Supporting Docker Secrets

[amir20]

Hello again,

Would you be open to supporting #{parameter_name}_FILE for also reading configurations from a file? I ask because Docker Secrets writes configurations to a file.

Someone asked on Dozzle if I support this amir20/dozzle#1927

I could support it but maybe this library should also support it. So the logic would be

1. Try the parameter from cli and look for --parameter-name
2. Then try for PARAMETER_NAME in ENV
3. Last if if PARAMETER_NAME_FILE is set, read that file.

What do you think?

[alexflint]

Yes it's worth considering for this library but just as an interim solution you might do something like this:

type DockerSecret struct {
  Value string
}

func (s *DockerSecret) UnmarshalText(b []byte) error {
  v, err := os.ReadFile(string(b))
  s.Value = string(v)
  return err
}

func main() {
  var args struct {
    Parameter *string `arg:"env:PARAMETER_NAME"`
    ParameterAlt *DockerSecret `arg:"env:PARAMETER_NAME_FILE"`
  }
  arg.MustParse(&args)
  if args.Parameter == nil && args.ParameterAlt != nil {
    args.Parameter = &args.parameterAlt.Value
  }
}

Closing for now but I'll tag this as a v2 feature for possible inclusion in #197.