MockHttpServletRequestBuilder sets content-length

Closes gh-23978

spring-test/src/main/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilder.java

@@ -687,6 +687,13 @@ public class MockHttpServletRequestBuilder
 			}
 		});
 
+		if (!ObjectUtils.isEmpty(this.content) &&
+				!this.headers.containsKey(HttpHeaders.CONTENT_LENGTH) &&
+				!this.headers.containsKey(HttpHeaders.TRANSFER_ENCODING)) {
+
+			request.addHeader(HttpHeaders.CONTENT_LENGTH, this.content.length);
+		}
+
 		String query = this.url.getRawQuery();
 		if (!this.queryParams.isEmpty()) {
 			String s = UriComponentsBuilder.newInstance().queryParams(this.queryParams).build().encode().getQuery();

spring-test/src/test/java/org/springframework/test/web/servlet/request/MockHttpServletRequestBuilderTests.java

@@ -389,6 +389,7 @@ public class MockHttpServletRequestBuilderTests {
 		byte[] result = FileCopyUtils.copyToByteArray(request.getInputStream());
 
 		assertThat(result).isEqualTo(body);
+		assertThat(request.getContentLength()).isEqualTo(body.length);
 	}
 
 	@Test