How to parse http response body to json format in golang?

Question

I get an response body. the format of the body is as below:

  [
    {
       "id":1,
       "name":"111" 
    },
    {
       "id":2,
       "name":"222" 
    }
  ]

I want to parse the body to json struct, my code is as below:

type Info struct {
      Id uint32 `json:id`
      Name string `json:name`
  }

  type Response struct {
      infos []Info
  }

  v := &Response{}
  data, err := ioutil.ReadAll(response.Body)
  if err := json.Unmarshal(data, v); err != nil {
      log.Fatalf("Parse response failed, reason: %v \n", err)
  }

It always give an error:cannot unmarshal array into Go value of type xxx, can someone give a help?

Do json.Unmarshal(data, &v.infos). If json is an array, you need to pass in a Go slice, if it's an object you need to pass in a Go struct, or map. — mkopriva
– mkopriva, Commented Oct 17, 2019 at 13:37

d33tah · Accepted Answer · 2020-07-20 08:35:33Z

17

I actually stumbled upon this question while googling entry-level Go questions, so I figured I'd leave a message:

package main

import (
        "encoding/json"
        "fmt"
        "net/http"
)

func main() {
        url := "https://skishore.github.com/inkstone/all.json"

        resp, err := http.Get(url)
        if err != nil {
                panic(err)
        }
        defer resp.Body.Close()

        var j interface{}
        err = json.NewDecoder(resp.Body).Decode(&j)
        if err != nil {
                panic(err)
        }
        fmt.Printf("%s", j)
}

This downloads an example JSON url, decodes it without any prior knowledge of its contents and prints to stdout. Keep in mind that it would be better to actually assign a type of some kind.

answered Jul 20, 2020 at 8:35

d33tah

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Comments

BMitch · Accepted Answer · 2025-05-07 14:21:50Z

This is the wrong type for the response:

  type Response struct {
      infos []Info
  }

First, infos is not public, so json marshalers will ignore it. But more importantly, the input is not a struct or json object, it is a slice or json array. Changing Response to a slice results in:

package main

import (
    "encoding/json"
    "fmt"
    "log"
)

func main() {

    data := []byte(`
  [
    {
       "id":1,
       "name":"111" 
    },
    {
       "id":2,
       "name":"222" 
    }
  ]
`)

    type Info struct {
        Id   uint32 `json:"id"`
        Name string `json:"name"`
    }

    type Response []Info

    v := &Response{}
    if err := json.Unmarshal(data, v); err != nil {
        log.Fatalf("Parse response failed, reason: %v \n", err)
    }

    fmt.Printf("%#v\n", v)
}

Which can be verified in the Go playground.

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