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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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41
imapserver/parse.go
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@ -7,8 +7,6 @@ import (
"strconv"
"strings"
"time"
"golang.org/x/exp/slog"
)
var (
@ -392,30 +390,37 @@ func (p *parser) xatom() string {
return p.xtakechars(atomChar, "atom")
}
func (p *parser) xdecodeMailbox(s string) string {
// UTF-7 is deprecated for IMAP4rev2-only clients, and not used with UTF8=ACCEPT.
// The future should be without UTF-7, we don't encode/decode it with modern
// clients. Most clients are IMAP4rev1, we need to handle UTF-7.
// ../rfc/3501:964 ../rfc/9051:7885
// Thunderbird will enable UTF8=ACCEPT and send "&" unencoded. ../rfc/9051:7953
if p.conn.utf8strings() {
return s
}
ns, err := utf7decode(s)
if err != nil {
p.xerrorf("decoding utf7 mailbox name: %v", err)
}
return ns
}
func (p *parser) xmailbox() string {
s := p.xastring()
// UTF-7 is deprecated in IMAP4rev2. IMAP4rev1 does not fully forbid
// UTF-8 returned in mailbox names. We'll do our best by attempting to
// decode utf-7. But if that doesn't work, we'll just use the original
// string.
// ../rfc/3501:964
if !p.conn.enabled[capIMAP4rev2] {
ns, err := utf7decode(s)
if err != nil {
p.conn.log.Infox("decoding utf7 or mailbox name", err, slog.String("name", s))
} else {
s = ns
}
}
return s
return p.xdecodeMailbox(s)
}
// ../rfc/9051:6605
func (p *parser) xlistMailbox() string {
var s string
if p.hasPrefix(`"`) || p.hasPrefix("{") {
return p.xstring()
s = p.xstring()
} else {
s = p.xtakechars(atomChar+listWildcards+respSpecials, "list-char")
}
return p.xtakechars(atomChar+listWildcards+respSpecials, "list-char")
// Presumably UTF-7 encoding applies to mailbox patterns too.
return p.xdecodeMailbox(s)
}
// ../rfc/9051:6707 ../rfc/9051:6848 ../rfc/5258:1095 ../rfc/5258:1169 ../rfc/5258:1196