refactor: refactor the SMTP sender

app/lib/smtp_client/endpoint.rb

@@ -0,0 +1,169 @@
+# frozen_string_literal: true
+
+module SMTPClient
+  class Endpoint
+
+    class SMTPSessionNotStartedError < StandardError
+    end
+
+    attr_reader :server
+    attr_reader :ip_address
+    attr_accessor :smtp_client
+
+    # @param server [Server] the server that this IP address is for
+    # @param ip_address [String] the IP address
+    def initialize(server, ip_address)
+      @server = server
+      @ip_address = ip_address
+    end
+
+    # Return a description of this server with its IP address
+    #
+    # @return [String]
+    def description
+      "#{@ip_address}:#{@server.port} (#{@server.hostname})"
+    end
+
+    # Return a string representation of this server
+    #
+    # @return [String]
+    def to_s
+      description
+    end
+
+    # Return true if this is an IPv6 address
+    #
+    # @return [Boolean]
+    def ipv6?
+      @ip_address.include?(":")
+    end
+
+    # Return true if this is an IPv4 address
+    #
+    # @return [Boolean]
+    def ipv4?
+      !ipv6?
+    end
+
+    # Start a new SMTP session and store the client with this server for future use as needed
+    #
+    # @param source_ip_address [IPAddress] the IP address to use as the source address for the connection
+    # @param allow_ssl [Boolean] whether to allow SSL for this connection, if false SSL mode is ignored
+    #
+    # @return [Net::SMTP]
+    def start_smtp_session(source_ip_address: nil, allow_ssl: true)
+      @smtp_client = Net::SMTP.new(@ip_address, @server.port)
+      @smtp_client.open_timeout = Postal::Config.smtp_client.open_timeout
+      @smtp_client.read_timeout = Postal::Config.smtp_client.read_timeout
+      @smtp_client.tls_hostname = @server.hostname
+
+      if source_ip_address
+        @source_ip_address = source_ip_address
+      end
+
+      if @source_ip_address
+        @smtp_client.source_address = ipv6? ? @source_ip_address.ipv6 : @source_ip_address.ipv4
+      end
+
+      if allow_ssl
+        case @server.ssl_mode
+        when SSLModes::AUTO
+          @smtp_client.enable_starttls_auto(self.class.ssl_context_without_verify)
+        when SSLModes::STARTTLS
+          @smtp_client.enable_starttls(self.class.ssl_context_with_verify)
+        when SSLModes::TLS
+          @smtp_client.enable_tls(self.class.ssl_context_with_verify)
+        else
+          @smtp_client.disable_starttls
+          @smtp_client.disable_tls
+        end
+      else
+        @smtp_client.disable_starttls
+        @smtp_client.disable_tls
+      end
+
+      @smtp_client.start(@source_ip_address ? @source_ip_address.hostname : self.class.default_helo_hostname)
+
+      @smtp_client
+    end
+
+    # Send a message to the current SMTP session (or create one if there isn't one for this endpoint).
+    # If sending messsage encouters some connection errors, retry again after re-establishing the SMTP
+    # session.
+    #
+    # @param raw_message [String] the raw message to send
+    # @param mail_from [String] the MAIL FROM address
+    # @param rcpt_to [String] the RCPT TO address
+    # @param retry_on_connection_error [Boolean] whether to retry the connection if there is a connection error
+    #
+    # @return [void]
+    def send_message(raw_message, mail_from, rcpt_to, retry_on_connection_error: true)
+      raise SMTPSessionNotStartedError if @smtp_client.nil? || (@smtp_client && !@smtp_client.started?)
+
+      @smtp_client.rset_errors
+      @smtp_client.send_message(raw_message, mail_from, [rcpt_to])
+    rescue Errno::ECONNRESET, Errno::EPIPE, OpenSSL::SSL::SSLError
+      if retry_on_connection_error
+        finish_smtp_session
+        start_smtp_session
+        return send_message(raw_message, mail_from, rcpt_to, retry_on_connection_error: false)
+      end
+
+      raise
+    end
+
+    # Reset the current SMTP session for this server if possible otherwise
+    # finish the session
+    #
+    # @return [void]
+    def reset_smtp_session
+      @smtp_client&.rset
+    rescue StandardError
+      finish_smtp_session
+    end
+
+    # Finish the current SMTP session for this server if possible.
+    #
+    # @return [void]
+    def finish_smtp_session
+      @smtp_client&.finish
+    rescue StandardError
+      nil
+    ensure
+      @smtp_client = nil
+    end
+
+    class << self
+
+      # Return the default HELO hostname to present to SMTP servers that
+      # we connect to
+      #
+      # @return [String]
+      def default_helo_hostname
+        Postal::Config.dns.helo_hostname ||
+          Postal::Config.postal.smtp_hostname ||
+          "localhost"
+      end
+
+      def ssl_context_with_verify
+        @ssl_context_with_verify ||= begin
+          c = OpenSSL::SSL::SSLContext.new
+          c.verify_mode = OpenSSL::SSL::VERIFY_PEER
+          c.cert_store = OpenSSL::X509::Store.new
+          c.cert_store.set_default_paths
+          c
+        end
+      end
+
+      def ssl_context_without_verify
+        @ssl_context_without_verify ||= begin
+          c = OpenSSL::SSL::SSLContext.new
+          c.verify_mode = OpenSSL::SSL::VERIFY_NONE
+          c
+        end
+      end
+
+    end
+
+  end
+end

app/lib/smtp_client/server.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module SMTPClient
+  class Server
+
+    attr_reader :hostname
+    attr_reader :port
+    attr_accessor :ssl_mode
+
+    def initialize(hostname, port: 25, ssl_mode: SSLModes::AUTO)
+      @hostname = hostname
+      @port = port
+      @ssl_mode = ssl_mode
+    end
+
+    # Return all IP addresses for this server by resolving its hostname.
+    # IPv6 addresses will be returned first.
+    #
+    # @return [Array<SMTPClient::Endpoint>]
+    def endpoints
+      ips = []
+
+      DNSResolver.local.aaaa(@hostname).each do |ip|
+        ips << Endpoint.new(self, ip)
+      end
+
+      DNSResolver.local.a(@hostname).each do |ip|
+        ips << Endpoint.new(self, ip)
+      end
+
+      ips
+    end
+
+  end
+end

app/lib/smtp_client/ssl_modes.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module SMTPClient
+  module SSLModes
+
+    AUTO = "Auto"
+    STARTTLS = "STARTLS"
+    TLS = "TLS"
+    NONE = "None"
+
+  end
+end