TCPKeepalive can be configured on both the server and client sides.

Currently, when Server.TCPKeepalive is set to false, if the net.Listener is created by the package itself, it does not override the default behavior of net.ListenConfig, which keeps TCP keepalive enabled.

Also added TCPKeepalive and TCPKeepalivePeriod fields to the client to make its behavior consistent with the server. The goal of this update is to ensure that whether TCP keepalive is enabled is entirely controlled by the configuration fields provided by the package when net.TCPConn is created by the package itself.

Author: newacorn

client.go

@@ -228,6 +228,13 @@ type Client struct {
 	// By default connection duration is unlimited.
 	MaxConnDuration time.Duration
 
+	// TCPKeepalivePeriod is the duration the connection needs to
+	// remain idle before TCP starts sending keepalive probes.
+	//
+	// This field is only effective when TCPKeepalive is set to true.
+	// A zero value indicates that the operating system's default setting will be used.
+	TCPKeepalivePeriod time.Duration
+
 	// Maximum number of attempts for idempotent calls.
 	//
 	// DefaultMaxIdemponentCallAttempts is used if not set.
@@ -315,6 +322,14 @@ type Client struct {
 
 	// StreamResponseBody enables response body streaming.
 	StreamResponseBody bool
+
+	// Whether the operating system should send tcp keep-alive messages on the tcp connection.
+	//
+	// By default tcp keep-alive connections are disabled.
+	//
+	// This option is used only if default TCP dialer is used,
+	// i.e. if Dial and DialTimeout are blank.
+	TCPKeepalive bool
 }
 
 // Get returns the status code and body of url.
@@ -527,6 +542,8 @@ func (c *Client) Do(req *Request, resp *Response) error {
 				MaxConns:                      c.MaxConnsPerHost,
 				MaxIdleConnDuration:           c.MaxIdleConnDuration,
 				MaxConnDuration:               c.MaxConnDuration,
+				TCPKeepalivePeriod:            c.TCPKeepalivePeriod,
+				TCPKeepalive:                  c.TCPKeepalive,
 				MaxIdemponentCallAttempts:     c.MaxIdemponentCallAttempts,
 				ReadBufferSize:                c.ReadBufferSize,
 				WriteBufferSize:               c.WriteBufferSize,
@@ -796,6 +813,13 @@ type HostClient struct {
 	// By default will not waiting, return ErrNoFreeConns immediately
 	MaxConnWaitTimeout time.Duration
 
+	// TCPKeepalivePeriod is the duration the connection needs to
+	// remain idle before TCP starts sending keepalive probes.
+	//
+	// This field is only effective when TCPKeepalive is set to true.
+	// A zero value indicates that the operating system's default setting will be used.
+	TCPKeepalivePeriod time.Duration
+
 	// Connection pool strategy. Can be either LIFO or FIFO (default).
 	ConnPoolStrategy ConnPoolStrategyType
 
@@ -871,6 +895,16 @@ type HostClient struct {
 	StreamResponseBody bool
 
 	connsCleanerRun bool
+
+	// Whether to enable tcp keep-alive connections.
+	//
+	// Whether the operating system should send tcp keep-alive messages on the tcp connection.
+	//
+	// By default tcp keep-alive connections are disabled.
+	//
+	// This option is used only if default TCP dialer is used,
+	// i.e. if Dial and DialTimeout are blank.
+	TCPKeepalive bool
 }
 
 type clientConn struct {
@@ -1886,6 +1920,22 @@ func (c *HostClient) dialHostHard(dialTimeout time.Duration) (conn net.Conn, err
 	// use dialTimeout to control the timeout of each dial. It does not work if dialTimeout is 0 or if
 	// c.DialTimeout has not been set and c.Dial has been set.
 	// attempt to dial all the available hosts before giving up.
+	if c.Dial == nil && c.DialTimeout == nil && c.TCPKeepalive {
+		d := &TCPDialer{Concurrency: defaultDialer.Concurrency, TCPKeepalive: true, TCPKeepalivePeriod: c.TCPKeepalivePeriod}
+		if dialTimeout > 0 {
+			if c.DialDualStack {
+				c.DialTimeout = d.DialDualStackTimeout
+			} else {
+				c.DialTimeout = d.DialTimeout
+			}
+		} else {
+			if c.DialDualStack {
+				c.Dial = d.DialDualStack
+			} else {
+				c.Dial = d.Dial
+			}
+		}
+	}
 
