Submit variable in payload of golang http.NewRequest

Question

I'm learning Golang so please excuse what may seem to be a basic question. I have searched for a couple of hours for clues as to how I might achieve sending variable data in my JSON formatted API POST from my golang app, but not found a clue or solution yet. I know the answer will be my lack of syntax knowledge.

So the problem is with the 'lastcontact' field I'm trying to POST. I want to use my 'dt' variable that contains the current datetime.

package main

import (
  "fmt"
  "strings"
  "net/http"
  "io/ioutil"
  "time"
)

func main() {

  dt := time.Now()
  url := "https://fakeapi.io/API/apiActions/update/"
  method := "POST"

  payload := strings.NewReader(`{
    "name" : "Dumpty",
    "saveconfig" : "true",
    "lastcontact" : {dt}
}`)

  client := &http.Client {
  }
  req, err := http.NewRequest(method, url, payload)

  if err != nil {
    fmt.Println(err)
    return
  }
  req.Header.Add("api-key", "gjhgjhgjhg")
  req.Header.Add("api-secret", "jhgjhgjhg")
  req.Header.Add("Content-Type", "application/json; charset=UTF-8")

  res, err := client.Do(req)
  if err != nil {
    fmt.Println(err)
    return
  }
  defer res.Body.Close()

  body, err := ioutil.ReadAll(res.Body)
  if err != nil {
    fmt.Println(err)
    return
  }
  fmt.Println(string(body))
}

Go doesn't support this kind of automatic string interpolation of variables. You need to either use the fmt package, or explicit string concatenation with +, or a struct/map value with json.Marshal. — mkopriva
– mkopriva, Commented Mar 28, 2021 at 15:21

Christian · Accepted Answer · 2021-03-28 15:46:00Z

1

You can use a struct to store your response type if you know the fields beforehand. If you don't, you could use a map[string]interface{} to store arbitrary data.

Then using json.Marshal to convert it to a correctly formatted JSON response.

type myStruct struct {
        Name        string    `json:"name"`
        SaveConfig  string    `json:"saveconfig"`
        LastContact time.Time `json:"lastcontact"`
    }

    dt := time.Now()

    myData := myStruct{
        Name:        "Dumpty",
        SaveConfig:  "true",
        LastContact: dt,
    }

    myBytes, err := json.Marshal(myData)
    // bytes.NewBuffer returns *bytes.Buffer
    // which implements the io.Reader interface
    // that you need for your http.NewRequest call
    payload := bytes.NewBuffer(myBytes)

Full playground example https://play.golang.org/p/Mc9UXT32Wi1

answered Mar 28, 2021 at 15:46

Christian

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1 Comment

Mikey007 Over a year ago

Thanks so much for your answer. Absolutely perfect. :-)

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