Enable keep-alive on server connections (gomodule#294)

Add the option to configure connection keep-alive using the new DialKeepAlive option.

This is set to 5 minutes by default to ensure that half-closed connections are detected.

Without this Pub/Sub connections can get disconnected by the redis server and we will never notice which can potentially deadlock applications.

Also:
* Add --redis-address <address> command line option to tests defaulting to 127.0.0.1. Without this all tests fail on machines with multiple addresses.

redis/conn.go

@@ -72,6 +72,7 @@ type DialOption struct {
 type dialOptions struct {
 	readTimeout  time.Duration
 	writeTimeout time.Duration
+	dialer       *net.Dialer
 	dial         func(network, addr string) (net.Conn, error)
 	db           int
 	password     string
@@ -94,17 +95,27 @@ func DialWriteTimeout(d time.Duration) DialOption {
 	}}
 }
 
-// DialConnectTimeout specifies the timeout for connecting to the Redis server.
+// DialConnectTimeout specifies the timeout for connecting to the Redis server when
+// no DialNetDial option is specified.
 func DialConnectTimeout(d time.Duration) DialOption {
 	return DialOption{func(do *dialOptions) {
-		dialer := net.Dialer{Timeout: d}
-		do.dial = dialer.Dial
+		do.dialer.Timeout = d
+	}}
+}
+
+// DialKeepAlive specifies the keep-alive period for TCP connections to the Redis server
+// when no DialNetDial option is specified.
+// If zero, keep-alives are not enabled. If no DialKeepAlive option is specified then
+// the default of 5 minutes is used to ensure that half-closed TCP sessions are detected.
+func DialKeepAlive(d time.Duration) DialOption {
+	return DialOption{func(do *dialOptions) {
+		do.dialer.KeepAlive = d
 	}}
 }
 
 // DialNetDial specifies a custom dial function for creating TCP
-// connections. If this option is left out, then net.Dial is
-// used. DialNetDial overrides DialConnectTimeout.
+// connections, otherwise a net.Dialer customized via the other options is used.
+// DialNetDial overrides DialConnectTimeout and DialKeepAlive.
 func DialNetDial(dial func(network, addr string) (net.Conn, error)) DialOption {
 	return DialOption{func(do *dialOptions) {
 		do.dial = dial
@@ -154,11 +165,16 @@ func DialUseTLS(useTLS bool) DialOption {
 // address using the specified options.
 func Dial(network, address string, options ...DialOption) (Conn, error) {
 	do := dialOptions{
-		dial: net.Dial,
+		dialer: &net.Dialer{
+			KeepAlive: time.Minute * 5,
+		},
 	}
 	for _, option := range options {
 		option.f(&do)
 	}
+	if do.dial == nil {
+		do.dial = do.dialer.Dial
+	}
 
 	netConn, err := do.dial(network, address)
 	if err != nil {

redis/test_test.go

@@ -38,6 +38,7 @@ var (
 	ErrNegativeInt = errNegativeInt
 
 	serverPath     = flag.String("redis-server", "redis-server", "Path to redis server binary")
+	serverAddress  = flag.String("redis-address", "127.0.0.1", "The address of the server")
 	serverBasePort = flag.Int("redis-port", 16379, "Beginning of port range for test servers")
 	serverLogName  = flag.String("redis-log", "", "Write Redis server logs to `filename`")
 	serverLog      = ioutil.Discard
@@ -136,6 +137,7 @@ func startDefaultServer() error {
 	defaultServer, defaultServerErr = NewServer(
 		"default",
 		"--port", strconv.Itoa(*serverBasePort),
+		"--bind", *serverAddress,
 		"--save", "",
 		"--appendonly", "no")
 	return defaultServerErr
@@ -147,7 +149,7 @@ func DialDefaultServer() (Conn, error) {
 	if err := startDefaultServer(); err != nil {
 		return nil, err
 	}
-	c, err := Dial("tcp", fmt.Sprintf(":%d", *serverBasePort), DialReadTimeout(1*time.Second), DialWriteTimeout(1*time.Second))
+	c, err := Dial("tcp", fmt.Sprintf("%v:%d", *serverAddress, *serverBasePort), DialReadTimeout(1*time.Second), DialWriteTimeout(1*time.Second))
 	if err != nil {
 		return nil, err
 	}