feat: allow custom proxyReq

Author: ronag

README.md

@@ -94,6 +94,24 @@ server.on('request', (req, res) => {
 })
 ```
 
+#### Follow Redirects
+
+```javascript
+const http = require('follow-redirects').http
+
+server.on('request', (req, res) => {
+  proxy.web(req, res, {
+    hostname: 'localhost'
+    port: 9000,
+    onReq: (req, options) => http.request(options)
+  }, err => {
+    if (err) {
+      console.error('proxy error', err)
+    }
+  })
+})
+```
+
 #### web (req, res, options, [callback])
 
 - `req`: [`http.IncomingMessage`](https://nodejs.org/api/http.html#http_class_http_incomingmessage) or [`http2.Http2ServerRequest`](https://nodejs.org/api/http2.html#http2_class_http2_http2serverrequest)
@@ -124,7 +142,7 @@ See [`upgrade`](https://nodejs.org/api/http.html#http_event_upgrade)
   - `proxyTimeout`: Proxy [`http.request(options)`](https://nodejs.org/api/http.html#http_http_request_options_callback) timeout
   - `proxyName`: Proxy name used for **Via** header
   - `timeout`: [`http.IncomingMessage`](https://nodejs.org/api/http.html#http_class_http_incomingmessage) or [`http2.Http2ServerRequest`](https://nodejs.org/api/http2.html#http2_class_http2_http2serverrequest) timeout
-  - `onReq(req, options)`: Called before proxy request
+  - `onReq(req, options)`: Called before proxy request. If returning a truthy value it will be used as the request.
     - `req`: [`http.IncomingMessage`](https://nodejs.org/api/http.html#http_class_http_incomingmessage) or [`http2.Http2ServerRequest`](https://nodejs.org/api/http2.html#http2_class_http2_http2serverrequest)
     - `options`: Options passed to [`http.request(options)`](https://nodejs.org/api/http.html#http_http_request_options_callback)
   - `onRes(req, resOrSocket)`: Called before proxy response
@@ -198,7 +216,7 @@ See [`request`](https://nodejs.org/api/http.html#http_event_request)
   - `proxyTimeout`: Proxy [`http.request(options)`](https://nodejs.org/api/http.html#http_http_request_options_callback) timeout
   - `proxyName`: Proxy name used for **Via** header
   - `timeout`: [`http.IncomingMessage`](https://nodejs.org/api/http.html#http_class_http_incomingmessage) or [`http2.Http2ServerRequest`](https://nodejs.org/api/http2.html#http2_class_http2_http2serverrequest) timeout
-  - `onReq(req, options)`: Called before proxy request
+  - `onReq(req, options)`: Called before proxy request. If returning a truthy value it will be used as the request.
     - `req`: [`http.IncomingMessage`](https://nodejs.org/api/http.html#http_class_http_incomingmessage) or [`http2.Http2ServerRequest`](https://nodejs.org/api/http2.html#http2_class_http2_http2serverrequest)
     - `options`: Options passed to [`http.request(options)`](https://nodejs.org/api/http.html#http_http_request_options_callback)
   - `onRes(req, headers)`: Called before proxy response

index.js

@@ -135,11 +135,15 @@ function proxy (req, res, head, {
     timeout: proxyTimeout
   }
 
+  let proxyReq
+
   if (onReq) {
-    onReq(req, options)
+    proxyReq = onReq(req, options)
   }
 
-  const proxyReq = http.request(options)
+  if (!proxyReq) {
+    proxyReq = http.request(options)
+  }
 
   proxyReq[kReq] = req
   proxyReq[kRes] = res
@@ -165,9 +169,7 @@ function proxy (req, res, head, {
     .on('error', onFinish)
     .pipe(proxyReq)
     .on('error', onFinish)
-    // NOTE http.ClientRequest emits "socket hang up" error when aborted
-    // before having received a response, i.e. there is no need to listen for
-    // proxyReq.on('aborted', ...).
+    .on('aborted', onProxyAborted)
     .on('timeout', onProxyTimeout)
     .on('response', onProxyResponse)
     .on('upgrade', onProxyUpgrade)