How to start MidiSmtpServer in Rails - ruby-on-rails

Question

I am trying to use MidiSmtpServer to receive email in a Heroku application, and have been using the code on one of the examples that the documents show. However, I don't know where to put that code for the SMTP server to start after Puma, or where to put it for it to start at all. Using on_worker_boot in puma.rb doesnt work.
puma.rb:
# Puma can serve each request in a thread from an internal thread pool.
# The `threads` method setting takes two numbers: a minimum and maximum.
# Any libraries that use thread pools should be configured to match
# the maximum value specified for Puma. Default is set to 5 threads for minimum
# and maximum; this matches the default thread size of Active Record.
#
max_threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }
min_threads_count = ENV.fetch("RAILS_MIN_THREADS") { max_threads_count }
threads min_threads_count, max_threads_count
# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
#
port ENV.fetch("PORT") { 3000 }
# Specifies the `environment` that Puma will run in.
#
environment ENV.fetch("RAILS_ENV") { "development" }
# Specifies the `pidfile` that Puma will use.
pidfile ENV.fetch("PIDFILE") { "tmp/pids/server.pid" }
# Specifies the number of `workers` to boot in clustered mode.
# Workers are forked web server processes. If using threads and workers together
# the concurrency of the application would be max `threads` * `workers`.
# Workers do not work on JRuby or Windows (both of which do not support
# processes).
#
# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
require "midi-smtp-server"
require "mail"
on_worker_boot do
class MySmtpd < MidiSmtpServer::Smtpd
def on_message_data_event(ctx)
puts "[#{ctx[:envelope][:from]}] for recipient(s): [#{ctx[:envelope][:to]}]..."
# Just decode message ones to make sure, that this message ist readable
#mail = Mail.read_from_string(ctx[:message][:data])
# handle incoming mail, just show the message source
puts #mail.to_s
end
end
# try to gracefully shutdown on Ctrl-C
trap("INT") do
puts "Interrupted, exit now..."
exit 0
end
# Output for debug
puts "#{Time.now}: Starting MySmtpd..."
# Create a new server instance listening at localhost interfaces 127.0.0.1:2525
# and accepting a maximum of 4 simultaneous connections
server = MySmtpd.new(2525, "0.0.0.0", 4)
# setup exit code
at_exit do
# check to shutdown connection
if server # Output for debug
puts "#{Time.now}: Shutdown MySmtpd..." # stop all threads and connections gracefully
server.stop
end # Output for debug
puts "#{Time.now}: MySmtpd down!\n"
end
# Start the server
server.start
# Run on server forever
server.join
end
# Use the `preload_app!` method when specifying a `workers` number.
# This directive tells Puma to first boot the application and load code
# before forking the application. This takes advantage of Copy On Write
# process behavior so workers use less memory.
#
# preload_app!
# Allow puma to be restarted by `rails restart` command.
plugin :tmp_restart

Answer 1

Applications running on Heroku are containerized, and running an SMTP server in or with the web process is not possible.
You need to instead look at services that provide inbound mail delivery. If you're using Rails 6, follow the documentation to set up ActionMailbox.