summaryrefslogtreecommitdiff
path: root/src/libcamera/yaml_parser.cpp
blob: c96e99e1317c55b9ff8caad141cf4758bdb76281 (plain)
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
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2022, Google Inc.
 *
 * yaml_parser.cpp - libcamera YAML parsing helper
 */

#include "libcamera/internal/yaml_parser.h"

#include <cstdlib>
#include <errno.h>
#include <functional>
#include <limits>

#include <libcamera/base/file.h>
#include <libcamera/base/log.h>

#include <yaml.h>

/**
 * \file libcamera/internal/yaml_parser.h
 * \brief A YAML parser helper
 */

namespace libcamera {

LOG_DEFINE_CATEGORY(YamlParser)

namespace {

/* Empty static YamlObject as a safe result for invalid operations */
static const YamlObject empty;

} /* namespace */

/**
 * \class YamlObject
 * \brief A class representing the tree structure of the YAML content
 *
 * The YamlObject class represents the tree structure of YAML content. A
 * YamlObject can be a dictionary or list of YamlObjects or a value if a tree
 * leaf.
 */

YamlObject::YamlObject()
	: type_(Type::Value)
{
}

YamlObject::~YamlObject() = default;

/**
 * \fn YamlObject::isValue()
 * \brief Return whether the YamlObject is a value
 *
 * \return True if the YamlObject is a value, false otherwise
 */

/**
 * \fn YamlObject::isList()
 * \brief Return whether the YamlObject is a list
 *
 * \return True if the YamlObject is a list, false otherwise
 */

/**
 * \fn YamlObject::isDictionary()
 * \brief Return whether the YamlObject is a dictionary
 *
 * \return True if the YamlObject is a dictionary, false otherwise
 */

/**
 * \fn YamlObject::size()
 * \brief Retrieve the number of elements in a dictionary or list YamlObject
 *
 * This function retrieves the size of the YamlObject, defined as the number of
 * child elements it contains. Only YamlObject instances of Dictionary or List
 * types have a size, calling this function on other types of instances is
 * invalid and results in undefined behaviour.
 *
 * \return The size of the YamlObject
 */
std::size_t YamlObject::size() const
{
	switch (type_) {
	case Type::Dictionary:
	case Type::List:
		return list_.size();
	default:
		return 0;
	}
}

/**
 * \fn template<typename T> YamlObject::get<T>() const
 * \brief Parse the YamlObject as a \a T value
 *
 * This function parses the value of the YamlObject as a \a T object, and
 * returns the value. If parsing fails (usually because the YamlObject doesn't
 * store a \a T value), std::nullopt is returned.
 *
 * \return The YamlObject value, or std::nullopt if parsing failed
 */

/**
 * \fn template<typename T> YamlObject::get<T>(const T &defaultValue) const
 * \brief Parse the YamlObject as a \a T value
 * \param[in] defaultValue The default value when failing to parse
 *
 * This function parses the value of the YamlObject as a \a T object, and
 * returns the value. If parsing fails (usually because the YamlObject doesn't
 * store a \a T value), the \a defaultValue is returned.
 *
 * \return The YamlObject value, or \a defaultValue if parsing failed
 */

#ifndef __DOXYGEN__

template<>
std::optional<bool> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	if (value_ == "true")
		return true;
	else if (value_ == "false")
		return false;

	return {};
}

template<>
std::optional<int16_t> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	if (value_ == "")
		return {};

	char *end;

	errno = 0;
	int16_t value = std::strtol(value_.c_str(), &end, 10);

	if ('\0' != *end || errno == ERANGE ||
	    value < std::numeric_limits<int16_t>::min() ||
	    value > std::numeric_limits<int16_t>::max())
		return {};

	return value;
}

template<>
std::optional<uint16_t> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	if (value_ == "")
		return {};

	/*
	 * libyaml parses all scalar values as strings. When a string has
	 * leading spaces before a minus sign, for example "  -10", strtoul
	 * skips leading spaces, accepts the leading minus sign, and the
	 * calculated digits are negated as if by unary minus. Rule it out in
	 * case the user gets a large number when the value is negative.
	 */
	std::size_t found = value_.find_first_not_of(" \t");
	if (found != std::string::npos && value_[found] == '-')
		return {};

	char *end;

	errno = 0;
	uint16_t value = std::strtoul(value_.c_str(), &end, 10);

	if ('\0' != *end || errno == ERANGE ||
	    value < std::numeric_limits<uint16_t>::min() ||
	    value > std::numeric_limits<uint16_t>::max())
		return {};

	return value;
}

template<>
std::optional<int32_t> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	if (value_ == "")
		return {};

	char *end;

	errno = 0;
	long value = std::strtol(value_.c_str(), &end, 10);

	if ('\0' != *end || errno == ERANGE ||
	    value < std::numeric_limits<int32_t>::min() ||
	    value > std::numeric_limits<int32_t>::max())
		return {};

	return value;
}

template<>
std::optional<uint32_t> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	if (value_ == "")
		return {};

