Nicknames with slashes appear as "undefined" (RELAYMSG)

[Mikaela]

Describe the bug

RELAYMSG or nicknames with slashes appear as "undefined" (@irc_undefined:liberta.casa) on Matrix.

To Reproduce

1. Join a room where you can see RELAYMSG
2. See a RELAYMSG'd user or if you are op (or oper with relaymsg privilege) on IRC, send one by yourself through /quote RELAYMSG #channel fake/relaymsg :message here

Expected behavior

"message here" appears to be sent by nickname "fake/relaymsg", but instead appears from user "undefined"

Screenshots

IRC:

[17:45:09] <fake/relaymsg> This is a message from fake/relaymsg
[17:45:10] <cranberry> lol
[17:45:13] <M1kaela/tg> This is a message from M1kaela/tg while we aren't actually relayed there

Desktop (please complete the following information):

• OS: Fedora 34
• Browser Edge
• Version: Versio 91.0.864.67 (Virallinen koontiversio) (64-bittinen)

Additional context

• Client used: https://develop.element.io/
• BridgeVersion: 0.27.0
• IRCd: ergo-2.7.0-rc1-36703580fc460ec2 irc.liberta.casa
• Possibly related: Cannot join channels with slashes (e.g. #r/a/dio on Rizon) using alias #500

[Mikaela]

Also possibly related: #712

[Mikaela]

I found out that /me messages from the unknown user also become messed up.

{
  "content": {
    "body": "\u0001ACTION nominates matrix-appservice-irc the biggest headache since Charybdis#255\u0001",
    "msgtype": "m.text"
  },
  "origin_server_ts": 1626610714905,
  "sender": "@irc_undefined:liberta.casa",
  "type": "m.room.message",
  "unsigned": {
    "age": 5619
  },
  "event_id": "$FCKonM2YAMuLG3vVgxB6zwpH0zkxMkZKPW3XTpRWGuY",
  "room_id": "!BOgGhzZDPlkGSgoSdO:liberta.casa"
}

I don't know if it's a separate issue or just strongly related to this one.

[Mikaela]

@Half-Shot could you acknowledge this issue too and give it label IRCv3?

Ref: ircv3/ircv3-specifications#417

RELAYMSG is also currently the most 👍'd issue on Solanum which is what Libera.Chat uses, solanum-ircd/solanum#159.

[Half-Shot]

We've not actively prioritised IRCv3 features in favour of trying to support existing features / performance improvements, and would probably wish for the community to look at implementing those. Sorry, the resources just aren't enough where we can look at these right now.

[emersonveenstra]

It's not actually an IRCv3 problem, it's because of matrix-org/node-irc#81.

However, dendrite actually enforces the allowed mxid characters so it will be unhappy (#1432), but maybe that's a problem for later, since dendrite is already unhappy with a lot of things the bridge does.

[poVoq]

Since this is still not fixed upstream... am I correct that it might be possible to work-around this issue by using a different RELAYMSG seperator than "/"? Has anyone tried some working ones that are unlikely to be used by regular nicknames?

Edit: Confirmed, if I use a IRC nickname legal seperator like | it starts working. Not ideal of course, but a work-around.