[RustyBower]

Replies are currently bridged as a Reply to "…" context line plus the message on IRC, and as plain messages on Discord. On IRC servers that support IRCv3 message tags, this makes them real replies in both directions:

• Discord → IRC: replies are sent with the +draft/reply client tag, so clients such as IRCCloud, The Lounge and recent WeeChat show them threaded under the original.
• IRC → Discord: IRC replies (+draft/reply, or +reply as some clients also send) to a bridged message are sent as Discord replies to its Discord copy.

How it works

• The bridge requests echo-message (KICL already requests message-tags). When the server echoes back a line the bridge sent, the bridge records the msgid the server assigned it against the Discord message it came from.
• For IRC messages bridged to Discord, the Discord message ID returned by the webhook or bot send is recorded against the IRC message's msgid.
• The mappings are kept in both directions in an in-memory LRU cache (2048 entries). Nothing is persisted.
• Discord webhooks can't send replies, so IRC replies that can be threaded are sent by the bot as <nick> text with a message reference. Everything else still goes through webhooks as before.

Fallback

Nothing changes unless the server supports it:

• no message-tags, or draft/reply blocked by CLIENTTAGDENY → no tags are sent
• no echo-message → msgids of the bridge's own messages aren't recorded

In those cases, and for replies to messages the bridge doesn't know (e.g. from before a restart), messages are bridged exactly as before, including the context line on IRC.

New options

irc {
    # Whether to send Discord replies as IRCv3 threaded replies (+draft/reply), if the server supports it.
    discord-reply-tags=true
    # Whether to also send the reply context line when a reply is sent threaded, for clients without
    # IRCv3 reply support. Unthreaded replies always get it.
    discord-reply-context-with-tags=false
}
discord-options {
    # Whether IRCv3 replies from IRC to bridged messages are sent as Discord replies.
    # Webhooks can't reply, so these are sent by the bot itself.
    thread-irc-replies=true
}

Bridge can now be created without the main Dis4IRC instance, so tests can use it on its own.

Testing

• An in-process fake IRCv3 server (test only) runs the real IRC pier. The tests cover:
  • msgid tracking via echo-message
  • reply tags for Discord-origin and IRC-origin parents
  • long replies being tagged on every part
  • the context line with and without threading
  • falling back without message-tags, without echo-message, and with CLIENTTAGDENY
• Unit tests for the ID cache, the reply-tag parsing and resolving IRC replies to Discord messages.
• Run live between a Discord server (webhook channel) and UnrealIRCd 6.2.7, which advertises CLIENTTAGDENY=*,-draft/reply,…, viewed in IRCCloud:
  • Discord replies to IRC and to Discord messages were threaded in IRCCloud.
  • IRCCloud replies to Discord and to IRC messages arrived as Discord replies.

The fake-server tests add about a minute to ./gradlew test, mostly KICL's send rate limit.