net: SplitHostPort has inconsistent error conditions

[adamhassel]

In net.SplitHostPort, giving a string with a port defined, but no hostname (e.g. ":80"), results in an empty host, a port and an empty error. Providing a hostname (or IP) with no port (e.g. "foo.bar.com"), results in an error.

I would think that both of these scenarios should behave in the same way: either both should return an error, or both should return an empty value and no error.

https://play.golang.org/p/-qKy6sik52

[bradfitz]

I think it's pretty consistent: if there's no colon, it returns an error: https://play.golang.org/p/77zhzVOa9g

In any case, we've had this same behavior for 4+ years now, so I don't think we want to change it now.

The new URL.Port and URL.Hostname methods in Go 1.8 should help with this, though, since I think they're more likely doing what you want.

[minux]

I think the ":80" shouldn't be an error as it's has well-defined meaning ((for listen) all interfaces, or (for dial) localhost.)