Xeger can cause stackoverflow and doesn't understand \d \w \s

fixes gh-589, fixes gh-590

spring-cloud-contract-spec/src/main/groovy/repackaged/nl/flotsam/xeger/Xeger.java

@@ -31,11 +31,16 @@ import dk.brics.automaton.Transition;
 /**
  * An object that will generate text from a regular expression. In a way, it's the opposite of a regular expression
  * matcher: an instance of this class will produce text that is guaranteed to match the regular expression passed in.
+ *
+ * slight modifications by Marcin Grzejszczak
  */
 public class Xeger {
 
 	private final Automaton automaton;
 	private Random random;
+	// Added by Marcin Grzejszczak
+	// may lead to stackoverflow when regex is unbounded
+	static int ITERATION_LIMIT = 200;
 
 	/**
 	 * Constructs a new instance, accepting the regular expression and the randomizer.
@@ -47,7 +52,12 @@ public class Xeger {
 	public Xeger(String regex, Random random) {
 		assert regex != null;
 		assert random != null;
-		this.automaton = new RegExp(regex).toAutomaton();
+		// https://stackoverflow.com/questions/1578789/how-do-i-generate-text-matching-a-regular-expression-from-a-regular-expression
+		String pattern = regex
+				.replace("\\d", "[0-9]")        // Used d=Digit
+				.replace("\\w", "[A-Za-z0-9_]") // Used =Word
+				.replace("\\s", "[ \t\r\n]");   // Used s="White"Space
+		this.automaton = new RegExp(pattern).toAutomaton();
 		this.random = random;
 	}
 
@@ -67,11 +77,15 @@ public class Xeger {
 	 */
 	public String generate() {
 		StringBuilder builder = new StringBuilder();
-		generate(builder, this.automaton.getInitialState());
+		int counter = 0;
+		generate(builder, this.automaton.getInitialState(), counter);
 		return builder.toString();
 	}
 
-	private void generate(StringBuilder builder, State state) {
+	private void generate(StringBuilder builder, State state, int counter) {
+		if (counter >= ITERATION_LIMIT) {
+			return;
+		}
 		List<Transition> transitions = state.getSortedTransitions(false);
 		if (transitions.size() == 0) {
 			assert state.isAccept();
@@ -85,7 +99,7 @@ public class Xeger {
 		// Moving on to next transition
 		Transition transition = transitions.get(option - (state.isAccept() ? 1 : 0));
 		appendChoice(builder, transition);
-		generate(builder, transition.getDest());
+		generate(builder, transition.getDest(), ++counter);
 	}
 
 	private void appendChoice(StringBuilder builder, Transition transition) {

spring-cloud-contract-spec/src/test/groovy/repackaged/nl/flotsam/xeger/XegerTest.java

@@ -17,12 +17,12 @@
  */
 package repackaged.nl.flotsam.xeger;
 
-import org.junit.Test;
-
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
 
+import org.junit.Test;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
@@ -38,6 +38,47 @@ public class XegerTest {
 		}
 	}
 
+	@Test
+	public void shouldNotGenerateMoreThanTheLimit() {
+		String regex = "[ab]{5}";
+		Xeger.ITERATION_LIMIT = 1;
+		Xeger generator = new Xeger(regex);
+		for (int i = 0; i < 100; i++) {
+			String text = generator.generate();
+			assertTrue(text.length() == 1);
+		}
+	}
+
+	@Test
+	public void shouldGenerateTextCorrectlyForDigitSign() {
+		String regex = "\\d+";
+		Xeger generator = new Xeger(regex);
+		for (int i = 0; i < 100; i++) {
+			String text = generator.generate();
+			assertTrue(text.matches(regex));
+		}
+	}
+
+	@Test
+	public void shouldGenerateTextCorrectlyForWordSign() {
+		String regex = "\\w+";
+		Xeger generator = new Xeger(regex);
+		for (int i = 0; i < 100; i++) {
+			String text = generator.generate();
+			assertTrue(text.matches(regex));
+		}
+	}
+
+	@Test
+	public void shouldGenerateTextCorrectlyForWhiteSpaceSign() {
+		String regex = "\\s+";
+		Xeger generator = new Xeger(regex);
+		for (int i = 0; i < 100; i++) {
+			String text = generator.generate();
+			assertTrue(text.matches(regex));
+		}
+	}
+
 	@Test
 	public void testRepeatableRegex() {
 		for (int x = 0; x < 1000; x++) {