Bypass proxy on loopback IPs (localhost, 127.*, ::1 etc) (#1361)

* Bypass proxy on loopback IPs

* Expect empty array instead of undefined

* Restore accidentally deleted test

* Fix formatting

* Fix linting

* Update proxy.ts

* Better ipv6 definitions

* Fix linting

* Update proxy.test.ts

packages/http-client/__tests__/proxy.test.ts

@@ -242,6 +242,31 @@ describe('proxy', () => {
     expect(_proxyConnects).toHaveLength(0)
   })
 
+  it('HttpClient bypasses proxy for loopback addresses (localhost, ::1, 127.*)', async () => {
+    // setup a server listening on localhost:8091
+    const server = http.createServer((request, response) => {
+      response.writeHead(200)
+      request.pipe(response)
+    })
+    server.listen(8091)
+    try {
+      process.env['http_proxy'] = _proxyUrl
+      const httpClient = new httpm.HttpClient()
+      let res = await httpClient.get('http://localhost:8091')
+      expect(res.message.statusCode).toBe(200)
+      res = await httpClient.get('http://127.0.0.1:8091')
+      expect(res.message.statusCode).toBe(200)
+
+      // no support for ipv6 for now
+      expect(httpClient.get('http://[::1]:8091')).rejects.toThrow()
+
+      // proxy at _proxyUrl was ignored
+      expect(_proxyConnects).toEqual([])
+    } finally {
+      server.close()
+    }
+  })
+
   it('proxyAuth not set in tunnel agent when authentication is not provided', async () => {
     process.env['https_proxy'] = 'http://127.0.0.1:8080'
     const httpClient = new httpm.HttpClient()

packages/http-client/src/proxy.ts

@@ -25,6 +25,11 @@ export function checkBypass(reqUrl: URL): boolean {
     return false
   }
 
+  const reqHost = reqUrl.hostname
+  if (isLoopbackAddress(reqHost)) {
+    return true
+  }
+
   const noProxy = process.env['no_proxy'] || process.env['NO_PROXY'] || ''
   if (!noProxy) {
     return false
@@ -67,3 +72,13 @@ export function checkBypass(reqUrl: URL): boolean {
 
   return false
 }
+
+function isLoopbackAddress(host: string): boolean {
+  const hostLower = host.toLowerCase()
+  return (
+    hostLower === 'localhost' ||
+    hostLower.startsWith('127.') ||
+    hostLower.startsWith('[::1]') ||
+    hostLower.startsWith('[0:0:0:0:0:0:0:1]')
+  )
+}