README.md

@@ -1019,9 +1019,8 @@ On the IRC listener, `MODE #channel <modes> [values...]` takes several letters
 in one string, e.g. `MODE #general +mt-i` or `MODE #general +ov alice bob`. It
 accepts `i`, `m`, `n`, `s`, `t`, `o` and `v` (with a nick) and `H` (with bits
 from 1 to 40 when setting), but not `b`, `k` or `l`. A letter whose value is
-missing is skipped. The changes made are echoed to the operator's connection and
-also sent to every channel member, the operator included, as one `MODE` line,
-e.g. `+o-v alice bob`.
+missing is skipped. The changes made are sent to every channel member as one
+`MODE` line, e.g. `+o-v alice bob`; the operator gets that line once.
 
 **Channel errors:**
 

internal/ircserver/relay.go

@@ -304,6 +304,15 @@ func (c *Conn) deliverTopicChange(
 	msg *db.IRCMessage,
 	text string,
 ) {
+	c.mu.Lock()
+	nick := c.nick
+	c.mu.Unlock()
+
+	// handleTopic already echoed our own topic change.
+	if msg.From == nick {
+		return
+	}
+
 	prefix := msg.From + "!" + msg.From + "@*"
 	channel := msg.To
 
@@ -315,6 +324,15 @@ func (c *Conn) deliverKickMsg(
 	msg *db.IRCMessage,
 	text string,
 ) {
+	c.mu.Lock()
+	nick := c.nick
+	c.mu.Unlock()
+
+	// handleKick already echoed our own kick.
+	if msg.From == nick {
+		return
+	}
+
 	prefix := msg.From + "!" + msg.From + "@*"
 	channel := msg.To
 
@@ -377,6 +395,15 @@ func (c *Conn) deliverMode(
 		return
 	}
 
+	c.mu.Lock()
+	nick := c.nick
+	c.mu.Unlock()
+
+	// applyChannelModes already echoed our own mode change.
+	if msg.From == nick {
+		return
+	}
+
 	prefix := msg.From + "!" + msg.From + "@*"
 
 	params := slices.Concat(

internal/ircserver/relay_test.go

@@ -292,3 +292,70 @@ func TestRelayNickDiffersOnlyInCase(t *testing.T) {
 		}
 	}
 }
+
+// TestRelayOwnChangeOnce checks that an IRC listener user who
+// sets a topic, changes a channel mode or kicks gets one TOPIC,
+// MODE or KICK line for it, and so does the other member.
+func TestRelayOwnChangeOnce(t *testing.T) {
+	t.Parallel()
+
+	for _, step := range []struct {
+		command, line string
+	}{
+		{"TOPIC", "TOPIC #dup :new topic"},
+		{"MODE", "MODE #dup +m"},
+		{"KICK", "KICK #dup carl :bye"},
+	} {
+		t.Run(step.command, func(t *testing.T) {
+			t.Parallel()
+
+			env := newTestEnv(t)
+
+			alice := env.dial(t)
+			alice.register("alice")
+			alice.joinAndDrain("#dup")
+
+			carl := env.dial(t)
+			carl.register("carl")
+			carl.joinAndDrain("#dup")
+
+			alice.send(step.line)
+
+			// The reply to alice's next command comes after her
+			// command has finished, so her own copy comes before it.
+			beforePong := alice.sendAndExpect("PING :done", "PONG")
+
+			// The relay sends a user's queue in order, so a message
+			// queued now arrives after any relayed copy.
+			for nick, client := range map[string]*testClient{
+				"alice": alice, "carl": carl,
+			} {
+				env.queueMessage(
+					t, nick, "PRIVMSG", "dave", nick,
+					[]string{"after the change"},
+				)
+
+				lines := client.readUntil(func(l string) bool {
+					return strings.HasSuffix(l, " :after the change")
+				})
+
+				if client == alice {
+					lines = slices.Concat(beforePong, lines)
+				}
+
+				var changes []string
+
+				for _, line := range lines {
+					if strings.Contains(line, " "+step.command+" #dup ") {
+						changes = append(changes, line)
+					}
+				}
+
+				if len(changes) != 1 {
+					t.Errorf("%s got %q, want one %s line",
+						nick, changes, step.command)
+				}
+			}
+		})
+	}
+}