[patch] Additions (mainly for exchange)

[Florian Lombard]

Hi all,

Here are the patch I worked on when having sync issues with Exchange
(online).
Exchange is very picky with messages, rejecting messages with too long
lines or binary content without explicit error messages.

All my additions are not enabled by default (ie. defaulting to normal
mbsync behaviour)

Common cfg section:

* Either skip or fix messages with lines more than xxx bytes
(typically no more than 9900 bytes with exchange)
MaxLineLength xxx (in bytes)
CutLongLines yes|no (fix or skip message)
* Allow to rescan all mails from a folder, ignoring the last sync
latest message pulled (usefull when playing with my new settings)
IgnoreMaxPulledUid yes|no
* Skip messages with raw binary content (bytes < 0x20 except CR/LF/TAB)
SkipBinaryContent yes|no
* Allow to delete non empty folders on slave (when you are sure about
what you're doing)
DeleteNonEmpty yes|no

Drivers cfg section (imap only):

* Suppress Keyword not supported warnings
IgnoreKeywordWarnings yes|no

Those patches have been extensively tested by myself with a hundred
mailboxes migration from xxx to exchange online via imap.
Patch is against 77acc268123b8233843ca9bc3dcf90669efde08f
The only missing part is long lines cutting when there's CR/LF
convertion (I don't use maildir++)

Regards,
F.LOMBARD.

[Oswald Buddenhagen]

Post by Florian Lombard
Here are the patch I worked on when having sync issues with Exchange
(online).

thanks. i'm not going to apply any part of this patch verbatim, but some
parts of it are worth serious consideration, and somebody may feel
adventurous enough to use your changes as-is.

Post by Florian Lombard
* Either skip or fix messages with lines more than xxx bytes
(typically no more than 9900 bytes with exchange)
MaxLineLength xxx (in bytes)
CutLongLines yes|no (fix or skip message)

as mentioned before, i'm concerned about the "sledge hammer" approach of
hard-cutting the lines, because that falsifies the messages' content,
which may very well render them unreadable (if it's not plain text).

meanwhile i found that this should at least not invalidate possibly
present signatures, simply because the respective standards require
complete normalization of the contents before signing - specifically to
avoid the problem.

still, a cleaner approach would be encapsulating the message in a MIME
structure. i found in the imapsync FAQ that "reformime -r7" would do
that (i'm not suggesting to use that, but it should serve as a good
example).

i'd be interested in samples of such messages with excessively long
lines to assess what the "target audience" actually is. i would expect
that messages which already are MIME-encoded would not have this
problem. but then, a sloppily encoded multipart text+html mail could
very well be broken as well.

Post by Florian Lombard
* Allow to rescan all mails from a folder, ignoring the last sync
latest message pulled (usefull when playing with my new settings)
IgnoreMaxPulledUid yes|no

that seems to be overkill to me given that it's a workaround and can be
easily achieved by hacking the sync state files, for example by sed'ing
them.
i suppose you implemented this to resume syncing after implementing the
line length workaround?

Post by Florian Lombard
* Skip messages with raw binary content (bytes < 0x20 except CR/LF/TAB)
SkipBinaryContent yes|no

i know that i suggested that this might be a problem, but i don't
remember whether you reported actual instances of that.
anyway, the treatment should be the same as for messages with excesively
long lines - MIME-encoding (presumably as quoted-printable).

Post by Florian Lombard
* Allow to delete non empty folders on slave (when you are sure about
what you're doing)
DeleteNonEmpty yes|no

i'll consider this.
my biggest concern is that some transient error would falsify the
mailbox list and thus cause the folders to be nuked. similary, a
permanent change in the server configuration would have that effect.
arguably, either wouldn't be so bad as such, as it would destroy only
the replica. however, it would be important to verify that the replica
does not contain any unpropagated mails (as opposed to any mails at all,
as is done currently).

Post by Florian Lombard
* Suppress Keyword not supported warnings
IgnoreKeywordWarnings yes|no

i wonder why a server would bleat about not supporting an optional
feature when it can (and probably does) announce that in a "civilized"
way, too. did these responses appear to be correlated with specific
messages, or did they always come when opening any mailbox?

Post by Florian Lombard
diff --git a/src/drv_imap.c b/src/drv_imap.c
index e24c7d8..10da0cb 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -1416,6 +1419,16 @@ imap_socket_read( void *aux )
resp = RESP_NO;
if (cmdp->param.failok)
goto doresp;
+ } else if (!strcmp( "BAD", arg )) {
+ resp = RESP_NO;
+ warn( "Warning: IMAP command '%s' returned an error: %s %s\n",
+ starts_with( cmdp->cmd, -1, "LOGIN", 5 ) ?
+ starts_with( cmdp->cmd, -1, "AUTHENTICATE PLAIN", 18 ) ?
+ cmdp->cmd,
+ arg, cmd ? cmd : "" );
+ goto doresp;
} else /*if (!strcmp( "BAD", arg ))*/
resp = RESP_CANCEL;

this hunk downgrades tagged BAD responses to warnings and suppresses the
subsequent client-side connection drop.
this doesn't seem like a terribly good idea to me - this server response
indicates that the client (allegedly) did something wrong. that may mean
that the subsequent command stream will be interpreted as garbage, which
may have unpredictable effects. it just isn't safe to continue at this
point.
i suppose you implemented this as a workaround before you identified the
line length issue?

[Florian Lombard]

Post by Oswald Buddenhagen

Post by Florian Lombard
Here are the patch I worked on when having sync issues with Exchange
(online).

thanks. i'm not going to apply any part of this patch verbatim, but some
parts of it are worth serious consideration, and somebody may feel
adventurous enough to use your changes as-is.

