Specify valid values

[cheshirex]

I didn't find anything like this in my searches, so apologies if this already exists and I just missed it.

I'm generally using Viper by unmarshaling a configuration into a structure.

What about having a feature to specify valid values, in terms of ranges or a specific set of possibilities? As an example, let's say you have a configuration specifying a port number. The range can be mostly restricted to a valid port by unmarshalling it into a uint16, for instance, but that still leaves 0 as a valid value that you might not want. Or maybe we'd want to restrict it further by saying it has to be a userspace port, so anything 1024 or less is no good.

Other possibilities along this line might be having a string that must be one of a set of possibilities -- it can be "aaa" or "bbb" but not anything that isn't pre-defined.

At the moment I validate this in my code by unmarshalling into a structure, and then calling a function that goes through all the relevant values and ensures they are valid.

Or if there's a better way to deal with things like this, I'm open to being enlightened. :-)

Thanks!

[sagikazarmark]

Hey @cheshirex

Here is one way I consider better:

type Config struct {
	Address string
	Port int
}

func (c Config) Validate() error {
	if c.Address == "" {
		return errors.New("address is required")
	}

	if c.Port < 1024 || c.Port > 5000 {
		return errors.New("port must be between 1024 and 5000")
	}
}

It's simple and elegant.

Viper does one thing which is configuration loading. Adding features like validation would make the library more complex with little benefit.

Hope that helps.

[cheshirex]

Thanks. That's about what I'm already doing.

I thought there may be a better way, because I see usage examples of reading directly from viper rather than populating and validating a struct, so I thought there must be something I was missing. Good to know I'm already doing the right thing, then.

Again, thanks!

[sagikazarmark]

I thought there may be a better way

IMHO that is the better way 🙂

I see usage examples of reading directly from viper rather than populating and validating a struct

Viper's config reading API is comfortable, but I discourage everyone from using it. Populating a struct is much-much better, because it doesn't tie your application to Viper.

So yeah, you are on the best possible path for using Viper. 😉