Support opening email links natively

[glennfu]

There's really only 1 way to do native email composition in an iOS app and doing so a much nicer experience to do it than to click on a mailto: link and have it switch you to the Mail app. I don't think there'll ever be a case where someone using turbolinks-ios will prefer it to be the other way.

So here's a PR for taking a mailto: link and converting it to a native email popup. I was inspired reading http://stackoverflow.com/questions/25604552/i-have-real-misunderstanding-with-mfmailcomposeviewcontroller-in-swift-ios8-in to see how to parse an email address and strip out the necessary components.

Note that in testing this, it can't be done on a simulator, you have to use a real device to compose emails. Let me know what you think and if there's anything you'd like me to change/add!

[zachwaugh]

Thanks for the PR! I think this is more an application-specific concern though, and would be out of scope for Turbolinks to handle.

[glennfu]

Unfortunately I wasn't able to find a way to implement this in my own application WITHOUT adding it directly to Turbolinks. I couldn't figure out how to override the Session's decidePolicyForNavigationAction. Do you have any tips there for how I can do it, or does Turbolinks need some other change to expose this?

[sstephenson]

See the instructions in Changing How Turbolinks Opens External URLs. Implement the session:openExternalURL: method in your Session delegate and perform the mailto: check there.

[glennfu]

Wow I really went in all the wrong places looking for that. I don't know how I forgot about it, thanks!

[sstephenson]

No problem!

[berardpb]

I might be doing something wrong, but I'm having a problem using the 'session:openExternalURL:' method. I'm trying to handle a mailto link, and, to start, just doing something basic:

func session(session: Session, openExternalURL URL: NSURL) {
        print("opening an external url: " + URL.absoluteString)
        let url = URL.absoluteString
        let url_elements = url.componentsSeparatedByString(":")
        if(url_elements[0] == "mailto"){
            print("we need to mail! to this address: " + url_elements[1])
        }
    }

For some reason, this is not firing when the page first loads. It only fires when I pull-to-refresh. Anyone have an idea as to what might be going on here?