===== http.Client =====

==== What is it? ====
`http.Client` is Go’s HTTP client used to send requests and receive responses.
It supports connection pooling and keep-alive by default.

==== What is it used for? ====
  * Call external APIs (GET/POST/PUT/DELETE).
  * Set timeouts and transport options.
  * Reuse connections efficiently.

==== Quick example (GET) ====
<code go>
package main

import (
    "io"
    "log"
    "net/http"
    "time"
)

func main() {
    client := &http.Client{
        Timeout: 5 * time.Second,
    }

    resp, err := client.Get("https://example.com")
    if err != nil {
        log.Fatal(err)
    }
    defer resp.Body.Close()

    b, _ := io.ReadAll(resp.Body)
    log.Println("status:", resp.Status)
    log.Println("body bytes:", len(b))
}
</code>

==== Example (custom request + headers) ====
<code go>
package main

import (
    "bytes"
    "log"
    "net/http"
    "time"
)

func main() {
    client := &http.Client{Timeout: 5 * time.Second}

    req, _ := http.NewRequest("POST", "https://example.com/api", bytes.NewBufferString(`{"a":1}`))
    req.Header.Set("Content-Type", "application/json")

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

    log.Println("status:", resp.StatusCode)
}
</code>

==== Notes / pitfalls (very important) ====
  * Always `defer resp.Body.Close()` to avoid leaking connections.
  * Prefer a reusable `http.Client` (do not create a new client per request in hot code).
  * Set `Timeout` (or use request context) to avoid hanging forever.
  * For advanced control, customize `Transport` (proxy, TLS settings, connection limits).

==== Related ====
  * [[go:stdlib:http_client|HTTP client]]
  * [[go:stdlib:net_http|net/http]]
  * [[go:concurrency:context|context.Context]]

==== Hard words (English) ====
  * **request** /rɪˈkwest/: yêu cầu
  * **response** /rɪˈspɑːns/: phản hồi
  * **connection pooling** /kəˈnekʃən ˈpuːlɪŋ/: gom/tái sử dụng kết nối
  * **reuse** /ˌriːˈjuːz/: tái sử dụng
  * **leak** /liːk/: rò rỉ (tài nguyên)
  * **hang** /hæŋ/: treo, chờ mãi
  * **transport** /ˈtrænspɔːrt/: tầng vận chuyển (cấu hình cách client kết nối)