /* skip! */
      if (rx == value)
        continue; /* skip! */
      t = forget (value);
      if (NULL == t)
      {
        GNUNET_break (0);
        json_decref (ret);
        json_decref (rx);
        return NULL;
      }
      if ( (NULL != fg) &&
           (NULL != (salt = json_object_get (fg,
                                             key))) )
      {
        /* 't' is to be forgotten! */
        struct GNUNET_HashCode hc;

        if (! json_is_string (salt))
        {
          GNUNET_break (0);
          json_decref (ret);
          json_decref (rx);
          return NULL;
        }
        if (GNUNET_OK !=
            dump_and_hash (t,
                           json_string_value (salt),
                           &hc))
        {
          GNUNET_break (0);
          json_decref (ret);
          json_decref (rx);
          return NULL;
        }
        if (NULL == rx)
          rx = json_object ();
        if (NULL == rx)
        {
          GNUNET_break (0);
          json_decref (ret);
          json_decref (rx);
          return NULL;
        }
        if (0 !=
            json_object_set_new (rx,
                                 key,
                                 GNUNET_JSON_from_data_auto (&hc)))
        {
          GNUNET_break (0);
          json_decref (ret);
          json_decref (rx);
          return NULL;
        }
        if (0 !=
            json_object_set_new (ret,
                                 key,
                                 json_null ()))
        {
          GNUNET_break (0);
          json_decref (ret);
          json_decref (rx);
          return NULL;
        }

      }
      else
      {
        /* 't' to be used without 'forgetting' */
        if (0 !=
            json_object_set_new (ret,
                                 key,
                                 t))
        {
          GNUNET_break (0);
          json_decref (ret);
          json_decref (rx);
          return NULL;
        }
      }
    } /* json_object_foreach */
    if (0 !=
        json_object_set_new (ret,
                             "_forgotten",
                             rx))
    {
      GNUNET_break (0);
      json_decref (ret);
      return NULL;
    }
    return ret;
  }
  return json_incref ((json_t *) in);
}


/**
 * Hash a JSON contract for binary signing.
 *
 * Contracts can contain "forgettable" parts. Those components of the JSON
 * object are indicated in a "_forgettable" field containing key-value
 * pairs. The keys are the names of other fields that are forgettable, and the
 * values are salt values to be used in the HKDF when hashing the forgettable
 * field. To compute the overall hash, the values of all "_forgettable" fields
 * are replaced with 'null', and the "_forgettable" field itself is removed,
 * and a special "_forgotten" field is added with a map of forgotten entries
 * to the respective HKDF values (see also #6365).
 *
 * Forgetting parts is not only applied at the top-level entry of the
 * contract, but recursively to all entries.
 *
 * See https://tools.ietf.org/html/draft-rundgren-json-canonicalization-scheme-15
 * for fun JSON canonicalization problems.  Callers must ensure that
 * those are avoided in the input. We will use libjanson's "JSON_COMPACT"
 * encoding for whitespace and "JSON_SORT_KEYS" to canonicalize as best
 * as we can.
 *
 * @param[in] json some JSON value
 * @param[out] hc resulting hash code
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
 */
int
TALER_JSON_contract_hash (const json_t *json,
                          struct GNUNET_HashCode *hc)
{
  int ret;
  json_t *cjson;

  cjson = forget (json);
  if (NULL == cjson)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  ret = dump_and_hash (cjson,
                       NULL,
                       hc);
  json_decref (cjson);
  return ret;
}


/**
 * Mark part of a contract object as 'forgettable'.
 *
 * @param[in,out] json some JSON object to modify
 * @param field name of the field to mark as forgettable
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
 */
int
TALER_JSON_contract_mark_forgettable (json_t *json,
                                      const char *field)
{
  json_t *fg;
  struct GNUNET_ShortHashCode salt;

  if (! json_is_object (json))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  if (NULL == json_object_get (json,
                               field))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  fg = json_object_get (json,
                        "_forgettable");
  if (NULL == fg)
  {
    fg = json_object ();
    if (0 !=
        json_object_set_new (json,
                             "_forgettable",
                             fg))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
  }

