After googling around Go applications configuration management packages that able to take parameters from environment configuration I came to a conclusion that there is none packages that able to do everything I want and yet have readable and testable source code.

Key intentions to create SEC:

Parse configuration into structure with support of infinitely nested structures.
Works properly with interfaces.
No goto's.
100% code coverage.
No external dependencies (only testify for tests).
Readable code and proper variables naming.
Debug mode

This list might be updated if new key intention arrives :).

SEC was written under impression from https://github.com/vrischmann/envconfig/.

Installation

Go modules and dep are supported. Other package managers might or might not work, MRs are welcome!

Usage

SEC is designed to be easy to use parser. There is only one requirement - passed data should be a pointer to structure. You cannot do something like:

var Data string
sec.Parse(&Data, nil)

This will throw errors, as any type you'll pass, except for pointer to structure. It is fine to use anonymous structures inside passed one as well as use structures and pointers to them.

SEC is unable to parse embedded unexported things except structures due to inability to get embedded field's address. Embed only structures, please.

The very valid way to use SEC:

type config struct{
    Database struct{
        URI string
        Options string
    }
    HTTPTimeout int
}

cfg := &config{}

err := Parse(cfg, nil)
if err != nil {
    log.Fatal(err)
}

You can set database URI using DATABASE_URI environment variable. Same for others variables, so you should define environment variables in uppercase despite on how they're written in struct definition. Taking example above, other fields can be set with DATABASE_OPTIONS and HTTPTIMEOUT environment variables.

Field tags

No field tags supported yet, this in ToDo.

Underlying interface

Due to nature how Go works with variables you can do something like that, if you want to work with interfaces to keep variables:

type config struct {
    DataToKeep interface{}
}

var timeout int

func main() {
    c := &config{}
    c.DataToKeep = &timeout
    err := sec.Parse(c, nil)
    ...
    log.Printf("Timeout is %d\n", (*c.DataToKeep.(*int)))
}

You can't do something like:

type config struct {
    DataToKeep interface{}
}

var timeout int

func main() {
    c := &config{}
    c.DataToKeep = 0
    err := sec.Parse(c, nil)
    ...
    log.Printf("Timeout is %d\n", (*c.DataToKeep.(*int)))
}

c.DataToKeep here will be always 0 because SEC will skip this field.

It is because values behind interface{} aren't addressable in Go. Anyway, it is not recommended way to store variables at all and might break.

Debug

To get additional debug output set SEC_DEBUG environment variable to true. If invalid boolean value will be passed it'll output error about that.

Debug output uses standart log package. This may change in future.