From a413681253a37ae451bfc4b518df456b064d687e Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Thu, 2 Dec 2021 19:29:44 +0100
Subject: [PATCH] Cancel pending commands on downstream disconnect

If a client queues a high number of commands and then disconnects,
remove all of the pending commands. This avoids unnecessarily
sending commands whose results won't be used.
---
 upstream.go | 12 ++++++++++++
 user.go     |  1 +
 2 files changed, 13 insertions(+)

diff --git a/upstream.go b/upstream.go
index db42827..87e41fe 100644
--- a/upstream.go
+++ b/upstream.go
@@ -385,6 +385,18 @@ func (uc *upstreamConn) dequeueCommand(cmd string) (*downstreamConn, *irc.Messag
 	return dc, msg
 }
 
+func (uc *upstreamConn) cancelPendingCommandsByDownstreamID(downstreamID uint64) {
+	for cmd := range uc.pendingCmds {
+		// We can't cancel the currently running command stored in
+		// uc.pendingCmds[cmd][0]
+		for i := len(uc.pendingCmds[cmd]) - 1; i >= 1; i-- {
+			if uc.pendingCmds[cmd][i].downstreamID == downstreamID {
+				uc.pendingCmds[cmd] = append(uc.pendingCmds[cmd][:i], uc.pendingCmds[cmd][i+1:]...)
+			}
+		}
+	}
+}
+
 func (uc *upstreamConn) parseMembershipPrefix(s string) (ms *memberships, nick string) {
 	memberships := make(memberships, 0, 4)
 	i := 0
diff --git a/user.go b/user.go
index 672381e..2d447d7 100644
--- a/user.go
+++ b/user.go
@@ -662,6 +662,7 @@ func (u *user) run() {
 			})
 
 			u.forEachUpstream(func(uc *upstreamConn) {
+				uc.cancelPendingCommandsByDownstreamID(dc.id)
 				uc.updateAway()
 				uc.updateMonitor()
 			})