[Dovecot] ID command and dovecot

[Jernej Porenta]

Heya,

we are seeing some strange issues with IMAP ID command using latest 
Roundcube builds on dovecot 2.2.10 responding "Input buffer full, aborting".

Roundcube webmail connects to IMAP server and issues ID command first 
with some long arguments to ID command, however shorter than 1024 
octets, which are specified in RFC2971 for ID IMAP extension.

The situation is easily reproducible (see http://pastebin.com/q4HX4wqb):
# telnet hostname 143
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE 
IDLE AUTH=PLAIN AUTH=LOGIN] Server ready.
. ID ("name" "Roundcube" "version" "1.0-git" "php" "5.3.3" "os" "Linux" 
"command" "<$long_less_than_1024_octets_string>")
* BYE Input buffer full, aborting

However, this problem does not occur when user is already logged in.

RFC2971 is saying "Field strings MUST NOT be longer than 30 octets. 
Value strings MUST NOT be longer than 1024 octets. Implementations MUST 
NOT send more than 30 field-value pairs."

IMHO, dovecot is handling ID command before successful login 
successfully only if the length of the whole command is less than 1024 
octets (exactly 861 octets is working fine, over that "Input buffer 
full" occurs).

I tried finding the reference in the source code, however I am unable to 
find where this limit actually occurs (maybe IMAP_ARG_STRING 
imap_arg->type?)

thank you in advance,

regards, Jernej