HTTP/1.1 报文结构与手写解析器

POST /api/login HTTP/1.1\r\n
Host: example.com\r\n
Content-Type: application/json\r\n
Content-Length: 29\r\n
\r\n
{"user":"neo","pwd":"123"}

// 运行环境：Node.js 14+（用 Buffer 处理二进制）
// 保存为 aj-l1.js，执行：node aj-l1.js

class HttpParser {
  constructor() {
    this.state = 'head'          // head -> body -> done
    this.buffer = Buffer.alloc(0)
  }
  // 喂入任意长度的二进制数据，true 表示整条报文解析完成
  push(chunk) {
    this.buffer = Buffer.concat([this.buffer, chunk])
    if (this.state === 'head') this._parseHead()
    if (this.state === 'body') this._parseBody()
    return this.state === 'done'
  }
  // 步骤1：按第一个空行 \r\n\r\n 切出头部
  _parseHead() {
    const sep = this.buffer.indexOf('\r\n\r\n')
    if (sep === -1) return       // 头部还没收齐，等更多数据
    const head = this.buffer.slice(0, sep).toString()
    const lines = head.split('\r\n')
    const [method, path, version] = lines[0].split(' ')
    const headers = {}
    for (let i = 1; i < lines.length; i++) {
      const idx = lines[i].indexOf(': ')
      headers[lines[i].slice(0, idx)] = lines[i].slice(idx + 2)
    }
    this.result = { method, path, version, headers }
    this.buffer = this.buffer.slice(sep + 4)
    // 决定 body 模式
    if (headers['Transfer-Encoding'] === 'chunked') this.state = 'chunked'
    else if (headers['Content-Length']) { this.need = +headers['Content-Length']; this.state = 'body' }
    else { this.state = 'done' }
  }
  // 步骤2：按 Content-Length 收齐 body
  _parseBody() {
    if (this.buffer.length < this.need) return
    this.result.body = this.buffer.slice(0, this.need).toString()
    this.buffer = this.buffer.slice(this.need)
    this.state = 'done'
  }
}

// 调用示例：喂入一条完整报文
const p = new HttpParser()
const raw = Buffer.from('POST /api/login HTTP/1.1\r\nHost: x\r\nContent-Length: 13\r\n\r\n{"a":1,"b":2}')
while (!p.push(raw)) {}
console.log(p.result)   // { method:'POST', path:'/api/login', ..., body:'{"a":1,"b":2}' }