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Published 6 days ago • verified publisherglenfordwilliams.comDart 3 compatible
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A powerful and extensible Liquid template engine for Dart. Supports full Liquid syntax, custom tags and filters, and high-performance parsing and rendering.

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Liquify - Liquid Template Engine for Dart #

Liquify Logo

GitHub release Pub Version GitHub Actions Workflow Status License issues - liquify

Liquify is a comprehensive Dart implementation of the Liquid template language, originally created by Shopify. This high-performance library allows you to parse, render, and extend Liquid templates in your Dart and Flutter applications.

Features #

  • Full support for standard Liquid syntax and semantics
  • Synchronous and asynchronous rendering
  • 🔒 Environment-scoped filters and tags for security and isolation
  • 🛡️ Strict mode for security sandboxing (blocks global registry access)
  • ⚡ Template-level customization via environment setup callbacks
  • Extensible architecture for custom tags and filters (both sync and async)
  • High-performance parsing and rendering
  • Strong typing and null safety
  • Comprehensive error handling and reporting
  • Support for complex data structures and nested objects
  • Easy integration with Dart and Flutter projects
  • Extensive set of built-in filters ported from LiquidJS
  • File system abstraction for template resolution
  • Environment cloning for inheritance patterns

Installation #

Add Liquify to your package's pubspec.yaml file:

dependencies:
  liquify: ^1.2.0

Or, for the latest development version:

dependencies:
  liquify:
    git: https://github.com/kingwill101/liquify.git

Then run dart pub get or flutter pub get to install the package.

Usage #

For detailed usage examples, please refer to the example directory in the repository. Here are some basic usage scenarios:

Basic Template Rendering #

Templates can be rendered both synchronously and asynchronously:

import 'package:liquify/liquify.dart';

void main() async {
  final data = {
    'name': 'Alice',
    'items': ['apple', 'banana', 'cherry']
  };

  final template = Template.parse(
    'Hello, {{ name | upcase }}! Your items are: {% for item in items %}{{ item }}{% unless forloop.last %}, {% endunless %}{% endfor %}.',
    data: data
  );
  
  // Synchronous rendering
  final syncResult = template.render();
  print(syncResult);
  // Output: Hello, ALICE! Your items are: apple, banana, cherry.

  // Asynchronous rendering (useful for async filters or includes)
  final asyncResult = await template.renderAsync();
  print(asyncResult);
  // Output: Hello, ALICE! Your items are: apple, banana, cherry.
}

You can also update the template context between renders:

final template = Template.parse('{{ greeting }} {{ name }}!');

// Update context
template.updateContext({
  'greeting': 'Hello',
  'name': 'World'
});

print(await template.renderAsync()); // "Hello World!"

// Update context again
template.updateContext({'greeting': 'Goodbye'});
print(await template.renderAsync()); // "Goodbye World!"

Secure Template Rendering with Environment Scoping #

For applications requiring security isolation or multi-tenancy:

// Create a secure template with custom filters
final secureTemplate = Template.parse(
  'Welcome {{ username | sanitize }}! You have {{ messages | size }} messages.',
  data: {'username': '<script>alert("xss")</script>John', 'messages': ['msg1', 'msg2']},
  environmentSetup: (env) {
    // Register only safe, sanitized filters
    env.registerLocalFilter('sanitize', (value, args, namedArgs) => 
      value.toString().replaceAll(RegExp(r'[<>]'), ''));
    env.registerLocalFilter('size', (value, args, namedArgs) => 
      (value as List).length);
  },
);

print(await secureTemplate.renderAsync());
// Output: Welcome scriptalert("xss")John! You have 2 messages.

Layout Support #

Liquify provides powerful template inheritance through the layout tag, allowing you to create reusable base templates and override specific sections using blocks. This feature is particularly useful for maintaining consistent page structures while allowing customization of specific sections.

Basic Layout Usage

Here's a simple example of using layouts:

// layouts/base.liquid
<!DOCTYPE html>
<html>
<head>
  <title>{% block title %}Default Title{% endblock %}</title>
</head>
<body>
  {% block content %}Default content{% endblock %}
</body>
</html>

// page.liquid
{% layout "layouts/base.liquid" %}
{% block title %}My Page Title{% endblock %}
{% block content %}
  <h1>Welcome to my page!</h1>
  <p>This is custom content.</p>
{% endblock %}

Passing Variables to Layouts

You can pass variables from your template to the layout:

{% assign page_title = "Welcome" %}
{% layout "layouts/base.liquid", title: page_title, year: 2024 %}

Multiple Named Blocks

Layouts can define multiple named blocks that can be selectively overridden:

// layouts/post.liquid
{% layout "layouts/base.liquid" %}

{% block meta %}
  <meta name="author" content="{{ post.author }}">
{% endblock %}

{% block content %}
  <article>
    <h1>{{ post.title }}</h1>
    {% block post_content %}{% endblock %}
  </article>
{% endblock %}

// blog-post.liquid
{% layout "layouts/post.liquid", post: post %}
{% block post_content %}
  {{ post.body }}
{% endblock %}

Default Block Contents

Blocks in layouts can include default content that will be used if not overridden:

{% block footer %}
  <footer>&copy; {{ year }} Default Footer</footer>
{% endblock %}

For more complex layout examples and advanced usage, please refer to the example directory in the repository.

