Marshalling to NonString type in Golang JSON POST Request

Question

I'm having a little bit of trouble handling types in Golang. I'm making a POST router.

Consider the following struct:

type DataBlob struct {
    Timestamp string
    Metric_Id int `json:"id,string,omitempty"`
    Value float32 `json:"id,string,omitempty"`
    Stderr float32 `json:"id,string,omitempty"`
}

This is my POST router using json.Unmarshal() from a decoded stream:

func Post(w http.ResponseWriter, req * http.Request) {
    body, err := ioutil.ReadAll(req.Body)
    if err != nil {
        panic()
    }

    var t DataBlob
    err = json.Unmarshal(body, &t)
    if err != nil {
        panic()
    }

    fmt.Printf("%s\n", t.Timestamp)
    fmt.Printf("%d\n", int(t.Metric_Id))
    fmt.Printf("%f\n", t.Value)
    fmt.Printf("%f\n", t.Stderr)
}

It seems that no matter what I make my values in my POST request:

{
    "timestamp": "2011-05-16 15:36:38",
    "metric_id": "28",
    "value": "4.5",
    "stderr": "8.5"
}

All the non-String values print as 0 or 0.000000, respectively. It also doesn't matter if I try to type convert inline after-the-fact, as I did with t.Metric_Id in the example.

If I edit my struct to just handle string types, the values print correctly.

I also wrote a version of the POST router using json.NewDecoder():

func Post(w http.ResponseWriter, req * http.Request) {
    decoder := json.NewDecoder(req.Body)

    var t DataBlob
    err := decoder.Decode(&t)
    if err != nil {
        panic()
    }

    fmt.Printf("%s\n", t.Timestamp)
    fmt.Printf("%d\n", t.Metric_Id)
    fmt.Printf("%f\n", t.Value)
    fmt.Printf("%f\n", t.Stderr)
}

This is building off of functionality described in this answer, although the solution doesn't appear to work.

I appreciate your help!

score 1 · Accepted Answer · answered Feb 27 '16 at 21:39

You need to change the names of your Datablob values. You've told the JSON decoder that they're all named "id". You should try something like the following. Also, take a look at the json.Marshal description and how it describes the tags for structs and how the json library handles them. https://golang.org/pkg/encoding/json/#Marshal

type DataBlob struct {
    Timestamp string
    Metric_Id int `json:"metric_id,string,omitempty"`
    Value float32 `json:"value,string,omitempty"`
    Stderr float32 `json:"stderr,string,omitempty"`
}

Marshalling to NonString type in Golang JSON POST Request

1 Answers1