Expand paths with tilde

[variadico]

Currently, if you pass a path with a tilde to nats.UserCredentials it fails
because it doesn't expand the tilde to mean the user's home directory.

This change adds support to expand paths with a tilde, such as "~/.nkeys".

Resolves #509

[coveralls]

Coverage decreased (-0.2%) to 92.187% when pulling 02f4e95 on add-tilde-support into 69eb740 on master.

[derekcollison]

Need a test, and do we need a dependency, is the logic that complex?

[variadico]

No, the logic isn't complex. However, the dep seems to handle a lot of edge cases.
https://github.com/mitchellh/go-homedir/blob/master/homedir.go

If we only want to solve the simple case, then we could probably just do this.

// Wally suggested just checking HOME.
if strings.HasPrefix(path, "~") {
    path = filepath.Join(os.Getenv("HOME"), path[1:])
}

Maybe at some point we'll get an issue saying that there is a bug in the expansion logic. Or maybe not.

Another option is that we could just copy the file over into the nats repo (with all the license stuff).

[wallyqs]

IMO checking whether $HOME or $home are being defined in env when ~ is the first char from the path would be good enough, then can return an error saying explicitly saying that $HOME has to be defined for it to work.

[ripienaar]

In my experience this handles the bulk of cases, hashi one is undeniably better but this is good enough for me.

func homeDir() (string, error) {
	if runtime.GOOS == "windows" {
		drive := os.Getenv("HOMEDRIVE")
		home := os.Getenv("HOMEDIR")

		if home == "" || drive == "" {
			return "", fmt.Errorf("Cannot determine home dir, ensure HOMEDRIVE and HOMEDIR is set")
		}

		return filepath.Join(os.Getenv("HOMEDRIVE"), os.Getenv("HOMEDIR")), nil
	}

	home := os.Getenv("HOME")

	if home == "" {
		return "", fmt.Errorf("Cannot determine home dir, ensure HOME is set")
	}

	return home, nil
}

[derekcollison]

I prefer to limit the dependencies unless we absolutely have to have them.

[variadico]

All right. Implemented homeDir. Added tests.
80090af

Wasn't sure if I should add tests for windows as well... I probably should, right?

[variadico]

Oookay, so turns out this homedir function is already in the stdlib.
https://golang.org/pkg/os/#UserHomeDir

The other one in os/user is bad because it uses cgo. This one in os, basically does what we were doing, i.e. just checking env vars.

So, I deleted the original function we had. I also cross compiled from Linux to Windows to verify os.UserHomeDir worked. It correctly printed the home dir in command prompt, powershell, and the linux subsystem.

One weird thing is I'm not sure how Windows users expect to give us a path. I added some Windows tests too, hopefully @ColinSullivan1 can take a look at those to see if they make sense.

[variadico]

Hey, @ColinSullivan1. Are these paths normally how Windows folks would give us a path?

[ColinSullivan1]

Not normally, unless running in some type of non-standard shell. paths would be \\foo\\bar, with backslashes escaped for the test. However, programmatically, / is accepted.

[variadico]

Cool. Backtick strings allow you to write a literal without escaping.

`\foo\bar` == "\\foo\\bar"

So is this fine?

[derekcollison]

Let's see if we can get one of these from @ColinSullivan1

[ColinSullivan1]

Will do...

[ColinSullivan1]

Golang doesn't check for %HOMEDRIVE%%HOMEPATH% which is also used. It'd be more complicated but great for users if env var expansion in general was supported.

[variadico]

Okay. I think we can do this with os.ExpandEnv.

[variadico]

os.UserHomeDir is only for Go 1.12 and up. 😬 Had to bring our version back. CI sets up tests for Go 1.11.

[kozlovic]

The comment that I have is with the use of t.Errorf() instead of t.Fatalf(). We usually use the later and the reason is that there is no reason to continue the test when some error occurs.

[kozlovic]

You still have 2 places with Errorf() instead of Fatalf().

[variadico]

Cool, good catch. Updated.

[kozlovic]

LGTM

[derekcollison]

Congrats! First PR merge!