Go Lang Help - Accessing Array/Slice of interfaces

Question

I'm trying to decode dynamic/random JSON responses in GO, with nested data

    body, _ := ioutil.ReadAll(response.Body)
    resp := make(map[string]interface{})
    err = json.Unmarshal(body, &resp)

    fmt.Printf("BODY: %T<\n", body)
    fmt.Printf("BODY: %s<\n", body)
    fmt.Printf("RESP: %s<\n", resp)
    fmt.Printf("RESP: %T<\n", resp)
    fmt.Printf("RESP[results]: %T<\n", resp["results"])
    fmt.Printf("RESP[results]: %s<\n", resp["results"])

body is the JSON result from the HTTP server and I unmarshall it and the result looks to be a slice of bytes.

BODY: []uint8

BODY: {"results":[{"code":500.0,"errors":["Configuration file 'c2-web-2.conf' already exists."],"status":"Object could not be created."}]}

So I unmarshall it into resp and that works as expected.

RESP: map[string]interface {}

RESP: map[results:[map[code:%!s(float64=500) errors:[Configuration file 'c2-web-2.conf' already exists.] status:Object could not be created.]]]<

I'm able to access the map with the key results.

RESP[results]: []interface {}

RESP[results]: [map[code:%!s(float64=500) errors:[Configuration file 'conf.d/hosts/c2-web-2.conf' already exists.] status:Object could not be created.]]<

Now what i want to access it the "code", "errors" and "status" which is in resp["results"] This looks like an array or slice and I've tried indexing it but I get the error at compile time

./create_host.go:62: invalid operation: resp["results"][0] (type interface {} does not support indexing)

I've done a lot of googling, tried unmarshalling the data within resp["results"] etc, but after a few days I have not made much progress.

How should I access the map which seems to be a member of an array? The data structure is not guaranteed so I can't create a structure and unmarshall into that.

Thanks

Len Smith · Accepted Answer · 2016-06-13 23:06:14Z

2

A co-worker provided the code fragement below which made it possible to access the map entries I was looking for.

    respBody, _ := ioutil.ReadAll(response.Body)

    var rsp interface{}
    if err := json.Unmarshal(respBody, &rsp); err != nil {
            log.Fatal(err)
    }
    resultMap := rsp.(map[string]interface{})["results"].([]interface{})[0].(map[string]interface{})
    fmt.Printf("test: %s<\n", resultMap["errors"] )

test: [Configuration file 'c2-web-2.conf' already exists.]<

answered Jun 13, 2016 at 23:06

Len Smith

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user94559 · Accepted Answer · 2016-06-13 01:14:21Z

1

I believe you need to do a type assertion. You have an interface{}, but you need some sort of slice to index into. Try resp["results"].([]interface{})[0]? (Sorry, haven't had a chance to test this myself.)

answered Jun 13, 2016 at 1:14

user94559

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