Hi, these changes appear to work for my purposes, but I'm only just trying them
out now. Perhaps others needing this functionality would like to as well. Thanks.

This adds an -events option to log JOINs, PARTs, etc., as mentioned in [1].
The log formatting in WriteMessage is copied from formatMessage in
soju/msgstore/znclog. It differs only in ZNC 1.9-style "Joins:" lines for
logged-in users [2]. "Joins:" parsing in UnmarshalLine should not be affected.

[1] https://todo.sr.ht/~emersion/chathistorysync/1
[2] https://github.com/znc/znc/pull/1870
---
 client.go   | 14 ++++++++++++
 main.go     |  4 ++++
 msgstore.go | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 79 insertions(+), 1 deletion(-)

diff --git a/client.go b/client.go
index 318bf0c..2db24bd 100644
--- a/client.go
+++ b/client.go
@@ -45,6 +45,7 @@ type client struct {
 	*ircConn
 
 	Debug bool
+	Events bool
 
 	caps struct {
 		chatHistory     bool
@@ -71,6 +72,9 @@ func dialTLS(addr string) (*client, error) {
 
 func (c *client) Register(nick, pass, netid string) {
 	caps := []string{"draft/chathistory", "sasl", "message-tags", "batch", "echo-message", "server-time", "causal.agency/passive", "soju.im/bouncer-networks"}
+	if c.Events {
+		caps = append(caps, "cap-notify", "draft/event-playback", "account-tag")
+	}
 	for _, name := range caps {
 		c.WriteMessage(&irc.Message{
 			Command: "CAP",
@@ -167,6 +171,16 @@ func (c *client) ReadMessage() (*message, error) {
 					return nil, fmt.Errorf("server doesn't support SASL authentication")
 				}
 			}
+		case "NEW":
+			for _, name := range msg.Params[2:] {
+				switch name {
+				case "draft/event-playback", "message-tags", "account-tag":
+					c.WriteMessage(&irc.Message{
+						Command: "CAP",
+						Params:  []string{"REQ", name},
+					})
+				}
+			}
 		}
 	case "BATCH":
 		name := strings.TrimLeft(msg.Params[0], "+-")
diff --git a/main.go b/main.go
index d6afc23..587cefb 100644
--- a/main.go
+++ b/main.go
@@ -41,8 +41,10 @@ type bouncerNetwork struct {
 func main() {
 	var afterStr string
 	var debug bool
+	var events bool
 	flag.StringVar(&afterStr, "after", "", "Only fetch logs after the specified date (format: YYYY-MM-DD)")
 	flag.BoolVar(&debug, "debug", false, "Enable debug logs")
+	flag.BoolVar(&events, "events", false, "Record JOINs, PARTs, etc.")
 	flag.Usage = func() {
 		fmt.Fprint(flag.CommandLine.Output(), usage)
 		flag.PrintDefaults()
@@ -109,6 +111,7 @@ func main() {
 	defer c.Close()
 
 	c.Debug = debug
+	c.Events = events
 	c.Register(nick, pass, "")
 	waitRegistered(c)
 
@@ -125,6 +128,7 @@ func main() {
 			}
 
 			c.Debug = debug
+			c.Events = events
 			c.Register(nick, pass, network.id)
 			waitRegistered(c)
 
diff --git a/msgstore.go b/msgstore.go
index 1b0f09c..6e696d4 100644
--- a/msgstore.go
+++ b/msgstore.go
@@ -78,6 +78,27 @@ func (mw *messageWriter) advance(t time.Time) error {
 	return nil
 }
 
+// parseCTCPMessage is ParseCTCPMessage from git.sr.ht/~emersion/soju/xirc.
+func parseCTCPMessage(msg *message) (cmd string, params string, ok bool) {
+	if (msg.Command != "PRIVMSG" && msg.Command != "NOTICE") || len(msg.Params) < 2 {
+		return "", "", false
+	}
+	text := msg.Params[1]
+
+	if !strings.HasPrefix(text, "\x01") {
+		return "", "", false
+	}
+	text = strings.Trim(text, "\x01")
+
+	words := strings.SplitN(text, " ", 2)
+	cmd = strings.ToUpper(words[0])
+	if len(words) > 1 {
+		params = words[1]
+	}
+
+	return cmd, params, true
+}
+
 func (mw *messageWriter) WriteMessage(msg *message) error {
 	t := msg.time.Local()
 
@@ -96,10 +117,49 @@ func (mw *messageWriter) WriteMessage(msg *message) error {
 
 	var s string
 	switch msg.Command {
+	case "NICK":
+		s = fmt.Sprintf("*** %s is now known as %s", msg.Prefix.Name, msg.Params[0])
+	case "JOIN":
+		s = fmt.Sprintf("*** Joins: %s (%s@%s)", msg.Prefix.Name, msg.Prefix.User, msg.Prefix.Host)
+		// ZNC 1.9 appends account: https://github.com/znc/znc/pull/1870.
+		if account, ok := msg.Tags.GetTag("account"); ok {
+			s += " " + account
+		}
+	case "PART":
+		var reason string
+		if len(msg.Params) > 1 {
+			reason = msg.Params[1]
+		}
+		s = fmt.Sprintf("*** Parts: %s (%s@%s) (%s)", msg.Prefix.Name, msg.Prefix.User, msg.Prefix.Host, reason)
+	case "KICK":
+		nick := msg.Params[1]
+		var reason string
+		if len(msg.Params) > 2 {
+			reason = msg.Params[2]
+		}
+		s = fmt.Sprintf("*** %s was kicked by %s (%s)", nick, msg.Prefix.Name, reason)
+	case "QUIT":
+		var reason string
+		if len(msg.Params) > 0 {
+			reason = msg.Params[0]
+		}
+		s = fmt.Sprintf("*** Quits: %s (%s@%s) (%s)", msg.Prefix.Name, msg.Prefix.User, msg.Prefix.Host, reason)
+	case "TOPIC":
+		var topic string
+		if len(msg.Params) > 1 {
+			topic = msg.Params[1]
+		}
+		s = fmt.Sprintf("*** %s changes topic to '%s'", msg.Prefix.Name, topic)
+	case "MODE":
+		s = fmt.Sprintf("*** %s sets mode: %s", msg.Prefix.Name, strings.Join(msg.Params[1:], " "))
 	case "NOTICE":
 		s = fmt.Sprintf("-%s- %s", msg.Prefix.Name, msg.Params[1])
 	case "PRIVMSG":
-		s = fmt.Sprintf("<%s> %s", msg.Prefix.Name, msg.Params[1])
+		if cmd, params, ok := parseCTCPMessage(msg); ok && cmd == "ACTION" {
+			s = fmt.Sprintf("* %s %s", msg.Prefix.Name, params)
+		} else {
+			s = fmt.Sprintf("<%s> %s", msg.Prefix.Name, msg.Params[1])
+		}
 	}
 	if s == "" {
 		return nil
-- 
2.45.2