1 /**
2 *******************************************************************************
3 * @file json_object_iterator.c
4 *
5 * Copyright (c) 2009-2012 Hewlett-Packard Development Company, L.P.
6 *
7 * This library is free software; you can redistribute it and/or modify
8 * it under the terms of the MIT license. See COPYING for details.
9 *
10 * @brief json-c forces clients to use its private data
11 * structures for JSON Object iteration. This API
12 * implementation corrects that by abstracting the
13 * private json-c details.
14 *
15 *******************************************************************************
16 */
17
18 #include <stddef.h>
19
20 #include "json.h"
21 #include "json_object_private.h"
22
23 #include "json_object_iterator.h"
24
25 /**
26 * How It Works
27 *
28 * For each JSON Object, json-c maintains a linked list of zero
29 * or more lh_entry (link-hash entry) structures inside the
30 * Object's link-hash table (lh_table).
31 *
32 * Each lh_entry structure on the JSON Object's linked list
33 * represents a single name/value pair. The "next" field of the
34 * last lh_entry in the list is set to NULL, which terminates
35 * the list.
36 *
37 * We represent a valid iterator that refers to an actual
38 * name/value pair via a pointer to the pair's lh_entry
39 * structure set as the iterator's opaque_ field.
40 *
41 * We follow json-c's current pair list representation by
42 * representing a valid "end" iterator (one that refers past the
43 * last pair) with a NULL value in the iterator's opaque_ field.
44 *
45 * A JSON Object without any pairs in it will have the "head"
46 * field of its lh_table structure set to NULL. For such an
47 * object, json_object_iter_begin will return an iterator with
48 * the opaque_ field set to NULL, which is equivalent to the
49 * "end" iterator.
50 *
51 * When iterating, we simply update the iterator's opaque_ field
52 * to point to the next lh_entry structure in the linked list.
53 * opaque_ will become NULL once we iterate past the last pair
54 * in the list, which makes the iterator equivalent to the "end"
55 * iterator.
56 */
57
58 /// Our current representation of the "end" iterator;
59 ///
60 /// @note May not always be NULL
61 static const void* kObjectEndIterValue = NULL;
62
63 /**
64 * ****************************************************************************
65 */
66 struct json_object_iterator
json_object_iter_begin(struct json_object * obj)67 json_object_iter_begin(struct json_object* obj)
68 {
69 struct json_object_iterator iter;
70 struct lh_table* pTable;
71
72 /// @note json_object_get_object will return NULL if passed NULL
73 /// or a non-json_type_object instance
74 pTable = json_object_get_object(obj);
75 JASSERT(NULL != pTable);
76
77 /// @note For a pair-less Object, head is NULL, which matches our
78 /// definition of the "end" iterator
79 iter.opaque_ = pTable->head;
80 return iter;
81 }
82
83 /**
84 * ****************************************************************************
85 */
86 struct json_object_iterator
json_object_iter_end(const struct json_object * obj)87 json_object_iter_end(const struct json_object* obj)
88 {
89 struct json_object_iterator iter;
90
91 JASSERT(NULL != obj);
92 JASSERT(json_object_is_type(obj, json_type_object));
93
94 iter.opaque_ = kObjectEndIterValue;
95
96 return iter;
97 }
98
99 /**
100 * ****************************************************************************
101 */
102 void
json_object_iter_next(struct json_object_iterator * iter)103 json_object_iter_next(struct json_object_iterator* iter)
104 {
105 JASSERT(NULL != iter);
106 JASSERT(kObjectEndIterValue != iter->opaque_);
107
108 iter->opaque_ = ((struct lh_entry *)iter->opaque_)->next;
109 }
110
111
112 /**
113 * ****************************************************************************
114 */
115 const char*
json_object_iter_peek_name(const struct json_object_iterator * iter)116 json_object_iter_peek_name(const struct json_object_iterator* iter)
117 {
118 JASSERT(NULL != iter);
119 JASSERT(kObjectEndIterValue != iter->opaque_);
120
121 return (const char*)(((struct lh_entry *)iter->opaque_)->k);
122 }
123
124
125 /**
126 * ****************************************************************************
127 */
128 struct json_object*
json_object_iter_peek_value(const struct json_object_iterator * iter)129 json_object_iter_peek_value(const struct json_object_iterator* iter)
130 {
131 JASSERT(NULL != iter);
132 JASSERT(kObjectEndIterValue != iter->opaque_);
133
134 return (struct json_object*)(((struct lh_entry *)iter->opaque_)->v);
135 }
136
137
138 /**
139 * ****************************************************************************
140 */
141 json_bool
json_object_iter_equal(const struct json_object_iterator * iter1,const struct json_object_iterator * iter2)142 json_object_iter_equal(const struct json_object_iterator* iter1,
143 const struct json_object_iterator* iter2)
144 {
145 JASSERT(NULL != iter1);
146 JASSERT(NULL != iter2);
147
148 return (iter1->opaque_ == iter2->opaque_);
149 }
150
151
152 /**
153 * ****************************************************************************
154 */
155 struct json_object_iterator
json_object_iter_init_default(void)156 json_object_iter_init_default(void)
157 {
158 struct json_object_iterator iter;
159
160 /**
161 * @note Make this a negative, invalid value, such that
162 * accidental access to it would likely be trapped by the
163 * hardware as an invalid address.
164 */
165 iter.opaque_ = NULL;
166
167 return iter;
168 }
169