Dinja

A minimal, zero-dependency Jinja templating engine for Dart, ported from llama.cpp. Focused on security, efficiency, and input marking.

Features

• Zero-Dependency: No external dependencies beyond the Dart SDK.
• Security-First: Built with specific "Input Marking" to prevent injection attacks when rendering user input.
• Lightweight: Ported from llama.cpp's minimal Jinja implementation.
• Chat Template Support: Specifically designed to faithfully render the complex chat templates used in LLM inference (e.g., Mistral, Llama 3).

Scope

This project is a minimal implementation of Jinja2. It does not support the full Jinja2 specification (e.g., custom tags, complex inheritance hierarchies, or filesystem loading are out of scope).

The primary goal is to support LLM Chat Templates and basic string rendering efficiently and securely in Dart.

Security: Input Marking

Dinja uses a taint-tracking mechanism similar to MarkupSafe in Python but adapted for this specific use case.

• JinjaString: A wrapper around strings that tracks which parts come from the template (safe) and which come from user input (unsafe).
• Automatic Escaping: untrusted user input is automatically escaped when rendered, while template structure remains untouched.

final template = Template('Hello {{ name }}');
// "name" contains HTML/special chars
final result = template.render({'name': '<script>alert(1)</script>'});
// Output: Hello &lt;script&gt;alert(1)&lt;/script&gt;

Getting started

Add dinja to your pubspec.yaml:

dependencies:
  dinja: ^1.0.0

Usage

Simple Rendering

import 'package:dinja/dinja.dart';

void main() {
  final template = Template('Hello, {{ name }}!');
  final result = template.render({'name': 'World'});
  print(result); // Hello, World!
}

Complex Templates

import 'package:dinja/dinja.dart';

void main() {
  final templateText = '''
{% for user in users %}
- {{ user.name }} ({{ user.role }})
{% endfor %}
''';
  final template = Template(templateText);
  final users = [
    {'name': 'Alice', 'role': 'Admin'},
    {'name': 'Bob', 'role': 'User'},
  ];
  final result = template.render({'users': users});
  print(result);
}

Rendering Chat Templates

Dinja is optimized for rendering chat templates (like those found in tokenizer_config.json for HuggingFace models).

import 'package:dinja/dinja.dart';

void main() {
  // A simplified Mistral-like template
  final templateSrc = "{{ bos_token }}{% for m in messages %}[INST] {{ m['content'] }} [/INST]{% endfor %}";
  final template = Template(templateSrc);

  final output = template.render({
    'bos_token': '<s>',
    'messages': [
      {'role': 'user', 'content': 'Hello!'},
      {'role': 'user', 'content': 'What is the capital of France?'}
    ]
  });

  print(output);
  // Output: <s>[INST] Hello! [/INST][INST] What is the capital of France? [/INST]
}

Additional information

This package is a direct port of the minimal Jinja implementation found in llama.cpp. It aims to provide the same functionality while adhering to Dart best practices.