show commit hash along with version

lib/routes/root.js

@@ -2,10 +2,39 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+const exec = require('child_process').exec;
+const fs = require('fs');
+const path = require('path');
+const util = require('util');
+
 const version = require('../../package.json').version;
 
+var commitHash;
+
 module.exports = {
   handler: function index(req, reply) {
-    reply({ version: version });
+    function sendReply() {
+      reply({
+        version: version,
+        commit: commitHash,
+      }).spaces(2);
+    }
+
+    if (commitHash) {
+      return sendReply();
+    }
+
+     // figure it out from git (either '.git', or '/home/app/git' for AwsBox)
+    var gitDir;
+    if (!fs.existsSync(path.join(__dirname, '..', '..', '.git'))) {
+      // try at '/home/app/git' for AwsBox deploys
+      gitDir = path.sep + path.join('home', 'app', 'git');
+    }
+    var cmd = util.format('git %s rev-parse HEAD',
+        gitDir ? '--git-dir=' + gitDir : '');
+    exec(cmd, function(err, stdout) {
+      commitHash = stdout.replace(/\s+/, '');
+      return sendReply();
+    });
   }
 };