	/*
	 * libyaml parses all scalar values as strings. When a string has
	 * leading spaces before a minus sign, for example "  -10", strtoul
	 * skips leading spaces, accepts the leading minus sign, and the
	 * calculated digits are negated as if by unary minus. Rule it out in
	 * case the user gets a large number when the value is negative.
	 */
	std::size_t found = value_.find_first_not_of(" \t");
	if (found != std::string::npos && value_[found] == '-')
		return {};

	char *end;

	errno = 0;
	unsigned long value = std::strtoul(value_.c_str(), &end, 10);

	if ('\0' != *end || errno == ERANGE ||
	    value < std::numeric_limits<uint32_t>::min() ||
	    value > std::numeric_limits<uint32_t>::max())
		return {};

	return value;
}

template<>
std::optional<double> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	if (value_ == "")
		return {};

	char *end;

	errno = 0;
	double value = std::strtod(value_.c_str(), &end);

	if ('\0' != *end || errno == ERANGE)
		return {};

	return value;
}

template<>
std::optional<std::string> YamlObject::get() const
{
	if (type_ != Type::Value)
		return {};

	return value_;
}

template<>
std::optional<Size> YamlObject::get() const
{
	if (type_ != Type::List)
		return {};

	if (list_.size() != 2)
		return {};

	auto width = list_[0].value->get<uint32_t>();
	if (!width)
		return {};

	auto height = list_[1].value->get<uint32_t>();
	if (!height)
		return {};

	return Size(*width, *height);
}

#endif /* __DOXYGEN__ */

/**
 * \fn template<typename T> YamlObject::getList<T>() const
 * \brief Parse the YamlObject as a list of \a T
 *
 * This function parses the value of the YamlObject as a list of \a T objects,
 * and returns the value as a \a std::vector<T>. If parsing fails, std::nullopt
 * is returned.
 *
 * \return The YamlObject value as a std::vector<T>, or std::nullopt if parsing
 * failed
 */

#ifndef __DOXYGEN__

template<typename T,
	 std::enable_if_t<
		 std::is_same_v<bool, T> ||
		 std::is_same_v<double, T> ||
		 std::is_same_v<int16_t, T> ||
		 std::is_same_v<uint16_t, T> ||
		 std::is_same_v<int32_t, T> ||
		 std::is_same_v<uint32_t, T> ||
		 std::is_same_v<std::string, T> ||
		 std::is_same_v<Size, T>> *>
std::optional<std::vector<T>> YamlObject::getList() const
{
	if (type_ != Type::List)
		return std::nullopt;

	std::vector<T> values;
	values.reserve(list_.size());

	for (const YamlObject &entry : asList()) {
		const auto value = entry.get<T>();
		if (!value)
			return std::nullopt;
		values.emplace_back(*value);
	}

	return values;
}

template std::optional<std::vector<bool>> YamlObject::getList<bool>() const;
template std::optional<std::vector<double>> YamlObject::getList<double>() const;
template std::optional<std::vector<int16_t>> YamlObject::getList<int16_t>() const;
template std::optional<std::vector<uint16_t>> YamlObject::getList<uint16_t>() const;
template std::optional<std::vector<int32_t>> YamlObject::getList<int32_t>() const;
template std::optional<std::vector<uint32_t>> YamlObject::getList<uint32_t>() const;
template std::optional<std::vector<std::string>> YamlObject::getList<std::string>() const;
template std::optional<std::vector<Size>> YamlObject::getList<Size>() const;

#endif /* __DOXYGEN__ */

/**
 * \fn YamlObject::asDict() const
 * \brief Wrap a dictionary YamlObject in an adapter that exposes iterators
 *
 * The YamlObject class doesn't directly implement iterators, as the iterator
 * type depends on whether the object is a Dictionary or List. This function
 * wraps a YamlObject of Dictionary type into an adapter that exposes
 * iterators, as well as begin() and end() functions, allowing usage of
 * range-based for loops with YamlObject. As YAML mappings are not ordered, the
 * iteration order is not specified.
 *
 * The iterator's value_type is a
 * <em>std::pair<const std::string &, const \ref YamlObject &></em>.
 *
 * If the YamlObject is not of Dictionary type, the returned adapter operates
 * as an empty container.
 *
 * \return An adapter of unspecified type compatible with range-based for loops
 */

