allow to set the server port via environment variable PORT

Author: striezel

changelog.md

@@ -11,6 +11,13 @@ application, major version changes in Plotly.js will also trigger a major
 version change in this application.
 
 
+## Version 1.5.0-pre1 (2021-08-01)
+
+* __[new feature]__
+The port to which the server binds can now be changed by setting the environment
+variable `PORT`. If `PORT` is not set or is not a valid port number, then the
+default port 3000 is used.
+
 ## Version 1.4.2 (2021-08-01)
 
 * __[maintenance]__

export-server/package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "plotly-node-export-server",
-  "version": "1.4.2",
+  "version": "1.5.0-pre1",
   "description": "Plotly.js Node.js export server",
   "repository": {
     "url": "https://gitlab.com/striezel/plotly-node-export-server.git",

export-server/package.json

@@ -27,7 +27,19 @@ const url = require('url');
 const uuidv4 = require('uuid/v4');
 
 const hostname = 'localhost';
-const port = 3000;
+// Use port from environment variable PORT, if it is set and valid.
+const parsedPort = parseInt(process.env.PORT);
+if (process.env.PORT) {
+  if (isNaN(parsedPort)) {
+   console.log('Warning: PORT environment variable is not a number, using port 3000!');
+  } else if (parsedPort <= 0 || parsedPort > 65535) {
+   console.log('Warning: PORT environment variable is not a number between 1 and 65535, using port 3000!');
+  } else if (parsedPort < 1024) {
+   // Unless user is root or admin, binding to well-known ports is usually denied by the OS.
+   console.log('Warning: Binding to ports below 1024 may require root / administrative privileges!');
+  }
+}
+const port = (parsedPort && parsedPort > 0 && parsedPort < 65536) ? parsedPort : 3000;
 
 // ** Preparation, step 1: **
 // Find the PhantomJS executable. It is usually located in the node_modules

export-server/server.js

@@ -51,6 +51,24 @@ You can simply start the application via
 which fires up the Node.js application. The server will then listen on
 <http://localhost:3000/> for incoming connections.
 
+If you want the server to listen on a different port, then you can set the
+environment variable `PORT` accordingly. On Linux-like systems you can do
+
+``` bash
+export PORT=4000
+npm start
+```
+
+The equivalent on Windows command prompt would be
+
+``` cmd
+SET PORT=4000
+npm start
+```
+
+In these cases the server will bind to port 4000 instead of the default port
+3000.
+
 ## Usage
 
 To generate a PNG file of a Plotly plot, just send an HTTP POST request to the