main.js

// cast-aws-proxy
// main.js
// julian lepinski 2015-2017

if (!process.env.PORT){
   try {
      var localConfig = require("./.local-config.json");
      for (var i in localConfig) process.env[i] = localConfig[i];
   } catch (e) {
      console.log("[error] no process.env.PORT or .local-config.json found; if you're running locally this app needs some config vars");
      process.exit(1);
   }
}

console.log("");
console.log("[init] cast-aws-proxy starting up...");

var http            = require("http");
var express         = require("express");
var request         = require("request");

var app             = express();
var targetURI       = process.env.ORIGIN_URI;
var forceOverwite   = process.env.OVERWRITE_EXISTING ? true : false;
var forcedHeaders   = require("./forced-headers.json");
var verboseLogging  = process.env.VERBOSE_LOGS ? true : false;
var remoteHeaders   = process.env.REMOTE_FORCED_HEADERS ? true : false;

if (!targetURI) {
   console.log("[error] no ORIGIN_URI present");
   process.exit(1);
}

if (remoteHeaders && process.env.REMOTE_FORCED_HEADERS.trim() !== "") {
   var remoteHeaderURL = process.env.REMOTE_FORCED_HEADERS;
   console.log("[config] loading remote headers from " + remoteHeaderURL);
   request(remoteHeaderURL, function (error, response, body) {
      if (error) {
         console.log("[error] there was a problem getting remote headers: " + error);
         process.exit(1);
      } else if (response && response.statusCode === 200) {
         try {
            forcedHeaders = JSON.parse(body);
            console.log("[config] remote headers loaded");
            completeAsyncStartup();
         } catch (e) {
            console.log("[error] there was a problem parsing the remote headers: " + e);
            process.exit(1);
         }
      } else {
         console.log("[error] there was an unspecified problem getting the remote headers");
         process.exit(1);
      }
   });
} else {
   completeAsyncStartup();
}

app.get("*", function (req, res) {
   verboseLog("[" + req.url + "] proxying request to " + targetURI + req.url);
   request(targetURI + req.url).pipe(res);

   res.oldWriteHead = res.writeHead;
   res.writeHead = function(statusCode, reasonPhrase, headers) {
      for (headerKey in forcedHeaders) {
         if (!res.get(headerKey) || forceOverwite) { 
            res.header(headerKey, forcedHeaders[headerKey]);
            verboseLog("[" + req.url + "] setting '" + headerKey + "' to '" + forcedHeaders[headerKey] + "'");
         } else {
            verboseLog("[" + req.url + "] not setting '" + headerKey + "', it exists and forceOverwrite=false");
         }
      }
      res.oldWriteHead(statusCode, reasonPhrase, headers);
   }
});

function verboseLog (log) {
   if (!verboseLogging) return;
   console.log(log);
}

function completeAsyncStartup() {
   console.log("[config] forced headers: " + JSON.stringify(forcedHeaders));
   console.log("[config] overwrite existing headers: " + forceOverwite);
   console.log("[config] verbose logging: " + verboseLogging);
   console.log("[init] proxying requests at port " + process.env.PORT + " to " + targetURI);
   app.listen(process.env.PORT);
}