iT邦幫忙

2026 iThome 鐵人賽
DAY 9
0
JavaScript

Learn HTTP With JS（2）系列 第 9 篇

Node.js TCP Client Socket 生命週期：lookup、connect 事件

18th鐵人賽
48 瀏覽

  • 分享至 

  • xImage
    •  

前言

TCP socket 分兩種

  • TCP client socket: 主動去連別人
  • TCP server socket: 開著 port 等別人連

這篇文章會介紹 TCP client socket 主動去連別人 對應的生命週期跟事件

TCP client socket 生命週期 1：lookup

✅ 正確觸發（lookup event 會在 DNS lookup 之後觸發）

import net from "net";

// ✅ host 為 domain name，會觸發 DNS lookup
const socket = net.connect({ host: "example.com", port: 80 });
socket.on("lookup", (err, address, family, host) =>
  console.log(performance.now(), { err, address, family, host }),
);

// Prints
// 635.062125 { err: null, address: '104.18.26.120', family: 4, host: 'example.com' }
// 635.566666 { err: null, address: '104.18.27.120', family: 4, host: 'example.com' }

❌ 不會觸發（指定 IP 的情況就不會觸發）

import net from "net";

// ❌ host 為 IP，不會觸發 DNS lookup
const socket = net.connect({ host: "104.18.26.120", port: 80 });
socket.on("lookup", (err, address, family, host) =>
  console.log(performance.now(), { err, address, family, host }),
);

❌ 不會觸發（TCP server socket 是被動等待連線）

import net from "net";

// TCP server
const server = net.createServer();
server.listen(5000, "localhost");
server.on("connection", (serverSocket) => {
  // ❌ serverSocket 是被動等待連線，不會觸發 DNS lookup
  serverSocket.on("lookup", console.log);
});

// TCP client
const clientSocket = net.connect({
  host: "localhost",
  port: 5000,
});

TCP client socket 生命週期 2：connect

成功把 domain name 解成 IP 之後，接下來就可以開始連線

"connect" 開頭的 events 有這四個：

針對 localhost 解出來的 addresses 為

import dns from "dns";
dns.lookup("localhost", { all: true }, (err, addresses) =>
  console.log(addresses),
);

// Prints
// [{ address: "::1", family: 6 }, { address: "127.0.0.1", family: 4 }]

每一個 address 的連線，都會觸發一個 connectionAttempt，並且可能會觸發以下三個其中一個

  • connect：連線成功
  • connectionAttemptFailed：連線失敗
  • connectionAttemptTimeout：連線超時

另外，autoSelectFamilyAttemptedAddresses 會記錄所有嘗試過的 address，其格式為

["::1:5000", "127.0.0.1:5000"];

正常情境

啟一個 TCP server 監聽 localhost:5000，並且開一個 TCP client 連過去

import net from "net";

const server = net.createServer();
server.listen(5000, "localhost");

const socket = net.connect({
  host: "localhost",
  port: 5000,
});
socket.on("connectionAttempt", (ip, port, family) => {
  console.log("connectionAttempt", { ip, port, family });
});
socket.on("connect", () => console.log("connect"));
socket.on("connectionAttemptFailed", (ip, port, family, error) => {
  console.log("connectionAttemptFailed", { ip, port, family, error });
});
socket.on("connectionAttemptTimeout", (ip, port, family) => {
  console.log("connectionAttemptTimeout", { ip, port, family });
});

// Prints
// connectionAttempt { ip: '::1', port: 5000, family: 6 }
// connect

最終觸發一次 "connectionAttempt" 跟 "connect" event

異常情境：server 沒開對應 port

將 TCP server 的 port 改成 5001

import net from "net";

const server = net.createServer();
server.listen(5001, "localhost");

const socket = net.connect({
  host: "localhost",
  port: 5000,
});
socket.on("connectionAttempt", (ip, port, family) => {
  console.log("connectionAttempt", { ip, port, family });
});
socket.on("connect", () => console.log("connect"));
socket.on("connectionAttemptFailed", (ip, port, family, error) => {
  console.log("connectionAttemptFailed", { ip, port, family, error });
});
socket.on("connectionAttemptTimeout", (ip, port, family) => {
  console.log("connectionAttemptTimeout", { ip, port, family });
});
// ✅ 記得監聽 on("error") 才不會讓 process exit
socket.on("error", (err) => console.log(err));

