Class: EventMachine::Protocols::SmtpServer

Inherits:
Connection
  • Object
show all
Includes:
LineText2
Defined in:
lib/em/protocols/smtpserver.rb

Overview

This is a protocol handler for the server side of SMTP. It's NOT a complete SMTP server obeying all the semantics of servers conforming to RFC2821. Rather, it uses overridable method stubs to communicate protocol states and data to user code. User code is responsible for doing the right things with the data in order to get complete and correct SMTP server behavior.

Simple SMTP server example:

class EmailServer < EM::P::SmtpServer
  def receive_plain_auth(user, pass)
    true
  end

  def get_server_domain
    "mock.smtp.server.local"
  end

  def get_server_greeting
    "mock smtp server greets you with impunity"
  end

  def receive_sender(sender)
    current.sender = sender
    true
  end

  def receive_recipient(recipient)
    current.recipient = recipient
    true
  end

  def receive_message
    current.received = true
    current.completed_at = Time.now

    p [:received_email, current]
    @current = OpenStruct.new
    true
  end

  def receive_ehlo_domain(domain)
    @ehlo_domain = domain
    true
  end

  def receive_data_command
    current.data = ""
    true
  end

  def receive_data_chunk(data)
    current.data << data.join("\n")
    true
  end

  def receive_transaction
    if @ehlo_domain
      current.ehlo_domain = @ehlo_domain
      @ehlo_domain = nil
    end
    true
  end

  def current
    @current ||= OpenStruct.new
  end

  def self.start(host = 'localhost', port = 1025)
    require 'ostruct'
    @server = EM.start_server host, port, self
  end

  def self.stop
    if @server
      EM.stop_server @server
      @server = nil
    end
  end

  def self.running?
    !!@server
  end
end

EM.run{ EmailServer.start }

– Useful paragraphs in RFC-2821: 4.3.2: Concise list of command-reply sequences, in essence a text representation of the command state-machine.

STARTTLS is defined in RFC2487. Observe that there are important rules governing whether a publicly-referenced server (meaning one whose Internet address appears in public MX records) may require the non-optional use of TLS. Non-optional TLS does not apply to EHLO, NOOP, QUIT or STARTTLS.

Constant Summary

HeloRegex =
/\AHELO\s*/i
EhloRegex =
/\AEHLO\s*/i
QuitRegex =
/\AQUIT/i
MailFromRegex =
/\AMAIL FROM:\s*/i
RcptToRegex =
/\ARCPT TO:\s*/i
DataRegex =
/\ADATA/i
NoopRegex =
/\ANOOP/i
RsetRegex =
/\ARSET/i
VrfyRegex =
/\AVRFY\s+/i
ExpnRegex =
/\AEXPN\s+/i
HelpRegex =
/\AHELP/i
StarttlsRegex =
/\ASTARTTLS/i
AuthRegex =
/\AAUTH\s+/i
@@parms =

Class variable containing default parameters that can be overridden in application code. Individual objects of this class will make an instance-local copy of the class variable, so that they can be reconfigured on a per-instance basis.

Chunksize is the number of data lines we'll buffer before sending them to the application. TODO, make this user-configurable.

{
  :chunksize => 4000,
  :verbose => false
}

Constants included from LineText2

LineText2::MaxBinaryLength

Instance Attribute Summary

Attributes inherited from Connection

#signature

Class Method Summary collapse

Instance Method Summary collapse

Methods included from LineText2

#receive_binary_data, #receive_data, #receive_end_of_binary_data, #set_binary_mode, #set_delimiter, #set_line_mode, #set_text_mode

Methods inherited from Connection

#associate_callback_target, #close_connection, #close_connection_after_writing, #comm_inactivity_timeout, #comm_inactivity_timeout=, #connection_completed, #detach, #error?, #get_cipher_bits, #get_cipher_name, #get_cipher_protocol, #get_idle_time, #get_outbound_data_size, #get_peer_cert, #get_peername, #get_pid, #get_proxied_bytes, #get_sni_hostname, #get_sock_opt, #get_sockname, #get_status, new, #notify_readable=, #notify_readable?, #notify_writable=, #notify_writable?, #pause, #paused?, #pending_connect_timeout, #pending_connect_timeout=, #proxy_completed, #proxy_incoming_to, #proxy_target_unbound, #receive_data, #reconnect, #resume, #send_data, #send_datagram, #send_file_data, #set_sock_opt, #ssl_handshake_completed, #ssl_verify_peer, #start_tls, #stop_proxying, #stream_file_data

Constructor Details

#initialize(*args) ⇒ SmtpServer

Returns a new instance of SmtpServer



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# File 'lib/em/protocols/smtpserver.rb', line 162

def initialize *args
  super
  @parms = @@parms
  init_protocol_state
end

Class Method Details

.parms=(parms = {}) ⇒ Object



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# File 'lib/em/protocols/smtpserver.rb', line 156

def self.parms= parms={}
  @@parms.merge!(parms)
end

Instance Method Details

#connection_endedObject

Sent when the remote peer has ended the connection.



