167 lines
4.6 KiB
Markdown
167 lines
4.6 KiB
Markdown
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---
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tags: [计算机网络, HTTP, HTTP/1.1, HTTP/2, HTTP/3, QUIC]
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create time: 2026-05-18 02:30
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---
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# HTTP/1.1 完全指南
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## 概述
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HTTP (HyperText Transfer Protocol) 是万维网的数据传输协议，从 Mosaic 浏览器的最初需求发展而来，至今仍是互联网上使用最广泛的协议之一。
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## HTTP 消息结构
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```
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Request 示例:
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POST /api/users HTTP/1.1 ← Request Line
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Host: api.example.com ← Headers
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Content-Type: application/json ← Header
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Content-Length: 42 ← Header
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Authorization: Bearer abc123 ← Header
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← Blank line separates headers from body
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{"name": "Alice", "email": "alice@example.com"} ← Body
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Response 示例:
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HTTP/1.1 201 Created ← Status Line
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Date: Mon, 17 May 2026 02:30:00 GMT ← Headers
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Location: https://api.example.com/users/42 ← Header
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Content-Type: application/json ← Header
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Content-Length: 35 ← Header
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{"id": 42, "name": "Alice"} ← Body
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```
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### Request Line 格式
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```
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METHOD SP Request-URI SP HTTP-Version CRLF
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```
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### 常用 Method
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| Method | 安全(Safe)? | 幂等(Idempotent)? | 含义 |
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|--------|-----------|------------------|------|
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| GET | ✅ | ✅ | 获取资源 |
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| HEAD | ✅ | ✅ | 只获取响应头 |
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| POST | ❌ | ❌ | 提交数据创建新资源 |
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| PUT | ❌ | ✅ | 替换整个资源 |
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| PATCH | ❌ | ❌ | 部分更新资源 |
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| DELETE | ❌ | ✅ | 删除资源 |
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| OPTIONS | ✅ | ✅ | 查询服务器支持的 Method |
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| CONNECT | N/A | N/A | 建立隧道(代理/HTTPS) |
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| TRACE | ✅ | ✅ | 回显收到的请求(调试) |
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### 常见 Status Code
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| 类别 | 含义 | 举例 |
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|------|------|------|
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| 1xx | 信息性 | 100 Continue, 101 Switching Protocols |
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| 2xx | 成功 | 200 OK, 201 Created, 204 No Content |
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| 3xx | 重定向 | 301 Moved Permanently, 302 Found, 304 Not Modified |
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| 4xx | 客户端错误 | 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 429 Too Many Requests |
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| 5xx | 服务端错误 | 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable |
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## Keep-Alive（持久连接）— HTTP/1.1 默认行为
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HTTP/1.1 中 `Connection: keep-alive` 是默认的——一个 TCP 连接可承载多个 HTTP 请求/响应：
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```
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单一 TCP 连接上的多次请求:
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TCP Established ✅
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Client → Server: GET /page1.html
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Server → Client: 200 + HTML
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Client → Server: GET /style.css
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Server → Client: 200 + CSS
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Client → Server: GET /app.js
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Server → Client: 200 + JS
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Client → Server: Connection: close (或超时自动关闭)
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Server → Client: ACK → TCP FIN
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```
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**好处：** 避免每次请求都进行三次握手 (+TLS 四次握手)。
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### Pipeline（管道化）— HTTP/1.1 的未启用功能
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理论上可以在同一个连接上**不等待前一个响应就发送下一个请求**：
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```
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Client 连续发三个请求:
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GET /a ← 不等响应
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GET /b
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GET /c
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Server 必须按顺序返回:
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200 /a
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200 /b
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200 /c
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```
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**为什么几乎没人用？**
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- Server 端实现复杂且 Bug 多
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- 一旦某个响应阻塞，后续所有响应都被卡住（HoL blocking）
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- HTTP/2 的多路复用彻底解决了这个问题
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## Chunked Transfer Encoding
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当不知道 Content-Length 时（如流式生成内容），使用 chunked 编码：
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```
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HTTP/1.1 200 OK
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Transfer-Encoding: chunked
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5\r\n\r\nHello\r\n ← 5 bytes of data: "Hello"
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7\r\n\r\n World!\r\n ← 7 bytes: " World!"
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0\r\n\r\n ← 终止 chunk
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```
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```go
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// Go net/http 中自动使用 chunked
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w.Header().Set("Transfer-Encoding", "chunked")
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w.Write([]byte("part 1"))
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w.Write([]byte("part 2"))
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w.WriteHeader(200) // WriteHeader 必须在 Write 之后才生效 chunked
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```
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## Go 中的 HTTP 客户端实践
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```go
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package main
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import (
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"fmt"
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"io"
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"net/http"
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"time"
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)
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func main() {
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client := &http.Client{
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Timeout: 10 * time.Second,
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Transport: &http.Transport{
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MaxIdleConns: 100,
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MaxIdleConnsPerHost: 10,
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IdleConnTimeout: 90 * time.Second,
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},
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}
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resp, err := client.Get("https://example.com")
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if err != nil {
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panic(err)
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}
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defer resp.Body.Close()
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io.Copy(os.Stdout, resp.Body)
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}
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```
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## 关联笔记
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- [[hhs/NETWORK/HTTP/2多路复用]] — HTTP/2 如何解决 HTTP/1.1 的问题
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- [[hhs/NETWORK/HTTP/3与QUIC]] — 基于 UDP 的下一代 HTTP
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- [[hhs/NETWORK/TCP三次握手与四次挥手]] — HTTP 依赖的底层 TCP 连接
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