From 438fffab99e2712c954ecda49c0c87694f7e8af3 Mon Sep 17 00:00:00 2001
From: Shivaram Lingamneni <slingamn@cs.stanford.edu>
Date: Fri, 21 Feb 2020 06:10:35 -0500
Subject: [PATCH] fix #725

---
 irc/commands.go |  5 +++++
 irc/handlers.go | 46 ++++++++++++++++++++++++++++++----------------
 irc/help.go     |  6 ++++++
 irc/modes.go    | 13 +++++++++++++
 4 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/irc/commands.go b/irc/commands.go
index 859636b8..7a6a65fb 100644
--- a/irc/commands.go
+++ b/irc/commands.go
@@ -116,6 +116,11 @@ func init() {
 			minParams: 1,
 			oper:      true,
 		},
+		"DEOPER": {
+			handler:   deoperHandler,
+			minParams: 0,
+			oper:      true,
+		},
 		"DLINE": {
 			handler:   dlineHandler,
 			minParams: 1,
diff --git a/irc/handlers.go b/irc/handlers.go
index 8f3827b9..f5999daa 100644
--- a/irc/handlers.go
+++ b/irc/handlers.go
@@ -2141,35 +2141,49 @@ func operHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *Resp
 	return false
 }
 
-// applies operator status to a client, who MUST NOT already be an operator
+// adds or removes operator status
+// XXX: to add oper, this calls into ApplyUserModeChanges, but to remove oper,
+// ApplyUserModeChanges calls into this, because the commands are asymmetric
+// (/OPER to add, /MODE self -o to remove)
 func applyOper(client *Client, oper *Oper, rb *ResponseBuffer) {
 	details := client.Details()
-	oldNickmask := details.nickMask
 	client.SetOper(oper)
-	newNickmask := client.NickMaskString()
-	if newNickmask != oldNickmask {
-		client.sendChghost(oldNickmask, oper.Vhost)
+	newDetails := client.Details()
+	if details.nickMask != newDetails.nickMask {
+		client.sendChghost(details.nickMask, newDetails.hostname)
 	}
 
-	// set new modes: modes.Operator, plus anything specified in the config
-	modeChanges := make([]modes.ModeChange, len(oper.Modes)+1)
-	modeChanges[0] = modes.ModeChange{
-		Mode: modes.Operator,
-		Op:   modes.Add,
+	if oper != nil {
+		// set new modes: modes.Operator, plus anything specified in the config
+		modeChanges := make([]modes.ModeChange, len(oper.Modes)+1)
+		modeChanges[0] = modes.ModeChange{
+			Mode: modes.Operator,
+			Op:   modes.Add,
+		}
+		copy(modeChanges[1:], oper.Modes)
+		applied := ApplyUserModeChanges(client, modeChanges, true)
+
+		client.server.snomasks.Send(sno.LocalOpers, fmt.Sprintf(ircfmt.Unescape("Client opered up $c[grey][$r%s$c[grey], $r%s$c[grey]]"), newDetails.nickMask, oper.Name))
+
+		rb.Broadcast(nil, client.server.name, RPL_YOUREOPER, details.nick, client.t("You are now an IRC operator"))
+		rb.Broadcast(nil, client.server.name, "MODE", details.nick, applied.String())
+	} else {
+		client.server.snomasks.Send(sno.LocalOpers, fmt.Sprintf(ircfmt.Unescape("Client deopered $c[grey][$r%s$c[grey]]"), newDetails.nickMask))
 	}
-	copy(modeChanges[1:], oper.Modes)
-	applied := ApplyUserModeChanges(client, modeChanges, true)
 
-	client.server.snomasks.Send(sno.LocalOpers, fmt.Sprintf(ircfmt.Unescape("Client opered up $c[grey][$r%s$c[grey], $r%s$c[grey]]"), client.nickMaskString, oper.Name))
-
-	rb.Broadcast(nil, client.server.name, RPL_YOUREOPER, details.nick, client.t("You are now an IRC operator"))
-	rb.Broadcast(nil, client.server.name, "MODE", details.nick, applied.String())
 	for _, session := range client.Sessions() {
 		// client may now be unthrottled by the fakelag system
 		session.resetFakelag()
 	}
 }
 
+// DEOPER
+func deoperHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *ResponseBuffer) bool {
+	// pretend they sent /MODE $nick -o
+	fakeModeMsg := ircmsg.MakeMessage(nil, "", "MODE", client.Nick(), "-o")
+	return umodeHandler(server, client, fakeModeMsg, rb)
+}
+
 // PART <channel>{,<channel>} [<reason>]
 func partHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *ResponseBuffer) bool {
 	channels := strings.Split(msg.Params[0], ",")
diff --git a/irc/help.go b/irc/help.go
index 4f0a19da..abcce6de 100644
--- a/irc/help.go
+++ b/irc/help.go
@@ -160,6 +160,12 @@ Prints debug information about the IRCd. <option> can be one of:
 * STARTCPUPROFILE: Starts the CPU profiler.
 * STOPCPUPROFILE: Stops the CPU profiler.
 * PROFILEHEAP: Writes out the CPU profiler info.`,
+	},
+	"deoper": {
+		oper: true,
+		text: `DEOPER
+
+DEOPER removes the IRCop privileges granted to you by a successful /OPER.`,
 	},
 	"dline": {
 		oper: true,
diff --git a/irc/modes.go b/irc/modes.go
index d8d1db8e..08610ee5 100644
--- a/irc/modes.go
+++ b/irc/modes.go
@@ -45,13 +45,26 @@ func ApplyUserModeChanges(client *Client, changes modes.ModeChanges, force bool)
 				}
 
 			case modes.Remove:
+				var removedSnomasks string
 				if client.SetMode(change.Mode, false) {
 					if change.Mode == modes.Invisible {
 						client.server.stats.ChangeInvisible(-1)
 					} else if change.Mode == modes.Operator || change.Mode == modes.LocalOperator {
+						removedSnomasks = client.server.snomasks.String(client)
 						client.server.stats.ChangeOperators(-1)
+						applyOper(client, nil, nil)
+						if removedSnomasks != "" {
+							client.server.snomasks.RemoveClient(client)
+						}
 					}
 					applied = append(applied, change)
+					if removedSnomasks != "" {
+						applied = append(applied, modes.ModeChange{
+							Mode: modes.ServerNotice,
+							Op:   modes.Remove,
+							Arg:  removedSnomasks,
+						})
+					}
 				}
 			}