Created a first draft of this action. (#14)

Reviewed-on: #14
Co-authored-by: Philipp Horstenkamp <philipp@horstenkamp.de>
Co-committed-by: Philipp Horstenkamp <philipp@horstenkamp.de>

node_modules/undici/docs/best-practices/proxy.md

@@ -0,0 +1,127 @@
+# Connecting through a proxy
+
+Connecting through a proxy is possible by:
+
+- Using [AgentProxy](../api/ProxyAgent.md).
+- Configuring `Client` or `Pool` constructor.
+
+The proxy url should be passed to the `Client` or `Pool` constructor, while the upstream server url
+should be added to every request call in the `path`.
+For instance, if you need to send a request to the `/hello` route of your upstream server,
+the `path` should be `path: 'http://upstream.server:port/hello?foo=bar'`.
+
+If you proxy requires basic authentication, you can send it via the `proxy-authorization` header.
+
+### Connect without authentication
+
+```js
+import { Client } from 'undici'
+import { createServer } from 'http'
+import proxy from 'proxy'
+
+const server = await buildServer()
+const proxyServer = await buildProxy()
+
+const serverUrl = `http://localhost:${server.address().port}`
+const proxyUrl = `http://localhost:${proxyServer.address().port}`
+
+server.on('request', (req, res) => {
+  console.log(req.url) // '/hello?foo=bar'
+  res.setHeader('content-type', 'application/json')
+  res.end(JSON.stringify({ hello: 'world' }))
+})
+
+const client = new Client(proxyUrl)
+
+const response = await client.request({
+  method: 'GET',
+  path: serverUrl + '/hello?foo=bar'
+})
+
+response.body.setEncoding('utf8')
+let data = ''
+for await (const chunk of response.body) {
+  data += chunk
+}
+console.log(response.statusCode) // 200
+console.log(JSON.parse(data)) // { hello: 'world' }
+
+server.close()
+proxyServer.close()
+client.close()
+
+function buildServer () {
+  return new Promise((resolve, reject) => {
+    const server = createServer()
+    server.listen(0, () => resolve(server))
+  })
+}
+
+function buildProxy () {
+  return new Promise((resolve, reject) => {
+    const server = proxy(createServer())
+    server.listen(0, () => resolve(server))
+  })
+}
+```
+
+### Connect with authentication
+
+```js
+import { Client } from 'undici'
+import { createServer } from 'http'
+import proxy from 'proxy'
+
+const server = await buildServer()
+const proxyServer = await buildProxy()
+
+const serverUrl = `http://localhost:${server.address().port}`
+const proxyUrl = `http://localhost:${proxyServer.address().port}`
+
+proxyServer.authenticate = function (req, fn) {
+  fn(null, req.headers['proxy-authorization'] === `Basic ${Buffer.from('user:pass').toString('base64')}`)
+}
+
+server.on('request', (req, res) => {
+  console.log(req.url) // '/hello?foo=bar'
+  res.setHeader('content-type', 'application/json')
+  res.end(JSON.stringify({ hello: 'world' }))
+})
+
+const client = new Client(proxyUrl)
+
+const response = await client.request({
+  method: 'GET',
+  path: serverUrl + '/hello?foo=bar',
+  headers: {
+    'proxy-authorization': `Basic ${Buffer.from('user:pass').toString('base64')}`
+  }
+})
+
+response.body.setEncoding('utf8')
+let data = ''
+for await (const chunk of response.body) {
+  data += chunk
+}
+console.log(response.statusCode) // 200
+console.log(JSON.parse(data)) // { hello: 'world' }
+
+server.close()
+proxyServer.close()
+client.close()
+
+function buildServer () {
+  return new Promise((resolve, reject) => {
+    const server = createServer()
+    server.listen(0, () => resolve(server))
+  })
+}
+
+function buildProxy () {
+  return new Promise((resolve, reject) => {
+    const server = proxy(createServer())
+    server.listen(0, () => resolve(server))
+  })
+}
+```
+