add keepAlive option to toggle Keep Alive

Author: felicienfrancois

README.md

@@ -114,6 +114,7 @@ __Arguments__
   * port - The port or named socket to listen on (default: 8080).
   * sslCaDir - Path to the certificates cache directory (default: process.cwd() + '/.http-mitm-proxy')
   * silent - if set to true, nothing will be written to console (default: false)
+  * keepAlive - enable [HTTP persistent connection](https://en.wikipedia.org/wiki/HTTP_persistent_connection)
   * timeout - The number of milliseconds of inactivity before a socket is presumed to have timed out. Defaults to no timeout.
   * httpAgent - The [http.Agent](https://nodejs.org/api/http.html#http_class_http_agent) to use when making http requests. Useful for chaining proxys. (default: internal Agent)
   * httpsAgent - The [https.Agent](https://nodejs.org/api/https.html#https_class_https_agent) to use when making https requests. Useful for chaining proxys. (default: internal Agent)

lib/proxy.js

@@ -48,8 +48,9 @@ Proxy.prototype.listen = function(options, callback) {
   this.silent = !!options.silent;
   this.httpPort = options.port || 8080;
   this.timeout = options.timeout || 0;
-  this.httpAgent = options.httpAgent || new http.Agent({ keepAlive: true });
-  this.httpsAgent = options.httpsAgent || new https.Agent({ keepAlive: true });
+  this.keepAlive = !!options.keepAlive;
+  this.httpAgent = options.httpAgent || new http.Agent({ keepAlive: this.keepAlive });
+  this.httpsAgent = options.httpsAgent || new https.Agent({ keepAlive: this.keepAlive });
   this.forceSNI = !!options.forceSNI;
   if (this.forceSNI && !this.silent) {
     console.log('SNI enabled. Clients not supporting SNI may fail');
@@ -703,9 +704,13 @@ Proxy.prototype._onHttpServerRequest = function(isSSL, clientToProxyRequest, pro
       }
       ctx.serverToProxyResponse.headers['transfer-encoding'] = 'chunked';
       delete ctx.serverToProxyResponse.headers['content-length'];
-      if (!ctx.serverToProxyResponse.headers['connection']) {
-        var keepAlive = ctx.clientToProxyRequest.headers && ctx.clientToProxyRequest.headers['connection'] && ctx.clientToProxyRequest.headers['connection'].trim().toLowerCase() === 'keep-alive';
-        ctx.serverToProxyResponse.headers['connection'] = keepAlive ? 'keep-alive' : 'close';
+      if (self.keepAlive) {
+        if (!ctx.serverToProxyResponse.headers['connection']) {
+          var keepAlive = ctx.clientToProxyRequest.headers && ctx.clientToProxyRequest.headers['connection'] && ctx.clientToProxyRequest.headers['connection'].trim().toLowerCase() === 'keep-alive';
+          ctx.serverToProxyResponse.headers['connection'] = keepAlive ? 'keep-alive' : 'close';
+        }
+      } else {
+        ctx.serverToProxyResponse.headers['connection'] = 'close';
       }
       return self._onResponseHeaders(ctx, function (err) {
         if (err) {