1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
|
### jsonschema extension
Since 0.174.0, the jsonschema extension implements Drafts 4, 6, 7, 2019-9 and 2020-12 of the [JSON Schema Specification](https://json-schema.org/specification).
Previous versions supported Draft 7.
The documentation below describes the new features for the jsonschema extension since 0.174.0.
For earlier releases, please refer to [jsonschema (until 0.174.0)](https://github.com/danielaparker/jsoncons/tree/main).
### Classes
<table border="0">
<tr>
<td><a href="json_schema.md">json_schema</a></td>
<td>A <code>json_schema</code> represents the compiled form of a JSON Schema document.</td>
</tr>
<tr>
<td><a href="evaluation_options.md">evaluation_options</a></td>
<td>Allows configuration of JSON Schema evaluation.</td>
</tr>
<tr>
<td><a href="validation_message.md">validation_message</a></td>
<td>A message type for reporting errors generated by a keyword.</td>
</tr>
<tr>
<td><a href="schema_version.md">schema_version</a></td>
<td>Supported JSON Schema dialects.</td>
</tr>
<tr>
<td><a href="json_validator.md">json_validator</a></td>
<td>JSON Schema validator. Deprecated (since 0.174.0)</td>
</tr>
</table>
### Functions
<table border="0">
<tr>
<td><a href="make_json_schema.md">make_json_schema</a></td>
<td>Processes a JSON Schema document and returns the compiled form as a <code>json_schema</code> (since 0.174.0).
</tr>
<tr>
<td><a href="make_schema.md">make_schema</a></td>
<td>Loads a JSON Schema and returns a shared pointer to a <code>json_schema</code>. Deprecated since 0.174.0. Removed in 1.0.0.
</tr>
</table>
### Compliance
#### Keywords
The jsoncons implementation passes all required tests in the [JSON Schema Test Suite](https://github.com/json-schema-org/JSON-Schema-Test-Suite/) for the keywords below.
You can check the [Bowtie project](https://github.com/bowtie-json-schema/bowtie) to see how jsoncons [compares with other implementations](https://bowtie.report/).
| Keyword | Draft 4 | Draft 6 | Draft 7 | Draft 2019-09 | Draft 2020-12 |
|:--------------------------:|:---------:|:---------:|:---------:|:---------:|:---------:|
| $anchor | | | | 🟢 | 🟢 |
| $defs | | | | 🟢 | 🟢 |
| $dynamicAnchor | | | | | 🟢 |
| $dynamicRef | | | | | 🟢 |
| $id | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| $recursiveAnchor | | | | 🟢 | |
| $recursiveRef | | | | 🟢 | |
| $ref | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| $vocabulary | | | | 🟢 | 🟢 |
| additionalItems | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| additionalProperties | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| allOf | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| anyOf | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| const | | 🟢 | 🟢 | 🟢 | 🟢 |
| contains | | 🟢 | 🟢 | 🟢 | 🟢 |
| contentEncoding | | | 🟢 | 🟢 | 🟢 |
| contentMediaType | | | 🟢 | 🟢 | 🟢 |
| definitions | 🟢 | 🟢 | 🟢 | | |
| dependencies | 🟢 | 🟢 | 🟢 | | |
| dependentRequired | | | | 🟢 | 🟢 |
| dependentSchemas | | | | 🟢 | 🟢 |
| enum | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| exclusiveMaximum (boolean) | 🟢 | | | | |
| exclusiveMaximum | | 🟢 | 🟢 | 🟢 | 🟢 |
| exclusiveMinimum (boolean) | 🟢 | | | | |
| exclusiveMinimum | | 🟢 | 🟢 | 🟢 | 🟢 |
| if-then-else | | | 🟢 | 🟢 | 🟢 |
| items | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| maxContains | | | | 🟢 | 🟢 |
| minContains | | | | 🟢 | 🟢 |
| maximum | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| maxItems | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| maxLength | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| maxProperties | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| minimum | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| minItems | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| minLength | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| minProperties | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| multipleOf | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| not | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| oneOf | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| pattern | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| patternProperties | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| prefixItems | | | | | 🟢 |
| properties | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| propertyNames | | 🟢 | 🟢 | 🟢 | 🟢 |
| required | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| type | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| unevaluatedItems | | | | 🟢 | 🟢 |
| unevaluatedProperties | | | | 🟢 | 🟢 |
| uniqueItems | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
#### Format
The implementation understands the following [formats](https://json-schema.org/understanding-json-schema/reference/string.html#format):
| Format | Draft 4 | Draft 6 | Draft 7 | Draft 2019-09 | Draft 2020-12 |
|:-------------:|:---------:|:---------:|:---------:|:---------:|:---------:|
| date | | 🟢 | 🟢 | 🟢 | 🟢 |
| date-time | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| email | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| hostname | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| ipv4 | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| ipv6 | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| json-pointer | | 🟢 | 🟢 | 🟢 | 🟢 |
| regex | 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| time | | 🟢 | 🟢 | 🟢 | 🟢 |
| uri (since 1.0.0)| 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
| uri-reference (since 1.0.0)| 🟢 | 🟢 | 🟢 | 🟢 | 🟢 |
Any other format type is ignored.