/**
 * \fn YamlObject::asList() const
 * \brief Wrap a list YamlObject in an adapter that exposes iterators
 *
 * The YamlObject class doesn't directly implement iterators, as the iterator
 * type depends on whether the object is a Dictionary or List. This function
 * wraps a YamlObject of List type into an adapter that exposes iterators, as
 * well as begin() and end() functions, allowing usage of range-based for loops
 * with YamlObject. As YAML lists are ordered, the iteration order is identical
 * to the list order in the YAML data.
 *
 * The iterator's value_type is a <em>const YamlObject &</em>.
 *
 * If the YamlObject is not of List type, the returned adapter operates as an
 * empty container.
 *
 * \return An adapter of unspecified type compatible with range-based for loops
 */

/**
 * \fn YamlObject::operator[](std::size_t index) const
 * \brief Retrieve the element from list YamlObject by index
 *
 * This function retrieves an element of the YamlObject. Only YamlObject
 * instances of List type associate elements with index, calling this function
 * on other types of instances is invalid and results in undefined behaviour.
 *
 * \return The YamlObject as an element of the list
 */
const YamlObject &YamlObject::operator[](std::size_t index) const
{
	if (type_ != Type::List || index >= size())
		return empty;

	return *list_[index].value;
}

/**
 * \fn YamlObject::contains()
 * \brief Check if an element of a dictionary exists
 *
 * This function check if the YamlObject contains an element. Only YamlObject
 * instances of Dictionary type associate elements with names, calling this
 * function on other types of instances is invalid and results in undefined
 * behaviour.
 *
 * \return True if an element exists, false otherwise
 */
bool YamlObject::contains(const std::string &key) const
{
	if (dictionary_.find(std::ref(key)) == dictionary_.end())
		return false;

	return true;
}

/**
 * \fn YamlObject::operator[](const std::string &key) const
 * \brief Retrieve a member by name from the dictionary
 *
 * This function retrieve a member of a YamlObject by name. Only YamlObject
 * instances of Dictionary type associate elements with names, calling this
 * function on other types of instances is invalid and results in undefined
 * behaviour.
 *
 * \return The YamlObject corresponding to the \a key member
 */
const YamlObject &YamlObject::operator[](const std::string &key) const
{
	if (type_ != Type::Dictionary || !contains(key))
		return empty;

	auto iter = dictionary_.find(key);
	return *iter->second;
}

#ifndef __DOXYGEN__

class YamlParserContext
{
public:
	YamlParserContext();
	~YamlParserContext();

	int init(File &file);
	int parseContent(YamlObject &yamlObject);

private:
	struct EventDeleter {
		void operator()(yaml_event_t *event) const
		{
			yaml_event_delete(event);
			delete event;
		}
	};
	using EventPtr = std::unique_ptr<yaml_event_t, EventDeleter>;

	static int yamlRead(void *data, unsigned char *buffer, size_t size,
			    size_t *sizeRead);

	EventPtr nextEvent();

	void readValue(std::string &value, EventPtr event);
	int parseDictionaryOrList(YamlObject::Type type,
				  const std::function<int(EventPtr event)> &parseItem);
	int parseNextYamlObject(YamlObject &yamlObject, EventPtr event);

	bool parserValid_;
	yaml_parser_t parser_;
};

/**
 * \class YamlParserContext
 * \brief Class for YamlParser parsing and context data
 *
 * The YamlParserContext class stores the internal yaml_parser_t and provides
 * helper functions to do event-based parsing for YAML files.
 */
YamlParserContext::YamlParserContext()
	: parserValid_(false)
{
}

/**
 * \class YamlParserContext
 * \brief Destructor of YamlParserContext
 */
YamlParserContext::~YamlParserContext()
{
	if (parserValid_) {
		yaml_parser_delete(&parser_);
		parserValid_ = false;
	}
}

/**
 * \fn YamlParserContext::init()
 * \brief Initialize a parser with an opened file for parsing
 * \param[in] fh The YAML file to parse
 *
 * Prior to parsing the YAML content, the YamlParserContext must be initialized
 * with a file to create an internal parser. The file needs to stay valid until
 * parsing completes.
 *
 * \return 0 on success or a negative error code otherwise
 * \retval -EINVAL The parser has failed to initialize
 */
int YamlParserContext::init(File &file)
{
	/* yaml_parser_initialize returns 1 when it succeededs */
	if (!yaml_parser_initialize(&parser_)) {
		LOG(YamlParser, Error) << "Failed to initialize YAML parser";
		return -EINVAL;
	}
	parserValid_ = true;
	yaml_parser_set_input(&parser_, &YamlParserContext::yamlRead, &file);

	return 0;
}

int YamlParserContext::yamlRead(void *data, unsigned char *buffer, size_t size,
				size_t *sizeRead)
{
	File *file = static_cast<File *>(data);

