# erlang_template_helper

**Repository Path**: mirrors_basho/erlang_template_helper

## Basic Information

- **Project Name**: erlang_template_helper
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2020-08-08
- **Last Updated**: 2026-01-24

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# 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:

```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}]`

```ruby
> 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:

```ruby
class String
  include Eth::Erlang::String
end

class Array
  include Eth::Erlang::Array
end
```

Using `to_erl_string`:

```ruby
> 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`:

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

Using `to_erl_tuple`:

```ruby
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:

```ruby
> 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:

```bash
$ ./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"
        }
      ]
    ]
  }
}
```

```bash
$ ./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