Since Draft 2019-09, format is no longer an assertion by default. It can be configured to be an assertion
by setting the evaluation option `require_format_validation` to `true`
### Schema dialect
jsoncons supports Drafts 4, 6, 7, 2019-9 and 2020-12 of the [JSON Schema Specification](https://json-schema.org/specification).
It needs to know the dialect of a schema resource in order to know how to process it. If a schema contains a **$schema** dialect identifier,
it uses that. Otherwise, it falls back on a default version you can provide through [evaluation_options](./evaluation_options.md), e.g.
```cpp
auto options = jsonschema::evaluation_options{}
.default_version(jsonschema::schema_version::draft7());
auto compiled = jsonschema::make_json_schema(schema, options);
```
If no default is provided, the latest supported version is assumed.
### URI resolution
jsoncons requires a user supplied schema resolver to resolve a URI reference to a schema resoure.
A schema resolver is a function object with the signature of `resolver` being equivalent to
<pre>
Json fun(const <a href="../corelib/utility/uri.md">jsoncons::uri</a>& uri);</pre>
If unable to resolve the resource, it should return <code>Json::null()</code>.
Here is an example of a schema resolver that resolves a URI to a physical pathname,
```cpp
std::string root_dir = "./input/jsonschema";
auto resolver = [&](const jsoncons::uri& uri) -> json
{
std::string pathname = root_dir + uri.path();
std::fstream is(pathname.c_str());
if (!is)
{
return json::null();
}
return json::parse(is);
};
```
### Default values
The JSON Schema Specification includes the ["default" keyword](https://json-schema.org/understanding-json-schema/reference/generic.html)
for specifying a default value, but doesn't prescribe how implementations should use it during validation.
Some implementations ignore the default keyword, others support updating the input JSON to fill in a default value
for a missing key/value pair. This implementation outputs a JSONPatch document that may be further applied to the input JSON to add the
missing key/value pairs.
### Custom error messages (since 1.2.0)
jsoncons supports custom error messages via an opt-in `errorMessage` keyword.
To enable this feature, refer to [custom error messages](./custom-error-messages.md).
### Examples
The example schemas are from [JSON Schema Miscellaneous Examples](https://json-schema.org/learn/miscellaneous-examples.html),
the [JSON Schema Test Suite](https://github.com/json-schema-org/JSON-Schema-Test-Suite), and user contributions.
[Three ways of validating](#eg1)
[Format validation](#eg2)
[Resolving references to schemas defined in external files](#eg3)
[Validate before decoding JSON into C++ class objects](#eg4)
[Default values](#eg5)
<div id="eg1"/>
#### Three ways of validating
This example illustrates the use of three overloads of the `validate` function that throw,
invoke a callback function, and write to a `json_visitor`.
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonschema/jsonschema.hpp>
#include <iostream>
using jsoncons::ojson;
namespace jsonschema = jsoncons::jsonschema;
int main()
std::string schema_str = R"(
{
"$id": "https://example.com/arrays.schema.json",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"description": "A representation of a person, company, organization, or place",
"type": "object",
"properties": {
"fruits": {
"type": "array",
"items": {
"type": "string"
}
},
"vegetables": {
"type": "array",
"items": { "$ref": "#/$defs/veggie" }
}
},
"$defs": {
"veggie": {
"type": "object",
"required": [ "veggieName", "veggieLike" ],
"properties": {
"veggieName": {
"type": "string",
"description": "The name of the vegetable."
},
"veggieLike": {
"type": "boolean",
"description": "Do I like this vegetable?"
