Limit SpEL expression length

This commit enforces a limit of the maximum size of a single SpEL
expression.

Closes gh-30325

Author: sbrannen

spring-expression/src/main/java/org/springframework/expression/spel/SpelMessage.java

@@ -268,15 +268,19 @@ public enum SpelMessage {
 
 	/** @since 5.2.23 */
 	MAX_REPEATED_TEXT_SIZE_EXCEEDED(Kind.ERROR, 1076,
-			"Repeated text results in too many characters, exceeding the threshold of ''{0}''"),
+			"Repeated text is too long, exceeding the threshold of ''{0}'' characters"),
 
 	/** @since 5.2.23 */
 	MAX_REGEX_LENGTH_EXCEEDED(Kind.ERROR, 1077,
-			"Regular expression contains too many characters, exceeding the threshold of ''{0}''"),
+			"Regular expression is too long, exceeding the threshold of ''{0}'' characters"),
 
 	/** @since 5.2.24 */
 	MAX_CONCATENATED_STRING_LENGTH_EXCEEDED(Kind.ERROR, 1078,
-			"Concatenated string is too long, exceeding the threshold of ''{0}'' characters");
+			"Concatenated string is too long, exceeding the threshold of ''{0}'' characters"),
+
+	/** @since 5.2.24 */
+	MAX_EXPRESSION_LENGTH_EXCEEDED(Kind.ERROR, 1079,
+			"SpEL expression is too long, exceeding the threshold of ''{0}'' characters");
 
 
 	private final Kind kind;

spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java

@@ -29,6 +29,7 @@
 import org.springframework.expression.ParserContext;
 import org.springframework.expression.common.TemplateAwareExpressionParser;
 import org.springframework.expression.spel.InternalParseException;
+import org.springframework.expression.spel.SpelEvaluationException;
 import org.springframework.expression.spel.SpelMessage;
 import org.springframework.expression.spel.SpelParseException;
 import org.springframework.expression.spel.SpelParserConfiguration;
@@ -92,6 +93,12 @@ class InternalSpelExpressionParser extends TemplateAwareExpressionParser {
 
 	private static final Pattern VALID_QUALIFIED_ID_PATTERN = Pattern.compile("[\\p{L}\\p{N}_$]+");
 
+	/**
+	 * Maximum length permitted for a SpEL expression.
+	 * @since 5.2.24
+	 */
+	private static final int MAX_EXPRESSION_LENGTH = 10_000;
+
 
 	private final SpelParserConfiguration configuration;
 
@@ -127,6 +134,8 @@ public InternalSpelExpressionParser(SpelParserConfiguration configuration) {
 	protected SpelExpression doParseExpression(String expressionString, @Nullable ParserContext context)
 			throws ParseException {
 
+		checkExpressionLength(expressionString);
+
 		try {
 			this.expressionString = expressionString;
 			Tokenizer tokenizer = new Tokenizer(expressionString);
@@ -148,6 +157,12 @@ protected SpelExpression doParseExpression(String expressionString, @Nullable Pa
 		}
 	}
 
+	private void checkExpressionLength(String string) {
+		if (string.length() > MAX_EXPRESSION_LENGTH) {
+			throw new SpelEvaluationException(SpelMessage.MAX_EXPRESSION_LENGTH_EXCEEDED, MAX_EXPRESSION_LENGTH);
+		}
+	}
+
 	//	expression
 	//    : logicalOrExpression
 	//      ( (ASSIGN^ logicalOrExpression)

spring-expression/src/test/java/org/springframework/expression/spel/EvaluationTests.java

@@ -60,6 +60,20 @@ class EvaluationTests extends AbstractExpressionTests {
 	@Nested
 	class MiscellaneousTests {
 
+		@Test
+		void expressionLength() {
+			String expression = "'X' + '%s'".formatted(" ".repeat(9_992));
+			assertThat(expression).hasSize(10_000);
+			Expression expr = parser.parseExpression(expression);
+			String result = expr.getValue(context, String.class);
+			assertThat(result).hasSize(9_993);
+			assertThat(result.trim()).isEqualTo("X");
+
+			expression = "'X' + '%s'".formatted(" ".repeat(9_993));
+			assertThat(expression).hasSize(10_001);
+			evaluateAndCheckError(expression, String.class, SpelMessage.MAX_EXPRESSION_LENGTH_EXCEEDED);
+		}
+
 		@Test
 		void createListsOnAttemptToIndexNull01() throws EvaluationException, ParseException {
 			ExpressionParser parser = new SpelExpressionParser(new SpelParserConfiguration(true, true));