Expose previous and current resource properties

[parsnips]

Issue #, if available:

#184

Description of changes:

Allows users to use their own Unmarshal strategy by exposing the making the raw resource bytes through a get method.

e.g.

       // Populate the previous model
	prevModel := &resource.Model{}
	if err := json.Unmarshal(req.GetPreviousResourcePropertiesBody(), prevModel); err != nil {
		log.Printf("Error unmarshaling prev model: %v", err)
		return handler.NewFailedEvent(err)
	}

	// Populate the current model
	currentModel := &resource.Model{}
	if err := json.Unmarshal(req.GetResourcePropertiesBody(), currentModel); err != nil {
		log.Printf("Error unmarshaling model: %v", err)
		return handler.NewFailedEvent(err)
	}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[kddejong]

Any reason for using the GetPreviousResourcePropertiesBody instead of just going with PreviousResourcePropertiesBody?

[parsnips]

The JVM has affected me more than I realized ;). I'll push up the shorter version.

[kddejong]

I like this idea. A lot of times when working with other packages they already have the models I need defined. They already have the logic for Marshaling and Unmarshaling as well.

The only thing that I got tripped up is when I have to send the response the stringify would fail a lot with non standard types

[parsnips]

The only thing that I got tripped up is when I have to send the response the stringify would fail a lot with non standard types

Yes I noticed that bool is sent in as a string in my case and now understand why the stringify and unstringify methods exist... In my case I just encapsulated that logic into a type... and used it in place of bools in my model.

eg:

type StringyBool bool

func (s *StringyBool) UnmarshalJSON(data []byte) error {
	asStr := string(data)
	if asStr == "true" {
		*s = true
	} else { // else if asStr == "false"
		*s = false
	}

	return nil
}

It's a matter of different approaches I guess.. but this one gives the end user a bit more flexibility.