print 出來的結果是

// `net.connect` 會根據 "localhost" 解出來的 addresses 依序嘗試連線
// 觸發 `connectionAttempt` 跟 `connectionAttemptFailed`
connectionAttempt { ip: '::1', port: 5000, family: 6 }
connectionAttemptFailed {
  ip: '::1',
  port: 5000,
  family: 6,
  error: Error: connect ECONNREFUSED ::1:5000
      at createConnectionError (node:net:1678:14)
      at afterConnectMultiple (node:net:1708:16) {
    errno: -4078,
    code: 'ECONNREFUSED',
    syscall: 'connect',
    address: '::1',
    port: 5000
  }
}
connectionAttempt { ip: '127.0.0.1', port: 5000, family: 4 }
connectionAttemptFailed {
  ip: '127.0.0.1',
  port: 5000,
  family: 4,
  error: Error: connect ECONNREFUSED 127.0.0.1:5000
      at createConnectionError (node:net:1678:14)
      at afterConnectMultiple (node:net:1708:16) {
    errno: -4078,
    code: 'ECONNREFUSED',
    syscall: 'connect',
    address: '127.0.0.1',
    port: 5000
  }
}
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError
// 代表的是 多個 error "聚合" 成的一個 error
// 當所有 IPv6 跟 IPv4 的連線嘗試都失敗，就會拋出
AggregateError
    at internalConnectMultiple (node:net:1134:18)
    at afterConnectMultiple (node:net:1715:7) {
  code: 'ECONNREFUSED',
  [errors]: [
    Error: connect ECONNREFUSED ::1:5000
        at createConnectionError (node:net:1678:14)
        at afterConnectMultiple (node:net:1708:16) {
      errno: -4078,
      code: 'ECONNREFUSED',
      syscall: 'connect',
      address: '::1',
      port: 5000
    },
    Error: connect ECONNREFUSED 127.0.0.1:5000
        at createConnectionError (node:net:1678:14)
        at afterConnectMultiple (node:net:1708:16) {
      errno: -4078,
      code: 'ECONNREFUSED',
      syscall: 'connect',
      address: '127.0.0.1',
      port: 5000
    }
  ]
}

執行順序如下

connection-attempt-failed-to-error

至於為何 Node.js 會把所有 addresses 都嘗試連線一次呢？根據 socket.connect 的官方文件，重點的預設值為：

  • family: 0：IPv6 跟 IPv4 都允許
  • autoSelectFamily: true：會嘗試連線所有的 IPv6 跟 IPv4，直到其中一個成功

異常情境：連線 timeout

由於 autoSelectFamilyAttemptTimeout 的最小值是 10ms，本機互連很難超過，所以我們使用 example.com:81 來當範例

先測試 example.com 解出來的 addresses

import dns from "dns";

dns.lookup("example.com", { all: true }, (err, addresses) =>
  console.log(addresses),
);
// Prints
// [{ address: '104.18.26.120', family: 4 }, { address: '104.18.27.120', family: 4 }]

再來連到 example.com:81 試試看

import net from "net";

const socket = net.connect({
  host: "example.com",
  port: 81,
  autoSelectFamilyAttemptTimeout: 10,
});
socket.on("connectionAttempt", (ip, port, family) => {
  console.log(performance.now(), "connectionAttempt", { ip, port, family });
});
socket.on("connect", () => console.log(performance.now(), "connect"));
socket.on("connectionAttemptFailed", (ip, port, family, error) => {
  console.log(performance.now(), "connectionAttemptFailed", {
    ip,
    port,
    family,
    error,
  });
});
socket.on("connectionAttemptTimeout", (ip, port, family) => {
  console.log(performance.now(), "connectionAttemptTimeout", {
    ip,
    port,
    family,
  });
});

