4 The facility wrap-json is based on the pack/unpack API on the
5 libray jansson. The two chapters below are copied from the
6 documentation of jansson library copyrighted by Petri Lehtinen
12 This section describes functions that help to create, or *pack*, complex
13 JSON values, especially nested objects and arrays. Value building is
14 based on a *format string* that is used to tell the functions about the
17 For example, the format string `"i"` specifies a single integer value,
18 while the format string `"[ssb]"` or the equivalent `"[s, s, b]"`
19 specifies an array value with two strings and a boolean as its items:
21 /* Create the JSON integer 42 */
22 wrap_json_pack(&result, "i", 42);
24 /* Create the JSON array ["foo", "bar", true] */
25 wrap_json_pack(&result, "[ssb]", "foo", "bar", 1);
27 Here's the full list of format specifiers. The type in parentheses
28 denotes the resulting JSON type, and the type in brackets (if any)
29 denotes the C type that is expected as the corresponding argument or
32 `s` (string) \[const char \*\]
34 : Convert a null terminated UTF-8 string to a JSON string.
36 `s?` (string) \[const char \*\]
38 : Like `s`, but if the argument is *NULL*, output a JSON null value.
40 `s*` (string) \[const char \*\]
42 : Like `s`, but if the argument is *NULL*, do not output any value.
43 This format can only be used inside an object or an array. If used
44 inside an object, the corresponding key is additionally suppressed
45 when the value is omitted. See below for an example.
47 `s#` (string) \[const char \*, int\]
49 : Convert a UTF-8 buffer of a given length to a JSON string.
51 `s%` (string) \[const char \*, size\_t\]
53 : Like `s#` but the length argument is of type size\_t.
57 : Like `s`, but concatenate to the previous string. Only valid after
58 `s`, `s#`, `+` or `+#`.
60 `+#` \[const char \*, int\]
62 : Like `s#`, but concatenate to the previous string. Only valid after
63 `s`, `s#`, `+` or `+#`.
65 `+%` (string) \[const char \*, size\_t\]
67 : Like `+#` but the length argument is of type size\_t.
71 : Output a JSON null value. No argument is consumed.
75 : Convert a C int to JSON boolean value. Zero is converted to `false`
76 and non-zero to `true`.
80 : Convert a C int to JSON integer.
82 `I` (integer) \[json\_int\_t\]
84 : Convert a C json\_int\_t to JSON integer.
88 : Convert a C double to JSON real.
90 `o` (any value) \[json\_t \*\]
92 : Output any given JSON value as-is. If the value is added to an array
93 or object, the reference to the value passed to `o` is stolen by the
96 `O` (any value) \[json\_t \*\]
98 : Like `o`, but the argument's reference count is incremented. This is
99 useful if you pack into an array or object and want to keep the
100 reference for the JSON value consumed by `O` to yourself.
102 `o?`, `O?` (any value) \[json\_t \*\]
104 : Like `o` and `O`, respectively, but if the argument is *NULL*,
105 output a JSON null value.
107 `o*`, `O*` (any value) \[json\_t \*\]
109 : Like `o` and `O`, respectively, but if the argument is *NULL*, do
110 not output any value. This format can only be used inside an object
111 or an array. If used inside an object, the corresponding key is
112 additionally suppressed. See below for an example.
116 : Build an array with contents from the inner format string. `fmt` may
117 contain objects and arrays, i.e. recursive value building is
122 : Build an object with contents from the inner format string `fmt`.
123 The first, third, etc. format specifier represent a key, and must be
124 a string (see `s`, `s#`, `+` and `+#` above), as object keys are
125 always strings. The second, fourth, etc. format specifier represent
126 a value. Any value may be an object or array, i.e. recursive value
127 building is supported.
129 Whitespace, `:` and `,` are ignored.
133 /* Build an empty JSON object */
134 wrap_json_pack(&result, "{}");
136 /* Build the JSON object {"foo": 42, "bar": 7} */
137 wrap_json_pack(&result, "{sisi}", "foo", 42, "bar", 7);
139 /* Like above, ':', ',' and whitespace are ignored */
140 wrap_json_pack(&result, "{s:i, s:i}", "foo", 42, "bar", 7);
142 /* Build the JSON array [[1, 2], {"cool": true}] */
143 wrap_json_pack(&result, "[[i,i],{s:b}]", 1, 2, "cool", 1);
145 /* Build a string from a non-null terminated buffer */
146 char buffer[4] = {'t', 'e', 's', 't'};
147 wrap_json_pack(&result, "s#", buffer, 4);
149 /* Concatenate strings together to build the JSON string "foobarbaz" */
150 wrap_json_pack(&result, "s++", "foo", "bar", "baz");
152 /* Create an empty object or array when optional members are missing */
153 wrap_json_pack(&result, "{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL);
154 wrap_json_pack(&result, "[s*,o*,O*]", NULL, NULL, NULL);
156 Parsing and Validating Values
157 -----------------------------
159 This section describes functions that help to validate complex values
160 and extract, or *unpack*, data from them. Like building values
161 <apiref-pack>, this is also based on format strings.
