From 1c285a1b728771eaaabb435ab6eb30b3abce6514 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Sat, 4 Dec 2021 20:07:23 +0100
Subject: [PATCH] Fallback to alt nick

If the nickname we want is taken, fallback to another one by
appending underscores. Use MONITOR to figure out when we can request
our desired nick again.

Closes: https://todo.sr.ht/~emersion/soju/35
---
 upstream.go | 50 ++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/upstream.go b/upstream.go
index c4d50e0..561da2f 100644
--- a/upstream.go
+++ b/upstream.go
@@ -774,6 +774,8 @@ func (uc *upstreamConn) handleMessage(ctx context.Context, msg *irc.Message) err
 			}
 		}
 
+		uc.updateMonitor()
+
 		uc.forEachDownstream(func(dc *downstreamConn) {
 			if dc.network == nil {
 				return
@@ -876,6 +878,7 @@ func (uc *upstreamConn) handleMessage(ctx context.Context, msg *irc.Message) err
 			uc.forEachDownstream(func(dc *downstreamConn) {
 				dc.updateNick()
 			})
+			uc.updateMonitor()
 		}
 	case "SETNAME":
 		if msg.Prefix == nil {
@@ -1522,6 +1525,27 @@ func (uc *upstreamConn) handleMessage(ctx context.Context, msg *irc.Message) err
 			uc.monitored.SetValue(prefix.Name, online)
 		}
 
+		// Check if the nick we want is now free
+		wantNick := GetNick(&uc.user.User, &uc.network.Network)
+		wantNickCM := uc.network.casemap(wantNick)
+		if !online && uc.nickCM != wantNickCM {
+			found := false
+			for _, target := range targets {
+				prefix := irc.ParsePrefix(target)
+				if uc.network.casemap(prefix.Name) == wantNickCM {
+					found = true
+					break
+				}
+			}
+			if found {
+				uc.logger.Printf("desired nick %q is now available", wantNick)
+				uc.SendMessage(&irc.Message{
+					Command: "NICK",
+					Params:  []string{wantNick},
+				})
+			}
+		}
+
 		uc.forEachDownstream(func(dc *downstreamConn) {
 			for _, target := range targets {
 				prefix := irc.ParsePrefix(target)
@@ -1687,7 +1711,22 @@ func (uc *upstreamConn) handleMessage(ctx context.Context, msg *irc.Message) err
 			return err
 		}
 		return fmt.Errorf("fatal server error: %v", text)
-	case irc.ERR_PASSWDMISMATCH, irc.ERR_ERRONEUSNICKNAME, irc.ERR_NICKNAMEINUSE, irc.ERR_NICKCOLLISION, irc.ERR_UNAVAILRESOURCE, irc.ERR_NOPERMFORHOST, irc.ERR_YOUREBANNEDCREEP:
+	case irc.ERR_NICKNAMEINUSE:
+		// At this point, we haven't received ISUPPORT so we don't know the
+		// maximum nickname length or whether the server supports MONITOR. Many
+		// servers have NICKLEN=30 so let's just use that.
+		if !uc.registered && len(uc.nick)+1 < 30 {
+			uc.nick = uc.nick + "_"
+			uc.nickCM = uc.network.casemap(uc.nick)
+			uc.logger.Printf("desired nick is not available, falling back to %q", uc.nick)
+			uc.SendMessage(&irc.Message{
+				Command: "NICK",
+				Params:  []string{uc.nick},
+			})
+			return nil
+		}
+		fallthrough
+	case irc.ERR_PASSWDMISMATCH, irc.ERR_ERRONEUSNICKNAME, irc.ERR_NICKCOLLISION, irc.ERR_UNAVAILRESOURCE, irc.ERR_NOPERMFORHOST, irc.ERR_YOUREBANNEDCREEP:
 		if !uc.registered {
 			return registrationError{msg}
 		}
@@ -2087,14 +2126,21 @@ func (uc *upstreamConn) updateMonitor() {
 			if !uc.monitored.Has(targetCM) {
 				if _, ok := add[targetCM]; !ok {
 					addList = append(addList, targetCM)
+					add[targetCM] = struct{}{}
 				}
-				add[targetCM] = struct{}{}
 			} else {
 				seen[targetCM] = struct{}{}
 			}
 		}
 	})
 
+	wantNick := GetNick(&uc.user.User, &uc.network.Network)
+	wantNickCM := uc.network.casemap(wantNick)
+	if _, ok := add[wantNickCM]; !ok && !uc.monitored.Has(wantNick) && !uc.isOurNick(wantNick) {
+		addList = append(addList, wantNickCM)
+		add[wantNickCM] = struct{}{}
+	}
+
 	removeAll := true
 	var removeList []string
 	for targetCM, entry := range uc.monitored.innerMap {