lmtp service timeouting even after receiving full message

[Arkadiusz Miśkiewicz]

I have a problem with some messages passed from exim to dovecot lmtp service:

From exim debug:

using socket /var/run/dovecot/lmtp                                                                                                                                                          
  LMTP<< 220 mbox8 ready                                                                                                
  LMTP>> LHLO mbox8...                                                                                                  
  LMTP<< 250-mbox8                                                                                                                                                                          
  LMTP<< 250-STARTTLS                                                                                                                                                                        
  LMTP<< 250-8BITMIME                                                                                                                                                                        
  LMTP<< 250-ENHANCEDSTATUSCODES                                                                                                                                                            
  LMTP<< 250 PIPELINING                                                                                                                                                                      
  LMTP>> MAIL FROM:...                                                                                                  
  LMTP<< 250 2.1.0 OK                                                                                                  
  LMTP>> RCPT TO:...                                                                                                    
  LMTP<< 250 2.1.5 OK                                                                                                  
  LMTP>> DATA                                                                                                          
  LMTP<< 354 OK                                                                                                        
  LMTP>> writing message and terminating "."                                                                            
cannot use sendfile for body: terminating dot wanted                                                                    
writing data block fd=6 size=6585 timeout=300                                                                          
  LMTP>> QUIT                                                                                                          
  LMTP<< 421 4.4.2 mbox8 Disconnected client for inactivity


now above "writting message and terminating" according to exim strace looks like this:

13413 22:07:24 write(2, "  LMTP>> writing message and terminating \".\"\n", 45) = 45 <0.000018>
13413 22:07:24 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2705, ...}) = 0 <0.000025>
13413 22:07:24 write(2, "cannot use sendfile for body: terminating dot wanted\n", 53) = 53 <0.000022>
13413 22:07:24 lseek(3, 19, SEEK_SET)   = 19 <0.000015>
[...]
13413 22:07:24 write(2, "writing data block fd=6 size=6585 timeout=300\n", 46) = 46 <0.000019>
13413 22:07:24 alarm(300)               = 0 <0.000013>
13413 22:07:24 write(6, "Return-path: 
[...]
\nwrap\"><br></span></div>.\n", 6585) = 6585 <0.000023>

and then exim waits for dovecot lmtp to say it accepted message but lmtp never does that.

Isn't .\n always enough for dovecot to signal end of message? Because exim wrote full message
to dovecot lmtp unix socket.

Now the interesting this - exim does only one write() with 6585 bytes to write that message to lmtp.
If exim needs more than one write() to do that (message is larger by some buffer) then it succeeds,
dovecot accepts it.

Could dovecot lmtp handling for single write() case be broken?

dovecot 2.2.35

-- 
Arkadiusz Miśkiewicz, arekm / ( maven.pl | pld-linux.org )