Replaced the creation of one new folder in tmpDir for each manifest to the creation in tmpDir of one manifest with unique generated uuid

Added some comments;
Renamed some parameters

index.js

@@ -1,11 +1,11 @@
-const express = require("express");
+const os = require("os");
+const fs = require("fs");
+const path = require("path");
 const crypto = require("crypto");
 const { spawn } = require("child_process");
-const os = require("os");
-const path = require("path");
 const archiver = require("archiver");
+const express = require("express");
 const async = require("async");
-const fs = require("fs");
 
 const _configuration = Object.freeze(require("./config.json"));
 
@@ -23,9 +23,7 @@ const Certificates = _configuration.certificates;
 */
 
 function removeDotFiles(from) {
-	return from.filter(e => {
-		return e.charAt(0) !== "."
-	});
+	return from.filter(e => e.charAt(0) !== ".");
 }
 
 function capitalizeFirst(str) {
@@ -51,6 +49,13 @@ function checkSignatureRequirements() {
 	return Promise.all([checkCertificate, checkKey]);
 }
 
+/**
+	Generates a unique UUID
+	From Github Gist: https://gist.github.com/jed/982883
+*/
+
+function UUIDGen(a){return a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,UUIDGen)}
+
 /**
 	Generates the cryptografic signature for the manifest file.
 	Spawns Openssl process since Node.js has no support for PKCSs.
@@ -60,7 +65,7 @@ function checkSignatureRequirements() {
 	@returns {Object} Promise
 */
 
-function generateManifestSignature(manifestPath) {
+function generateManifestSignature(manifestUUID) {
 	return new Promise(function(done, rejected) {
 		checkSignatureRequirements()
 		.then(function() {
@@ -74,7 +79,7 @@ function generateManifestSignature(manifestPath) {
 				"-certfile", path.resolve(Certificates.dir, Certificates.files["wwdr_pem"]),
 				"-signer", path.resolve(Certificates.dir, Certificates.files["certificate"]),
 				"-inkey", path.resolve(Certificates.dir, Certificates.files["key"]),
-				"-in", path.resolve(`${manifestPath}/manifest.json`),
+				"-in", path.resolve(`${os.tmpdir()}/manifest-${manifestUUID}.json`),
 //				"-out", path.resolve("passCreator", "event.pass", "./signature"),
 				"-outform", "DER",
 				"-passin", `pass:${Certificates.credentials["dev_pem_key"]}`
@@ -103,18 +108,28 @@ function generateManifestSignature(manifestPath) {
 	});
 }
 
-function generateManifest(fromObject, tempFolderPath) {
+/**
+	Generates a Buffer of JSON file (manifest)
+	@function generateManifest
+	@params {Object} fromObject - Manifest content
+	@params {String} manifestUUID
+	@return {Promise} - Promise with the manifest buffer
+	@see https://apple.co/2IhJr0Q (PassKit Package Structure)
+	@see https://apple.co/2K2aY3v (Passes Are Cryptographically Signed and Compressed)
+*/
+
+function generateManifest(fromObject, manifestUUID) {
 	return new Promise(function(done, failed) {
 		if (!fromObject || typeof fromObject !== "object" && typeof fromObject !== "string") {
 			return failed("generateManifest: Argument 0 is required and must be of an object or a string (source object)");
 		}
 
-		if (!tempFolderPath || typeof tempFolderPath !== "string") {
-			return failed("generateManifest: Argument 1 is required and must be a string (temporary folder path for manifest)");
+		if (!manifestUUID || typeof manifestUUID !== "string") {
+			return failed("generateManifest: Argument 1 is required and must be a string (unique uuid).");
 		}
 
 		const source = typeof fromObject === "object" ? JSON.stringify(fromObject) : fromObject;
-		let manifestWS = fs.createWriteStream(`${tempFolderPath}/manifest.json`);
+		let manifestWS = fs.createWriteStream(`${os.tmpdir()}/manifest-${manifestUUID}.json`);
 
 		manifestWS.write(source);
 		manifestWS.end();
@@ -164,18 +179,6 @@ instance.get("/gen/:type/", function (req, res) {
 			return;
 		}
 
-		/*
-		 * Creating a temporary directory to keep the manifest.json of each pass.
-		 * This is done to pass the file as openssl parameter.
-		 * It would be better to pass openssl a buffer but sadly it seems not possible.
-		 * Feel free to contribute if you think there's a better way to achieve this.
-		*/
-
-		fs.mkdtemp(path.join(os.tmpdir(), "passkitWebServer-"), function(err, tempFolder) {
-			if (err) {
-				throw err;
-			}
-
 		// Manifest dictionary
 		let manifestRaw = {};
 		let archive = archiver("zip");
@@ -209,12 +212,14 @@ instance.get("/gen/:type/", function (req, res) {
 				throw new Error(`Unable to compile manifest. ${error}`);
 			}
 
-				generateManifest(manifestRaw, tempFolder)
+			let uuid = UUIDGen();
+
+			generateManifest(manifestRaw, uuid)
 			.then(function(manifestBuffer) {
 
 				archive.append(manifestBuffer, { name: "manifest.json" });
 
-					generateManifestSignature(tempFolder)
+				generateManifestSignature(uuid)
 				.then(function(signatureBuffer) {
 
 					if (!fs.existsSync("output")) {
@@ -246,5 +251,4 @@ instance.get("/gen/:type/", function (req, res) {
 			});
 		});
 	});
-	});
 });