Connection limit for thick daemon.

Signed-off-by: Julius Hinze <juliusmh@proton.me>

cmd/multus-daemon/main.go

@@ -29,6 +29,7 @@ import (
 	"sync"
 	"syscall"
 
+	"golang.org/x/net/netutil"
 	utilwait "k8s.io/apimachinery/pkg/util/wait"
 
 	"gopkg.in/k8snetworkplumbingwg/multus-cni.v4/pkg/logging"
@@ -106,7 +107,7 @@ func main() {
 		}
 	}
 
-	if err := startMultusDaemon(ctx, daemonConf, ignoreReadinessIndicator); err != nil {
+	if err := startMultusDaemon(ctx, daemonConf, ignoreReadinessIndicator, daemonConf.ConnectionLimit); err != nil {
 		logging.Panicf("failed start the multus thick-plugin listener: %v", err)
 		os.Exit(3)
 	}
@@ -140,7 +141,7 @@ func main() {
 	logging.Verbosef("multus daemon is exited")
 }
 
-func startMultusDaemon(ctx context.Context, daemonConfig *srv.ControllerNetConf, ignoreReadinessIndicator bool) error {
+func startMultusDaemon(ctx context.Context, daemonConfig *srv.ControllerNetConf, ignoreReadinessIndicator bool, connectionLimit *int) error {
 	if user, err := user.Current(); err != nil || user.Uid != "0" {
 		return fmt.Errorf("failed to run multus-daemon with root: %v, now running in uid: %s", err, user.Uid)
 	}
@@ -167,6 +168,11 @@ func startMultusDaemon(ctx context.Context, daemonConfig *srv.ControllerNetConf,
 		return fmt.Errorf("failed to start the CNI server using socket %s. Reason: %+v", api.SocketPath(daemonConfig.SocketDir), err)
 	}
 
+	if limit := connectionLimit; limit != nil && *limit > 0 {
+		logging.Debugf("connection limit: %d", *limit)
+		l = netutil.LimitListener(l, *limit)
+	}
+
 	server.Start(ctx, l)
 
 	go func() {

pkg/server/types.go

@@ -77,6 +77,7 @@ type ControllerNetConf struct {
 	LogLevel           string              `json:"logLevel"`
 	LogToStderr        bool                `json:"logToStderr,omitempty"`
 	PerNodeCertificate *PerNodeCertificate `json:"perNodeCertificate,omitempty"`
+	ConnectionLimit    *int                `json:"connectionLimit,omitempty"`
 
 	MetricsPort *int `json:"metricsPort,omitempty"`
 

vendor/golang.org/x/net/netutil/listen.go

@@ -0,0 +1,87 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package netutil provides network utility functions, complementing the more
+// common ones in the net package.
+package netutil // import "golang.org/x/net/netutil"
+
+import (
+	"net"
+	"sync"
+)
+
+// LimitListener returns a Listener that accepts at most n simultaneous
+// connections from the provided Listener.
+func LimitListener(l net.Listener, n int) net.Listener {
+	return &limitListener{
+		Listener: l,
+		sem:      make(chan struct{}, n),
+		done:     make(chan struct{}),
+	}
+}
+
+type limitListener struct {
+	net.Listener
+	sem       chan struct{}
+	closeOnce sync.Once     // ensures the done chan is only closed once
+	done      chan struct{} // no values sent; closed when Close is called
+}
+
+// acquire acquires the limiting semaphore. Returns true if successfully
+// acquired, false if the listener is closed and the semaphore is not
+// acquired.
+func (l *limitListener) acquire() bool {
+	select {
+	case <-l.done:
+		return false
+	case l.sem <- struct{}{}:
+		return true
+	}
+}
+func (l *limitListener) release() { <-l.sem }
+
+func (l *limitListener) Accept() (net.Conn, error) {
+	if !l.acquire() {
+		// If the semaphore isn't acquired because the listener was closed, expect
+		// that this call to accept won't block, but immediately return an error.
+		// If it instead returns a spurious connection (due to a bug in the
+		// Listener, such as https://golang.org/issue/50216), we immediately close
+		// it and try again. Some buggy Listener implementations (like the one in
+		// the aforementioned issue) seem to assume that Accept will be called to
+		// completion, and may otherwise fail to clean up the client end of pending
+		// connections.
+		for {
+			c, err := l.Listener.Accept()
+			if err != nil {
+				return nil, err
+			}
+			c.Close()
+		}
+	}
+
+	c, err := l.Listener.Accept()
+	if err != nil {
+		l.release()
+		return nil, err
+	}
+	return &limitListenerConn{Conn: c, release: l.release}, nil
+}
+
+func (l *limitListener) Close() error {
+	err := l.Listener.Close()
+	l.closeOnce.Do(func() { close(l.done) })
+	return err
+}
+
+type limitListenerConn struct {
+	net.Conn
+	releaseOnce sync.Once
+	release     func()
+}
+
+func (l *limitListenerConn) Close() error {
+	err := l.Conn.Close()
+	l.releaseOnce.Do(l.release)
+	return err
+}

vendor/modules.txt

@@ -213,6 +213,7 @@ golang.org/x/net/http2/hpack
 golang.org/x/net/idna
 golang.org/x/net/internal/httpcommon
 golang.org/x/net/internal/timeseries
+golang.org/x/net/netutil
 golang.org/x/net/trace
 # golang.org/x/oauth2 v0.28.0
 ## explicit; go 1.23.0