Marshmallow package provides a simple API to perform flexible and performant JSON unmarshalling in Go.

Marshmallow specializes in dealing with unstructured struct - when some fields are known and some aren't, with zero performance overhead nor extra coding needed. While unmarshalling, marshmallow allows fully retaining the original data and access it via a typed struct and a dynamic map.

• Install
• Usage
• Performance Benchmark And Alternatives
• When Should I Use Marshmallow
• API

go get -u github.com/perimeterx/marshmallow

package main

import (
	"fmt"
	"github.com/perimeterx/marshmallow"
)

func main() {
	v := struct {
		Foo string `json:"foo"`
		Boo []int  `json:"boo"`
	}{}
	result, err := marshmallow.Unmarshal([]byte(`{"foo":"bar","boo":[1,2,3],"goo":12.6}`), &v)
	fmt.Printf("v=%+v, result=%+v, err=%v", v, result, err)
	// Output: v={Foo:bar Boo:[1 2 3]}, result=map[boo:[1 2 3] foo:bar goo:12.6], err=<nil>
}

Examples can be found here

Marshmallow performs best when dealing with mixed data - when some fields are known and some are unknown. More info below. Other solutions are available for this kind of use case, each solution is explained and documented in the link below. The full benchmark test can be found here.

Marshmallow provides the best performance (up to X3 faster) while not requiring any extra coding. In fact, marshmallow performs as fast as normal json.Unmarshal call, however, such a call causes loss of data for all the fields that did not match the given struct. With marshmallow you never lose any data.

Marshmallow is best suited for use cases where you are interested in all the input data, but you have predetermined information only about a subset of it. For instance, if you plan to reference two specific fields from the data, then iterate all the data and apply some generic logic. How does it look with the native library:

func isAllowedToDrive(data []byte) (bool, error) {
	result := make(map[string]interface{})
	err := json.Unmarshal(data, &result)
	if err != nil {
		return false, err
	}

	age, ok := result["age"]
	if !ok {
		return false, nil
	}
	a, ok := age.(float64)
	if !ok {
		return false, nil
	}
	if a < 17 {
		return false, nil
	}

	hasDriversLicense, ok := result["has_drivers_license"]
	if !ok {
		return false, nil
	}
	h, ok := hasDriversLicense.(bool)
	if !ok {
		return false, nil
	}
	if !h {
		return false, nil
	}

	for key := range result {
		if strings.Contains(key, "prior_conviction") {
			return false, nil
		}
	}

	return true, nil
}

And with marshmallow:

func isAllowedToDrive(data []byte) (bool, error) {
	v := struct {
		Age               int  `json:"age"`
		HasDriversLicense bool `json:"has_drivers_license"`
	}{}
	result, err := marshmallow.Unmarshal(data, &v)
	if err != nil {
		return false, err
	}

	if v.Age < 17 || !v.HasDriversLicense {
		return false, nil
	}

	for key := range result {
		if strings.Contains(key, "prior_conviction") {
			return false, nil
		}
	}

	return true, nil
}

Marshmallow exposes two main API functions - Unmarshal and UnmarshalFromJSONMap. While unmarshalling, marshmallow supports the following optional options:

• Setting the mode for handling invalid data using the WithMode function.
• Excluding known fields from the result map using the WithExcludeKnownFieldsFromMap function.
• Skipping struct population to boost performance using the WithSkipPopulateStruct function.

In order to capture unknown nested fields, structs must implement JSONDataErrorHandler. More info here.

Marshmallow also supports caching of refection information using EnableCache and EnableCustomCache.

Reporting issues and requesting features may be done in our GitHub issues page. Discussions may be conducted in our GitHub discussions page. For any further questions or comments you can reach us out at [email protected].

Any type of contribution is warmly welcome and appreciated ❤️ Please read our contribution guide for more info.

If you're looking for something to get started with, tou can always follow our issues page and look for good first issue and help wanted labels.

Marshmallow logo and assets by Adva Rom are licensed under a Creative Commons Attribution 4.0 International License.