4 The facility wrap-json is based on the pack/unpack API on the
5 library 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.
69 `y` (byte array) \[const uint8_t \*, size\_t\]
71 : Convert the byte array whose length is given to
72 its base64url string representation.
74 `Y` (byte array) \[const uint8_t \*, size\_t\]
76 : Like 'y' but output is base64.
78 `y?`, `Y?` (byte array or null) \[const uint8_t \*, size\_t\]
80 : Like 'y' or 'Y' but allows to output a JSON null value
81 either when the buffer is *NULL* or when the size is *0*.
83 `y*`, `y*` (optional byte array) \[const uint8_t \*, size\_t\]
85 : Like 'y' or 'Y' but do not put JSON value
86 either when the buffer is *NULL* or when the size is *0*.
87 This format can only be used inside an object or an array. If used
88 inside an object, the corresponding key is additionally suppressed
89 when the value is omitted. See below for an example.
93 : Output a JSON null value. No argument is consumed.
97 : Convert a C int to JSON boolean value. Zero is converted to `false`
98 and non-zero to `true`.
100 `i` (integer) \[int\]
102 : Convert a C int to JSON integer.
104 `I` (integer) \[json\_int\_t\]
106 : Convert a C json\_int\_t to JSON integer.
108 `f` (real) \[double\]
110 : Convert a C double to JSON real.
112 `o` (any value) \[json\_t \*\]
114 : Output any given JSON value as-is. If the value is added to an array
115 or object, the reference to the value passed to `o` is stolen by the
118 `O` (any value) \[json\_t \*\]
120 : Like `o`, but the argument's reference count is incremented. This is
121 useful if you pack into an array or object and want to keep the
122 reference for the JSON value consumed by `O` to yourself.
124 `o?`, `O?` (any value) \[json\_t \*\]
126 : Like `o` and `O`, respectively, but if the argument is *NULL*,
127 output a JSON null value.
129 `o*`, `O*` (any value) \[json\_t \*\]
131 : Like `o` and `O`, respectively, but if the argument is *NULL*, do
132 not output any value. This format can only be used inside an object
133 or an array. If used inside an object, the corresponding key is
134 additionally suppressed. See below for an example.
138 : Build an array with contents from the inner format string. `fmt` may
139 contain objects and arrays, i.e. recursive value building is
144 : Build an object with contents from the inner format string `fmt`.
145 The first, third, etc. format specifier represent a key, and must be
146 a string (see `s`, `s#`, `+` and `+#` above), as object keys are
147 always strings. The second, fourth, etc. format specifier represent
148 a value. Any value may be an object or array, i.e. recursive value
149 building is supported.
151 Whitespace, `:` and `,` are ignored.
155 /* Build an empty JSON object */
156 wrap_json_pack(&result, "{}");
158 /* Build the JSON object {"foo": 42, "bar": 7} */
159 wrap_json_pack(&result, "{sisi}", "foo", 42, "bar", 7);
161 /* Like above, ':', ',' and whitespace are ignored */
162 wrap_json_pack(&result, "{s:i, s:i}", "foo", 42, "bar", 7);
164 /* Build the JSON array [[1, 2], {"cool": true}] */
165 wrap_json_pack(&result, "[[i,i],{s:b}]", 1, 2, "cool", 1);
167 /* Build a string from a non-null terminated buffer */
168 char buffer[4] = {'t', 'e', 's', 't'};
169 wrap_json_pack(&result, "s#", buffer, 4);
171 /* Concatenate strings together to build the JSON string "foobarbaz" */
172 wrap_json_pack(&result, "s++", "foo", "bar", "baz");
174 /* Create an empty object or array when optional members are missing */
175 wrap_json_pack(&result, "{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL);
176 wrap_json_pack(&result, "[s*,o*,O*]", NULL, NULL, NULL);
178 Parsing and Validating Values
179 -----------------------------
181 This section describes functions that help to validate complex values
182 and extract, or *unpack*, data from them. Like building values
183 <apiref-pack>, this is also based on format strings.
