defmodule Dotenvy do
@moduledoc """
`Dotenvy` is an Elixir port of the original [dotenv](https://github.com/bkeepers/dotenv) Ruby gem.
It is designed to help applications follow the principles of
the [12-factor app](https://12factor.net/) and its recommendation to store
configuration in the environment.
Unlike other configuration helpers, `Dotenvy` enforces no convention for the naming
of your files: `.env` is a common choice, you may name your configuration files whatever
you wish.
See the [strategies](docs/strategies.md) for examples of various use cases.
"""
import Dotenvy.Transformer
alias Dotenvy.Transformer.Error
require Logger
@typedoc """
An input source may be either a path to an env file or a map with string keys,
e.g. `"envs/.env"` or `%{"FOO" => "bar"}`. This allows users to specify a list
of env files interspersed with other values from other sources, e.g. `System.get_env()`
or values fetched from a secure parameter store.
"""
@type input_source :: String.t() | %{optional(String.t()) => String.t()}
@default_parser Dotenvy.Parser
@doc """
A parser implementation should receive the `contents` read from a file,
a map of `vars` (with string keys, as would come from `System.get_env/0`),
and a keyword list of `opts`.
This callback is provided to help facilitate testing. See `Dotenvy.Parser`
for the default implementation.
"""
@callback parse(contents :: binary(), vars :: map(), opts :: keyword()) ::
{:ok, map()} | {:error, any()}
@doc """
Reads an env variable and converts its output or returns a default value.
> #### Use `env!/2` when possible {: .info}
>
> Use of `env!/2` is recommended over `env!/3` because it creates a stronger contract with
> the environment: your app literally will not start when required env variables are missing.
If the given `variable` is *set*, its value is converted to
the given `type`. The provided `default` value is _only_ used when the
variable is _not_ set; **the `default` value is returned as-is, without conversion**.
This allows greater control of the output.
This function may raise an error when the conversion is delegated to `Dotenvy.Transformer.to!/2`
-- see its documentation for a list of supported types.
This function attempts to read a value from a local data store of sourced values;
it will fall back to `System.fetch_env/1` when no locally stored variable is available.
## Examples
iex> env!("PORT", :integer, 5432)
5433
iex> env!("NOT_SET", :boolean, %{not: "converted"})
%{not: "converted"}
iex> System.put_env("HOST", "")
iex> env!("HOST", :string!, "localhost")
** (RuntimeError) Error converting HOST to string!: non-empty value required
"""
@doc since: "0.3.0"
@spec env!(
variable :: binary(),
type :: Dotenvy.Transformer.conversion_type(),
default :: any()
) :: any() | no_return()
def env!(variable, type, default) do
case fetch_var(variable) do
:error -> default
{:ok, value} -> to!(value, type)
end
rescue
error in Error ->
reraise "Error converting #{variable} to #{type}: #{error.message}", __STACKTRACE__
end
@deprecated "Use `Dotenvy.env!/3` instead"
@spec env(variable :: binary(), type :: atom(), default :: any()) :: any() | no_return()
def env(variable, type \\ :string, default \\ nil)
def env(variable, type, default), do: env!(variable, type, default)
@doc """
Reads the given env `variable` and converts its value to the given `type`.
This function attempts to read a value from a local data store of sourced values;
it will fall back to `System.fetch_env/1` when no locally stored variable is available.
This function may raise an error because type conversion is delegated to
`Dotenvy.Transformer.to!/2` -- see its documentation for a list of supported types.
## Examples
iex> env!("PORT", :integer)
5432
iex> env!("ENABLED", :boolean)
true
"""
@spec env!(variable :: binary(), type :: Dotenvy.Transformer.conversion_type()) ::
any() | no_return()
def env!(variable, type \\ :string)
def env!(variable, type) do
case fetch_var(variable) do
:error -> raise "Application environment variable #{variable} not set"
{:ok, value} -> to!(value, type)
end
rescue
error in Error ->
reraise "Error converting variable #{variable} to #{type}: #{error.message}", __STACKTRACE__
error ->
reraise error, __STACKTRACE__
end
@doc """
Like its Bash namesake command, `source/2` accumulates values from the given input(s).
The accumulated values are stored via a side effect function to make them available
to the `env!/2` and `env!/3` functions.
Think of `source/2` as a _merging operation_ which can accept maps (like `Map.merge/2`)
or paths to env files.
Inputs are processed from left to right so that values can be overridden by each
subsequent input. As with `Map.merge/2`, the right-most input takes precedence.
## Options
- `:parser` module that implements `c:Dotenvy.parse/3` callback. Default: `Dotenvy.Parser`
- `:require_files` specifies which of the given `files` (if any) *must* be present.
When `true`, all the listed files must exist.
When `false`, none of the listed files must exist.
When some of the files are required and some are optional, provide a list
specifying which files are required. If a file listed here is not included
in the function's `files` argument, it is ignored. Default: `false`
- `:side_effect` an arity 1 function called after the successful parsing inputs.
The default is an internal function that stores the values inside a process dictionary so
the values are available to the `env!/2` and `env!/3` functions.
You may also set this value to `false` to disable a side-effect altogether, but this will
effectively neutralize the `env!/2` function.
