Allow setting proxyDomain to auto

Author: nikitaeverywhere

config.js

@@ -1,11 +1,10 @@
 const env = process.env.APP__ENV_NAME || "local";
 const isLocal = env === "local" || env === "test";
-const proxyDomain = process.env.PROXY_DOMAIN || "localhost";
 
 export default {
     isLocalEnv: isLocal,
     httpPort: process.env.PORT || 80,
-    proxyDomain: proxyDomain, // Your domain
+    proxyDomain: "",          // Domain to proxy calls through. Leave it empty to use the requested domain as a proxy domain
     proxy: {                  // Proxy configuration is here
         domains: [            // These domains are replaced in any proxied response (including scripts, URLs and redirects)
             "adservice.google.com",
@@ -48,7 +47,7 @@ export default {
             "www.googletagmanager.com": [
                 {
                     regex: /"https\:\/\/s","http:\/\/a","\.adroll\.com/,
-                    replace: `"https://${ proxyDomain }/s","http://${ proxyDomain }/a",".adroll.com`
+                    replace: ({ host }) => `"https://${ host }/s","http://${ host }/a",".adroll.com`
                 }
             ],
             "eb2.3lift.com": [

readme.md

@@ -60,6 +60,8 @@ Proxied: www.google-analytics.com/collect?v=1&_v=j73&a=531530768&t=pageview&_s=1
 
 Check the [test-static/index.html](test-static/index.html) file's code to see how to bind the proxied analytics to your front end.
 
+Later, you can containerize this repository and route the incoming traffic to `/gtm-proxy` path (for example) through this container in order to avoid analytics blocking.
+
 ## Configuration 
 
 You can configure which third-parties to proxy/replace and how to do it in the config file. Find the actual configuration in [config.js](config.js) file:

src/modules/proxy.js

@@ -15,13 +15,13 @@ const maskRegex = new RegExp(
     Array.from(maskPaths).join("|").replace(/\//g, "\\/"),
     "gi"
 );
-const replaceDomains = (match, pos, str) => {
+const replaceDomainsForHost = (host) => (match, pos, str) => {
     const escapedSlashes = str[pos - 2] === "\\" && str[pos - 2] === "/"
     const r = `${
         escapedSlashes
-            ? config.proxyDomain.replace(/\//g, "\\/") + "\\"
-            : config.proxyDomain
-    }/${ match }`
+            ? (config.proxyDomain || host).replace(/\//g, "\\/") + "\\"
+            : (config.proxyDomain || host)
+    }/${ match }`;
     return r;
 };
 
@@ -37,7 +37,7 @@ export function createDefaultProxy (targetDomain, proxyOptionsOverride = {}) {
                 ? proxyOptionsOverride["proxyReqOptDecorator"](proxyRequest, originalRequest)
                 : proxyRequest;
         },
-        userResHeaderDecorator: (headers) => {
+        userResHeaderDecorator: (headers, { headers: { host } }) => {
             if (headers.location) {
                 if (config.proxy.specialContentReplace[servername]) { // Keep before other replacements
                     const replacements = config.proxy.specialContentReplace[servername];
@@ -46,20 +46,20 @@ export function createDefaultProxy (targetDomain, proxyOptionsOverride = {}) {
                     }
                 }
                 headers.location = headers.location
-                    .replace(replaceDomainRegex, replaceDomains)
+                    .replace(replaceDomainRegex, replaceDomainsForHost(host))
                     .replace(maskRegex, match => mask(match));
             }
             return headers;
         },
-        userResDecorator: (_, proxyResData) => {
+        userResDecorator: (_, proxyResData, { headers: { host } }) => {
             if (_.req.res && _.req.res.client && _.req.res.client.servername) {
                 servername = _.req.res.client.servername;
             }
-            let pre = proxyResData.toString().replace(replaceDomainRegex, replaceDomains);
+            let pre = proxyResData.toString().replace(replaceDomainRegex, replaceDomainsForHost(host));
             if (config.proxy.specialContentReplace[servername]) {
                 const replacements = config.proxy.specialContentReplace[servername];
                 for (const r of replacements) {
-                    pre = pre.replace(r.regex, r.replace);
+                    pre = pre.replace(r.regex, r.replace instanceof Function ? r.replace({ host }) : r.replace);
                 }
             }
             pre = pre.replace(maskRegex, (match) => { // Mask configured URLs