Add protection against StackOverflowError in JsonValueWriter

This commit adds validation for the maximum JSON nesting depth in
the JsonValueWriter. This helps prevent StackOverflowError that can
potentially occur due to excessive recursion when dealing with deeply
nested JSON structures.

Signed-off-by: Dmytro Nosan <[email protected]>

Author: nosan

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/json/JsonValueWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -46,6 +46,8 @@
  */
 class JsonValueWriter {
 
+	private static final int MAX_NESTING_DEPTH = 1000;
+
 	private final Appendable out;
 
 	private MemberPath path = MemberPath.ROOT;
@@ -140,6 +142,7 @@ else if (value instanceof Number || value instanceof Boolean) {
 	 */
 	void start(Series series) {
 		if (series != null) {
+			validateNestingDepth();
 			this.activeSeries.push(new ActiveSeries(series));
 			append(series.openChar);
 		}
@@ -267,6 +270,13 @@ private void writeString(Object value) {
 		}
 	}
 
+	private void validateNestingDepth() {
+		if (this.activeSeries.size() > MAX_NESTING_DEPTH) {
+			throw new IllegalStateException("JSON nesting depth (%s) exceeds maximum depth of %s (current path: %s)"
+				.formatted(this.activeSeries.size(), MAX_NESTING_DEPTH, this.path));
+		}
+	}
+
 	private void append(String value) {
 		try {
 			this.out.append(value);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/json/JsonValueWriterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.boot.json;
 
+import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -240,6 +241,34 @@ void endWhenNotStartedThrowsException() {
 			.isThrownBy(() -> valueWriter.end(Series.ARRAY)));
 	}
 
+	@Test
+	void illegalStateExceptionShouldBeThrownWhenCollectionExceededNestingDepth() {
+		List<Object> list = new ArrayList<>();
+		list.add(list);
+		doWrite((valueWriter) -> assertThatIllegalStateException().isThrownBy(() -> valueWriter.write(list))
+			.withMessageStartingWith(
+					"JSON nesting depth (1001) exceeds maximum depth of 1000 (current path: [0][0][0][0][0][0][0][0][0][0][0][0]"));
+	}
+
+	@Test
+	void illegalStateExceptionShouldBeThrownWhenMapExceededNestingDepth() {
+		Map<String, Object> map = new LinkedHashMap<>();
+		map.put("foo", Map.of("bar", map));
+		doWrite((valueWriter) -> assertThatIllegalStateException().isThrownBy(() -> valueWriter.write(map))
+			.withMessageStartingWith(
+					"JSON nesting depth (1001) exceeds maximum depth of 1000 (current path: foo.bar.foo.bar.foo.bar.foo"));
+	}
+
+	@Test
+	void illegalStateExceptionShouldBeThrownWhenIterableExceededNestingDepth() {
+		List<Object> list = new ArrayList<>();
+		list.add(list);
+		doWrite((valueWriter) -> assertThatIllegalStateException()
+			.isThrownBy(() -> valueWriter.write((Iterable<Object>) list::iterator))
+			.withMessageStartingWith(
+					"JSON nesting depth (1001) exceeds maximum depth of 1000 (current path: [0][0][0][0][0][0][0][0][0][0][0][0]"));
+	}
+
 	private <V> String write(V value) {
 		return doWrite((valueWriter) -> valueWriter.write(value));
 	}