File System and Template Resolution #

Liquify provides flexible ways to resolve and load templates from various sources. The Root class is the base for implementing template resolution strategies.

Using MapRoot for In-Memory Templates

MapRoot is a simple implementation of Root that stores templates in memory:

import 'package:liquify/liquify.dart';

void main() {
  final fs = MapRoot({
    'resume.liquid': '''
Name: {{ name }}
Skills: {{ skills | join: ", " }}
{% render 'greeting.liquid' with name: name, greeting: "Welcome" %}
''',
    'greeting.liquid': '{{ greeting }}, {{ name }}!',
  });

  final context = {
    'name': 'Alice Johnson',
    'skills': ['Dart', 'Flutter', 'Liquid'],
  };

  final template = Template.fromFile('resume.liquid', fs, data: context);
  print(template.render());
}

Custom Template Resolution

For more complex scenarios, such as loading templates from a file system or a database, you can create a custom subclass of Root:

class FileSystemRoot extends Root {
  final String basePath;

  FileSystemRoot(this.basePath);
  
  @override
  String? resolve(String path) {
    final file = File('$basePath/$path');
    if (file.existsSync()) {
      return file.readAsStringSync();
    }
    return null;
  }
}

void main() async {
  final fs = FileSystemRoot('/path/to/templates');
  final template = Template.fromFile('resume.liquid', fs, data: context);
  
  // Sync rendering
  print(template.render());
  
  // Async rendering (recommended for templates with includes or async filters)
  print(await template.renderAsync());
}

// Example with async template resolution
class AsyncFileSystemRoot extends Root {
  final String basePath;

  AsyncFileSystemRoot(this.basePath);
  
  @override
  Future<String?> resolveAsync(String path) async {
    final file = File('$basePath/$path');
    if (await file.exists()) {
      return await file.readAsString();
    }
    return null;
  }
}

The async support is particularly useful when:

  • Loading templates from remote sources
  • Using async filters or tags
  • Processing large templates with many includes
  • Implementing database-backed template storage

This approach allows you to implement custom logic for resolving and loading templates from any source, such as a file system, database, or network resource.

The render tag uses this resolution mechanism to include and render other templates, allowing for modular and reusable template structures.

Environment-Scoped Registry (Advanced Security & Isolation) #

Liquify provides powerful environment-scoped filters and tags that allow you to create isolated template execution contexts. This feature is particularly useful for multi-tenant applications, security sandboxing, and plugin systems.

Basic Environment Usage

import 'package:liquify/liquify.dart';

void main() async {
  // Template with environment setup callback
  final template = Template.parse(
    'Hello {{ name | emphasize }}! {% custom_greeting %}',
    data: {'name': 'World'},
    environmentSetup: (env) {
      // Register custom filters and tags for this template only
      env.registerLocalFilter('emphasize', (value, args, namedArgs) => 
        '***${value.toString().toUpperCase()}***');
      env.registerLocalTag('custom_greeting', (content, filters) => 
        CustomGreetingTag(content, filters));
    },
  );

  print(await template.renderAsync());
  // Output: Hello ***WORLD***! 🎉 Welcome! 🎉
}

Security Sandboxing with Strict Mode

void main() async {
  // Create a secure environment that blocks global registry access
  final secureEnv = Environment.withStrictMode();
  
  // Only register safe, sanitized filters
  secureEnv.registerLocalFilter('sanitize', (value, args, namedArgs) {
    return value.toString()
      .replaceAll(RegExp(r'<[^>]*>'), '') // Remove HTML tags
      .replaceAll(RegExp(r'[<>"\']'), ''); // Remove dangerous characters
  });
  
  secureEnv.registerLocalFilter('truncate', (value, args, namedArgs) {
    final maxLen = args.isNotEmpty ? args[0] as int : 50;
    final str = value.toString();
    return str.length > maxLen ? '${str.substring(0, maxLen)}...' : str;
  });

  final secureTemplate = Template.parse(
    'Safe content: {{ userInput | sanitize | truncate: 20 }}',
    data: {'userInput': '<script>alert("XSS")</script>This is user input'},
    environment: secureEnv,
  );

  print(await secureTemplate.renderAsync());
  // Output: Safe content: scriptalert("XSS")Th...
  