 	c.addrsLock.Lock()
 	n := len(c.addrs)
@@ -2326,6 +2376,12 @@ type pipelineConnClient struct {
 	WriteBufferSize     int
 	ReadTimeout         time.Duration
 	WriteTimeout        time.Duration
+	// TCPKeepalivePeriod is the duration the connection needs to
+	// remain idle before TCP starts sending keepalive probes.
+	//
+	// This field is only effective when TCPKeepalive is set to true.
+	// A zero value indicates that the operating system's default setting will be used.
+	TCPKeepalivePeriod time.Duration
 
 	chLock sync.Mutex
 
@@ -2335,6 +2391,14 @@ type pipelineConnClient struct {
 	DisableHeaderNamesNormalizing bool
 	DisablePathNormalizing        bool
 	IsTLS                         bool
+
+	// Whether the operating system should send tcp keep-alive messages on the tcp connection.
+	//
+	// By default tcp keep-alive connections are disabled.
+	//
+	// This option is used only if default TCP dialer is used,
+	// i.e. if Dial is blank.
+	TCPKeepalive bool
 }
 
 type pipelineWork struct {
@@ -2666,6 +2730,14 @@ func (c *pipelineConnClient) init() {
 
 func (c *pipelineConnClient) worker() error {
 	tlsConfig := c.cachedTLSConfig()
+	if c.TCPKeepalive && c.Dial == nil {
+		d := &TCPDialer{Concurrency: defaultDialer.Concurrency, TCPKeepalive: true, TCPKeepalivePeriod: c.TCPKeepalivePeriod}
+		if c.DialDualStack {
+			c.Dial = d.DialDualStack
+		} else {
+			c.Dial = d.Dial
+		}
+	}
 	conn, err := dialAddr(c.Addr, c.Dial, nil, c.DialDualStack, c.IsTLS, tlsConfig, 0, c.WriteTimeout)
 	if err != nil {
 		return err

server.go

@@ -294,9 +294,11 @@ type Server struct {
 	// worker pool of the Server. Idle workers beyond this time will be cleared.
 	MaxIdleWorkerDuration time.Duration
 
-	// Period between tcp keep-alive messages.
+	// TCPKeepalivePeriod is the duration the connection needs to
+	// remain idle before TCP starts sending keepalive probes.
 	//
-	// TCP keep-alive period is determined by operation system by default.
+	// This field is only effective when TCPKeepalive is set to true.
+	// A zero value indicates that the operating system's default setting will be used.
 	TCPKeepalivePeriod time.Duration
 
 	// Maximum request body size.
@@ -329,11 +331,14 @@ type Server struct {
 	// By default keep-alive connections are enabled.
 	DisableKeepalive bool
 
-	// Whether to enable tcp keep-alive connections.
-	//
 	// Whether the operating system should send tcp keep-alive messages on the tcp connection.
 	//
-	// By default tcp keep-alive connections are disabled.
+	// When this field is set to false, it is only effective if the net.Listener
+	// is created by this package itself. i.e. listened by ListenAndServe, ListenAndServeUNIX,
+	// ListenAndServeTLS and  ListenAndServeTLSEmbed method.
+	//
+	// If you have created a net.Listener yourself and configured TCP keepalive,
+	// this field should be set to false to avoid redundant additional system calls.
 	TCPKeepalive bool
 