}
}
}
}
}
)";
std::string data_str = R"(
{
"fruits": [ "apple", "orange", "pear" ],
"vegetables": [
{
"veggieName": "potato",
"veggieLike": true
},
{
"veggieName": "broccoli",
"veggieLike": "false"
},
{
"veggieName": "carrot",
"veggieLike": false
},
{
"veggieName": "Swiss Chard"
}
]
}
)";
ojson schema = ojson::parse(schema_str);
jsonschema::json_schema<ojson> compiled = jsonschema::make_json_schema(std::move(schema));
ojson data = ojson::parse(data_str);
std::cout << "\n(1) Validate using exceptions\n";
try
{
compiled.validate(data);
}
catch (const std::exception& e)
{
std::cout << e.what() << "\n";
}
std::cout << "\n(2) Validate using reporter callback\n";
auto reporter = [](const jsonschema::validation_message& message) -> jsonschema::walk_result
{
std::cout << message.instance_location().string() << ": " << message.message() << "\n";
return jsonschema::walk_result::advance;
};
compiled.validate(data, reporter);
std::cout << "\n(3) Validate outputting to a json decoder\n";
jsoncons::json_decoder<ojson> decoder;
compiled.validate(data, decoder);
ojson output = decoder.get_result();
std::cout << pretty_print(output) << "\n";
}
```
Output:
```
(1) Validate using exceptions
/vegetables/1/veggieLike: Expected boolean, found string
(2) Validate using reporter callback
/vegetables/1/veggieLike: Expected boolean, found string
/vegetables/3: Required property 'veggieLike' not found.
(3) Validate outputting to a json decoder
[
{
"valid": false,
"evaluationPath": "/properties/vegetables/items/$ref/properties/veggieLike/type",
"schemaLocation": "https://example.com/arrays.schema.json#/$defs/veggie/properties/veggieLike",
"instanceLocation": "/vegetables/1/veggieLike",
"error": "Expected boolean, found string"
},
{
"valid": false,
"evaluationPath": "/properties/vegetables/items/$ref/required",
"schemaLocation": "https://example.com/arrays.schema.json#/$defs/veggie/required",
"instanceLocation": "/vegetables/3",
"error": "Required property 'veggieLike' not found."
}
]
```
<div id="eg2"/>
#### Format validation
Since Draft 2019-09, format validation is disabled by default, but may be enabled by setting the
evaluation option `require_format_validation` to `true`.
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonschema/jsonschema.hpp>
#include <iostream>
using jsoncons::json;
using jsoncons::ojson;
namespace jsonschema = jsoncons::jsonschema;
int main()
{
json schema = json::parse(R"(
{
"$id": "/test_schema",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"properties": {
"Date": {
"format": "date-time",
"type": "string"
}
},
"required": [
"Date"
],
"type": "object",
"unevaluatedProperties": false
}
)");
auto compiled = jsoncons::jsonschema::make_json_schema(schema,
jsonschema::evaluation_options{}.require_format_validation(true));
json data = json::parse(R"(
{ "Date" : "2024-03-19T26:34:56Z" }
)");
jsoncons::json_decoder<ojson> decoder;
compiled.validate(data, decoder);
ojson output = decoder.get_result();
std::cout << pretty_print(output) << "\n";
}
```
Output:
```json
[
{
"valid": false,
"evaluationPath": "/properties/Date/format",
"schemaLocation": "/test_schema#/properties/Date/format",
"instanceLocation": "/Date",
"error": "'2024-03-19T26:34:56Z' is not a RFC 3339 date-time string."
},
{
"valid": false,
"evaluationPath": "/unevaluatedProperties/Date",
"schemaLocation": "/test_schema",
"instanceLocation": "/Date",
"error": "Unevaluated property 'Date' but the schema does not allow unevaluated properties."
}
]
```
<div id="eg3"/>
#### Resolving references to schemas defined in external files
In this example, the main schema is defined by
```cpp
std::string main_schema = R"(
{
"$id" : "https://www.example.com/main",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "http://localhost:1234/draft2020-12/object",
"type": "object",
"properties": {
"name": {"$ref": "/name-defs.json#/$defs/orNull"}
}
}
)";
```
The main schema includes a reference using the `$ref` keyword to a
second schema defined in an external file, `name-defs.json`,
```json
{
"$id" : "https://www.example.com/other",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$defs": {
"orNull": {
"anyOf": [
{
"type": "null"
},
{
"$ref": "#"
}
]
}
},
"type": "string"
}
```
When building the main schema, the schema builder needs to resolve the URI 'https://www.example.com/name-defs.json#/$defs/orNull'
via a URI resolver. The resolver does not need to supply that specific subschema, it is enough to supply the schema document '/name-defs.json'.
The schema builder than processes that schema document and makes multiple entries into an internal validator registry,
including an entry for 'https://www.example.com/name-defs.json#/$defs/orNull'.