  GNUNET_CRYPTO_random_block (GNUNET_CRYPTO_QUALITY_NONCE,
                              &salt,
                              sizeof (salt));
  if (0 !=
      json_object_set_new (fg,
                           field,
                           GNUNET_JSON_from_data_auto (&salt)))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Forget part of a contract object.
 *
 * @param[in,out] json some JSON object to modify
 * @param field name of the field to forget
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
 */
int
TALER_JSON_contract_part_forget (json_t *json,
                                 const char *field)
{
  const json_t *fg;
  const json_t *part;
  json_t *fp;
  json_t *rx;
  struct GNUNET_HashCode hc;
  const char *salt;

  if (! json_is_object (json))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  if (NULL == (part = json_object_get (json,
                                       field)))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  fg = json_object_get (json,
                        "_forgettable");
  if (NULL == fg)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  salt = json_string_value (json_object_get (fg,
                                             field));
  if (NULL == salt)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }

  /* need to recursively forget to compute 'hc' */
  fp = forget (part);
  if (NULL == fp)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  if (GNUNET_OK !=
      dump_and_hash (fp,
                     salt,
                     &hc))
  {
    json_decref (fp);
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  json_decref (fp);

  rx = json_object_get (json,
                        "_forgotten");
  if (NULL == rx)
  {
    rx = json_object ();
    if (0 !=
        json_object_set_new (json,
                             "_forgotten",
                             rx))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
  }
  /* remember field as 'forgotten' */
  if (0 !=
      json_object_set_new (rx,
                           field,
                           GNUNET_JSON_from_data_auto (&hc)))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  /* finally, set 'forgotten' field to null */
  if (0 !=
      json_object_set_new (json,
                           field,
                           json_null ()))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Extract the Taler error code from the given @a json object.
 * Note that #TALER_EC_NONE is returned if no "code" is present.
 *
 * @param json response to extract the error code from
 * @return the "code" value from @a json
 */
enum TALER_ErrorCode
TALER_JSON_get_error_code (const json_t *json)
{
  const json_t *jc;

  if (NULL == json)
  {
    GNUNET_break_op (0);
    return TALER_EC_INVALID_RESPONSE;
  }
  jc = json_object_get (json, "code");
  /* The caller already knows that the JSON represents an error,
     so we are dealing with a missing error code here.  */
  if (NULL == jc)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Expected Taler error code `code' in JSON, but field does not exist!\n");
    return TALER_EC_INVALID;
  }
  if (json_is_integer (jc))
    return (enum TALER_ErrorCode) json_integer_value (jc);
  GNUNET_break_op (0);
  return TALER_EC_INVALID;
}


/**
 * Extract the Taler error hint from the given @a json object.
 * Note that NULL is returned if no "hint" is present.
 *
 * @param json response to extract the error hint from
 * @return the "hint" value from @a json; only valid as long as @a json is valid
 */
const char *
TALER_JSON_get_error_hint (const json_t *json)
{
  const json_t *jc;

  if (NULL == json)
  {
    GNUNET_break_op (0);
    return NULL;
  }
  jc = json_object_get (json, "hint");
  if (NULL == jc)
    return NULL; /* no hint, is allowed */
  if (! json_is_string (jc))
  {
    /* Hints must be strings */
    GNUNET_break_op (0);
    return NULL;
  }
  return json_string_value (jc);
}


/**
 * Extract the Taler error code from the given @a data object, which is expected to be in JSON.
 * Note that #TALER_EC_INVALID is returned if no "code" is present or if @a data is not in JSON.
 *
 * @param data response to extract the error code from
 * @param data_size number of bytes in @a data
 * @return the "code" value from @a json
 */
enum TALER_ErrorCode
TALER_JSON_get_error_code2 (const void *data,
                            size_t data_size)
{
  json_t *json;
  enum TALER_ErrorCode ec;
  json_error_t err;

  json = json_loads (data,
                     data_size,
                     &err);
  if (NULL == json)
    return TALER_EC_INVALID;
  ec = TALER_JSON_get_error_code (json);
  json_decref (json);
  if (ec == TALER_EC_NONE)
    return TALER_EC_INVALID;
  return ec;
}


/* End of json/json.c */