 	// Aggressively reduces memory usage at the cost of higher CPU usage
@@ -1623,7 +1628,7 @@ func (s *Server) getNextProto(c net.Conn) (proto string, err error) {
 //
 // Accepted connections are configured to enable TCP keep-alives.
 func (s *Server) ListenAndServe(addr string) error {
-	ln, err := net.Listen("tcp4", addr)
+	ln, err := createTCPListener("tcp4", addr)
 	if err != nil {
 		return err
 	}
@@ -1639,7 +1644,7 @@ func (s *Server) ListenAndServeUNIX(addr string, mode os.FileMode) error {
 	if err := os.Remove(addr); err != nil && !os.IsNotExist(err) {
 		return fmt.Errorf("unexpected error when trying to remove unix socket file %q: %w", addr, err)
 	}
-	ln, err := net.Listen("unix", addr)
+	ln, err := createTCPListener("unix", addr)
 	if err != nil {
 		return err
 	}
@@ -1661,7 +1666,7 @@ func (s *Server) ListenAndServeUNIX(addr string, mode os.FileMode) error {
 //
 // Accepted connections are configured to enable TCP keep-alives.
 func (s *Server) ListenAndServeTLS(addr, certFile, keyFile string) error {
-	ln, err := net.Listen("tcp4", addr)
+	ln, err := createTCPListener("tcp4", addr)
 	if err != nil {
 		return err
 	}
@@ -1680,7 +1685,7 @@ func (s *Server) ListenAndServeTLS(addr, certFile, keyFile string) error {
 //
 // Accepted connections are configured to enable TCP keep-alives.
 func (s *Server) ListenAndServeTLSEmbed(addr string, certData, keyData []byte) error {
-	ln, err := net.Listen("tcp4", addr)
+	ln, err := createTCPListener("tcp4", addr)
 	if err != nil {
 		return err
 	}
@@ -2983,3 +2988,19 @@ var stateName = map[ConnState]string{
 func (c ConnState) String() string {
 	return stateName[c]
 }
+
+// If the net.Listener is created by us, we override the default TCP
+// keepalive behavior of net.ListenConfig, so that whether TCP keepalive is
+// enabled is entirely determined by Server.KeepAlive.
+//
+// In the implementation of the net package, TCPListener
+// by default always enables KeepAlive for new connections.
+func createTCPListener(network, addr string) (ln net.Listener, err error) {
+	var lc net.ListenConfig
+	// Overriding the default TCP keepalive behavior of
+	// net.ListenConfig, whether TCP keepalive is enabled
+	// is determined by Server.KeepAlive.
+	lc.KeepAlive = -1
+	ln, err = lc.Listen(context.Background(), network, addr)
+	return
+}

tcpdialer.go

@@ -159,10 +159,22 @@ type TCPDialer struct {
 	// DNSCacheDuration may be used to override the default DNS cache duration (DefaultDNSCacheDuration)
 	DNSCacheDuration time.Duration
 
+	// TCPKeepalivePeriod is the duration the connection needs to
+	// remain idle before TCP starts sending keepalive probes.
+	//
+	// This field is only effective when TCPKeepalive is set to true.
+	// A zero value indicates that the operating system's default setting will be used.
+	TCPKeepalivePeriod time.Duration
+
 	once sync.Once
 
 	// DisableDNSResolution may be used to disable DNS resolution
 	DisableDNSResolution bool
+
+	// Whether the operating system should send tcp keep-alive messages on the tcp connection.
+	//
+	// By default tcp keep-alive connections are disabled.
+	TCPKeepalive bool
 }
 
 // Dial dials the given TCP addr using tcp4.
@@ -344,6 +356,9 @@ func (d *TCPDialer) tryDial(
 	if d.LocalAddr != nil {
 		dialer.LocalAddr = d.LocalAddr
 	}
+	// Overriding the default behavior of net.Dialer,
+	// whether TCP keepalive is enabled is determined by Dialer.KeepAlive.
+	dialer.KeepAlive = -1
 
 	ctx, cancelCtx := context.WithDeadline(context.Background(), deadline)
 	defer cancelCtx()
@@ -354,6 +369,18 @@ func (d *TCPDialer) tryDial(
 		}
 		return nil, wrapDialWithUpstream(err, addr)
 	}
+	if tc, ok := conn.(*net.TCPConn); ok && d.TCPKeepalive {
+		if err = tc.SetKeepAlive(d.TCPKeepalive); err != nil {
+			_ = tc.Close()
+			return nil, err
+		}
+		if d.TCPKeepalivePeriod > 0 {
+			if err = tc.SetKeepAlivePeriod(d.TCPKeepalivePeriod); err != nil {
+				_ = tc.Close()
+				return nil, err
+			}
+		}
+	}
 	return conn, nil
 }