185 While a JSON value is unpacked, the type specified in the format string
186 is checked to match that of the JSON value. This is the validation part
187 of the process. In addition to this, the unpacking functions can also
188 check that all items of arrays and objects are unpacked. This check be
189 enabled with the format specifier `!` or by using the flag
190 `JSON_STRICT`. See below for details.
192 Here's the full list of format specifiers. The type in parentheses
193 denotes the JSON type, and the type in brackets (if any) denotes the C
194 type whose address should be passed.
196 `s` (string) \[const char \*\]
198 : Convert a JSON string to a pointer to a null terminated UTF-8
199 string. The resulting string is extracted by using
200 json\_string\_value() internally, so it exists as long as there are
201 still references to the corresponding JSON string.
203 `s%` (string) \[const char \*, size\_t \*\]
205 : Convert a JSON string to a pointer to a null terminated UTF-8 string
208 `y` (byte array) \[uint8_t \*\*, size\_t \*\]
210 : Convert an input string base64url encoded to its
211 byte array representation. The result and its length
212 are stored. The returned buffer must be freed by the caller.
214 `Y` (byte array) \[uint8_t \*\*, size\_t \*\]
216 : Like 'y' but input is base64.
220 : Expect a JSON null value. Nothing is extracted.
222 `b` (boolean) \[int\]
224 : Convert a JSON boolean value to a C int, so that `true` is converted
225 to 1 and `false` to 0.
227 `i` (integer) \[int\]
229 : Convert a JSON integer to C int.
231 `I` (integer) \[json\_int\_t\]
233 : Convert a JSON integer to C json\_int\_t.
235 `f` (real) \[double\]
237 : Convert a JSON real to C double.
239 `F` (integer or real) \[double\]
241 : Convert a JSON number (integer or real) to C double.
243 `o` (any value) \[json\_t \*\]
245 : Store a JSON value with no conversion to a json\_t pointer.
247 `O` (any value) \[json\_t \*\]
249 : Like `O`, but the JSON value's reference count is incremented.
253 : Convert each item in the JSON array according to the inner format
254 string. `fmt` may contain objects and arrays, i.e. recursive value
255 extraction is supported.
259 : Convert each item in the JSON object according to the inner format
260 string `fmt`. The first, third, etc. format specifier represent a
261 key, and must be `s`. The corresponding argument to unpack functions
262 is read as the object key. The second fourth, etc. format specifier
263 represent a value and is written to the address given as the
264 corresponding argument. **Note** that every other argument is read
265 from and every other is written to.
267 `fmt` may contain objects and arrays as values, i.e. recursive value
268 extraction is supported.
272 : This special format specifier is used to enable the check that all
273 object and array items are accessed, on a per-value basis. It must
274 appear inside an array or object as the last format specifier before
275 the closing bracket or brace.
279 : This special format specifier is the opposite of `!`. This is the default.
280 It must appear inside an array or object as the last format specifier
281 before the closing bracket or brace.
283 Whitespace, `:` and `,` are ignored.
287 /* root is the JSON integer 42 */
289 wrap_json_unpack(root, "i", &myint);
292 /* root is the JSON object {"foo": "bar", "quux": true} */
295 wrap_json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
296 assert(strcmp(str, "bar") == 0 && boolean == 1);
298 /* root is the JSON array [[1, 2], {"baz": null} */
299 wrap_json_check(root, "[[i,i], {s:n}]", "baz");
300 /* returns 0 for validation success, nothing is extracted */
302 /* root is the JSON array [1, 2, 3, 4, 5] */
304 wrap_json_unpack(root, "[ii!]", &myint1, &myint2);
305 /* returns -1 for failed validation */
307 /* root is an empty JSON object */
308 int myint = 0, myint2 = 0, myint3 = 0;
309 wrap_json_unpack(root, "{s?i, s?[ii]}",
311 "bar", &myint2, &myint3);
312 /* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */
317 Copyright (c) 2009-2016 Petri Lehtinen <petri@digip.org>
319 Permission is hereby granted, free of charge, to any person obtaining a copy
320 of this software and associated documentation files (the "Software"), to deal
321 in the Software without restriction, including without limitation the rights
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323 copies of the Software, and to permit persons to whom the Software is
324 furnished to do so, subject to the following conditions:
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