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# File 'lib/em/protocols/smtpserver.rb', line 629

def connection_ended
end

#get_server_domainObject

The domain name returned in the first line of the response to a successful EHLO or HELO command.



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# File 'lib/em/protocols/smtpserver.rb', line 589

def get_server_domain
  "Ok EventMachine SMTP Server"
end

#get_server_greetingObject

The greeting returned in the initial connection message to the client.



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# File 'lib/em/protocols/smtpserver.rb', line 584

def get_server_greeting
  "EventMachine SMTP Server"
end

#init_protocol_stateObject



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# File 'lib/em/protocols/smtpserver.rb', line 278

def init_protocol_state
  @state ||= []
end

#parms=(parms = {}) ⇒ Object



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# File 'lib/em/protocols/smtpserver.rb', line 168

def parms= parms={}
  @parms.merge!(parms)
end

#post_initObject

In SMTP, the server talks first. But by a (perhaps flawed) axiom in EM, #post_init will execute BEFORE the block passed to #start_server, for any given accepted connection. Since in this class we'll probably be getting a lot of initialization parameters, we want the guts of post_init to run AFTER the application has initialized the connection object. So we use a spawn to schedule the post_init to run later. It's a little weird, I admit. A reasonable alternative would be to set parameters as a class variable and to do that before accepting any connections.

OBSOLETE, now we have @@parms. But the spawn is nice to keep as an illustration.



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# File 'lib/em/protocols/smtpserver.rb', line 183

def post_init
  #send_data "220 #{get_server_greeting}\r\n" (ORIGINAL)
  #(EM.spawn {|x| x.send_data "220 #{x.get_server_greeting}\r\n"}).notify(self)
  (EM.spawn {|x| x.send_server_greeting}).notify(self)
end

#process_auth(str) ⇒ Object

– So far, only AUTH PLAIN is supported but we should do at least LOGIN as well. TODO, support clients that send AUTH PLAIN with no parameter, expecting a 3xx response and a continuation of the auth conversation.



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# File 'lib/em/protocols/smtpserver.rb', line 348

def process_auth str
  if @state.include?(:auth)
    send_data "503 auth already issued\r\n"
  elsif str =~ /\APLAIN\s?/i
    if $'.length == 0
      # we got a partial response, so let the client know to send the rest
      @state << :auth_incomplete
      send_data("334 \r\n")
    else
      # we got the initial response, so go ahead & process it
      process_auth_line($')
    end
    #elsif str =~ /\ALOGIN\s+/i
  else
    send_data "504 auth mechanism not available\r\n"
  end
end

#process_auth_line(line) ⇒ Object



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# File 'lib/em/protocols/smtpserver.rb', line 366

def process_auth_line(line)
  plain = line.unpack("m").first
  _,user,psw = plain.split("\000")
  
  succeeded = proc {
    send_data "235 authentication ok\r\n"
    @state << :auth
  }
  failed = proc {
    send_data "535 invalid authentication\r\n"
  }
  auth = receive_plain_auth user,psw
  
  if auth.respond_to?(:callback)
    auth.callback(&succeeded)
    auth.errback(&failed)
  else
    (auth ? succeeded : failed).call
  end
  
  @state.delete :auth_incomplete
end

#process_dataObject

– Unusually, we can deal with a Deferrable returned from the user application. This was added to deal with a special case in a particular application, but it would be a nice idea to add it to the other user-code callbacks.



