Carbon

Email library written in Crystal.

Installation

Add this to your application's shard.yml:

dependencies:
  carbon:
    github: luckyframework/carbon

Adapters

• Carbon::SendGridAdapter- Ships with Carbon.
• Carbon::AwsSesAdapter - See keizo3/carbon_aws_ses_adapter.
• Carbon::SendInBlueAdapter - See atnos/carbon_send_in_blue_adapter.
• Carbon::SmtpAdapter - See oneiros/carbon_smtp_adapter.

Usage

First, create a base class for your emails

require "carbon"

# You can setup defaults in this class
abstract class BaseEmail < Carbon::Email
  # For example, set up a default 'from' address
  from Carbon::Address.new("My App Name", "support@myapp.com")
  # Use a string if you just need the email address
  from "support@myapp.com"
end

Configure the mailer class

BaseEmail.configure do |settings|
  settings.adapter = Carbon::SendGridAdapter.new(api_key: "SEND_GRID_API_KEY")
end

Create a class for your email

# Create an email class
class WelcomeEmail < BaseEmail
  def initialize(@name : String, @email_address : String)
  end

  to @email_address
  subject "Welcome, #{@name}!"
  header "My-Custom-Header", "header-value"
  reply_to "no-reply@noreply.com"
  # You can also do just `text` or `html` if you don't want both
  templates text, html
end

Create templates

Templates go in the same folder the email is in:

• Text email: <folder_email_class_is_in>/templates/<underscored_class_name>/text.ecr
• HTML email: <folder_email_class_is_in>/templates/<underscored_class_name>/html.ecr

So if your email class is in src/my_app/emails/welcome_email.cr, then your templates would go in src/my_app/emails/welcome_email/text|html.ecr.

# in <folder_of_email_class>/templates/welcome_email/text.ecr
# Templates have access to instance variables and methods in the email.
Welcome, <%= @name %>!

# in <folder_of_email_class>/templates/welcome_email/html.ecr
<h1>Welcome, <%= @name %>!</h1>

For more information on what you can do with Embedded Crystal (ECR), see the official Crystal documentation.

Deliver the email

# Send the email right away!
WelcomeEmail.new("Kate", "kate@example.com").deliver

# Send the email in the background using `spawn`
WelcomeEmail.new("Kate", "kate@example.com").deliver_later

Delay email delivery

The built-in delay uses the deliver_later_strategy setting set to Carbon::SpawnStrategy. You can create your own custom delayed strategy that inherits from Carbon::DeliverLaterStrategy and defines a run method that takes a Carbon::Email and a block.

One example might be a job processor:

# Define your new delayed strategy
class SendEmailInJobStrategy < Carbon::DeliverLaterStrategy

  # `block.call` will run `deliver`, but you can call
  # `deliver` yourself on the `email` when you need.
  def run(email : Carbon::Email, &block)
    EmailJob.perform_later(email)
  end
end

class EmailJob < JobProcessor
  def perform(email : Carbon::Email)
    email.deliver
  end
end

# configure to use your new delayed strategy
BaseEmail.configure do |settings|
  settings.deliver_later_strategy = SendEmailInJobStrategy.new
end

Testing

Change the adapter

# In spec/spec_helper.cr or wherever you configure your code
BaseEmail.configure do
  # This adapter will capture all emails in memory
  settings.adapter = Carbon::DevAdapter.new
end

Reset emails before each spec and include expectations

# In spec/spec_helper.cr

# This gives you the `be_delivered` expectation
include Carbon::Expectations

Spec.before_each do
  Carbon::DevAdapter.reset
end

Integration testing

# Let's say we have a class that signs the user up and sends the welcome email
# that was described at the beginning of the README
class SignUpUser
  def initialize(@name : String, @email_address : String)
  end

  def run
    sign_user_up
    WelcomeEmail.new(name: @name, email_address: @email_address).deliver_now
  end
end

it "sends an email after the user signs up" do
  SignUpUser.new(name: "Emily", email_address: "em@gmail.com").run

  # Test that this email was sent
  WelcomeEmail.new(name: "Emily", email_address: "em@gmail.com").should be_delivered
end

Unit testing

Unit testing is simple. Instantiate your email and test the fields you care about.

it "builds a nice welcome email" do
  email = WelcomeEmail.new(name: "David", email_address: "david@gmail.com")
  # Note that recipients are converted to an array of Carbon::Address
  # So if you use a string value for the `to` field, you'll get an array of
  # Carbon::Address instead.
  email.to.should eq [Carbon::Address.new("david@gmail.com")]
  email.text_body.should contain "Welcome"
  email.html_body.should contain "Welcome"
end

Note that unit testing can be superfluous in most cases. Instead, try unit testing just fields that have complex logic. The compiler will catch most other issues.

Development

• shards install
• Make changes
• crystal spec -D skip-integration (will skip sending test emails to SendGrid)
• crystal spec requires a SEND_GRID_API_KEY ENV variable. Set this in a .env file:

# in .env
# If you want to run tests that actually test emails against the SendGrid server
SEND_GRID_API_KEY=get_from_send_grid

Note: When you open a PR, Github Actions will not run the integration suite. If you need the integeration suite to run, the RUN_INTEGRATION_SPECS env var must be set to true.

Contributing

1. Fork it ( https://github.com/luckyframework/carbon/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Make your changes
4. Run ./script/test to run the specs, build shards, and check formatting
5. Commit your changes (git commit -am 'Add some feature')
6. Push to the branch (git push origin my-new-feature)
7. Create a new Pull Request

Contributors

• paulcsmith Paul Smith - creator, maintainer