Convert yaml to json without struct

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.

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().

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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.