Restrict forwards in MockMvcWebConnection to 100

This change restricts the maximum number of forwards in MockMvcWebConnection to 100,
in case a forward is configured in a way that causes a loop. This is necessary in HtmlUnit
backed tests, unlike in classic MockMvc tests in which the forwards are not actually resolved.

See gh-29557
Closes gh-29866

Co-authored-by: Simon Baslé <sbasle@vmware.com>

spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/MockMvcWebConnection.java

@@ -68,6 +68,8 @@ public final class MockMvcWebConnection implements WebConnection {
 
 	private WebClient webClient;
 
+	private static int MAX_FORWARDS = 100;
+
 
 	/**
 	 * Create a new instance that assumes the context path of the application
@@ -133,10 +135,15 @@ public final class MockMvcWebConnection implements WebConnection {
 
 		MockHttpServletResponse httpServletResponse = getResponse(requestBuilder);
 		String forwardedUrl = httpServletResponse.getForwardedUrl();
-		while (forwardedUrl != null) {
+		int forwards = 0;
+		while (forwardedUrl != null && forwards < MAX_FORWARDS) {
 			requestBuilder.setForwardPostProcessor(new ForwardRequestPostProcessor(forwardedUrl));
 			httpServletResponse = getResponse(requestBuilder);
 			forwardedUrl = httpServletResponse.getForwardedUrl();
+			forwards += 1;
+		}
+		if (forwards == MAX_FORWARDS) {
+			throw new IllegalStateException("Forwarded more than " + forwards + " times in a row, potential infinite forward loop");
 		}
 		storeCookies(webRequest, httpServletResponse.getCookies());
 

spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/ForwardController.java

@@ -31,4 +31,9 @@ public class ForwardController {
 		return "forward:/a";
 	}
 
+	@RequestMapping("/infiniteForward")
+	public String infiniteForward() {
+		return "forward:/infiniteForward";
+	}
+
 }

spring-test/src/test/java/org/springframework/test/web/servlet/htmlunit/MockMvcWebConnectionTests.java

@@ -29,6 +29,7 @@ import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 
 /**
@@ -80,6 +81,13 @@ public class MockMvcWebConnectionTests {
 		assertThat(page.getWebResponse().getContentAsString()).isEqualTo("hello");
 	}
 
+	@Test
+	public void infiniteForward() {
+		this.webClient.setWebConnection(new MockMvcWebConnection(this.mockMvc, this.webClient, ""));
+		assertThatIllegalStateException().isThrownBy(() -> this.webClient.getPage("http://localhost/infiniteForward"))
+						.withMessage("Forwarded more than 100 times in a row, potential infinite forward loop");
+	}
+
 	@Test
 	@SuppressWarnings("resource")
 	public void contextPathDoesNotStartWithSlash() throws IOException {