YAML Parser Library

A PHP YAML parser built for learning and understanding the YAML 1.2 specification.

Features

• Tag support: Parse standard and application-specific YAML tags.
• Anchor and alias support: Resolve anchors and aliases automatically.
• Error handling: Provide detailed messages with line and column information.
• Merge key support: Support merge keys for mappings, although they are not part of YAML 1.2.

Installation

composer require maxbeckers/php-yaml-parser

Usage

Basic Parsing

use MaxBeckers\YamlParser\YamlParser;

$yamlParser = new YamlParser();
$data = $yamlParser->parseFile('config.yaml');

Plain array output

Basic parsing returns \ArrayObject instances instead of arrays. With parsePlainArray(), \ArrayObject is used only for recursive structures that require reference handling.

use MaxBeckers\YamlParser\YamlParser;

$yamlParser = new YamlParser();

// Prefer plain arrays for normal structures.
// Circular reference paths are promoted to ArrayObject automatically.
$data = $yamlParser->parsePlainArray($yamlContent);

Parsing Configuration

use MaxBeckers\YamlParser\Config\ParsingConfig;
use MaxBeckers\YamlParser\YamlParser;

$yamlParser = new YamlParser(config: new ParsingConfig(
    strictMode: true,
    returnPlainArrays: true,
    maxDepth: 64,
    maxFileSize: 10 * 1024 * 1024,
    preserveMetadata: true,
));
$data = $yamlParser->parseFile('config.yaml');

Available options are strictMode, returnPlainArrays, maxDepth, maxFileSize, and preserveMetadata.

Custom Tag Handlers

Application-specific tags can transform scalar or collection values during scanning:

use MaxBeckers\YamlParser\Tag\CustomTagHandler;

$yamlParser->getTagRegistry()->register(
    new CustomTagHandler(
        '!env',
        static fn (mixed $value): string => getenv((string) $value) ?: (string) $value,
    ),
);

$data = $yamlParser->parse('database_host: !env DATABASE_HOST');

Handlers may accept a second NodeMetadataInterface argument to inspect the tag and its source line and column. %TAG shorthand can be handled by registering the expanded tag URI.

Metadata and Diagnostics

Enable preserveMetadata to query line, column, tag, anchor, and alias data after parsing:

use MaxBeckers\YamlParser\Config\ParsingConfig;
use MaxBeckers\YamlParser\Service\ErrorReporter;
use MaxBeckers\YamlParser\YamlParser;

$yaml = <<<'YAML'
name: Jane
items:
  - one
YAML;

$parser = new YamlParser(config: new ParsingConfig(preserveMetadata: true));
$result = $parser->parse($yaml);

$provider = $parser->getMetadataProvider();
$valueMetadata = $provider->getMetadata('items.0');      // value node metadata
$keyMetadata = $provider->getKeyMetadata('name');        // key node metadata
$wrapped = $provider->getValueWithMetadata($result, 'items.0');

$reporter = new ErrorReporter();
echo $reporter->formatForPath('Invalid list item', $provider, 'items.0');
// Invalid list item at line 3, column 4

Contributing

Contributions are welcome. Feel free to submit issues or pull requests.

Acknowledgments

Developed with reference to the YAML 1.2.2 Specification.

License

This project is licensed under the MIT License - see the LICENSE file for details.

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Questions or Issues? Please open an issue on GitHub.

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