## Examples
The simplest implementation is to parse a single file by including its path:
iex> Dotenvy.source(".env")
{:ok, %{
"TIMEOUT" => "5000",
"DATABASE_URL" => "postgres://postgres:postgres@localhost/myapp",
# ...etc...
}
}
More commonly, you will source _multiple_ files (often based on the `config_env()`)
and you will defer to pre-existing system variables. The most common pattern looks like this:
iex> Dotenvy.source([
"\#\{config_env()\}.env",
"\#\{config_env()\}.override.env",
System.get_env()
])
In the above example, the `prod.env`, `dev.env`, and `test.env` files would be version-controlled,
but the `*.override.env` variants would be ignored, giving developers the ability to override
values without needing to modify versioned files.
> #### Give Precedence to System Envs! {: .warning}
>
> Don't forget to include `System.get_env()` as the final input to `source/2` so that
> system environment variables take precedence over values sourced from `.env` files.
>
> When you run a shell command like `❯ LOG_LEVEL=debug mix run`, your expectation is probably that
> the `LOG_LEVEL` variable would be set to `debug`, overriding whatever may have been defined
> in your sourced `.env` files. Similarly, you may export env vars in your Bash profile.
> System env vars are not granted precedence automatically: you must explicitly include
> `System.get_env()` as the final input to `source/2`.
If your env files are making use of variable substitution based on system env vars,
e.g. `${PWD}` (see the [Dotenv File Format](docs/dotenv-file-format.md)), then you
would need to include `System.get_env()` _before_ your inputs.
For example, if your `.env` references the system `HOME` variable:
```
# .env
CACHE_DIR=${HOME}/cache
```
then your `source/2` command would need to make the system env vars available
to the parser by including them as one of the inputs, e.g.
iex> Dotenvy.source([System.get_env(), ".env"])
Including the `System.get_env()` before your files means that your files have final
say over the values, potentially overriding any pre-existing system env vars. In
some cases, you may wish to reference the system vars both _before and after_ your own
.env files, e.g.
iex> Dotenvy.source([System.get_env(), ".env", System.get_env()])
or you may wish to cherry-pick which variables you need to make available for
variable substitution:
iex> Dotenvy.source([
%{"HOME" => System.get_env("HOME")},
".env",
System.get_env()
])
This syntax favors explicitness so there is no confusion over what might have been
"automagically" accumulated.
"""
@spec source(inputs :: input_source() | [input_source()], opts :: keyword()) ::
{:ok, %{optional(String.t()) => String.t()}} | {:error, any()}
def source(files, opts \\ [])
def source(file, opts) when is_binary(file), do: source([file], opts)
def source(inputs, opts) when is_list(inputs) do
side_effect = Keyword.get(opts, :side_effect, &put_all_vars/1)
require_files = Keyword.get(opts, :require_files, false)
with :ok <- verify_inputs(inputs, require_files),
{:ok, vals} <- acc_vals(inputs, %{}, opts) do
if is_function(side_effect), do: side_effect.(vals)
{:ok, vals}
end
end
@doc """
As `source/2`, but returns a map on success or raises on error.
"""
@spec source!(files :: binary() | [binary()], opts :: keyword()) ::
%{optional(String.t()) => String.t()} | no_return()
def source!(files, opts \\ [])
def source!(file, opts) when is_binary(file), do: source!([file], opts)
def source!(files, opts) when is_list(files) do
case source(files, opts) do
{:ok, vars} -> vars
{:error, error} -> raise error
end
end
defp fetch_var(variable) do
:dotenvy_vars
|> Process.get(%{})
|> Map.fetch(variable)
|> case do
{:ok, value} -> {:ok, value}
:error -> System.fetch_env(variable)
end
end
defp put_all_vars(vars), do: Process.put(:dotenvy_vars, vars)
# handles the parsing of a single file or an input map
defp acc_vals([], acc, _opts), do: {:ok, acc}
defp acc_vals([map | remaining], acc, opts) when is_map(map) do
acc_vals(remaining, Map.merge(acc, map), opts)
end
defp acc_vals([file | remaining], acc, opts) when is_binary(file) do
parser = Keyword.get(opts, :parser, @default_parser)
require_files = Keyword.get(opts, :require_files, false)
with {:ok, contents} <- read_file(file, require_files),
{:ok, new_vars} <- parser.parse(contents, acc, opts) do
acc_vals(remaining, Map.merge(acc, new_vars), opts)
else
:continue ->
acc_vals(remaining, acc, opts)
{:error, error} ->
{:error, "There was error with file #{inspect(file)}: #{inspect(error)}"}
end
end
@spec verify_inputs(list(), list() | boolean()) :: :ok | {:error, any()}
defp verify_inputs(_, true), do: :ok
defp verify_inputs(_, false), do: :ok
defp verify_inputs(inputs, require_files) do
input_set = inputs |> Enum.filter(fn x -> is_binary(x) end) |> MapSet.new()
required_set = MapSet.new(require_files)
case MapSet.equal?(required_set, input_set) || MapSet.subset?(required_set, input_set) do
true -> :ok
false -> {:error, "Missing one or more files specified by :require_files"}
end
end
# Reads the file after checking whether or not it exists
@spec read_file(file :: binary(), true | false | [binary()]) ::
{:ok, binary()} | {:error, any()} | :continue
defp read_file(file, false) do
case File.exists?(file) do
true -> File.read(file)
false -> :continue
end
end
defp read_file(file, true) do
case File.exists?(file) do
true -> File.read(file)
false -> {:error, "file not found"}
end
end
defp read_file(file, require_files) when is_list(require_files) do
file
|> read_file(Enum.member?(require_files, file))
end
end