You're welcome. I know this is not production level code (either by the
way I did it or with the liberties I took with standards ;) )

Post by Oswald Buddenhagen

Post by Florian Lombard
* Either skip or fix messages with lines more than xxx bytes
(typically no more than 9900 bytes with exchange)
MaxLineLength xxx (in bytes)
CutLongLines yes|no (fix or skip message)

as mentioned before, i'm concerned about the "sledge hammer" approach of
hard-cutting the lines, because that falsifies the messages' content,
which may very well render them unreadable (if it's not plain text).

Well you have the choice of just skipping them to allow the sync to
complete if you're concerned about the messages integrity

Post by Oswald Buddenhagen
meanwhile i found that this should at least not invalidate possibly
present signatures, simply because the respective standards require
complete normalization of the contents before signing - specifically to
avoid the problem.
still, a cleaner approach would be encapsulating the message in a MIME
structure. i found in the imapsync FAQ that "reformime -r7" would do
that (i'm not suggesting to use that, but it should serve as a good
example).

I had a look at that, and found that completely overkill for my usage
(see below)

Post by Oswald Buddenhagen
i'd be interested in samples of such messages with excessively long
lines to assess what the "target audience" actually is. i would expect
that messages which already are MIME-encoded would not have this
problem. but then, a sloppily encoded multipart text+html mail could
very well be broken as well.

100% of those messages where having bad html code without line breaks
Non binary attachments where always correctly line wrapped.
It was either poorly done html signatures or even javascript (yeah,
inside an email !)
So I wasn't worried about the integrity of those messages, which where
already breaking the rules, but I needed the contents (messages from
customers we needed to keep)

Post by Oswald Buddenhagen

Post by Florian Lombard
* Allow to rescan all mails from a folder, ignoring the last sync
latest message pulled (usefull when playing with my new settings)
IgnoreMaxPulledUid yes|no

that seems to be overkill to me given that it's a workaround and can be
easily achieved by hacking the sync state files, for example by sed'ing
them.
i suppose you implemented this to resume syncing after implementing the
line length workaround?

Yes it was mainly a flag I used for debugging (editing hundreds of sync
state files wasn't an option)

Post by Oswald Buddenhagen

Post by Florian Lombard
* Skip messages with raw binary content (bytes < 0x20 except CR/LF/TAB)
SkipBinaryContent yes|no

i know that i suggested that this might be a problem, but i don't
remember whether you reported actual instances of that.
anyway, the treatment should be the same as for messages with excesively
long lines - MIME-encoding (presumably as quoted-printable).

Those where bogus messages with the raw attachment in binary but with
base 64 headers correctly set.
Near 100% (if not 100%) of those where in the sent folder and are
probably the result of gmail + buggy email client (but you can still
open the attachment with gmail !)

Post by Oswald Buddenhagen

Post by Florian Lombard
* Allow to delete non empty folders on slave (when you are sure about
what you're doing)
DeleteNonEmpty yes|no

i'll consider this.
my biggest concern is that some transient error would falsify the
mailbox list and thus cause the folders to be nuked. similary, a
permanent change in the server configuration would have that effect.
arguably, either wouldn't be so bad as such, as it would destroy only
the replica. however, it would be important to verify that the replica
does not contain any unpropagated mails (as opposed to any mails at all,
as is done currently).

Well, when you are sure about your settings, this can be usefull, as my
users where renaming folders while I was working on the sync
At start I was logging to the mailbox, deleted the folder, and syncing
again.

Post by Oswald Buddenhagen

Post by Florian Lombard
* Suppress Keyword not supported warnings
IgnoreKeywordWarnings yes|no

i wonder why a server would bleat about not supporting an optional
feature when it can (and probably does) announce that in a "civilized"
way, too. did these responses appear to be correlated with specific
messages, or did they always come when opening any mailbox?

Well, "exchange online", that sums it all ...
Tied to specific messages, I guess it happened when there was a word
between bracket in the message subject (no debug log of that)
Happends only one time, when the message is synced.
A rather ugly hack, but I needed clean logs to spot errors.

Post by Oswald Buddenhagen

Post by Florian Lombard
diff --git a/src/drv_imap.c b/src/drv_imap.c
index e24c7d8..10da0cb 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -1416,6 +1419,16 @@ imap_socket_read( void *aux )
resp = RESP_NO;
if (cmdp->param.failok)
goto doresp;
+ } else if (!strcmp( "BAD", arg )) {
+ resp = RESP_NO;
+ warn( "Warning: IMAP command '%s' returned an error: %s %s\n",
+ starts_with( cmdp->cmd, -1, "LOGIN", 5 ) ?
+ starts_with( cmdp->cmd, -1, "AUTHENTICATE PLAIN", 18 ) ?
+ cmdp->cmd,
+ arg, cmd ? cmd : "" );
+ goto doresp;
} else /*if (!strcmp( "BAD", arg ))*/
resp = RESP_CANCEL;

this hunk downgrades tagged BAD responses to warnings and suppresses the
subsequent client-side connection drop.
this doesn't seem like a terribly good idea to me - this server response
indicates that the client (allegedly) did something wrong. that may mean
that the subsequent command stream will be interpreted as garbage, which
may have unpredictable effects. it just isn't safe to continue at this
point.
i suppose you implemented this as a workaround before you identified the
line length issue?

I implemented that before the binary content issue
It's exchange which is breaking all the rules that "forced" me to do
that to sync most of the messages
Cutting the connexion instead of reporting the right error is not the
right thing to do, but that's what exchange does (with Error 10 or 11,
but with BAD reponse)

Hope this helped