Add host-chsk-url-fn

[danielcompton]

It would be helpful for people using cross domain channel sockets to have a simplified chsk-url-fn for making connections to different hosts. This PR adds the function, and documentation on how to use it.

[danielcompton]

If you'd prefer fewer functions in the main Sente ns, the other option I thought of was making default-chsk-fn take a map of config and return a function. The function would override any config provided by window-location, with the initial config provided. This would be a breaking change though, and more complex to use.

[ptaoussanis]

Hi Daniel, thanks for this.

As I mentioned last time this came up (in #50), I'm not convinced it makes sense to add any specialised code for the use case you're describing.

An appropriate chsk-url-fn can usually be expressed more flexibly and transparently as a small inline fn, no?

What problem are you actually trying to solve here? Is it that you feel users won't understand how to write an appropriate chsk-url-fn? Could that not better be solved by adding a short cross-domain example to the default-chsk-url-fn docstring? (Just trying to understand your motivation better).

Cheers :-)

[danielcompton]

I thought that users may not understand how to write the chsk-url-fn correctly. A docstring would be fine too if you'd prefer that.

[ptaoussanis]

Okay, going to simplify this. Will keep :chsk-url-fn for the moment as an advanced/undocumented feature.

For the simpler common-case that you're describing, have added a :host key to the client-side make-channel-socket! options. Does that handle your case okay?

[danielcompton]

Sure, if you prefer that, I'm happy with any of the options.

[ptaoussanis]

Great, closing this then. Change is up on the dev branch and [com.taoensso/sente "1.6.0-alpha2"] on Clojars. Cheers :-)