Using Golang json.NewDecoder / json.NewEncoder

Question

I'm a total noob at go and I'm trying to understand what I'm missing here. I'm expecting to use dec.Decode to loop over the json values and end up with a map of the response. What I'm getting is the entire json string as the key to the first element of the map. What am I missing?

Example response:

2015/03/02 10:03:16 map[error:invalid_request error_description:that is not a recognized WePay API call error_code:1001] map[string]interface {}

package main

import (
    "encoding/json"
    "io"
    "log"
    "net/http"
    "reflect"
)

func main() {
    var v map[string]interface{}
    resp, err := http.Get("https://wepayapi.com/v2/")
    if err != nil {
        log.Println("Error: " + err.Error())
    }   
    defer resp.Body.Close()

    // resp.Body is an io.ReadCloser... NewDecoder expects an io.Reader
    dec := json.NewDecoder(resp.Body)

    // Decode reads the next JSON-encoded value from its input and stores it in the value pointed to by v.
    for err := dec.Decode(&v); err != nil && err != io.EOF; {
        log.Println("ERROR: " + err.Error())
        return
    }   
    log.Println(v, reflect.TypeOf(v))
}

Can you show us a sample, or the structure of the json returned? — Mr_Pink
– Mr_Pink, Commented Mar 2, 2015 at 16:29
From what I see, you clearly have a map with three keys, error, error_description and error_code. Just print len(v) or v["error_code"]. — Ainar-G
– Ainar-G, Commented Mar 2, 2015 at 16:31
It was decoding the JSON correctly all long. I was reading the log line as essentially map["error_description:that is not a recognized WePay API call error_code:1001 error:invalid_request"] (the key as the entire JSON string) instead of it being a map with these 3 values. Bottom line I'm an idiot ;) — JSP
– JSP, Commented Mar 2, 2015 at 16:45

Arjan · Accepted Answer · 2015-09-28 21:36:50Z

2

Decoder will decode the whole JSON value at once (in this case the error object), you don;y have to call it in a loop:

if err := dec.Decode(&v); err != nil {
    log.Println("ERROR: " + err.Error())
    return
}

As a response you get a map equavalent of this JSON:

{"error":"invalid_request","error_description":"that is not a recognized WePay API call","error_code":1001}

Result:

map[string]interface{} {
    "error":"invalid_request",
    "error_description":"that is not a recognized WePay API call",
    "error_code":1001,
}

edited Sep 28, 2015 at 21:36

answered Mar 2, 2015 at 16:30

Arjan

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2 Comments

Vinit Gaikwad Over a year ago

How to retrieve individual values from this interface?

Arjan Over a year ago

@VinitGaikwad result["error"].(string) and similar for the others

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