# Burnex
<!--MDOC !-->
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Compare an email address against 3900+ burner email domains (temporary email
providers) based on this list from
[https://github.com/wesbos/burner-email-providers](https://github.com/wesbos/burner-email-providers).
## Installation
Add `:burnex` to your list of dependencies in `mix.exs`.
```elixir
def deps do
[
{:burnex, "~> 3.1.0"}
]
end
```
## Usage
Be aware that Burnex will not check if the email is RFC compliant, it will only
check the domain (everything that comes after `@`).
```elixir
iex> Burnex.is_burner?("my-email@gmail.com")
false
iex> Burnex.is_burner?("my-email@yopmail.fr")
true
iex> Burnex.is_burner? "invalid.format.yopmail.fr"
false
iex> Burnex.is_burner? "\"this is a valid address! crazy right ?\"@yopmail.fr"
true
iex> Burnex.providers |> MapSet.member?("yopmail.fr")
true
```
### With an Ecto changeset
Following code ensures email has a valid format then check if it belongs to a burner provider:
```elixir
def changeset(model, params) do
model
|> cast(params, @required_fields ++ @optional_fields)
|> validate_required([:email])
|> validate_email()
end
@email_regex ~r/\A([\w+\-].?)+@[a-z\d\-]+(\.[a-z]+)*\.[a-z]+\z/i
defp validate_email(%{changes: %{email: email}} = changeset) do
case Regex.match?(@email_regex, email) do
true ->
case Burnex.is_burner?(email) do
true -> add_error(changeset, :email, "forbidden_provider")
false -> changeset
end
false -> add_error(changeset, :email, "invalid_format")
end
end
defp validate_email(changeset), do: changeset
```
### MX record DNS resolution
As an extra precaution against newly-created burner domains,
you can use Burnex to do MX record DNS resolution.
This is done like this:
```
iex> Burnex.check_domain_mx_record("gmail.com")
:ok
iex> Burnex.check_domain_mx_record("gmail.dklfsd")
{:error, "Cannot find MX records"}
```
Here is an example function to check if an email is valid:
```elixir
# Use a regex capture to get the "domain" part of an email
@email_regex ~r/^\S+@(\S+\.\S+)$/
# hard-code some trusted domains to avoid checking their MX record every time
@good_email_domains [
"gmail.com",
"fastmail.com"
]
defp email_domain(email), do: Regex.run(@email_regex, String.downcase(email))
defp is_not_burner?(email, domain) do
with {:is_burner, false} <- {:is_burner, Burnex.is_burner?(email)},
{:check_mx_record, :ok} <- {:check_mx_record, Burnex.check_domain_mx_record(domain)} do
true
else
{:is_burner, true} ->
{false, "forbidden email"}
{:check_mx_record, {:error, error_message}} when is_binary(error_message) ->
{false, error_message}
{:check_mx_record, :error} ->
{false, "forbidden provider"}
end
end
@spec is_valid?(String.t()) :: true | {false, String.t()}
def is_valid?(email) do
case email_domain(email) do
[_ | [domain]] when domain in @good_email_domains ->
true
[_ | [domain]] ->
is_not_burner?(email, domain)
_ ->
{false, "Email in bad format"}
end
end
```
## License
This software is licensed under MIT license. Copyright (c) 2018- Benjamin Piouffle.