	Span<unsigned char> buf{ buffer, size };
	ssize_t ret = file->read(buf);
	if (ret < 0)
		return 0;

	*sizeRead = ret;
	return 1;
}

/**
 * \fn YamlParserContext::nextEvent()
 * \brief Get the next event
 *
 * Get the next event in the current YAML event stream, and return nullptr when
 * there is no more event.
 *
 * \return The next event on success or nullptr otherwise
 */
YamlParserContext::EventPtr YamlParserContext::nextEvent()
{
	EventPtr event(new yaml_event_t);

	/* yaml_parser_parse returns 1 when it succeeds */
	if (!yaml_parser_parse(&parser_, event.get()))
		return nullptr;

	return event;
}

/**
 * \fn YamlParserContext::parseContent()
 * \brief Parse the content of a YAML document
 * \param[in] yamlObject The result of YamlObject
 *
 * Check YAML start and end events of a YAML document, and parse the root object
 * of the YAML document into a YamlObject.
 *
 * \return 0 on success or a negative error code otherwise
 * \retval -EINVAL The parser has failed to validate end of a YAML file
 */
int YamlParserContext::parseContent(YamlObject &yamlObject)
{
	/* Check start of the YAML file. */
	EventPtr event = nextEvent();
	if (!event || event->type != YAML_STREAM_START_EVENT)
		return -EINVAL;

	event = nextEvent();
	if (!event || event->type != YAML_DOCUMENT_START_EVENT)
		return -EINVAL;

	/* Parse the root object. */
	event = nextEvent();
	if (parseNextYamlObject(yamlObject, std::move(event)))
		return -EINVAL;

	/* Check end of the YAML file. */
	event = nextEvent();
	if (!event || event->type != YAML_DOCUMENT_END_EVENT)
		return -EINVAL;

	event = nextEvent();
	if (!event || event->type != YAML_STREAM_END_EVENT)
		return -EINVAL;

	return 0;
}

/**
 * \fn YamlParserContext::readValue()
 * \brief Parse event scalar and fill its content into a string
 * \param[in] value The string reference to fill value
 *
 * A helper function to parse a scalar event as string. The caller needs to
 * guarantee the event is of scaler type.
 */
void YamlParserContext::readValue(std::string &value, EventPtr event)
{
	value.assign(reinterpret_cast<char *>(event->data.scalar.value),
		     event->data.scalar.length);
}

/**
 * \fn YamlParserContext::parseDictionaryOrList()
 * \brief A helper function to abstract the common part of parsing dictionary or list
 *
 * \param[in] isDictionary True for parsing a dictionary, and false for a list
 * \param[in] parseItem The callback to handle an item
 *
 * A helper function to abstract parsing an item from a dictionary or a list.
 * The differences of them in a YAML event stream are:
 *
 * 1. The start and end event types are different
 * 2. There is a leading scalar string as key in the items of a dictionary
 *
 * The caller should handle the leading key string in its callback parseItem
 * when it's a dictionary.
 *
 * \return 0 on success or a negative error code otherwise
 * \retval -EINVAL The parser is failed to initialize
 */
int YamlParserContext::parseDictionaryOrList(YamlObject::Type type,
					     const std::function<int(EventPtr event)> &parseItem)
{
	yaml_event_type_t endEventType = YAML_SEQUENCE_END_EVENT;
	if (type == YamlObject::Type::Dictionary)
		endEventType = YAML_MAPPING_END_EVENT;

