Casemapping (RFC 3454) does not work for channel names

[mk-fg]

Hi,

Trying to use matrix2051 with ZNC-ERC bouncer-client combination, immediately bumped into error notice like following when sending message from client in a channel listed as !RrkYlRwPmZqHGhPFvf:foss.wtf:
[11:13:07] -server.- Error while sending message: {:room_not_found, "!rrkylrwpmzqhghpfvf:foss.wtf"}

I think the issue might be lack of casemapping for channel names, which client expects, but server does not seem to implement, since afaik on IRC !RrkYlRwPmZqHGhPFvf:foss.wtf and !rrkylrwpmzqhghpfvf:foss.wtf channel/user names should generally be equivalent.

matrix2051 advertises CASEMAPPING=rfc3454 in particular, which explicitly includes ASCII letters (listed at the start of B2/B3 appendixes there) and I think should be backwards-compatible in this case, even if client reads this as CASEMAPPING=ascii.

I'm not sure if there is an option to not support any case-mapping on IRC, as at least in ERC client, any unknown/missing CASEMAPPING values fallback to RFC 1459, which maps ascii letters + some non-letter characters, and there's no "none" option supported.

To report it more strictly:

• What I did: tried sending message (any content) to a matrix channel !RrkYlRwPmZqHGhPFvf:foss.wtf, with ascii upper/lower-case letters in its name, from an ERC client (built into emacs text editor).

• Expected result: message gets dispatched over Matrix protocol with no errors and can be seen in the channel there.

• Actual result: [11:13:07] -server.- Error while sending message: {:room_not_found, "!rrkylrwpmzqhghpfvf:foss.wtf"} notice in response, message cannot be seen in Matrix channel.

• Steps to reproduce:

  • Create any non-encrypted private channel, its name will almost certainly contain mixed-case letters in matrix2051 representation.

  • Use client that maps IRC names internally to some "canonical" representation using casemapping and resulting mapped names, or otherwise send PRIVMSG IRC command with channel name in all-upper/lower-case.

    For example, following command can be used in clients for testing: /msg <lowercase-chan-name> test

  • Note error notice in response instead of successful message send.

Wasn't able to find this reported under Issues from a quick look and search.
(if it is, maybe can include more keywords/info in the title)

Thanks.

[mk-fg]

Also, in rare case that anyone might stumble upon this issue specifically because of ERC keyword, with this ircd or others, simple workaround (disabling casemapping for channels entirely) can be:

(defun erc-add-default-channel-downcase-fix (old-func channel)
  (push channel erc-default-recipients))
(advice-add 'erc-add-default-channel :around #'erc-add-default-channel-downcase-fix)

Or with additional (if (not (string-search ":" channel)) (funcall old-func channel) ...) check if this should be limited to matrix2051 channels, which I think should always have : in their names, which is seldom used in these otherwise.

[progval]

another possible workaround is to set a canonical alias for the Matrix room and use that instead of the room id.