front_matter_parser

FrontMatterParser

FrontMatterParser is a library to parse a front matter from strings or files. It allows writing syntactically correct source files, marking front matters as comments in the source file language.

Installation

Add this line to your application's Gemfile:

gem 'front_matter_parser'

or, to get the development version:

gem 'front_matter_parser', github: 'waiting-for-dev/front_matter_parser'

And then execute:

$ bundle

Or install it yourself as:

$ gem install front_matter_parser

Usage

Front matters must be between two lines with three dashes ---.

For example, given a file example.md:

---
title: Hello World
category: Greetings
---
Some actual content

You can parse it:

parsed = FrontMatterParser::Parser.parse_file('example.md')
parsed.front_matter #=> {'title' => 'Hello World', 'category' => 'Greetings'}
parsed.content #=> 'Some actual content'

You can directly apply [] method to get a front matter value:

parsed['category'] #=> 'Greetings'

Syntax autodetection

FrontMatterParser detects the syntax of a file by its extension and it supposes that the front matter is within that syntax comment delimiters.

For example, given a file example.haml:

-#
   ---
   title: Hello
   ---
Content

The -# and the indentation enclose the front matter as a comment. FrontMatterParser is aware of that, so you can simply do:

title = FrontMatterParser::Parser.parse_file('example.haml')['title'] #=> 'Hello'

Following there is a relation of known syntaxes and their known comment delimiters:

Syntax	Single line comment	Start multiline comment	End multiline comment
haml		-#	(indentation)
slim		/	(indentation)
liquid		{% comment %}	{% endcomment %}
md
html		<!--	-->
erb		<%#	%>
coffee	#
sass	//
scss	//

Parsing a string

You can as well parse a string providing manually the syntax:

string = File.read('example.slim')
FrontMatterParser::Parser.new(:slim).call(string)

Custom parsers

You can implement your own parsers for other syntaxes. Most of the times, they will need to parse a syntax with single line comments, multi line comments or closed by indentation comments. For these cases, this library provides helper factory methods. For example, if they weren't already implemented, you could do something like:

CoffeeParser = FrontMatterParser::SyntaxParser::SingleLineComment['#']
HtmlParser = FrontMatterParser::SyntaxParser::MultiLineComment['<!--', '-->']
SlimParser = FrontMatterParser::SyntaxParser::IndentationComment['/']

You would use them like this:

slim_parser = SlimParser.new

# For a file
FrontMatterParser::Parser.parse_file('example.slim', syntax_parser: slim_parser)

# For a string
FrontMatterParser::Parser.new(slim_parser).call(string)

For more complex scenarios, a parser can be anything responding to a method call(string) which returns a hash interface with :front_matter and :content keys, or nil if no front matter is found.

Custom loaders

Once a front matter is matched from a string, it is loaded as if it were a YAML text. However, you can also implement your own loaders. They just need to implement a call(string) method. You would use it like the following:

json_loader = ->(string) { JSON.load(string) }

# For a file
FrontMatterParser::Parser.parse_file('example.md', loader: json_loader)

# For a string
FrontMatterParser::Parser.new(:md, loader: json_loader).call(string)

If you need to allow one or more classes for the built-in YAML loader, you can just create a custom loader based on it and provide needed classes in a allowlist_classes: param:

loader = FrontMatterParser::Loader::Yaml.new(allowlist_classes: [Time])
parsed = FrontMatterParser::Parser.parse_file('example.md', loader: loader)
puts parsed['timestamp']

Development

There are docker and docker-compose files configured to create a development environment for this gem. So, if you use Docker you only need to run:

docker-compose up -d

An then, for example:

docker-compose exec app rspec

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Release Policy

front_matter_parser follows the principles of semantic versioning.

Other ruby front matter parsers

• front-matter Can parse YAML front matters with single line comments delimiters. YAML must be correctly indented.
• ruby_front_matter Can parse JSON front matters and can configure front matter global delimiters, but does not accept comment delimiters.

LICENSE

Copyright 2013 Marc Busqué - [e-mail]

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.