Added file list backend

.vscode/launch.json

+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "pwa-chrome",
+            "request": "launch",
+            "name": "Launch Chrome against localhost",
+            "url": "http://localhost:8080",
+            "webRoot": "${workspaceFolder}"
+        }
+    ]
+}
\ No newline at end of file

backend/list_files.php

+<?php
+
+header("Access-Control-Allow-Origin: *");
+header('Access-Control-Allow-Credentials: true');
+header("Access-Control-Allow-Methods: PUT, GET, POST, DELETE");
+header("Access-Control-Allow-Headers: Origin, X-Requested-With, Content-Type, Accept");
+header("Content-Type: application/json; charset=UTF-8");
+
+
+$postData = file_get_contents("php://input");
+$postData = json_decode($postData, true);
+
+$uname = $postData['username'];
+
+$dir = "../users/" . $uname;
+$contents = scandir($dir);
+$f_list = array();
+
+foreach ($contents as $fname)
+{
+    $ext = pathinfo($fname, PATHINFO_EXTENSION);
+    
+    if((strcmp($ext, "java") == 0) || (strcmp($ext, "cpp") == 0) || (strcmp($ext, "py") == 0))
+    {
+        array_push($f_list, $fname);
+    }
+}
+
+echo json_encode($f_list);
+?>
\ No newline at end of file