print 出來的結果是

765.0478 connectionAttempt { ip: '104.18.26.120', port: 81, family: 4 }
776.1741 connectionAttemptTimeout { ip: '104.18.26.120', port: 81, family: 4 }
776.762 connectionAttempt { ip: '104.18.27.120', port: 81, family: 4 }
21811.692 connectionAttemptFailed {
  ip: '104.18.27.120',
  port: 81,
  family: 4,
  error: Error: connect ETIMEDOUT 104.18.27.120:81
      at createConnectionError (node:net:1678:14)
      at afterConnectMultiple (node:net:1708:16) {
    errno: -4039,
    code: 'ETIMEDOUT',
    syscall: 'connect',
    address: '104.18.27.120',
    port: 81
  }
}
AggregateError
    at internalConnectMultiple (node:net:1134:18)
    at afterConnectMultiple (node:net:1715:7) {
  code: 'ETIMEDOUT',
  [errors]: [
    Error: connect ETIMEDOUT 104.18.26.120:81
        at createConnectionError (node:net:1678:14)
        at Timeout.internalConnectMultipleTimeout (node:net:1737:38)
        at listOnTimeout (node:internal/timers:610:11)
        at processTimers (node:internal/timers:543:7) {
      errno: -4039,
      code: 'ETIMEDOUT',
      syscall: 'connect',
      address: '104.18.26.120',
      port: 81
    },
    Error: connect ETIMEDOUT 104.18.27.120:81
        at createConnectionError (node:net:1678:14)
        at afterConnectMultiple (node:net:1708:16) {
      errno: -4039,
      code: 'ETIMEDOUT',
      syscall: 'connect',
      address: '104.18.27.120',
      port: 81
    }
  ]
}

執行順序如下

connection-attempt-timeout-to-error

  • 第一組 IP 104.18.26.120 經過 10ms 就 timeout
  • 第二組 IP 104.18.27.120 由於是最後一組，所以不受 10ms 的 timeout 限制（畢竟要以連線成功為優先）

我們可以從 Node.js 原始碼 看到最後一組 address 確實不受 timeout 限制

function internalConnectMultiple(context, canceled) {
  // ... other code

  if (current < context.addresses.length - 1) {
    debug(
      "connect/multiple: setting the attempt timeout to %d ms",
      context.timeout,
    );

    // If the attempt has not returned an error, start the connection timer
    context[kTimeout] = setTimeout(
      internalConnectMultipleTimeout,
      context.timeout,
      context,
      req,
      self._handle,
    );
  }
}

TCP server socket 不會觸發 connect events

import net from "net";

// TCP server
const server = net.createServer();
server.listen(5000, "localhost");
server.on("connection", (serverSocket) => {
  // ❌ serverSocket 是被動等待連線，不會觸發 connect events
  serverSocket.on("connectionAttempt", console.log);
  serverSocket.on("connect", console.log);
  serverSocket.on("connectionAttemptTimeout", console.log);
  serverSocket.on("connectionAttemptFailed", console.log);
});

// TCP client
const clientSocket = net.connect({
  host: "localhost",
  port: 5000,
});

小結

event emitted on client socket emitted on server socket
lookup ✅ ❌
connectionAttempt ✅ ❌
connect ✅ ❌
connectionAttemptTimeout ✅ ❌
connectionAttemptFailed ✅ ❌

tcp-client-connect-state-machine


上一篇
Node.js net.Socket 教學：TCP 連線應用
系列文
Learn HTTP With JS（2） 共 9 篇
  1. 5
    stream.Readable 生命週期
  2. 6
    stream.Readable 錯誤處理與比較解析
  3. 7
    stream objectMode 與 pipe 實戰教學
  4. 8
    Node.js net.Socket 教學：TCP 連線應用
  5. 9
    Node.js TCP Client Socket 生命週期：lookup、connect 事件
完整目錄
圖片
  熱門推薦
圖片
{{ item.channelVendor }} | {{ item.webinarstarted }} |
{{ formatDate(item.duration) }}
直播中

尚未有邦友留言

立即登入留言
iThome鐵人賽
參賽組數
270 組
團體組數
10 組
累計文章數
2544 篇
最後報名日
9/15
iT+看影片追技術 看影片追技術 看更多
熱門tag
15th鐵人賽 16th鐵人賽 13th鐵人賽 14th鐵人賽 17th鐵人賽 12th鐵人賽 11th鐵人賽 鐵人賽 2019鐵人賽 javascript 2018鐵人賽 python 2017鐵人賽 18th鐵人賽 windows php c# linux windows server css
熱門問題
熱門回答
熱門文章
IT邦幫忙