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imapserver: allow creating mailboxes with characters &#*%, and encode mailbox names in imap with imaputf7 when needed

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the imapserver started with imap4rev2-only and utf8=only.  to prevent potential
issues with imaputf7, which makes "&" special, we refused any mailbox with an
"&" in the name. we already tried decoding utf7, falling back to using a
mailbox name verbatim. that behaviour wasn't great. we now treat the enabled
extensions IMAP4rev2 and/or UTF8=ACCEPT as indication whether mailbox names are
in imaputf7. if they are, the encoding must be correct.

we now also send mailbox names in imaputf7 when imap4rev2/utf8=accept isn't
enabled.

and we now allow "*" and "%" (wildcard characters for matching) in mailbox
names. not ideal for IMAP LIST with patterns, but not enough reason to refuse
them in mailbox names. people that migrate may run into this, possibly as
blocker.

we also allow "#" in mailbox names, but not as first character, to prevent
potential clashes with IMAP namespaces in the future.

based on report from Damian Poddebniak using
https://github.com/duesee/imap-flow and issue #110, thanks for reporting!
This commit is contained in:
Mechiel Lukkien
2024-01-01 13:15:25 +01:00
parent a9940f9855
commit d84c96eca5
7 changed files with 150 additions and 51 deletions
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16
store/account.go
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@ -2599,12 +2599,18 @@ func CheckMailboxName(name string, allowInbox bool) (normalizedName string, isIn
if strings.HasPrefix(name, "/") || strings.HasSuffix(name, "/") || strings.Contains(name, "//") {
return "", false, errors.New("bad slashes in mailbox name")
}
// "%" and "*" are difficult to use with the IMAP LIST command, but we allow mostly
// allow them. ../rfc/3501:1002 ../rfc/9051:983
if strings.HasPrefix(name, "#") {
return "", false, errors.New("mailbox name cannot start with hash due to conflict with imap namespaces")
}
// "#" and "&" are special in IMAP mailbox names. "#" for namespaces, "&" for
// IMAP-UTF-7 encoding. We do allow them. ../rfc/3501:1018 ../rfc/9051:991
for _, c := range name {
switch c {
case '%', '*', '#', '&':
return "", false, fmt.Errorf("character %c not allowed in mailbox name", c)
}
// ../rfc/6855:192
// ../rfc/3501:999 ../rfc/6855:192 ../rfc/9051:979
if c <= 0x1f || c >= 0x7f && c <= 0x9f || c == 0x2028 || c == 0x2029 {
return "", false, errors.New("control characters not allowed in mailbox name")
}