  // Attempting to use global filters will return null in strict mode
  print(secureEnv.getFilter('dangerous_global_filter')); // null
}

Environment Isolation Between Templates

void main() async {
  // Template A with specific formatting
  final templateA = Template.parse(
    'Result: {{ value | format }}',
    data: {'value': 'test'},
    environmentSetup: (env) {
      env.registerLocalFilter('format', (value, args, namedArgs) => 
        'TEMPLATE_A_FORMAT:$value');
    },
  );

  // Template B with different formatting
  final templateB = Template.parse(
    'Result: {{ value | format }}',
    data: {'value': 'test'},
    environmentSetup: (env) {
      env.registerLocalFilter('format', (value, args, namedArgs) => 
        'TEMPLATE_B_FORMAT:$value');
    },
  );

  print(await templateA.renderAsync()); // Result: TEMPLATE_A_FORMAT:test
  print(await templateB.renderAsync()); // Result: TEMPLATE_B_FORMAT:test
}

Environment Cloning and Inheritance

void main() async {
  // Create a base environment with common filters
  final baseEnv = Environment();
  baseEnv.registerLocalFilter('base_format', (value, args, namedArgs) => 
    'BASE:$value');
  baseEnv.registerLocalTag('base_tag', (content, filters) => 
    BaseTag(content, filters));

  // Clone and extend for specific use cases
  final childEnv = baseEnv.clone();
  childEnv.registerLocalFilter('child_format', (value, args, namedArgs) => 
    'CHILD:$value');
  childEnv.registerLocalTag('child_tag', (content, filters) => 
    ChildTag(content, filters));

  final template = Template.parse(
    '''
    Base: {{ text | base_format }}
    Child: {{ text | child_format }}
    {% base_tag %}{% child_tag %}
    ''',
    data: {'text': 'test'},
    environment: childEnv,
  );

  print(await template.renderAsync());
  // Output:
  // Base: BASE:test
  // Child: CHILD:test
  // [BASE_TAG][CHILD_TAG]
}

Dynamic Environment Modification

void main() async {
  final template = Template.parse(
    'Filtered: {{ message | transform }}',
    data: {'message': 'hello'},
  );

  // Register initial filter
  template.environment.registerLocalFilter('transform', (value, args, namedArgs) => 
    'INITIAL:$value');

  print(await template.renderAsync()); // Filtered: INITIAL:hello

  // Dynamically change the filter behavior
  template.environment.registerLocalFilter('transform', (value, args, namedArgs) => 
    'UPDATED:$value');

  print(await template.renderAsync()); // Filtered: UPDATED:hello
}

Use Cases for Environment-Scoped Registry

  1. Multi-tenant Applications: Each tenant gets their own isolated environment
  2. Security Sandboxing: Restrict template capabilities for untrusted content
  3. Plugin Systems: Plugins can register their own filters/tags without conflicts
  4. API Versioning: Different API versions with different template capabilities
  5. Theme Systems: Different themes with custom visual filters
  6. Content Management: Different content types with specialized processing

Priority System

The environment-scoped registry follows a clear priority system:

  1. Local filters/tags (registered via registerLocalFilter/registerLocalTag)
  2. Global filters/tags (registered via FilterRegistry.register/TagRegistry.register)
  3. Strict mode blocks access to global registries entirely

This ensures predictable behavior while maintaining flexibility.

Custom Tags and Filters #

Liquify allows you to create custom tags and filters. For detailed examples, please refer to the example directory in the repository.

API Documentation #

Detailed API documentation is available here.

Contributing #

Contributions are welcome! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

License #

This project is licensed under the MIT License.

Acknowledgements #

  • Shopify for the original Liquid template language
  • The Dart team for the excellent language and tools
  • LiquidJS for their comprehensive set of filters, which we've ported to Dart
  • liquid_dart for their initial Dart implementation, which served as inspiration for this project
  • LiquidJS: A popular JavaScript implementation of Liquid templates
  • liquid_dart: An earlier Dart implementation of Liquid templates (now unmaintained)

Liquify aims to provide a modern, maintained, and feature-rich Liquid template engine for the Dart ecosystem, building upon the work of these excellent projects.

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Publisher

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Metadata

A powerful and extensible Liquid template engine for Dart. Supports full Liquid syntax, custom tags and filters, and high-performance parsing and rendering.

Repository (GitHub)

Topics

#liquid #templating #teamplate-engine #dart

Documentation

API reference

Funding

Consider supporting this project:

www.buymeacoffee.com

License

MIT (license)

Dependencies

args, file, gato, html, html_unescape, intl, logging, petitparser, timezone

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