Convert yaml to json without struct

Services: 
-   Orders: 
    -   ID: $save ID1
        SupplierOrderCode: $SupplierOrderCode
    -   ID: $save ID2
        SupplierOrderCode: 111111

I want to convert this yaml string to json, cause the source data is dynamic, so I can't map it to a struct:

var body interface{}
err := yaml.Unmarshal([]byte(s), &body)

Then I want to convert that interface to json string again:

b, _ := json.Marshal(body)

But an error occur:

panic: json: unsupported type: map[interface {}]interface {}

Foreword: I optimized and improved the below solution, and released it as a library here: github.com/icza/dyno. The below convert() function is available as dyno.ConvertMapI2MapS().

The problem is that if you use the most generic interface{} type to unmarshal into, the default type used by the github.com/go-yaml/yaml package to unmarshal key-value pairs will be map[interface{}]interface{}.

First idea would be to use map[string]interface{}:

var body map[string]interface{}

But this attempt falls short if the depth of the yaml config is more than one, as this body map will contain additional maps whose type will again be map[interface{}]interface{}.

The problem is that the depth is unknown, and there may be other values than maps, so using map[string]map[string]interface{} is not good.

A viable approach is to let yaml unmarshal into a value of type interface{}, and go through the result recursively, and convert each encountered map[interface{}]interface{} to a map[string]interface{} value. Both maps and slices have to be handled.

Here's an example of this converter function:

func convert(i interface{}) interface{} {
	switch x := i.(type) {
	case map[interface{}]interface{}:
		m2 := map[string]interface{}{}
		for k, v := range x {
			m2[k.(string)] = convert(v)
		}
		return m2
	case []interface{}:
		for i, v := range x {
			x[i] = convert(v)
		}
	}
	return i
}

And using it:

func main() {
	fmt.Printf("Input: %s\n", s)
	var body interface{}
	if err := yaml.Unmarshal([]byte(s), &body); err != nil {
		panic(err)
	}

	body = convert(body)

	if b, err := json.Marshal(body); err != nil {
		panic(err)
	} else {
		fmt.Printf("Output: %s\n", b)
	}
}

const s = `Services:
-   Orders:
    -   ID: $save ID1
        SupplierOrderCode: $SupplierOrderCode
    -   ID: $save ID2
        SupplierOrderCode: 111111
`

Output:

Input: Services:
-   Orders:
    -   ID: $save ID1
        SupplierOrderCode: $SupplierOrderCode
    -   ID: $save ID2
        SupplierOrderCode: 111111

Output: {"Services":[{"Orders":[
    {"ID":"$save ID1","SupplierOrderCode":"$SupplierOrderCode"},
    {"ID":"$save ID2","SupplierOrderCode":111111}]}]}

One thing to note: by switching from yaml to JSON via Go maps you'll lose the order of the items, as elements (key-value pairs) in a Go map are not ordered. This may or may not be a problem.

http://sigs.k8s.io/yaml is "a wrapper around go-yaml designed to enable a better way of handling YAML when marshaling to and from structs". Among other things, it provides yaml.YAMLToJSON method that should do what you want.

I was having the same issue and the icza's answer helped me.
Additionally I improved the convert() function a little bit, so it visits existing map[string]interface{} nodes to search for inherited map[interface{}]interface{} nodes deep inside.

func convert(i interface{}) interface{} {
	switch x := i.(type) {
	case map[interface{}]interface{}:
		m2 := map[string]interface{}{}
		for k, v := range x {
			m2[k.(string)] = convert(v)
		}
		return m2
	case map[string]interface{}:
		m2 := map[string]interface{}{}
		for k, v := range x {
			m2[k] = convert(v)
		}
		return m2
	case []interface{}:
		for i, v := range x {
			x[i] = convert(v)
		}
	}
	return i
}