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# File 'lib/em/protocols/smtpserver.rb', line 394

def process_data
  unless @state.include?(:rcpt)
    send_data "503 Operation sequence error\r\n"
  else
    succeeded = proc {
      send_data "354 Send it\r\n"
      @state << :data
      @databuffer = []
    }
    failed = proc {
      send_data "550 Operation failed\r\n"
    }

    d = receive_data_command

    if d.respond_to?(:callback)
      d.callback(&succeeded)
      d.errback(&failed)
    else
      (d ? succeeded : failed).call
    end
  end
end

#process_data_line(ln) ⇒ Object

Send the incoming data to the application one chunk at a time, rather than one line at a time. That lets the application be a little more flexible about storing to disk, etc. Since we clear the chunk array every time we submit it, the caller needs to be aware to do things like dup it if he wants to keep it around across calls.

Resets the transaction upon disposition of the incoming message. RFC5321 says this about the MAIL FROM command:

"This command tells the SMTP-receiver that a new mail transaction is
 starting and to reset all its state tables and buffers, including any
 recipients or mail data."

Equivalent behaviour is implemented by resetting after a completed transaction.

User-written code can return a Deferrable as a response from receive_message.



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# File 'lib/em/protocols/smtpserver.rb', line 542

def process_data_line ln
  if ln == "."
    if @databuffer.length > 0
      receive_data_chunk @databuffer
      @databuffer.clear
    end


    succeeded = proc {
      send_data "250 Message accepted\r\n"
      reset_protocol_state
    }
    failed = proc {
      send_data "550 Message rejected\r\n"
      reset_protocol_state
    }
    d = receive_message

    if d.respond_to?(:set_deferred_status)
      d.callback(&succeeded)
      d.errback(&failed)
    else
      (d ? succeeded : failed).call
    end

    @state.delete :data
  else
    # slice off leading . if any
    ln.slice!(0...1) if ln[0] == ?.
    @databuffer << ln
    if @databuffer.length > @@parms[:chunksize]
      receive_data_chunk @databuffer
      @databuffer.clear
    end
  end
end

#process_ehlo(domain) ⇒ Object

– EHLO/HELO is always legal, per the standard. On success it always clears buffers and initiates a mail “transaction.” Which means that a MAIL FROM must follow.

Per the standard, an EHLO/HELO or a RSET “initiates” an email transaction. Thereafter, MAIL FROM must be received before RCPT TO, before DATA. Not sure what this specific ordering achieves semantically, but it does make it easier to implement. We also support user-specified requirements for STARTTLS and AUTH. We make it impossible to proceed to MAIL FROM without fulfilling tls and/or auth, if the user specified either or both as required. We need to check the extension standard for auth to see if a credential is discarded after a RSET along with all the rest of the state. We'll behave as if it is. Now clearly, we can't discard tls after its been negotiated without dropping the connection, so that flag doesn't get cleared.



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# File 'lib/em/protocols/smtpserver.rb', line 301

def process_ehlo domain
  if receive_ehlo_domain domain
    send_data "250-#{get_server_domain}\r\n"
    if @@parms[:starttls]
      send_data "250-STARTTLS\r\n"
    end
    if @@parms[:auth]
      send_data "250-AUTH PLAIN\r\n"
    end
    send_data "250-NO-SOLICITING\r\n"
    # TODO, size needs to be configurable.
    send_data "250 SIZE 20000000\r\n"
    reset_protocol_state
    @state << :ehlo
  else
    send_data "550 Requested action not taken\r\n"
  end
end

#process_expnObject

TODO - implement this properly, the implementation is a stub!



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# File 'lib/em/protocols/smtpserver.rb', line 248

def process_expn
  send_data "502 Command not implemented\r\n"
end

#process_helo(domain) ⇒ Object



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# File 'lib/em/protocols/smtpserver.rb', line 320

def process_helo domain
  if receive_ehlo_domain domain.dup
    send_data "250 #{get_server_domain}\r\n"
    reset_protocol_state
    @state << :ehlo
  else
    send_data "550 Requested action not taken\r\n"
  end
end

#process_helpObject

TODO - implement this properly, the implementation is a stub!



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# File 'lib/em/protocols/smtpserver.rb', line 232

def process_help
  send_data "250 Ok, but unimplemented\r\n"
end

#process_mail_from(sender) ⇒ Object

– Requiring TLS is touchy, cf RFC2784. Requiring AUTH seems to be much more reasonable. We don't currently support any notion of deriving an authentication from the TLS negotiation, although that would certainly be reasonable. We DON'T allow MAIL FROM to be given twice. We DON'T enforce all the various rules for validating the sender or the reverse-path (like whether it should be null), and notifying the reverse path in case of delivery problems. All of that is left to the calling application.



