Making minimal modification to JSON data without a structure in golang - json

Question

I have a solr response in JSON format which looks like this:
{
"responseHeader": {
"status": 0,
"QTime": 0,
"params": {
"q": "solo",
"wt": "json"
}
},
"response": {
"numFound": 2,
"start": 0,
"docs": [
{
<Large nested JSON element>
},
{
<Large nested JSON element>
}
]
}
}
Now, in my Golang app, I would like to quickly remove the "responseHeader" so that I can return the "response" alone. How can I do this without creating large structures?
Edit 1
The answer by evanmcdonnal was the solution to this problem, but it had some minor typos, this is what I ended up using:
var temp map[string]interface{}
if err := json.Unmarshal(body, &temp); err != nil {
panic(err.Error())
}
result, err := json.Marshal(temp["response"])

Answer 1

Here's a really brief example of how to do this quickly and easily. The steps are; unmarshal into the universal map[string]interface{} then, assuming no errors, marshal only the inner object which you want.
var temp := &map[string]interface{}
if err := json.Unmarshal(input, temp); err != nil {
return err;
}
return json.Marshal(temp["response"])

Answer 2

I wrote a package µjson to do exactly that: performing generic transformations on JSON documents without unmarshalling them.
Run on Go Playground
input := []byte(`
{
"responseHeader": {
"status": 0,
"QTime": 0,
"params": {
"q": "solo",
"wt": "json"
}
},
"response": {
"numFound": 2,
"start": 0,
"docs": [
{ "name": "foo" },
{ "name": "bar" }
]
}
}`)
blacklistFields := [][]byte{
[]byte(`"responseHeader"`), // note the quotes
}
b := make([]byte, 0, 1024)
err := ujson.Walk(input, func(_ int, key, value []byte) bool {
for _, blacklist := range blacklistFields {
if bytes.Equal(key, blacklist) {
// remove the key and value from the output
return false
}
}
// write to output
if len(b) != 0 && ujson.ShouldAddComma(value, b[len(b)-1]) {
b = append(b, ',')
}
if len(key) > 0 {
b = append(b, key...)
b = append(b, ':')
}
b = append(b, value...)
return true
})
if err != nil {
panic(err)
}
fmt.Printf("%s", b)
// Output: {"response":{"numFound":2,"start":0,"docs":[{"name":"foo"},{"name":"bar"}]}}
You can read more about it on the blog post. I put the answer here just in case someone else might need it.