ErlangTemplateHelper

This library allows one to specify Erlang config and args files in JSON. This is useful when deploying an Erlang application with Chef. For example, here is a snippet of a Riak config file specified in JSON:

{
  "riak_kv": {
    "storage_backend": "riak_kv_multi_backend",
    "multi_backend_default": "first_backend",
    "multi_backend": [
      ["__tuple", "first_backend", "riak_kv_bitcask_backend", {
        "data_root": "__string_/var/lib/riak/bitcask"}],
      ["__tuple", "second_backend", "riak_kv_leveldb_backend", {
        "data_root": "__string_/var/lib/riak/leveldb"}]
    ]
  }
}

Usage

Config

• JSON strings are Erlang atoms unless prefixed with __binary_, or __string_. The prefix __atom_ is also recognized.
  • "ok" becomes ok
  • "__binary_0b:" becomes <<"0b:">>
  • "__string_127.0.0.1" becomes "127.0.0.1"
  • "__atom_ok" becomes ok
  • Atoms will be single quoted when necessary
    • "riak@127.0.0.1" becomes 'riak@127.0.0.1'
• JSON arrays are Erlang lists unless prefixed with __tuple. The prefix __list is also recognized.
  • [1, 2, 3] becomes [1, 2, 3]
  • ["__tuple", 1, 2, 3] becomes {1, 2, 3}
  • ["__list", 1, 2, 3] becomes [1, 2, 3]
• JSON objects are Erlang proplists.
  • {"storage_backend":"bitcask"} becomes [{storage_backend, bitcask}]

> require "erlang_template_helper"
=> true
> config = Eth::Config.new({"riak_kv" => {"storage_backend" => "bitcask"}})
=> [{riak_kv, [{storage_backend, bitcask}]}]
> puts config.pp
[
	{riak_kv, [
		{storage_backend, bitcask}
	]}
]
=> nil

String, Array Helpers

Helper methods are provided for the String and Array classes as an alternate to using prefixes in Ruby code. They need to be included into the appropriate class before using.

Including the modules:

class String
  include Eth::Erlang::String
end

class Array
  include Eth::Erlang::Array
end

Using to_erl_string:

> class String; include Eth::Erlang::String; end
=> String
> Eth::Config.new({"data_root" => "/var/lib/riak/leveldb".to_erl_string})
=> [{data_root, "/var/lib/riak/leveldb"}].

Using to_erl_binary:

> class String; include Eth::Erlang::String; end
=> String
> Eth::Config.new({"0b:".to_erl_binary => "be_blocks"})
=> [{<<"0b:">>, be_blocks}].

Using to_erl_tuple:

class Array; include Eth::Erlang::Array; end
> Eth::Config.new(["be_default", "riak_kv_eleveldb_backend", {"max_open_files" => 20}].to_erl_tuple)
=> {be_default, riak_kv_eleveldb_backend, [{max_open_files, 20}]}.

Args

Arguments can be specified as a simple JSON object. Nested objects are flattened by joining the keys and final value by a single space. For example:

> require "erlang_template_helper"
=> true
> args = Eth::Args.new({"-name" => "riak@127.0.0.1", "-env" => {"ERL_MAX_PORTS" => 4096}})
=> -name riak@127.0.0.1 -env ERL_MAX_PORTS 4096
> puts args.pp
-name riak@127.0.0.1
-env ERL_MAX_PORTS 4096
=> nil

Command line applications

Two command line applications are provided in bin. These are:

• config_to_json
• json_to_config

These applications allow one to convert between Erlang config format and the JSON specification used by ErlangTemplateHelper. They work as follows:

$ ./bin/config_to_json test/examples/multi_backend.config -p
{
  "riak_kv": {
    "multi_backend_prefix_list": {
      "__binary_0b:": "be_blocks"
    },
    "multi_backend": [
      [
        "__tuple",
        "be_default",
        "riak_kv_eleveldb_backend",
        {
          "cache_size": 47721858,
          "data_root": "__string_/var/lib/riak/leveldb",
          "max_open_files": 50
        }
      ],
      [
        "__tuple",
        "be_blocks",
        "riak_kv_bitcask_backend",
        {
          "data_root": "__string_/var/lib/riak/bitcask"
        }
      ]
    ]
  }
}

$ ./bin/json_to_config test/examples/multi_backend.json -p  
[
	{riak_kv, [
		{multi_backend_prefix_list, [
			{<<"0b:">>, be_blocks}
		]}, 
		{multi_backend, [
			{be_default, riak_kv_eleveldb_backend, [
					{cache_size, 47721858}, 
					{data_root, "/var/lib/riak/leveldb"}, 
					{max_open_files, 50}
				]}, 
			{be_blocks, riak_kv_bitcask_backend, [
					{data_root, "/var/lib/riak/bitcask"}
				]}
		]}
	]}
].

Contributing

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