Project for PV249 - Example SMTP Server with forwarding via smtp

Gemfile

source :rubygems

gem "eventmachine"

smtpserver.rb

#!/usr/bin/env ruby

# Example SMTP Server in Ruby for course FI:PV249
#
# @author Jiri Zapletal <yaplik@gmail.com>
# @license BSD

require 'bundler/setup'
Bundler.require(:default)
require 'resolv'

def resolv(email)
    if m = /@(.*)/i.match(email) then
        domain = m[1]
    else
        return nil
    end

    # get mx exchanges by priority
    mx = Resolv::DNS.open do
        |dns| dns.getresources(domain, Resolv::DNS::Resource::IN::MX)
    end.sort do
        |a,b| a.preference <=> b.preference
    end.map do
        |x| x.exchange.to_s
    end

    if mx.any? then
            return mx
    end

    # fallback
    begin
        tmp = Resolv.getaddresses(domain)
        return tmp
    rescue Resolv::ResolvError
        return []
    end
end

module SmtpProtocol
    include EventMachine::Protocols::LineText2

    def post_init
        reset_state
        send_line("220 mail.example.net SMTP Ruby Server")
    end

    def reset_state
        @mail = nil
        @rcpt = []
        @data = ""
        @clients = []
        @queue_ids = []
    end

    def send_line(data)
        puts "[S] " + data
        send_data(data + "\r\n")
    end

    def receive_line(line)
        puts "[C] " + line

        case
          when m = /^HELO (.*)$/i.match(line)
            send_line "250 Hello"
          when m = /^EHLO (.*)$/i.match(line)
            send_line "250-mail.example.net"
            send_line "250-STARTTLS"
            send_line "250 DSN"
          when m = /^STARTTLS$/i.match(line)
            send_line "220 2.0.0 Ready to start TLS"
            start_tls
          when m = /^MAIL FROM:(.*)$/i.match(line)
            if @from != nil then
                send_line "503 5.5.1 Error: nested MAIL command"
                return
            end
            @from = m[1]
            send_line "250 2.1.0 Ok"
          when m = /^RCPT TO:(.*)/i.match(line)
            if @from == nil then
                send_line "503 5.5.1 Error: need MAIL command"
                return
            end
            @rcpt << m[1]
            send_line "250 2.1.5 Ok"
          when m = /^RSET$/i.match(line)
            reset_state
            send_line "250 2.0.0 Ok"
          when m = /^DATA$/i.match(line)
            if @rcpt.count == 0 then
                send_line "503 5.5.1 Error: need RCPT command"
                return
            end

            send_line "354 End data with <CR><LF>.<CR><LF>"
            set_text_mode
          when m = /^QUIT$/i.match(line)
            send_line "221 Bye"
            close_connection_after_writing
          else
            puts "[error]", line
            send_line "502 5.5.2 Error: command not recognized"
          end
    end

    def receive_binary_data(data)
        if /\r\n\.\r\n$/.match(data) then
            @data += data[0..-5]
            forward_mail(@from, @rcpt, @data)
            set_line_mode
        else
            @data += data
        end
    end

    def unbind
        puts "[C Disconnected]"
        reset_state
    end

    def forward_mail(from, to, data)
        puts "Email from #{from} to #{to.join(",")}"

        @data = "Received: by Ruby Example SMTP forwarder\r\n" + @data

        @rcpt.each do |to|
            exchanges = resolv(to.tr("<>", ""))
            next if exchanges.empty?

            puts "Connecting to #{exchanges[0]}:25"
            client = EventMachine.connect(exchanges[0], 25, SmtpClientProtocol)
            client.send_mail(@from, to, @data)
            client.notify_server = self
            @clients << client
        end
    end

    def client_done(client, sent, queue_id = nil)
        @clients.delete(client)
        @queue_ids << queue_id

        if not sent then
            send_line "421 Failed to forward message"
            reset_state
            return
        end

        if @clients.empty? then
            send_line "250 2.0.0 Ok: message has been forwarded successfully as " + @queue_ids.join(",")
            reset_state
        end
    end
end

module SmtpClientProtocol
    include EventMachine::Protocols::LineText2

    def post_init
        @state = :from
        @from = nil
        @rcpt = nil
        @data = ""

        @notify_server = nil
        @queue_id = nil
        @sent = false
    end

    def send_mail(from, rcpt, data)
        @from = from
        @rcpt = rcpt
        @data = data
    end

    def send_line(data)
        puts "[C][C] " + data
        send_data(data + "\r\n")
    end

    def receive_line(line)
        puts "[C][S] " + line

    case
      when m = /^220 /i.match(line)
        send_line "HELO localhost"
      when m = /^250 (.*)$/i.match(line)
        case @state
          when :from then
            send_line "QUIT" and return if @from == nil
            send_line "MAIL FROM: " + @from
            @state = :rcpt
          when :rcpt then
            send_line "QUIT" and return if @rcpt == nil
            send_line "RCPT TO: " + @rcpt
            @state = :data
          when :data then
            send_line "DATA"
            @state = :quit
          when :quit
            m = /Queued as (.*)/i.match(line)
            @queue_id = m[1] if m
            @sent = true
            send_line "QUIT"
            close_connection_after_writing
        end
      when m = /^354 (.*)$/i.match(line)
        send_line @data
        send_line "."
      when m = /^221 /i.match(line) #221 2.0.0 Bye; after QUIT
        close_connection
      when m = /^[45]/i.match(line) #quit on errors
        puts "[error]:" + line
        send_line "QUIT"
        close_connection_after_writing
      else
        puts "[error]" + line
        send_line "QUIT"
        close_connection_after_writing
      end
    end

    def notify_server=(obj)
        @notify_server = obj
    end

    def unbind
        puts "[C][S Disconnected]"
        @notify_server.send(:client_done, self, @sent, @queue_id) unless @notify_server == nil
    end
end

EventMachine.run do
    Signal.trap("INT")  { EventMachine.stop }
    Signal.trap("TERM") { EventMachine.stop }

    EventMachine.start_server("0.0.0.0", 8025, SmtpProtocol)
end