package main

import (
    "bytes"
    "encoding/json"
    "log"
    "net/http"
    "sync"
    "time"
)

const (
    TIMEOUT = 50 // Timeout for HTTP request
    URL     = "https://example.com/data.json"
    REQUEST = "https://example.com/update"
)


var client = http.Client{Timeout: TIMEOUT * time.Millisecond}

type (
    Data struct {
        Jwt  string `json:"jwt"`
        Items []GetItem `json:"items"`
    }
    GetItem struct {
        Name string `json:"name"`
        Code string `json:"code"`
    }
    RequestItem struct {
        Jwt string `json:"jwt"`
        Code string `json:"code"`
    }
)


func main() {
    callMethod()
}

func callMethod() {
    var wg sync.WaitGroup
    data, err := getJSON()
    if err != nil {
        log.Fatal(err)
    }
    jwt := data.Jwt
    for _, item := range data.Items {
        r, _ := json.Marshal(RequestItem{
            jwt, item.Code,
        })
        wg.Add(1)
        go func (item []byte) {
            _,_ = client.Post(REQUEST, "application/json", bytes.NewBuffer(item))
            wg.Done()
        }(r)
    }
    wg.Wait()

}

func getJSON() (*Data, error) {
    var result Data
    response, err := http.Get(URL)
    if err != nil {
        return nil, err
    }
    err = json.NewDecoder(response.Body).Decode(&result)
    if err != nil {
        return nil, err
    }
    return &result, nil
}