How to unmarshal a field that can be an array or a string in Go?

Question

I\'m trying to unmarshal this file:

{
  \"@babel/code-frame@7.0.0\": {
    \"licenses\": \"MIT\",
    \"repository\": \"https://github.com/babel/babel/tree/maste         


        

Answer 1

Unfortunately, there is no real automatic solution for this provided by the json package.

But you can unmarshal the dependencies to a map[string]*json.RawMessage instead of map[string]string. json.RawMessage is just a []byte, so you can decide on the type of the message based on the first byte.

Example:

for _, value := range dependencies {
    depVal := map[string]*json.RawMessage{}

    _ = json.Unmarshal(*value, &depVal)

    // check if the first character of the RawMessage is a bracket
    if rune([]byte(*depVal["licenses"])[0]) == '[' {
        var licenses []string
        json.Unmarshal(*depVal["licenses"], &licenses)
        fmt.Println(licenses)
        // do something with the array
    }

    result = append(result, Dependency{
        URL:     string(*depVal["repository"]),
        License: string(*depVal["licenses"]),
    })
}

Another solution would be to use 2 structs. One contains the dependencies as string, the other as array. You can then try to call json.Unmarshal on both of them. Example:

type Dependency struct {
    Licenses string
    // other fields
}

type DependencyWithArr struct {
    Licenses []string
    // other fields
}

// in your function
for _, value := range dependencies {
    type1 := Dependency{}
    type2 := DependencyWithArr{}

    err = json.Unmarshal(*value, &type1)
    if err != nil {
        err = json.Unmarshal(*value, &type2)
        // use the array type
    } else {
        // use the single string type
    }
}