net: the KeepAlive comment in Dialer is not accurate

[spacewander]

The comment says that KeepAlive specifies the interval:

go/src/net/dial.go

Lines 171 to 181 in 396a48b

	// KeepAlive specifies the interval between keep-alive
	// probes for an active network connection.
	//
	// KeepAlive is ignored if KeepAliveConfig.Enable is true.
	//
	// If zero, keep-alive probes are sent with a default value
	// (currently 15 seconds), if supported by the protocol and operating
	// system. Network protocols or operating systems that do
	// not support keep-alive ignore this field.
	// If negative, keep-alive probes are disabled.
	KeepAlive time.Duration

In fact, it is used as the idle time:

go/src/net/tcpsock.go

Line 289 in 396a48b

func newTCPConn(fd *netFD, keepAliveIdle time.Duration, keepAliveCfg KeepAliveConfig, preKeepAliveHook func(*netFD), keepAliveHook func(KeepAliveConfig)) *TCPConn {

The KeepAlive field is passed as the second argument, which means idle instead of the interval. It is equal to the Idle field in the KeepAliveConfig:

type KeepAliveConfig struct {
    // If Enable is true, keep-alive probes are enabled.
    Enable bool

    // Idle is the time that the connection must be idle before
    // the first keep-alive probe is sent.
    // If zero, a default value of 15 seconds is used.
    Idle time.Duration

    // Interval is the time between keep-alive probes.
    // If zero, a default value of 15 seconds is used.
    Interval time.Duration

    // Count is the maximum number of keep-alive probes that
    // can go unanswered before dropping a connection.
    // If zero, a default value of 9 is used.
    Count int
}

[prattmic]

cc @neild