https support for proxy relay

Fix for issue #563

Author: arenevier

src/chain.ts

@@ -1,4 +1,5 @@
 import http from 'http';
+import https from 'https';
 import dns from 'dns';
 import { URL } from 'url';
 import { EventEmitter } from 'events';
@@ -80,7 +81,8 @@ export const chain = (
         options.headers.push('proxy-authorization', getBasicAuthorizationHeader(proxy));
     }
 
-    const client = http.request(proxy.origin, options as unknown as http.ClientRequestArgs);
+    const fn = proxy.protocol === 'https:' ? https.request : http.request;
+    const client = fn(proxy.origin, options as unknown as http.ClientRequestArgs);
 
     client.on('connect', (response, targetSocket, clientHead) => {
         countTargetBytes(sourceSocket, targetSocket);

src/server.ts

@@ -453,9 +453,9 @@ export class Server extends EventEmitter {
                 throw new Error(`Invalid "upstreamProxyUrl" provided: ${error} (was "${funcResult.upstreamProxyUrl}"`);
             }
 
-            if (!['http:', ...SOCKS_PROTOCOLS].includes(handlerOpts.upstreamProxyUrlParsed.protocol)) {
+            if (!['http:', 'https:', ...SOCKS_PROTOCOLS].includes(handlerOpts.upstreamProxyUrlParsed.protocol)) {
                 // eslint-disable-next-line max-len
-                throw new Error(`Invalid "upstreamProxyUrl" provided: URL must have one of the following protocols: "http", ${SOCKS_PROTOCOLS.map((p) => `"${p.replace(':', '')}"`).join(', ')} (was "${funcResult.upstreamProxyUrl}")`);
+                throw new Error(`Invalid "upstreamProxyUrl" provided: URL must have one of the following protocols: "http", "https", ${SOCKS_PROTOCOLS.map((p) => `"${p.replace(':', '')}"`).join(', ')} (was "${funcResult.upstreamProxyUrl}")`);
             }
         }