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# File 'lib/em/protocols/smtpserver.rb', line 464

def process_mail_from sender
  if (@@parms[:starttls]==:required and !@state.include?(:starttls))
    send_data "550 This server requires STARTTLS before MAIL FROM\r\n"
  elsif (@@parms[:auth]==:required and !@state.include?(:auth))
    send_data "550 This server requires authentication before MAIL FROM\r\n"
  elsif @state.include?(:mail_from)
    send_data "503 MAIL already given\r\n"
  else
    unless receive_sender sender
      send_data "550 sender is unacceptable\r\n"
    else
      send_data "250 Ok\r\n"
      @state << :mail_from
    end
  end
end

#process_noopObject



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# File 'lib/em/protocols/smtpserver.rb', line 335

def process_noop
  send_data "250 Ok\r\n"
end

#process_quitObject



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# File 'lib/em/protocols/smtpserver.rb', line 330

def process_quit
  send_data "221 Ok\r\n"
  close_connection_after_writing
end

#process_rcpt_to(rcpt) ⇒ Object

– Since we require :mail_from to have been seen before we process RCPT TO, we don't need to repeat the tests for TLS and AUTH. Note that we don't remember or do anything else with the recipients. All of that is on the user code. TODO: we should enforce user-definable limits on the total number of recipients per transaction. We might want to make sure that a given recipient is only seen once, but for now we'll let that be the user's problem.

User-written code can return a deferrable from receive_recipient.



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# File 'lib/em/protocols/smtpserver.rb', line 493

def process_rcpt_to rcpt
  unless @state.include?(:mail_from)
    send_data "503 MAIL is required before RCPT\r\n"
  else
    succeeded = proc {
      send_data "250 Ok\r\n"
      @state << :rcpt unless @state.include?(:rcpt)
    }
    failed = proc {
      send_data "550 recipient is unacceptable\r\n"
    }

    d = receive_recipient rcpt

    if d.respond_to?(:set_deferred_status)
      d.callback(&succeeded)
      d.errback(&failed)
    else
      (d ? succeeded : failed).call
    end

=begin
  unless receive_recipient rcpt
    send_data "550 recipient is unacceptable\r\n"
  else
    send_data "250 Ok\r\n"
    @state << :rcpt unless @state.include?(:rcpt)
  end
=end
  end
end

#process_rsetObject



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# File 'lib/em/protocols/smtpserver.rb', line 418

def process_rset
  reset_protocol_state
  receive_reset
  send_data "250 Ok\r\n"
end

#process_starttlsObject

– STARTTLS may not be issued before EHLO, or unless the user has chosen to support it.

If :starttls_options is present and :starttls is set in the parms pass the options in :starttls_options to start_tls. Do this if you want to use your own certificate e.g. => “/etc/ssl/cert.pem”, :private_key_file => “/etc/ssl/private/cert.key”



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# File 'lib/em/protocols/smtpserver.rb', line 437

def process_starttls
  if @@parms[:starttls]
    if @state.include?(:starttls)
      send_data "503 TLS Already negotiated\r\n"
    elsif ! @state.include?(:ehlo)
      send_data "503 EHLO required before STARTTLS\r\n"
    else
      send_data "220 Start TLS negotiation\r\n"
      start_tls(@@parms[:starttls_options] || {})
      @state << :starttls
    end
  else
    process_unknown
  end
end

#process_unknownObject



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# File 'lib/em/protocols/smtpserver.rb', line 339

def process_unknown
  send_data "500 Unknown command\r\n"
end

#process_vrfyObject

RFC2821, 3.5.3 Meaning of VRFY or EXPN Success Response:

A server MUST NOT return a 250 code in response to a VRFY or EXPN
command unless it has actually verified the address.  In particular,
a server MUST NOT return 250 if all it has done is to verify that the
syntax given is valid.  In that case, 502 (Command not implemented)
or 500 (Syntax error, command unrecognized) SHOULD be returned.

TODO - implement this properly, the implementation is a stub!



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# File 'lib/em/protocols/smtpserver.rb', line 244

def process_vrfy
  send_data "502 Command not implemented\r\n"
end

#receive_data_chunk(data) ⇒ Object

Sent when data from the remote peer is available. The size can be controlled by setting the :chunksize parameter. This call can be made multiple times. The goal is to strike a balance between sending the data to the application one line at a time, and holding all of a very large message in memory.



