C:/Users/Atul/AppData/Local/GitHub/PortableGit_015aa71ef18c047ce8509ffb2f9e4bb0e3e73f13/shot is a POST endpoint instead of GET.

htmlshot/app.js

@@ -1,6 +1,7 @@
 var spawn = require('child_process').spawn;
 var fs = require('fs');
 var express = require('express');
+var bodyParser = require('body-parser');
 
 var app = express();
 
@@ -12,10 +13,14 @@ app.get('/', function(req, res, next) {
   fs.createReadStream(__dirname + '/index.html').pipe(res);
 });
 
-app.get('/shot', function(req, res, next) {
-  var html = (req.query.html || '').trim();
+app.post('/shot', bodyParser.urlencoded({
+  extended: false
+}), function(req, res, next) {
+  var html = (req.body.html || '').trim();
   if (!html) return res.sendStatus(204);
   res.type('image/png');
+  res.set('Content-Disposition',
+          'attachment; filename="awesome-thing.png"');
   spawn(process.execPath, [RENDER, html]).stdout.pipe(res);
 });
 

htmlshot/index.html

@@ -4,7 +4,7 @@
 <h1>HTMLShot</h1>
 <p>Paste some HTML in the text field below and we'll give you a
   handy screenshot.</p>
-<form method="GET" action="shot">
+<form method="POST" action="shot">
   <textarea name="html" rows="25" cols="80" placeholder="Paste HTML here"></textarea>
   <br>
   <button type="Submit">Submit</button>

htmlshot/package.json

@@ -3,7 +3,8 @@
   "version": "0.0.1",
   "description": "",
   "dependencies": {
-    "express": "4.10.7"
+    "express": "4.10.7",
+    "body-parser": "^1.10.1"
   },
   "devDependencies": {},
   "scripts": {