{
  "topic": "http-keepalive",
  "type": "single_choice",
  "schema_version": "1.0.0",
  "generated": "2026-09-02T21:20:00+08:00",
  "questions": [
    {
      "id": "sc-001",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "Keep-Alive",
        "HTTP/1.1"
      ],
      "question": "HTTP/1.1 默认是否启用 Keep-Alive？",
      "options": {
        "A": "默认不启用",
        "B": "默认启用",
        "C": "需要手动配置",
        "D": "仅 HTTPS 启用"
      },
      "answer": "B",
      "explanation": "HTTP/1.1 默认启用 Keep-Alive，建一次连接后可以连续发多个请求，不用每次重新握手。这是 HTTP/1.1 最重要的默认优化。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-002",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "Keep-Alive",
        "Connection头"
      ],
      "question": "服务器通过哪个响应头告诉客户端连接可以复用？",
      "options": {
        "A": "Connection: close",
        "B": "Connection: Keep-Alive",
        "C": "Keep-Alive: true",
        "D": "Reuse: true"
      },
      "answer": "B",
      "explanation": "服务器通过 Connection: Keep-Alive 响应头告诉客户端这个连接可以复用。Connection: close 表示不要复用。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-003",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "Keep-Alive",
        "timeout",
        "max"
      ],
      "question": "Keep-Alive: timeout=5, max=100 中 max=100 的含义是？",
      "options": {
        "A": "最大并发连接数为 100",
        "B": "空闲超时 100 秒",
        "C": "单连接最多处理 100 个请求后强制关闭",
        "D": "最大响应大小 100KB"
      },
      "answer": "C",
      "explanation": "max=100 表示单连接最多处理 100 个请求后强制关闭。timeout=5 表示空闲超过 5 秒没新请求就关闭连接。两者取先触发的那个。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-004",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "队头阻塞",
        "HTTP/1.1"
      ],
      "question": "Keep-Alive 引入了什么问题？",
      "options": {
        "A": "带宽不足",
        "B": "队头阻塞",
        "C": "DNS 解析慢",
        "D": "TLS 握手失败"
      },
      "answer": "B",
      "explanation": "Keep-Alive 解决了频繁握手问题，但引入了队头阻塞——同一连接上的请求严格串行，后一个请求必须等前一个响应返回。浏览器用多开 6 个连接来弥补。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-005",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "HTTP/1.1",
        "浏览器",
        "6连接"
      ],
      "question": "HTTP/1.1 的 Keep-Alive 存在队头阻塞，浏览器用什么方式弥补？",
      "options": {
        "A": "使用 HTTP/2",
        "B": "同时开 6 个 TCP 连接",
        "C": "使用 UDP 协议",
        "D": "增大窗口大小"
      },
      "answer": "B",
      "explanation": "浏览器同时开 6 个 TCP 连接来弥补 HTTP/1.1 的队头阻塞问题——一条收银通道排队太慢，所以超市开了 6 个收银台，但每个收银台内部还是串行的。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-006",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "Keep-Alive",
        "HTTP/1.0"
      ],
      "question": "HTTP/1.0 的连接模型是怎样的？",
      "options": {
        "A": "一个连接串行多个请求",
        "B": "一个请求一个连接，用完即弃",
        "C": "一个连接并行多个请求",
        "D": "使用 UDP 协议"
      },
      "answer": "B",
      "explanation": "HTTP/1.0 没有 Keep-Alive，一个请求一个连接，用完即弃。每个资源都要走一遍握手流程，光握手就比传数据花的时间还多。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-007",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "Keep-Alive",
        "空闲连接"
      ],
      "question": "Keep-Alive 连接在空闲时会占用什么资源？",
      "options": {
        "A": "只占用 CPU",
        "B": "占用内存和文件描述符",
        "C": "不占用任何资源",
        "D": "只占用网络带宽"
      },
      "answer": "B",
      "explanation": "Keep-Alive 连接在空闲时仍然占内存和 fd。如果客户端长时间不发新请求，服务器应该主动关闭。合理设置 timeout 参数很重要。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-008",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "Keep-Alive",
        "演进"
      ],
      "question": "HTTP 连接复用的演进路线正确的是？",
      "options": {
        "A": "Keep-Alive → HTTP/1.0 → HTTP/2",
        "B": "无 Keep-Alive → Keep-Alive → HTTP/2 多路复用 → HTTP/3 QUIC",
        "C": "HTTP/2 → Keep-Alive → HTTP/3",
        "D": "TCP → UDP → HTTP/3"
      },
      "answer": "B",
      "explanation": "演进路线：HTTP/1.0 无 Keep-Alive → HTTP/1.1 默认 Keep-Alive → 浏览器并行连接缓解队头阻塞 → HTTP/2 多路复用 → HTTP/3 QUIC 基于 UDP 的多路复用。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-009",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "Keep-Alive",
        "Connection头"
      ],
      "question": "不想复用连接时，服务器应该返回什么头？",
      "options": {
        "A": "Connection: Keep-Alive",
        "B": "Connection: close",
        "C": "Keep-Alive: false",
        "D": "Connection: none"
      },
      "answer": "B",
      "explanation": "不想复用连接时，服务器返回 Connection: close，告诉客户端处理完当前请求后关闭连接。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-010",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "Keep-Alive",
        "服务器"
      ],
      "question": "服务器因超时关闭了连接，但客户端下次复用时才发现连接已死，这种情况应该怎么处理？",
      "options": {
        "A": "忽略错误",
        "B": "开启连接健康检查或设置合理的超时",
        "C": "增大连接池",
        "D": "使用 HTTP/1.0"
      },
      "answer": "B",
      "explanation": "服务器因超时关闭了连接，但客户端不知道，下次复用时才发现连接已死。需要开启连接健康检查或设置合理的超时来避免这个问题。",
      "source": null,
      "related": []
    }
  ]
}