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# File 'lib/em/protocols/smtpserver.rb', line 646

def receive_data_chunk data
  @smtps_msg_size ||= 0
  @smtps_msg_size += data.join.length
  STDERR.write "<#{@smtps_msg_size}>"
end

#receive_data_commandObject

Called when the remote peer sends the DATA command. Returning false will cause us to send a 550 error to the peer. This can be useful for dealing with problems that arise from processing the whole set of sender and recipients.



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# File 'lib/em/protocols/smtpserver.rb', line 637

def receive_data_command
  true
end

#receive_ehlo_domain(domain) ⇒ Object

A false response from this user-overridable method will cause a 550 error to be returned to the remote client.



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# File 'lib/em/protocols/smtpserver.rb', line 596

def receive_ehlo_domain domain
  true
end

#receive_line(ln) ⇒ Object



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# File 'lib/em/protocols/smtpserver.rb', line 193

def receive_line ln
  @@parms[:verbose] and $>.puts ">>> #{ln}"

  return process_data_line(ln) if @state.include?(:data)
  return process_auth_line(ln) if @state.include?(:auth_incomplete)

  case ln
  when EhloRegex
    process_ehlo $'.dup
  when HeloRegex
    process_helo $'.dup
  when MailFromRegex
    process_mail_from $'.dup
  when RcptToRegex
    process_rcpt_to $'.dup
  when DataRegex
    process_data
  when RsetRegex
    process_rset
  when VrfyRegex
    process_vrfy
  when ExpnRegex
    process_expn
  when HelpRegex
    process_help
  when NoopRegex
    process_noop
  when QuitRegex
    process_quit
  when StarttlsRegex
    process_starttls
  when AuthRegex
    process_auth $'.dup
  else
    process_unknown
  end
end

#receive_messageObject

Sent after a message has been completely received. User code must return true or false to indicate whether the message has been accepted for delivery.



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# File 'lib/em/protocols/smtpserver.rb', line 655

def receive_message
  @@parms[:verbose] and $>.puts "Received complete message"
  true
end

#receive_plain_auth(user, password) ⇒ Object

Return true or false to indicate that the authentication is acceptable.



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# File 'lib/em/protocols/smtpserver.rb', line 601

def receive_plain_auth user, password
  true
end

#receive_recipient(rcpt) ⇒ Object

Receives the argument of a RCPT TO command. Can be given multiple times per transaction. Return false to reject the recipient.



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# File 'lib/em/protocols/smtpserver.rb', line 616

def receive_recipient rcpt
  true
end

#receive_resetObject

Sent when the remote peer issues the RSET command. Since RSET is not allowed to fail (according to the protocol), we ignore any return value from user overrides of this method.



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# File 'lib/em/protocols/smtpserver.rb', line 624

def receive_reset
end

#receive_sender(sender) ⇒ Object

Receives the argument of the MAIL FROM command. Return false to indicate to the remote client that the sender is not accepted. This can only be successfully called once per transaction.



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# File 'lib/em/protocols/smtpserver.rb', line 609

def receive_sender sender
  true
end

#receive_transactionObject

This is called when the protocol state is reset. It happens when the remote client calls EHLO/HELO or RSET.



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# File 'lib/em/protocols/smtpserver.rb', line 662

def receive_transaction
end

#reset_protocol_stateObject

– This is called at several points to restore the protocol state to a pre-transaction state. In essence, we “forget” having seen any valid command except EHLO and STARTTLS. We also have to callback user code, in case they're keeping track of senders, recipients, and whatnot.

We try to follow the convention of avoiding the verb “receive” for internal method names except receive_line (which we inherit), and using only receive_xxx for user-overridable stubs.

init_protocol_state is called when we initialize the connection as well as during reset_protocol_state. It does NOT call the user override method. This enables us to promise the users that they won't see the overridable fire except after EHLO and RSET, and after a message has been received. Although the latter may be wrong. The standard may allow multiple DATA segments with the same set of senders and recipients.



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# File 'lib/em/protocols/smtpserver.rb', line 271

def reset_protocol_state
  init_protocol_state
  s,@state = @state,[]
  @state << :starttls if s.include?(:starttls)
  @state << :ehlo if s.include?(:ehlo)
  receive_transaction
end

#send_server_greetingObject



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# File 'lib/em/protocols/smtpserver.rb', line 189

def send_server_greeting
  send_data "220 #{get_server_greeting}\r\n"
end

#unbindObject



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# File 'lib/em/protocols/smtpserver.rb', line 424

def unbind
  connection_ended
end