Add tcp option to set keep alive value on the tcp layer

client.go

@@ -393,7 +393,7 @@ func (c *client) attemptConnection() (net.Conn, byte, bool, error) {
 			tlsCfg = c.options.OnConnectAttempt(broker, c.options.TLSConfig)
 		}
 		// Start by opening the network connection (tcp, tls, ws) etc
-		conn, err = openConnection(broker, tlsCfg, c.options.ConnectTimeout, c.options.HTTPHeaders, c.options.WebsocketOptions)
+		conn, err = openConnection(broker, tlsCfg, c.options.ConnectTimeout, c.options.HTTPHeaders, c.options.WebsocketOptions, c.options.Dialer)
 		if err != nil {
 			ERROR.Println(CLI, err.Error())
 			WARN.Println(CLI, "failed to connect to broker, trying next")

netconn.go

@@ -37,7 +37,7 @@ import (
 
 // openConnection opens a network connection using the protocol indicated in the URL.
 // Does not carry out any MQTT specific handshakes.
-func openConnection(uri *url.URL, tlsc *tls.Config, timeout time.Duration, headers http.Header, websocketOptions *WebsocketOptions) (net.Conn, error) {
+func openConnection(uri *url.URL, tlsc *tls.Config, timeout time.Duration, headers http.Header, websocketOptions *WebsocketOptions, dialer *net.Dialer) (net.Conn, error) {
 	switch uri.Scheme {
 	case "ws":
 		conn, err := NewWebsocket(uri.String(), nil, timeout, headers, websocketOptions)
@@ -48,7 +48,7 @@ func openConnection(uri *url.URL, tlsc *tls.Config, timeout time.Duration, heade
 	case "mqtt", "tcp":
 		allProxy := os.Getenv("all_proxy")
 		if len(allProxy) == 0 {
-			conn, err := net.DialTimeout("tcp", uri.Host, timeout)
+			conn, err := dialer.Dial("tcp", uri.Host)
 			if err != nil {
 				return nil, err
 			}
@@ -68,9 +68,9 @@ func openConnection(uri *url.URL, tlsc *tls.Config, timeout time.Duration, heade
 		// this check is preserved for compatibility with older versions
 		// which used uri.Host only (it works for local paths, e.g. unix://socket.sock in current dir)
 		if len(uri.Host) > 0 {
-			conn, err = net.DialTimeout("unix", uri.Host, timeout)
+			conn, err = dialer.Dial("unix", uri.Host)
 		} else {
-			conn, err = net.DialTimeout("unix", uri.Path, timeout)
+			conn, err = dialer.Dial("unix", uri.Path)
 		}
 
 		if err != nil {
@@ -80,14 +80,13 @@ func openConnection(uri *url.URL, tlsc *tls.Config, timeout time.Duration, heade
 	case "ssl", "tls", "mqtts", "mqtt+ssl", "tcps":
 		allProxy := os.Getenv("all_proxy")
 		if len(allProxy) == 0 {
-			conn, err := tls.DialWithDialer(&net.Dialer{Timeout: timeout}, "tcp", uri.Host, tlsc)
+			conn, err := tls.DialWithDialer(dialer, "tcp", uri.Host, tlsc)
 			if err != nil {
 				return nil, err
 			}
 			return conn, nil
 		}
 		proxyDialer := proxy.FromEnvironment()
-
 		conn, err := proxyDialer.Dial("tcp", uri.Host)
 		if err != nil {
 			return nil, err

options.go

@@ -23,6 +23,7 @@ package mqtt
 
 import (
 	"crypto/tls"
+	"net"
 	"net/http"
 	"net/url"
 	"strings"
@@ -96,6 +97,7 @@ type ClientOptions struct {
 	HTTPHeaders             http.Header
 	WebsocketOptions        *WebsocketOptions
 	MaxResumePubInFlight    int // // 0 = no limit; otherwise this is the maximum simultaneous messages sent while resuming
+	Dialer                  *net.Dialer
 }
 
 // NewClientOptions will create a new ClientClientOptions type with some
@@ -137,6 +139,7 @@ func NewClientOptions() *ClientOptions {
 		ResumeSubs:              false,
 		HTTPHeaders:             make(map[string][]string),
 		WebsocketOptions:        &WebsocketOptions{},
+		Dialer:                  &net.Dialer{Timeout: 30 * time.Second},
 	}
 	return o
 }
@@ -355,6 +358,7 @@ func (o *ClientOptions) SetWriteTimeout(t time.Duration) *ClientOptions {
 // Default 30 seconds. Currently only operational on TCP/TLS connections.
 func (o *ClientOptions) SetConnectTimeout(t time.Duration) *ClientOptions {
 	o.ConnectTimeout = t
+	o.Dialer.Timeout = t
 	return o
 }
 
@@ -419,3 +423,9 @@ func (o *ClientOptions) SetMaxResumePubInFlight(MaxResumePubInFlight int) *Clien
 	o.MaxResumePubInFlight = MaxResumePubInFlight
 	return o
 }
+
+// SetDialer sets the tcp dialer options used in a tcp connection
+func (o *ClientOptions) SetDialer(dialer *net.Dialer) *ClientOptions {
+	o.Dialer = dialer
+	return o
+}