Class: EventMachine::Protocols::SmtpServer

Inherits:
Connection
  • Object
show all
Includes:
LineText2
Defined in:
lib/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.

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 collapse

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, LineText2::MaxLineLength

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, #set_delimiter, #set_line_mode, #set_text_mode

Methods inherited from Connection

#close_connection, #close_connection_after_writing, #comm_inactivity_timeout, #comm_inactivity_timeout=, #connection_completed, #get_peername, #get_pid, #receive_data, #reconnect, #send_data, #send_datagram, #send_file_data, #set_comm_inactivity_timeout, #start_tls, #stream_file_data

Constructor Details

#initialize(*args) ⇒ SmtpServer

Returns a new instance of SmtpServer.



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# File 'lib/protocols/smtpserver.rb', line 89

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

Class Method Details

.parms=(parms = {}) ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 83

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

Instance Method Details

#connection_ended ⇒ Object

Sent when the remote peer has ended the connection.



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# File 'lib/protocols/smtpserver.rb', line 475

def connection_ended
end

#get_server_domain ⇒ Object

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



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# File 'lib/protocols/smtpserver.rb', line 442

def get_server_domain
	"Ok EventMachine SMTP Server"
end

#get_server_greeting ⇒ Object

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



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

def get_server_greeting
	"EventMachine SMTP Server"
end

#init_protocol_state ⇒ Object 



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

def init_protocol_state
	@state ||= []
end

#parms=(parms = {}) ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 95

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

#post_init ⇒ Object

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/protocols/smtpserver.rb', line 110

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/protocols/smtpserver.rb', line 253

def process_auth str
	if @state.include?(:auth)
		send_data "503 auth already issued\r\n"
	elsif str =~ /\APLAIN\s+/i
		plain = Base64::decode64($'.dup)
		discard,user,psw = plain.split("\000")
		if receive_plain_auth user,psw
			send_data "235 authentication ok\r\n"
			@state << :auth
		else
			send_data "535 invalid authentication\r\n"
		end
	#elsif str =~ /\ALOGIN\s+/i
	else
		send_data "504 auth mechanism not available\r\n"
	end
end

#process_data ⇒ Object

– 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/protocols/smtpserver.rb', line 276

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.

DON’T reset the transaction upon disposition of the incoming message. This means another DATA command can be accepted with the same sender and recipients. If the client wants to reset, he can call RSET. Not sure whether the standard requires a transaction-reset at this point, but it appears not to.

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



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# File 'lib/protocols/smtpserver.rb', line 396

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"
		}
		failed = proc {
			send_data "550 Message rejected\r\n"
		}

		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] == 46
		@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/protocols/smtpserver.rb', line 206

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 LOGIN\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_helo(domain) ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 225

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_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/protocols/smtpserver.rb', line 341

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_noop ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 240

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

#process_quit ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 235

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.



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# File 'lib/protocols/smtpserver.rb', line 368

def process_rcpt_to rcpt
	unless @state.include?(:mail_from)
		send_data "503 MAIL is required before RCPT\r\n"
	else
		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

#process_rset ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 300

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

#process_starttls ⇒ Object

– STARTTLS may not be issued before EHLO, or unless the user has chosen to support it. TODO, must support user-supplied certificates.



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# File 'lib/protocols/smtpserver.rb', line 314

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
			@state << :starttls
		end
	else
		process_unknown
	end
end

#process_unknown ⇒ Object 



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

def process_unknown
	send_data "500 Unknown command\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/protocols/smtpserver.rb', line 492

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

#receive_data_command ⇒ Object

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/protocols/smtpserver.rb', line 483

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/protocols/smtpserver.rb', line 449

def receive_ehlo_domain domain
	true
end

#receive_line(ln) ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 120

def receive_line ln
	@@parms[:verbose] and $>.puts ">>> #{ln}"
	if @state.include?(:data)
		process_data_line ln
	elsif ln =~ EhloRegex
		process_ehlo $'.dup
	elsif ln =~ HeloRegex
		process_helo $'.dup
	elsif ln =~ MailFromRegex
		process_mail_from $'.dup
	elsif ln =~ RcptToRegex
		process_rcpt_to $'.dup
	elsif ln =~ DataRegex
		process_data
	elsif ln =~ RsetRegex
		process_rset
	elsif ln =~ VrfyRegex
		process_vrfy
	elsif ln =~ ExpnRegex
		process_expn
	elsif ln =~ HelpRegex
		process_help
	elsif ln =~ NoopRegex
		process_noop
	elsif ln =~ QuitRegex
		process_quit
	elsif ln =~ StarttlsRegex
		process_starttls
	elsif ln =~ AuthRegex
		process_auth $'.dup
	else
		process_unknown
	end
end

#receive_message ⇒ Object

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/protocols/smtpserver.rb', line 501

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/protocols/smtpserver.rb', line 454

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/protocols/smtpserver.rb', line 469

def receive_recipient rcpt
	true
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/protocols/smtpserver.rb', line 462

def receive_sender sender
	true
end

#receive_transaction ⇒ Object

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/protocols/smtpserver.rb', line 508

def receive_transaction
end

#reset_protocol_state ⇒ Object

– 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/protocols/smtpserver.rb', line 176

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_greeting ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 116

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

#unbind ⇒ Object 



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# File 'lib/protocols/smtpserver.rb', line 305

def unbind
	connection_ended
end