Added a basic input validation for shortUrl

src/main/java/tk/draganczuk/url/Routes.java

@@ -1,5 +1,6 @@
 package tk.draganczuk.url;
 
+import org.eclipse.jetty.http.HttpStatus;
 import spark.Request;
 import spark.Response;
 
@@ -29,15 +30,21 @@ public class Routes {
 			shortUrl = Utils.randomString();
 		}
 
-		return urlFile.addUrl(longUrl, shortUrl);
+		if (Utils.validate(shortUrl)) {
+			return urlFile.addUrl(longUrl, shortUrl);
+		} else {
+			res.status(HttpStatus.BAD_REQUEST_400);
+			return "shortUrl not valid ([a-z0-9]+)";
+		}
 	}
 
-	public static String goToLongUrl(Request req, Response res){
+
+	public static String goToLongUrl(Request req, Response res) {
 		String shortUrl = req.params("shortUrl");
 		var longUrlOpt = urlFile
-			.findForShortUrl(shortUrl);
+				.findForShortUrl(shortUrl);
 
-		if(longUrlOpt.isEmpty()){
+		if (longUrlOpt.isEmpty()) {
 			res.status(404);
 			return "";
 		}

src/main/java/tk/draganczuk/url/Utils.java

@@ -1,10 +1,14 @@
 package tk.draganczuk.url;
 
 import java.util.Random;
+import java.util.regex.Pattern;
 
 public class Utils {
 	private static final Random random = new Random(System.currentTimeMillis());
 
+	private static final String SHORT_URL_PATTERN = "[a-z0-9]+";
+	private static final Pattern PATTERN = Pattern.compile(SHORT_URL_PATTERN);
+
 	public static String randomString() {
 		int leftLimit = 48; // numeral '0'
 		int rightLimit = 122; // letter 'z'
@@ -18,4 +22,9 @@ public class Utils {
 						StringBuilder::append)
 				.toString();
 	}
+
+	public static boolean validate(String shortUrl) {
+		return PATTERN.matcher(shortUrl)
+				.matches();
+	}
 }