---
layout: page
title: 位於 Proxy 背後的 Express
description: Learn how to configure Express.js applications to work correctly behind reverse proxies, including using the trust proxy setting to handle client IP addresses.
menu: guide
redirect_from: "  "
---

# 位於 Proxy 背後的 Express

When running an Express app behind a reverse proxy, some of the Express APIs may return different values than expected. In order to adjust for this, the `trust proxy` application setting may be used to expose information provided by the reverse proxy in the Express APIs. The most common issue is express APIs that expose the client's IP address may instead show an internal IP address of the reverse proxy.

<div class="doc-box doc-info" markdown="1">
When configuring the `trust proxy` setting, it is important to understand the exact setup of the reverse proxy. Since this setting will trust values provided in the request, it is important that the combination of the setting in Express matches how the reverse proxy operates.
</div>

The application setting `trust proxy` may be set to one of the values listed in the following table.

<table class="doctable" border="1" markdown="1">
  <thead><tr><th>類型</th><th>值</th></tr></thead>
  <tbody>
    <tr>
      <td>布林</td>
<td markdown="1">
若為 `true`，會將用戶端的 IP 位址視為 `X-Forwarded-*` 標頭中的最左側項目。

若為 `false`，會將應用程式視為直接面對網際網路，且用戶端的 IP 位址衍生自 `req.connection.remoteAddress`。這是預設值。 This is the default setting.

<div class="doc-box doc-warn" markdown="1">
When setting to `true`, it is important to ensure that the last reverse proxy trusted is removing/overwriting all of the following HTTP headers: `X-Forwarded-For`, `X-Forwarded-Host`, and `X-Forwarded-Proto`, otherwise it may be possible for the client to provide any value.
</div>
</td>
    </tr>
    <tr>
      <td>IP addresses</td>
<td markdown="1">
An IP address, subnet, or an array of IP addresses and subnets to trust as being a reverse proxy. The following list shows the pre-configured subnet names:

- loopback - `127.0.0.1/8`、`::1/128`
- linklocal - `169.254.0.0/16`、`fe80::/10`
- uniquelocal - `10.0.0.0/8`、`172.16.0.0/12`、`192.168.0.0/16`、`fc00::/7`

您可以採下列任何方式來設定 IP 位址：

```js
app.set('trust proxy', 'loopback') // specify a single subnet
app.set('trust proxy', 'loopback, 123.123.123.123') // specify a subnet and an address
app.set('trust proxy', 'loopback, linklocal, uniquelocal') // specify multiple subnets as CSV
app.set('trust proxy', ['loopback', 'linklocal', 'uniquelocal']) // specify multiple subnets as an array
```

When specified, the IP addresses or the subnets are excluded from the address determination process, and the untrusted IP address nearest to the application server is determined as the client's IP address. This works by checking if `req.socket.remoteAddress` is trusted. If so, then each address in `X-Forwarded-For` is checked from right to left until the first non-trusted address.

</td>
    </tr>
    <tr>
      <td>號碼</td>
<td markdown="1">
Use the address that is at most `n` number of hops away from the Express application. `req.socket.remoteAddress` is the first hop, and the rest are looked for in the `X-Forwarded-For` header from right to left. A value of `0` means that the first untrusted address would be `req.socket.remoteAddress`, i.e. there is no reverse proxy.

<div class="doc-box doc-warn" markdown="1">
When using this setting, it is important to ensure there are not multiple, different-length paths to the Express application such that the client can be less than the configured number of hops away, otherwise it may be possible for the client to provide any value.
</div>
</td>
    </tr>
    <tr>
      <td>Function</td>
<td markdown="1">
Custom trust implementation.

```js
app.set('trust proxy', (ip) => {
  if (ip === '127.0.0.1' || ip === '123.123.123.123') return true // trusted IPs
  else return false
})
```

</td>
    </tr>
  </tbody>
</table>

Enabling `trust proxy` will have the following impact:

<ul>
  <li markdown="1">[req.hostname](/{{ page.lang }}/api.html#req.hostname) 值會衍生自 `X-Forwarded-Host` 標頭中所設定的值，且該值可能由用戶端或 Proxy 所設定。
  </li>
  <li markdown="1">反向 Proxy 可能設定 `X-Forwarded-Proto`，以告知應用程式它是 `https` 或 `http` 或甚至是無效的名稱。[req.protocol](/{{ page.lang }}/api.html#req.protocol) 會反映此值。
   This value is reflected by [req.protocol](/{{ page.lang }}/api.html#req.protocol).
  </li>
  <li markdown="1">[req.ip](/{{ page.lang }}/api.html#req.ip) 和 [req.ips](/{{ page.lang }}/api.html#req.ips) 值中會移入 `X-Forwarded-For` 中的位址清單。
  </li>
</ul>

會使用 [proxy-addr](https://www.npmjs.com/package/proxy-addr) 套件來實作 `trust proxy` 設定。如需相關資訊，請參閱其說明文件。 For more information, see its documentation.
