variable is empty but later has a value - go

Question

I'm trying to develop a Terraform provider but I have a problem of the first request body. Here is the code:
type Body struct {
id string
}
func resourceServerCreate(d *schema.ResourceData, m interface{}) error {
key := d.Get("key").(string)
token := d.Get("token").(string)
workspace_name := d.Get("workspace_name").(string)
board_name := d.Get("board_name").(string)
resp, err := http.Post("https://api.trello.com/1/organizations?key="+key+"&token="+token+"&displayName="+workspace_name,"application/json",nil)
if err != nil {
log.Fatalln(err)
}
defer resp.Body.Close()
//lettura body.
body := new(Body)
json.NewDecoder(resp.Body).Decode(body)
log.Println("[ORCA MADONNA] il log funzia "+body.id)
d.Set("board_id",body.id)
resp1, err1 := http.Post("https://api.trello.com/1/boards?key="+key+"&token="+token+"&idOrganization="+body.id+"&=&name="+board_name,"application/json",nil)
if err1 != nil {
log.Fatalln(resp1)
}
defer resp1.Body.Close()
d.SetId(board_name)
return resourceServerRead(d, m)
}
In the log is empty, but the second call have it and work fine. How is it possible?

Answer 1

Go doesn't force you to check error responses, therefore it's easy to make silly mistakes. Had you checked the return value from Decode(), you would have immediately discovered a problem.
err := json.NewDecoder(resp.Body).Decode(body)
if err != nil {
log.Fatal("Decode error: ", err)
}
Decode error: json: Unmarshal(non-pointer main.Body)
So your most immediate fix is to use & to pass a pointer to Decode():
json.NewDecoder(resp.Body).Decode(&body)
Also of note, some programming editors will highlight this mistake for you:
Here's a working demonstration, including a corrected Body structure as described at json.Marshal(struct) returns “{}”:
package main
import (
"bytes"
"encoding/json"
"fmt"
"log"
"net/http"
"time"
)
type JSON = map[string]interface{}
type JSONArray = []interface{}
func ErrFatal(err error, msg string) {
if err != nil {
log.Fatal(msg+": ", err)
}
}
func handleTestRequest(w http.ResponseWriter, req *http.Request) {
w.Write(([]byte)("{\"id\":\"yourid\"}"))
}
func launchTestServer() {
http.HandleFunc("/", handleTestRequest)
go http.ListenAndServe(":8080", nil)
time.Sleep(1 * time.Second) // allow server to get started
}
// Medium: "Don’t use Go’s default HTTP client (in production)"
var restClient = &http.Client{
Timeout: time.Second * 10,
}
func DoREST(method, url string, headers, payload JSON) *http.Response {
requestPayload, err := json.Marshal(payload)
ErrFatal(err, "json.Marshal(payload")
request, err := http.NewRequest(method, url, bytes.NewBuffer(requestPayload))
ErrFatal(err, "NewRequest "+method+" "+url)
for k, v := range headers {
request.Header.Add(k, v.(string))
}
response, err := restClient.Do(request)
ErrFatal(err, "DoRest client.Do")
return response
}
type Body struct {
Id string `json:"id"`
}
func clientDemo() {
response := DoREST("POST", "http://localhost:8080", JSON{}, JSON{})
defer response.Body.Close()
var body Body
err := json.NewDecoder(response.Body).Decode(&body)
ErrFatal(err, "Decode")
fmt.Printf("Body: %#v\n", body)
}
func main() {
launchTestServer()
for i := 0; i < 5; i++ {
clientDemo()
}
}