Update content-length when reconstructing body

Closes gh-32471

Author: rstoyanchev

spring-web/src/main/java/org/springframework/http/server/ServletServerHttpRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -242,7 +242,7 @@ private static boolean isFormPost(HttpServletRequest request) {
 	 * from the body, which can fail if any other code has used the ServletRequest
 	 * to access a parameter, thus causing the input stream to be "consumed".
 	 */
-	private static InputStream getBodyFromServletRequestParameters(HttpServletRequest request) throws IOException {
+	private InputStream getBodyFromServletRequestParameters(HttpServletRequest request) throws IOException {
 		ByteArrayOutputStream bos = new ByteArrayOutputStream(1024);
 		Writer writer = new OutputStreamWriter(bos, FORM_CHARSET);
 
@@ -268,7 +268,12 @@ private static InputStream getBodyFromServletRequestParameters(HttpServletReques
 		}
 		writer.flush();
 
-		return new ByteArrayInputStream(bos.toByteArray());
+		byte[] bytes = bos.toByteArray();
+		if (bytes.length > 0 && getHeaders().containsKey(HttpHeaders.CONTENT_LENGTH)) {
+			getHeaders().setContentLength(bytes.length);
+		}
+
+		return new ByteArrayInputStream(bytes);
 	}
 
 }

spring-web/src/test/java/org/springframework/http/server/ServletServerHttpRequestTests.java

@@ -203,4 +203,17 @@ void getFormBodyWhenQueryParamsAlsoPresent() throws IOException {
 		assertThat(result).as("Invalid content returned").isEqualTo(content);
 	}
 
+	@Test // gh-32471
+	void getFormBodyWhenNotEncodedCharactersPresent() throws IOException {
+		mockRequest.setContentType("application/x-www-form-urlencoded; charset=UTF-8");
+		mockRequest.setMethod("POST");
+		mockRequest.addParameter("name", "Test");
+		mockRequest.addParameter("lastName", "Test@er");
+		mockRequest.addHeader("Content-Length", 26);
+
+		byte[] result = FileCopyUtils.copyToByteArray(request.getBody());
+		assertThat(result).isEqualTo("name=Test&lastName=Test%40er".getBytes(StandardCharsets.UTF_8));
+		assertThat(request.getHeaders().getContentLength()).isEqualTo(result.length);
+	}
+
 }