Add delay option for socket.setKeepAlive

[betimer]

Pull Request check-list

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

Description of change

Add option for socket_initialdelay when calling socket.setKeepAlive from node API

[betimer]

This is critical as because of this issue: nodejs/node#24689 though at this stage cannot sure if it is node issue

[stockholmux]

I'm going to go ahead and merge, but I think we should investigate the root cause here as we might need a default that isn't 0.

[betimer]

@stockholmux I strongly agree to have a value which is not the default 0.
Created this PR to add the option but does not change the existing behaviour.
I think something like 5000~60000 milliseconds would be fine.

I can make the change if this sounds OK, also may i know when we might get the new version?

[stockholmux]

I consulted with some colleagues on this. I don't think there is actually a rational/universal initial delay default. I'm ok with this as-is.

[betimer]

Nice. no worries, as long as this already provides an interface to whom, like us, facing the issue, to change the setting. Thank you @stockholmux

[RidgeA]

Hi @betimer !
Is it possible to install the latest version of the library from NPM?
As I can see the library version was updated on NPM more than a year ago...

[Fundebug]

@anhzhi I found that idle redis connection will be disconnected every 2 hours, it is strange. It is solved by using your code:

client.on('connect', function () {
    var socket = client.stream
    socket.setKeepAlive(true, 30 * 1000)
})

[RidgeA]

This would work, but it is an ugly workaround. There is a special option for this, the package just need to be updated on npm. We have switched to ioredis package.