Syntax error in UIDNEXT response code. Unexpected token: [atom: 0]

[infinity223]

Hi there!

C#, Windows, 64bit, .NET 4.5.2, latest nuget version.

I got a pretty straight forward code for logging into the mail account, checking all folders (with count of messages) and printing them out in a richtextbox.

                                using (var client = new ImapClient(new ProtocolLogger("imap.log")))
                                {
                                    client.Connect(imapHost, imapPort, useSSL);
                                    client.AuthenticationMechanisms.Remove("XOAUTH2");
                                    client.Authenticate(login, haslo);

                                    foreach (var folder in client.GetFolders(client.PersonalNamespaces[0]))
                                    {
                                        folder.Open(FolderAccess.ReadOnly);
                                        //richTextBox2.AppendText("\n" + folder.Name + ": ");
                                        //richTextBox2.AppendText(folder.Count.ToString());
                                    }
                                    client.Disconnect(true);
                                }

client.Connect is provided with correct informations, checked it three times, same as Authenticate.

Problem is with

folder.Open(FolderAccess.ReadOnly);

.. and only on some of the hosts, not all of them (right now I found that problem on two).

Here is what exception is throwing out:

MailKit.Net.Imap.ImapProtocolException: Syntax error in UIDNEXT response code. Unexpected token: [atom: 0]
   w MailKit.Net.Imap.ImapEngine.ParseNumber(ImapToken token, Boolean nonZero, String format, Object[] args)
   w MailKit.Net.Imap.ImapEngine.<ParseResponseCodeAsync>d__167.MoveNext()

Logs says:

Connected to imaps://poczta.o2.pl:993/
S: * OK IMAP4 ready
C: A00000000 CAPABILITY
S: * CAPABILITY IMAP4rev1 UIDPLUS LITERAL+ CHILDREN NAMESPACE XLIST ID IDLE MOVE XAOL-MOVE AUTH=PLAIN
S: A00000000 OK completed
C: A00000001 AUTHENTICATE PLAIN
S: + 
C: AGJ5YnZ5bmVhaHYuZWJsdGhqdGZmbUBvMi5wbABHWUtUTS5rdHVkMzM5
S: A00000001 OK Login completed
C: A00000002 CAPABILITY
S: * CAPABILITY IMAP4rev1 UIDPLUS LITERAL+ CHILDREN NAMESPACE XLIST ID IDLE MOVE XAOL-MOVE
S: A00000002 OK CAPABILITY completed
C: A00000003 NAMESPACE
S: * NAMESPACE (("" "/")) NIL NIL
S: A00000003 OK NAMESPACE completed
C: A00000004 LIST "" "INBOX"
S: * LIST (\Noinferiors) "/" "INBOX"
S: A00000004 OK List completed
C: A00000005 XLIST "" "*"
S: * XLIST (\Noinferiors \Drafts) "/" "Drafts"
S: * XLIST (\Noinferiors) "/" "INBOX"
S: * XLIST (\Noinferiors \Archive) "/" "INBOX/Archive"
S: * XLIST (\HasChildren) "/" "Segregator"
S: * XLIST (\HasNoChildren) "/" "Segregator/Newslettery"
S: * XLIST (\HasNoChildren) "/" "Segregator/Oferty"
S: * XLIST (\HasNoChildren) "/" "Segregator/Spo&AUI-eczno&AVs-ci"
S: * XLIST (\Noinferiors \Sent) "/" "Sent"
S: * XLIST (\Noinferiors \Junk) "/" "Spam"
S: * XLIST (\Noinferiors \Trash) "/" "Trash"
S: A00000005 OK List completed
C: A00000006 LIST "" "*"
S: * LIST (\Noinferiors \Drafts) "/" "Drafts"
S: * LIST (\Noinferiors) "/" "INBOX"
S: * LIST (\Noinferiors \Archive) "/" "INBOX/Archive"
S: * LIST (\HasChildren) "/" "Segregator"
S: * LIST (\HasNoChildren) "/" "Segregator/Newslettery"
S: * LIST (\HasNoChildren) "/" "Segregator/Oferty"
S: * LIST (\HasNoChildren) "/" "Segregator/Spo&AUI-eczno&AVs-ci"
S: * LIST (\Noinferiors \Sent) "/" "Sent"
S: * LIST (\Noinferiors \Junk) "/" "Spam"
S: * LIST (\Noinferiors \Trash) "/" "Trash"
S: A00000006 OK List completed
C: A00000007 EXAMINE Drafts
S: * 0 EXISTS
S: * 0 RECENT
S: * OK [UNSEEN 0] UIDs valid
S: * OK [UIDVALIDITY 0] UIDs valid
S: * OK [UIDNEXT 0] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()]
S: * OK [NOMODSEQ] Sorry, this mailbox format doesn't support modsequences
S: A00000007 OK [READ-ONLY] SELECT completed

draftbox is clear (0 messages).
I checked it on other host, with clear mailbox and UIDNEXT is 1.

I did check skipping "Drafts" folder, and on clear INBOX I got:

C: B00000007 EXAMINE INBOX
S: * 0 EXISTS
S: * 0 RECENT
S: * OK [UNSEEN 0] UIDs valid
S: * OK [UIDVALIDITY 0] UIDs valid
S: * OK [UIDNEXT 0] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()]
S: * OK [NOMODSEQ] Sorry, this mailbox format doesn't support modsequences

So it looks like when I got clear mailbox folder for some cases UIDNEXT is 0.
On a full mailbox folder (like 700 messages) it seems that it is working just fine.

[jstedfast]

Hello!

Thanks so much for providing the protocol logs! 😍

As you have discovered, the problem is that the UIDNEXT value is 0.

The syntax grammar, according to rfc3501 (page 85):

resp-text-code  = "ALERT" /
                  "BADCHARSET" [SP "(" astring *(SP astring) ")" ] /
                  capability-data / "PARSE" /
                  "PERMANENTFLAGS" SP "("
                  [flag-perm *(SP flag-perm)] ")" /
                  "READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
                  "UIDNEXT" SP nz-number / "UIDVALIDITY" SP nz-number /
                  "UNSEEN" SP nz-number /
                  atom [SP 1*<any TEXT-CHAR except "]">]

As we see here, the value for both UIDNEXT and UIDVALIDITY are supposed to be nz-number, which is defined as:

nz-number       = digit-nz *DIGIT
                    ; Non-zero unsigned 32-bit integer
                    ; (0 < n < 4,294,967,296)

This is why MailKit is throwing the exception.

That said, you'll probably notice based on the syntax above, that MailKit isn't throwing an exception for UIDVALIDITY which is also 0 in your logs and is parsed before UIDNEXT (since it appears before UIDNEXT in the logs). Same with UNSEEN.

The reason for this is because MailKit already has work-arounds for those.

The reason that UIDNEXT is not allowed (by the spec) to be 0 is because a UID of 0 is not allowed:

uniqueid        = nz-number
                    ; Strictly ascending

Anyway, I'll add a work-around for UIDNEXT as well so it won't throw an exception. Syntax errors like this are generally trivial to deal with ;-)

[infinity223]

Thanks so much for the fix. Is there a way to push it to nuget?

Tried build master branch but I got errors sadly :(

[jstedfast]

FWIW, every commit results in a new automated build/nuget package published to https://www.myget.org/feed/mimekit/package/nuget/MailKit

These packages are not "official releases", but they are very handy in situations like this ;-)

I normally only do a release/push to nuget.org every few months when I've collected enough fixes that I feel it's worth doing. Otherwise there'd be days where there are like 10+ new versions released ;-)