Pass extra info to custom action mailer delivery class - ruby-on-rails

Question

I have a 3rd party email integration library that I want to use to send email as one of my users. To send email I make an API call using an access_token that I save for each user.
To still use action mailer, I've created a custom delivery class like this:
module Mail
class CustomMailDelivery
attr_reader :settings
def initialize(settings)
#settings = settings
end
def deliver!(mail)
# use 3rd party client here
end
end
end
I'm configuring this in an initializer:
ActionMailer::Base.add_delivery_method :custom, Mail::CustomMailDelivery, {
app_id: ENV.fetch('3RDPARTY_APP_ID'),
app_secret: ENV.fetch('3RDPARTY_APP_SECRET'),
}
This allows me to set the delivery method on a per-mailer basis:
class LeadMailer < ApplicationMailer
self.delivery_method = :custom
...
end
The problem is, I need to pass the user that is sending this message along, so I can get their access_token.
I don't want to rely on fetching the EmailAccount using the sender's email address because it seems like this could break down the road (it's possible this email address might not be the same as the sending user).
In other words, I'd like to pass it explicitly, so it is easy to understand and I avoid any confusion.
Is there a way to provide per-mail context to a custom action mailer delivery class?

Answer 1

I ended up passing this data with a custom message header, which I later delete when handling the message.
class CustomMailer < ApplicationMailer
self.delivery_method = :custom
attr_reader :sending_account
def mail(params)
raise 'You must call set_sending_account before calling mail.' unless sending_email_account
super(params.merge({
Mail::CustomMailDelivery::ACCOUNT_ID_HEADER => sending_account.id
}))
end
def set_sending_account(account)
#sending_account = account
end
end
This way mailers that need this behavior subclass from this class and are forced to provide the custom data.
In the delivery class I yank this value out of the headers:
module Mail
class CustomMailDelivery
attr_reader :settings
# we'll hijack email headers in order to pass over some required data from the mailer to this class
ACCOUNT_ID_HEADER = '__account_id'
def initialize(settings)
#settings = settings
end
def deliver!(mail)
account = account_for(mail)
client = third_party_api_client(account.access_token)
client.send_message(...)
end
private
def third_party_api_client(access_token)
# ...
end
def account_for(mail)
header_field = mail[ACCOUNT_ID_HEADER]
missing_account_id_header! unless header_field
email_account = Account.find(header_field.value)
# remove the header field so it doesn't show up in the actual email
mail[ACCOUNT_ID_HEADER] = nil
account
end
def missing_account_id_header!
raise "Missing required header: #{ACCOUNT_ID_HEADER}"
end
end
end
This solution is not very elegant, but works.

Answer 2

Thanks for the idea, I put together a shorter version by using register_observer and register_interceptor.
It's basically the same idea, except you don't need to redefine too much delivery stuff. You just hook in the mail workflow.
First, declare the hook:
ActionMailer::Base.register_observer(MailToActionEventObserver)
ActionMailer::Base.register_interceptor(MailToActionEventObserver)
Then, the easy part is that the hooks are static methods inside of the same class:
class MailToActionEventObserver
def self.delivered_email(mail)
# Here you can use #passed_argument because it is called just after
# self.delivering_email
end
def self.delivering_email(mail)
#passed_argument = mail['MY-PERSONAL-HEADER'].to_s
# Now remove the temporary header:
mail['MY-PERSONAL-HEADER'] = nil
end
end
Now, same as your answer #Ben, just need to pass the argument as a header in the mailer:
def my_custom_mail
headers['MY-PERSONAL-HEADER'] = 'whatever-value'
mail(...)
end