Post Marshaled JSON data as URL Encoded Form Data

Issue

I’m trying to send a POST request by converting an auth structure to application/x-www-form-urlencoded data.

package main

import (
    "bytes"
    "encoding/json"
    "io/ioutil"
    "log"
    "net/http"
)

type Payload struct {
    Username string `json:"username"`
    Password string `json:"password"`
    GrantType string `json:"grant_type"`
    Scope string `json:"scope"`
}

func main() {

    var endpoint string = "https://api.io/v1/oauth/token"

    jsonPay := &Payload{
        Username: "email",
        Password: "pass",
        GrantType: "password",
        Scope: "SPACE SEPARATED STRINGS",
    }

    //byteArr, err := json.Marshal(jsonPay)
    //if err != nil {
    //    log.Printf("Unable to map structure\n%v", err)
    //}

    payloadBuf := new(bytes.Buffer)
    json.NewEncoder(payloadBuf).Encode(jsonPay)

    req, err := http.NewRequest("POST", endpoint, payloadBuf)
    if err != nil {
        log.Fatal(err)
    }
    req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
    req.Header.Add("Accept", "application/json")

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }
    log.Printf(string(body))

}

I’ve tried:

  1. Sending a JSON encoded payload buffer, which returns

    {"error":"invalid_request","error_description":"Missing grant type"}
    
  2. Using bytes.NewReader with the marshaled JSON object, which also returns

    {"error":"invalid_request","error_description":"Missing grant type"}
    
  3. Using strings.NewReader with the JSON encoded payload buffer, which returns

    cannot use payloadBuf (variable of type *bytes.Buffer) as type string in argument to strings.NewReader
    

The curl request looks like:

curl --request POST \
  --url https://api.io/v1/oauth/token \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --data 'username=email' \
  --data 'password=pass' \
  --data 'grant_type=password' \
  --data 'scope=SPACE SEPARATED STRINGS'

and works with:

package main

import (
    "io/ioutil"
    "log"
    "net/http"
    "net/url"
    "strings"
)

func main() {

    const endpoint string = "https://api.io/v1/oauth/token"

    payload := url.Values{
        "username":   {"email"},
        "password":   {"pass"},
        "grant_type": {"password"},
        "scope":      {"SPACE SEPARATED STRINGS"},
    }

    req, err := http.NewRequest("POST", endpoint, strings.NewReader(payload.Encode()))
    if err != nil {
        log.Printf("Unable to perform POST request:\n%v", err)
    }
    req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
    req.Header.Add("Accept", "application/json")

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }
    log.Println(string(body))
}

How do I post marshaled JSON data as application/x-www-form-urlencoded

Solution

Implemented @RedBlue’s suggestion:

package main

import (
    "io/ioutil"
    "log"
    "net/http"
    "strings"
    "net/url"
)

type Payload struct {
    Username string `json:"username"`
    Password string `json:"password"`
    GrantType string `json:"grant_type"`
    Scope string `json:"scope"`
}

func main() {

    const endpoint string = "https://api.io/v1/oauth/token"

    formData := &Payload{
        Username: "email",
        Password: "pass",
        GrantType: "password",
        Scope: "SPACE SEPARATED STRINGS",
    }

    payload := url.Values{
        "username":   {formData.Username},
        "password":   {formData.Password},
        "grant_type": {formData.GrantType},
        "scope":      {formData.Scope},
    }

    req, err := http.NewRequest("POST", endpoint, strings.NewReader(payload.Encode()))
    if err != nil {
        log.Printf("Unable to perform POST request:\n%v", err)
    }
    req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
    req.Header.Add("Accept", "application/json")

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }
    log.Println(string(body))
}

Answered By – Saurabh

Answer Checked By – Mildred Charles (GoLangFix Admin)

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