(Subject line altered - original was confused)
On Friday 30 September 2011 00:07:08 Michael M Slusarz wrote:
Quoting Andrew Richards ar-dovecotlist@acrconsulting.co.uk:
Hi,
I've noticed a possible minor issue with long encoded filenames for attachments where these filenames are split across multiple lines. My understanding of character encoding and MIME is not as good as it should be, so I may easily have got this all mixed up, in which case sorry for the noise...
Although I understand the preferred method for handling filenames split across multiple lines (because they're too long to fit on one line in the message) is that suggested in RFC2184/2231, so for example, filename*0*=iso-8859-1''accented_characters_here_%EA%CA%E6 filename*1=etc%2Epdf
I find that some mail clients do this instead, filename="=?ISO-8859-1?Q?accented_characters_here_=EA=CA=E6?= =?ISO-8859-1?Q?etc=2Epdf?="
In Dovecot this results in, 0 fetch 25 body
- 25 FETCH (BODY (("text" "plain" ("charset" "ISO-8859-1") NIL NIL "7bit" 239 8)("application" "pdf" ("name" "=?ISO-8859-1?Q?accented_characters_here_=EA=CA=E6?= =?ISO-8859-1?Q?etc=2Epdf?=") NIL NIL "base64" 219130) "mixed"))
esp. note the unwanted space - or in fact the sequence ?= =? between the two sections of the filename. I think a possible tweak for Dovecot would be to combine the filename parts in this situation to remove the ?= =?.
Correcting myself: ...remove the ?= =?ISO-8859-1?Q? (not just ?= =?) to generate the string in this example, "=?ISO-8859-1?Q?accented_characters_here_=EA=CA=E6etc=2Epdf?="
I'm not sure if an IMAP client should know to combine the parts in their current format. FWIW I see that Courier does the same as Dovecot in this situation.
Dovecot's behavior is correct. There's nothing "special" about that name parameter - it's not RFC 2231 encoded - so the IMAP server should output the exact header text as-is. Those two parts were separated by space in the original header - they should be separated by space when grabbing the fetch data.
I can accept that Dovecot's behaviour is technically correct, but my point is that (if I've understood correctly) with some large mailers like Gmail acting in a non-RFC2231 manner, is it worth adapting Dovecot to play nicely with them. Possibly I'm conflating 2 separate issues: Munging together non-RFC2231 attachment filename parts, large mailers not using RFC2231 to handle long non- ASCII filenames.
If the *client* wants to workaround these broken messages, it can do whatever munging is wants to translate the contents of the "name" parameter. But that should be up to the client. An IMAP server should not be making wild assumptions about what the original sender wanted to do with the message vs. what it actually sent.
FYI: A workaround is to do something like this when sending a message:
Content-Dispostion: attachment; filename="=?ISO-8859-1?Q?accented_characters_here_=EA=CA=E6?= =?ISO-8859-1?Q?etc=2Epdf?="; filename*0*=iso-8859-1''accented_characters_here_%EA%CA%E6; filename*1=etc%2Epdf
Sure: I accept that that's the preferred way to handle long filenames that need to be encoded - but I'm noting that there are badly-behaved large mailers that don't do so, so I wonder if it's worth Dovecot mitigating the effects.
Best regards,
Andrew.