Updated functionality and Readme

 * Updated Readme with full info
 * Updated grab-ngrok.js to use JSON.parse instead of Regex
 * Added better error catching for if Ngrok is not running properly
 * Added success message with new routing URL

README.md

@@ -1 +1,10 @@
 # gcp-proxy-func
+Very simple Google Cloud Function that proxies requests using Express and `http-proxy-middleware`. You define the address that requests should be proxied to by filling out config.js (copy `config.example.js` to `config.js`, and then change the URL).
+
+# Using
+Fill in `config.js`, and then either zip up the files and upload via Gcloud admin, or use [the Gcloud CLI](https://cloud.google.com/sdk/gcloud/) and `npm run deploy`. Or see below if using this to proxy to Ngrok.
+
+# Ngrok
+If you want to use this to have a stable Google Cloud Function address that proxies requests to a dynamic Ngrok address ([see this blog post for details](https://joshuatz.com/posts/2019/using-google-cloud-functions-permanent-url-to-proxy-ngrok-requests/)), you can automatically redeploy the function with the correct Ngrok public URL after it has changed, by using `npm run ngrok-deploy`.
+
+This command will grab the Ngrok public URL via the localhost API, update config.js by using `fs` to write to the file, and then redeploy your GCloud function to point to the updated URL.

grab-ngrok.js

@@ -2,27 +2,37 @@
 const fs = require('fs');
 const http = require('http');
 
+const ngrokErr = new Error('Could not parse Ngrok response. Is Ngrok running? Is port 4040 being blocked?');
+
 // Query ngrok local API
-http.get('http://127.0.0.1:4040/api/tunnels', (res) => {
+const req = http.get('http://127.0.0.1:4040/api/tunnels', (res) => {
 
 	let data = '';
 	res.on('data', (chunk) => {
-		console.log(chunk);
 		data += chunk;
 	});
 
 	res.on('end', () => {
 		// Extract public URL
-		const publicUrl = /public_url":\s*"(https[^"]+)/.exec(data)[1];
-
-		// Update config.js file
-		const configText = `
+		try {
+			const ngrokTunnelInfo = JSON.parse(data);
+			// Assume first tunnel
+			const publicUrl = ngrokTunnelInfo.tunnels[0].public_url;
+			// Update config.js file
+			const configText = `
 module.exports = {
 	destination: '${publicUrl}'
 }
 `;
-		fs.writeFileSync('./config.js', configText);
-		console.log('config updated!');
-		return true;
+				fs.writeFileSync('./config.js', configText);
+				console.log('config updated!');
+				return publicUrl;
+		} catch (e) {
+			throw ngrokErr;
+		}
 	});
-});
+});
+
+req.on('error', (err) => {
+	throw ngrokErr;
+})

package.json

@@ -6,7 +6,7 @@
 	"scripts": {
 		"test": "echo \"Error: no test specified\" && exit 1",
 		"ngrok-deploy": "node grab-ngrok.js && npm run deploy",
-		"deploy": "gcloud functions deploy proxy --runtime nodejs8 --trigger-http --memory=128 --timeout=60s"
+		"deploy": "gcloud functions deploy proxy --runtime nodejs8 --trigger-http --memory=128 --timeout=60s && node success-msg.js"
 	},
 	"keywords": [],
 	"author": "Joshua Tzucker",

success-msg.js

@@ -0,0 +1,3 @@
+// @ts-check
+const config = require('./config');
+console.log(`Success! GCloud config updated to route traffic to ${config.destination}`);