Go

package main

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

type Client struct {
	BaseURL, User, Pass, DeviceID string
	HTTP                          *http.Client
}

type Response struct {
	Code    string          `json:"code"`
	Message string          `json:"message"`
	Results json.RawMessage `json:"results"`
}

func (c *Client) Post(path string, body any) (*Response, error) {
	buf, _ := json.Marshal(body)
	req, err := http.NewRequest(http.MethodPost, c.BaseURL+path, bytes.NewReader(buf))
	if err != nil {
		return nil, err
	}
	req.SetBasicAuth(c.User, c.Pass)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-Device-Id", c.DeviceID)

	res, err := c.HTTP.Do(req)
	if err != nil {
		return nil, err
	}
	defer res.Body.Close()

	var out Response
	if err := json.NewDecoder(res.Body).Decode(&out); err != nil {
		return nil, fmt.Errorf("HTTP %d: %w", res.StatusCode, err)
	}
	if res.StatusCode >= 300 {
		return &out, fmt.Errorf("%s: %s", out.Code, out.Message)
	}
	return &out, nil
}

func main() {
	c := &Client{
		BaseURL:  "http://localhost:3000",
		User:     "admin",
		Pass:     "changeme",
		DeviceID: "my-device",
		HTTP:     &http.Client{Timeout: 60 * time.Second},
	}
	res, err := c.Post("/send/message", map[string]any{
		"phone":   "628123456789",
		"message": "Hello from Go",
	})
	if err != nil {
		panic(err)
	}
	fmt.Println(string(res.Results))
}