163 While a JSON value is unpacked, the type specified in the format string
164 is checked to match that of the JSON value. This is the validation part
165 of the process. In addition to this, the unpacking functions can also
166 check that all items of arrays and objects are unpacked. This check be
167 enabled with the format specifier `!` or by using the flag
168 `JSON_STRICT`. See below for details.
170 Here's the full list of format specifiers. The type in parentheses
171 denotes the JSON type, and the type in brackets (if any) denotes the C
172 type whose address should be passed.
174 `s` (string) \[const char \*\]
176 : Convert a JSON string to a pointer to a null terminated UTF-8
177 string. The resulting string is extracted by using
178 json\_string\_value() internally, so it exists as long as there are
179 still references to the corresponding JSON string.
181 `s%` (string) \[const char \*, size\_t \*\]
183 : Convert a JSON string to a pointer to a null terminated UTF-8 string
188 : Expect a JSON null value. Nothing is extracted.
190 `b` (boolean) \[int\]
192 : Convert a JSON boolean value to a C int, so that `true` is converted
193 to 1 and `false` to 0.
195 `i` (integer) \[int\]
197 : Convert a JSON integer to C int.
199 `I` (integer) \[json\_int\_t\]
201 : Convert a JSON integer to C json\_int\_t.
203 `f` (real) \[double\]
205 : Convert a JSON real to C double.
207 `F` (integer or real) \[double\]
209 : Convert a JSON number (integer or real) to C double.
211 `o` (any value) \[json\_t \*\]
213 : Store a JSON value with no conversion to a json\_t pointer.
215 `O` (any value) \[json\_t \*\]
217 : Like `O`, but the JSON value's reference count is incremented.
221 : Convert each item in the JSON array according to the inner format
222 string. `fmt` may contain objects and arrays, i.e. recursive value
223 extraction is supported.
227 : Convert each item in the JSON object according to the inner format
228 string `fmt`. The first, third, etc. format specifier represent a
229 key, and must be `s`. The corresponding argument to unpack functions
230 is read as the object key. The second fourth, etc. format specifier
231 represent a value and is written to the address given as the
232 corresponding argument. **Note** that every other argument is read
233 from and every other is written to.
235 `fmt` may contain objects and arrays as values, i.e. recursive value
236 extraction is supported.
240 : This special format specifier is used to enable the check that all
241 object and array items are accessed, on a per-value basis. It must
242 appear inside an array or object as the last format specifier before
243 the closing bracket or brace.
247 : This special format specifier is the opposite of `!`. This is the default.
248 It must appear inside an array or object as the last format specifier
249 before the closing bracket or brace.
251 Whitespace, `:` and `,` are ignored.
255 /* root is the JSON integer 42 */
257 wrap_json_unpack(root, "i", &myint);
260 /* root is the JSON object {"foo": "bar", "quux": true} */
263 wrap_json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
264 assert(strcmp(str, "bar") == 0 && boolean == 1);
266 /* root is the JSON array [[1, 2], {"baz": null} */
267 wrap_json_check(root, "[[i,i], {s:n}]", "baz");
268 /* returns 0 for validation success, nothing is extracted */
270 /* root is the JSON array [1, 2, 3, 4, 5] */
272 wrap_json_unpack(root, "[ii!]", &myint1, &myint2);
273 /* returns -1 for failed validation */
275 /* root is an empty JSON object */
276 int myint = 0, myint2 = 0, myint3 = 0;
277 wrap_json_unpack(root, "{s?i, s?[ii]}",
279 "bar", &myint2, &myint3);
280 /* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */
286 Copyright (c) 2009-2016 Petri Lehtinen <petri@digip.org>
288 Permission is hereby granted, free of charge, to any person obtaining a copy
289 of this software and associated documentation files (the "Software"), to deal
290 in the Software without restriction, including without limitation the rights
291 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
292 copies of the Software, and to permit persons to whom the Software is
293 furnished to do so, subject to the following conditions:
295 The above copyright notice and this permission notice shall be included in
296 all copies or substantial portions of the Software.
298 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
299 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
300 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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