	/*
	 * Add a safety counter to make sure we don't loop indefinitely in case
	 * the YAML file is malformed.
	 */
	for (unsigned int sentinel = 1000; sentinel; sentinel--) {
		auto evt = nextEvent();
		if (!evt)
			return -EINVAL;

		if (evt->type == endEventType)
			return 0;

		int ret = parseItem(std::move(evt));
		if (ret)
			return ret;
	}

	LOG(YamlParser, Error) << "The YAML file contains a List or Dictionary"
				  " whose size exceeds the parser's limit (1000)";

	return -EINVAL;
}

/**
 * \fn YamlParserContext::parseNextYamlObject()
 * \brief Parse next YAML event and read it as a YamlObject
 * \param[in] yamlObject The result of YamlObject
 * \param[in] event The leading event of the object
 *
 * Parse next YAML object separately as a value, list or dictionary.
 *
 * \return 0 on success or a negative error code otherwise
 * \retval -EINVAL Fail to parse the YAML file.
 */
int YamlParserContext::parseNextYamlObject(YamlObject &yamlObject, EventPtr event)
{
	if (!event)
		return -EINVAL;

	switch (event->type) {
	case YAML_SCALAR_EVENT:
		yamlObject.type_ = YamlObject::Type::Value;
		readValue(yamlObject.value_, std::move(event));
		return 0;

	case YAML_SEQUENCE_START_EVENT: {
		yamlObject.type_ = YamlObject::Type::List;
		auto &list = yamlObject.list_;
		auto handler = [this, &list](EventPtr evt) {
			list.emplace_back(std::string{}, std::make_unique<YamlObject>());
			return parseNextYamlObject(*list.back().value, std::move(evt));
		};
		return parseDictionaryOrList(YamlObject::Type::List, handler);
	}

	case YAML_MAPPING_START_EVENT: {
		yamlObject.type_ = YamlObject::Type::Dictionary;
		auto &list = yamlObject.list_;
		auto handler = [this, &list](EventPtr evtKey) {
			/* Parse key */
			if (evtKey->type != YAML_SCALAR_EVENT) {
				LOG(YamlParser, Error) << "Expect key at line: "
						       << evtKey->start_mark.line
						       << " column: "
						       << evtKey->start_mark.column;
				return -EINVAL;
			}

			std::string key;
			readValue(key, std::move(evtKey));

			/* Parse value */
			EventPtr evtValue = nextEvent();
			if (!evtValue)
				return -EINVAL;

			auto &elem = list.emplace_back(std::move(key),
						       std::make_unique<YamlObject>());
			return parseNextYamlObject(*elem.value, std::move(evtValue));
		};
		int ret = parseDictionaryOrList(YamlObject::Type::Dictionary, handler);
		if (ret)
			return ret;

		auto &dictionary = yamlObject.dictionary_;
		for (const auto &elem : list)
			dictionary.emplace(elem.key, elem.value.get());

		return 0;
	}

	default:
		LOG(YamlParser, Error) << "Invalid YAML file";
		return -EINVAL;
	}
}

#endif /* __DOXYGEN__ */

/**
 * \class YamlParser
 * \brief A helper class for parsing a YAML file
 *
 * The YamlParser class provides an easy interface to parse the contents of a
 * YAML file into a tree of YamlObject instances.
 *
 * Example usage:
 *
 * \code{.unparsed}
 *
 * name:
 * 	"John"
 * numbers:
 * 	- 1
 * 	- 2
 *
 * \endcode
 *
 * The following code illustrates how to parse the above YAML file:
 *
 * \code{.cpp}
 *
 * std::unique_ptr<YamlObject> root = YamlParser::parse(fh);
 * if (!root)
 *   return;
 *
 * if (!root->isDictionary())
 *   return;
 *
 * const YamlObject &name = (*root)["name"];
 * std::cout << name.get<std::string>("") << std::endl;
 *
 * const YamlObject &numbers = (*root)["numbers"];
 * if (!numbers.isList())
 *   return;
 *
 * for (std::size_t i = 0; i < numbers.size(); i++)
 *   std::cout << numbers[i].get<int32_t>(0) << std::endl;
 *
 * \endcode
 *
 * The YamlParser::parse() function takes an open FILE, parses its contents, and
 * returns a pointer to a YamlObject corresponding to the root node of the YAML
 * document.
 *
 * The parser preserves the order of items in the YAML file, for both lists and
 * dictionaries.
 */

/**
 * \brief Parse a YAML file as a YamlObject
 * \param[in] file The YAML file to parse
 *
 * The YamlParser::parse() function takes a file, parses its contents, and
 * returns a pointer to a YamlObject corresponding to the root node of the YAML
 * document.
 *
 * \return Pointer to result YamlObject on success or nullptr otherwise
 */
std::unique_ptr<YamlObject> YamlParser::parse(File &file)
{
	YamlParserContext context;

	if (context.init(file))
		return nullptr;

	std::unique_ptr<YamlObject> root(new YamlObject());

	if (context.parseContent(*root)) {
		LOG(YamlParser, Error) << "Failed to parse YAML content";
		return nullptr;
	}

	return root;
}

} /* namespace libcamera */