===== HTTP Server (net/http) =====

==== What is it? ====
An **HTTP server** is a program (service) that:
  * **listens** on an address (host:port),
  * accepts incoming HTTP connections/requests,
  * runs a **handler** to process each request,
  * writes an HTTP response (status + headers + body).

In Go, the standard library package `net/http` provides everything needed to build an HTTP server.

==== What is it used for? ====
  * Build REST APIs and microservices.
  * Serve web pages, JSON, files, webhooks.
  * Provide health checks (e.g. `/health`) for monitoring/load balancers.

==== Core building blocks ====
  * **Handler**: processes requests and writes responses  
    * `http.Handler` (interface)
    * `http.HandlerFunc` (function adapter)
  * **ResponseWriter**: writes status code, headers, and body.
  * **Request**: method, URL, headers, body, context.
  * **ServeMux (router)**: maps URL paths to handlers  
    * `http.DefaultServeMux` is the default global mux.
    * `http.NewServeMux()` creates a dedicated mux.

==== Minimal server (custom mux) ====
<code go>
package main

import (
    "log"
    "net/http"
)

func main() {
    mux := http.NewServeMux()

    mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        w.Write([]byte("hello"))
    })

    mux.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
        w.WriteHeader(http.StatusOK)
        w.Write([]byte("ok"))
    })

    log.Println("listening on :8080")
    log.Fatal(http.ListenAndServe(":8080", mux))
}
</code>

==== Common patterns ====
  * **Default mux pattern** (quick demos): use `http.HandleFunc` + `ListenAndServe(..., nil)`
  * **Custom mux pattern** (recommended): `mux := http.NewServeMux()` and pass it to server
  * **Middleware pattern**: wrap handlers (logging, auth, recover, rate limit)

==== Production notes (important) ====
For production, prefer `http.Server{...}` with timeouts and graceful shutdown.
Time-outs help protect against slow-client attacks and avoid hanging connections.

==== Related pages ====
  * [[go:stdlib:http_server_struct|http.Server]]
  * [[go:stdlib:http_listenandserve|http.ListenAndServe]]
  * [[go:stdlib:http_client|http.Client]]
  * [[go:stdlib:middleware|Middleware]]
  * [[go:stdlib:httptest|httptest]]

==== Hard words (English) ====
  * **server** /ˈsɝːvər/: máy chủ / dịch vụ phục vụ
  * **service** /ˈsɝːvɪs/: dịch vụ
  * **listen** /ˈlɪsən/: lắng nghe (mở cổng nhận kết nối)
  * **accept** /əkˈsept/: chấp nhận kết nối/nhận vào
  * **handler** /ˈhændlər/: bộ xử lý request
  * **interface** /ˈɪntərfeɪs/: giao diện (hợp đồng)
  * **adapter** /əˈdæptər/: bộ chuyển/đệm để khớp kiểu
  * **router** /ˈruːtər/: bộ định tuyến (map path -> handler)
  * **multiplexer (mux)** /ˈmʌltɪˌpleksər/: bộ chọn route theo đường dẫn
  * **webhook** /ˈwebhʊk/: callback qua HTTP
  * **load balancer** /ˈloʊd ˌbælənser/: cân bằng tải
  * **middleware** /ˈmɪdəlwer/: lớp trung gian (bọc handler)
  * **graceful shutdown** /ˈɡreɪsfəl ˈʃʌtdaʊn/: tắt êm
  * **timeout** /ˈtaɪmaʊt/: hết thời gian chờ
  * **hanging** /ˈhæŋɪŋ/: treo/chờ mãi