PING a quiet IRC listener client before closing it (closes #155)

serve closed a connection after five minutes with nothing read and never
sent a PING, so a quiet registered client lost its session. It now sends
PING :<server> after pingInterval with nothing read, and closes the
connection when nothing is read within pongDeadline after that. Every
line read starts both waits again. readTimeout is removed.

Unregistered connections are sent the PING too, so a PONG before
registration is now ignored instead of answered with ERR_NOTREGISTERED.

Model: opus-5-5

internal/ircserver/conn.go

@@ -20,7 +20,6 @@ import (
 
 const (
 	maxLineLen      = 512
-	readTimeout     = 5 * time.Minute
 	writeTimeout    = 30 * time.Second
 	killWriteWindow = 2 * time.Second
 	dnsTimeout      = 3 * time.Second
@@ -46,6 +45,11 @@ type Conn struct {
 	serverSfx string
 	commands  map[string]cmdHandler
 
+	// pingInterval and pongDeadline are the constants of the
+	// same names, except in tests, which shorten them.
+	pingInterval time.Duration
+	pongDeadline time.Duration
+
 	// writeMu serializes writes to conn, which come from
 	// serve(), from the relay goroutine and, for KILL, from
 	// Disconnect.
@@ -96,6 +100,9 @@ func newConn(
 		serverSfx: srvName,
 		remoteIP:  host,
 		hostname:  resolveHost(ctx, host),
+
+		pingInterval: pingInterval,
+		pongDeadline: pongDeadline,
 	}
 
 	conn.commands = conn.buildCommandMap()
@@ -214,17 +221,28 @@ func resolveHost(ctx context.Context, addr string) string {
 
 // serve is the main loop for a single IRC client connection.
 // Cancelling ctx when it returns stops the relay goroutine.
+// When nothing has been read for pingInterval the client is
+// sent a PING, and when nothing is read within pongDeadline
+// after that the connection is closed.
 func (c *Conn) serve(ctx context.Context) {
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 	defer c.cleanup(ctx)
 
+	ping := time.AfterFunc(c.pingInterval, func() {
+		c.send("PING :" + c.serverSfx)
+	})
+	defer ping.Stop()
+
 	scanner := bufio.NewScanner(c.conn)
 	scanner.Buffer(make([]byte, maxLineLen), maxLineLen)
 
 	for {
+		// Every line read starts both waits again.
+		ping.Reset(c.pingInterval)
+
 		_ = c.conn.SetReadDeadline(
-			time.Now().Add(readTimeout),
+			time.Now().Add(c.pingInterval + c.pongDeadline),
 		)
 
 		if !scanner.Scan() {
@@ -366,7 +384,7 @@ func (c *Conn) handleMessage(
 	msg *Message,
 ) {
 	// Before registration, only NICK, USER, PASS, PING,
-	// QUIT, and CAP are accepted.
+	// PONG, QUIT, and CAP are accepted.
 	if !c.registered {
 		c.handlePreRegistration(ctx, msg)
 
@@ -452,6 +470,10 @@ func (c *Conn) handlePreRegistration(
 	case irc.CmdPing:
 		c.handlePing(msg)
 
+		return
+	case irc.CmdPong:
+		// The answer to serve's PING, which unregistered
+		// clients are sent too.
 		return
 	case irc.CmdQuit:
 		c.handleQuit(msg)