json-c/json_pointer.c

/*
 * Copyright (c) 2016 Alexandru Ardelean.
 *
 * This is free software; you can redistribute it and/or modify
 * it under the terms of the MIT license. See COPYING for details.
 *
 */

#include "config.h"

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <ctype.h>

#include "json_pointer.h"

/**
 * JavaScript Object Notation (JSON) Pointer
 *   RFC 6901 - https://tools.ietf.org/html/rfc6901
 */

static void string_replace_all_occurrences_with_char(char *s, const char *occur, char repl_char)
{
	int slen = strlen(s);
	int skip = strlen(occur) - 1; /* length of the occurence, minus the char we're replacing */
	char *p = s;
	while ((p = strstr(p, occur))) {
		*p = repl_char;
		p++;
		slen -= skip;
		memcpy(p, (p + skip), slen - (p - s) + 1); /* includes null char too */
	}
}

static int is_valid_index(struct json_object *jo, const char *path, int32_t *idx)
{
	int i, len = strlen(path);
	/* this code-path optimizes a bit, for when we reference the 0-9 index range in a JSON array
	   and because leading zeros not allowed */
	if (len == 1) {
		if (isdigit(path[0])) {
			*idx = (path[0] - '0');
			goto check_oob;
		}
		errno = EINVAL;
		return 0;
	}
	/* leading zeros not allowed per RFC */
	if (path[0] == '0') {
		errno = EINVAL;
		return 0;
	}
	/* RFC states base-10 decimals */
	for (i = 0; i < len; i++) {
		if (!isdigit(path[i])) {
			errno = EINVAL;
			return 0;
		}
	}

	*idx = strtol(path, NULL, 10);
	if (*idx < 0) {
		errno = EINVAL;
		return 0;
	}
check_oob:
	len = json_object_array_length(jo);
	if (*idx >= len) {
		errno = ENOENT;
		return 0;
	}

	return 1;
}

static int json_pointer_get_single_path(struct json_object *obj, char *path, struct json_object **value)
{
	if (json_object_is_type(obj, json_type_array)) {
		int32_t idx;
		if (!is_valid_index(obj, path, &idx))
			return -1;
		obj = json_object_array_get_idx(obj, idx);
		if (obj) {
			if (value)
				*value = obj;
			return 0;
		}
		/* Entry not found */
		errno = ENOENT;
		return -1;
	}

	/* RFC states that we first must eval all ~1 then all ~0 */
	string_replace_all_occurrences_with_char(path, "~1", '/');
	string_replace_all_occurrences_with_char(path, "~0", '~');

	if (!json_object_object_get_ex(obj, path, value)) {
		errno = ENOENT;
		return -1;
	}

	return 0;
}

static int json_pointer_set_single_path(
	struct json_object *parent,
	const char *path,
	struct json_object *value)
{
	if (json_object_is_type(parent, json_type_array)) {
		int32_t idx;
		/* RFC (Chapter 4) states that '-' may be used to add new elements to an array */
		if (path[0] == '-' && path[1] == '\0')
			return json_object_array_add(parent, value);
		if (!is_valid_index(parent, path, &idx))
			return -1;
		return json_object_array_put_idx(parent, idx, value);
	}

	/* path replacements should have been done in json_pointer_get_single_path(),
	   and we should still be good here */
	if (json_object_is_type(parent, json_type_object))
		return json_object_object_add(parent, path, value);

	/* Getting here means that we tried to "dereference" a primitive JSON type (like string, int, bool).
	   i.e. add a sub-object to it */
	errno = ENOENT;
	return -1;
}

static int json_pointer_get_recursive(
	struct json_object *obj,
	char *path,
	struct json_object **value)
{
	char *endp;
	int rc;

	/* All paths (on each recursion level must have a leading '/' */
	if (path[0] != '/') {
		errno = EINVAL;
		return -1;
	}
	path++;

	endp = strchr(path, '/');
	if (endp)
		*endp = '\0';

	/* If we err-ed here, return here */
	if ((rc = json_pointer_get_single_path(obj, path, &obj)))
		return rc;

	if (endp) {
		*endp = '/'; /* Put the slash back, so that the sanity check passes on next recursion level */
		return json_pointer_get_recursive(obj, endp, value);
	}

	/* We should be at the end of the recursion here */
    if (value)
		*value = obj;

	return 0;
}

int json_pointer_get(struct json_object *obj, const char *path, struct json_object **res)
{
	char *path_copy = NULL;
	int rc;

	if (!obj || !path) {
		errno = EINVAL;
		return -1;
	}

	if (path[0] == '\0') {
		if (res)
			*res = obj;
		return 0;
	}

	/* pass a working copy to the recursive call */
	if (!(path_copy = strdup(path))) {
		errno = ENOMEM;
		return -1;
	}
	rc = json_pointer_get_recursive(obj, path_copy, res);
	free(path_copy);

	return rc;
}

int json_pointer_set(struct json_object **obj, const char *path, struct json_object *value)
{
	const char *endp;
	char *path_copy = NULL;
	struct json_object *set = NULL;
	int rc;

	if (!obj || !path) {
		errno = EINVAL;
		return -1;
	}

	if (path[0] == '\0') {
		json_object_put(*obj);
		*obj = value;
		return 0;
	}

	if (path[0] != '/') {
		errno = EINVAL;
		return -1;
	}

	/* If there's only 1 level to set, stop here */
	if ((endp = strrchr(path, '/')) == path) {
		path++;
		return json_pointer_set_single_path(*obj, path, value);
	}

	/* pass a working copy to the recursive call */
	if (!(path_copy = strdup(path))) {
		errno = ENOMEM;
		return -1;
	}
	path_copy[endp - path] = '\0';
	rc = json_pointer_get_recursive(*obj, path_copy, &set);
	free(path_copy);

	if (rc)
		return rc;

	endp++;
	return json_pointer_set_single_path(set, endp, value);
}