```cpp
int main()
{
json schema = json::parse(main_schema);
// Data
json data = json::parse(R"(
{
"name": {
"name": null
}
}
)");
try
{
// Throws schema_error if JSON Schema compilation fails
jsonschema::json_schema<json> compiled = jsonschema::make_json_schema(schema, resolver);
std::string root_dir = "./input/jsonschema";
auto resolver = [&](const jsoncons::uri& uri) -> json
{
std::cout << "Requested URI: " << uri.string() << "\n";
std::cout << "base: " << uri.base().string() << ", path: " << uri.path() << "\n\n";
std::string pathname = root_dir + uri.path();
std::fstream is(pathname.c_str());
if (!is)
{
return json::null();
}
return json::parse(is);
};
// Will call the message handler function object for each schema violation
compiled.validate(data, reporter);
}
catch (const std::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
Requested URI: https://www.example.com/name-defs.json#/$defs/orNull
base: https://www.example.com/name-defs.json, path: /name-defs.json
/name: Must be valid against at least one schema, but found no matching schemas
Expected null, found object
Expected string, found object
```
<div id="eg4"/>
#### Validate before decoding JSON into C++ class objects
This example illustrates decoding data that validates against "oneOf"
into a `std::variant`.
```cpp
// for brevity
using jsoncons::json;
namespace jsonschema = jsoncons::jsonschema;
int main()
{
std::string schema_str = R"(
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"title": "job",
"description": "job properties json schema",
"$defs": {
"os_properties": {
"type": "object",
"properties": {
"command": {
"description": "this is the OS command to run",
"type": "string",
"minLength": 1
}
},
"required": [ "command" ],
"additionalProperties": false
},
"db_properties": {
"type": "object",
"properties": {
"query": {
"description": "this is db query to run",
"type": "string",
"minLength": 1
}
},
"required": [ "query" ],
"additionalProperties": false
},
"api_properties": {
"type": "object",
"properties": {
"target": {
"description": "this is api target to run",
"type": "string",
"minLength": 1
}
},
"required": [ "target" ],
"additionalProperties": false
}
},
"type": "object",
"properties": {
"name": {
"description": "name of the flow",
"type": "string",
"minLength": 1
},
"run": {
"description": "job run properties",
"type": "object",
"oneOf": [
{ "$ref": "#/$defs/os_properties" },
{ "$ref": "#/$defs/db_properties" },
{ "$ref": "#/$defs/api_properties" }
]
}
},
"required": [ "name", "run" ],
"additionalProperties": false
}
)";
std::string data_str = R"(
{
"name": "testing flow",
"run" : {
"command": "some command"
}
}
)";
try
{
json schema = json::parse(schema_str);
json data = json::parse(data_str);
// Throws schema_error if JSON Schema compilation fails
jsonschema::json_schema<json> compiled = jsonschema::make_json_schema(schema);
// Test that input is valid before attempting to decode
if (compiled.is_valid(data))
{
const ns::job_properties v = data.as<ns::job_properties>(); // You don't need to reparse data_str
std::string output;
jsoncons::encode_json_pretty(v, output);
std::cout << output << std::endl;
// Verify that output is valid
json test = json::parse(output);
assert(compiled.is_valid(test));
}
else
{
std::cout << "Invalid input\n";
}
}
catch (const std::exception& e)
{
std::cout << e.what() << '\n';
}
}
```
Output:
```
{
"name": "testing flow",
"run": {
"command": "some command"
}
}
```
<div id="eg5"/>
#### Default values
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonschema/jsonschema.hpp>
#include <jsoncons_ext/jsonpatch/jsonpatch.hpp>
#include <fstream>
// for brevity
using jsoncons::json;
namespace jsonschema = jsoncons::jsonschema;
namespace jsonpatch = jsoncons::jsonpatch;
int main()
{
json schema = json::parse(R"(
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"properties": {
"bar": {
"type": "string",
"minLength": 4,
"default": "bad"
}
}
}
)");
try
{
// Data
json data = json::parse("{}");
// will throw schema_error if JSON Schema compilation fails
jsonschema::json_schema<json> compiled = jsonschema::make_json_schema(schema);
// will throw a validation_error when a schema violation happens
json patch;
compiled.validate(data, patch);
std::cout << "Patch: " << patch << "\n";
std::cout << "Original data: " << data << "\n";
jsonpatch::apply_patch(data, patch);
std::cout << "Patched data: " << data << "\n\n";
}
catch (const std::exception& e)
{
std::cout << e.what() << "\n";
}
}
```
Output:
```
Patch: [{"op":"add","path":"/bar","value":"bad"}]
Original data: {}
Patched data: {"bar":"bad"}
```
|
