Polish "Restore max-http-header-size default value support"

Fix Jetty and Undertow customizers to restore Spring Boot 2.0
behavior where a negative or zero `max-http-header-size` indicates
that the server default should be used.

Closes gh-14986

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/JettyWebServerFactoryCustomizer.java

@@ -75,7 +75,7 @@ public class JettyWebServerFactoryCustomizer implements
 		propertyMapper.from(jettyProperties::getSelectors).whenNonNull()
 				.to(factory::setSelectors);
 		propertyMapper.from(properties::getMaxHttpHeaderSize).whenNonNull()
-				.asInt(DataSize::toBytes)
+				.asInt(DataSize::toBytes).when(this::isPositive)
 				.to((maxHttpHeaderSize) -> customizeMaxHttpHeaderSize(factory,
 						maxHttpHeaderSize));
 		propertyMapper.from(jettyProperties::getMaxHttpPostSize).asInt(DataSize::toBytes)

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/UndertowWebServerFactoryCustomizer.java

@@ -86,7 +86,7 @@ public class UndertowWebServerFactoryCustomizer implements
 		propertyMapper.from(this::getOrDeduceUseForwardHeaders)
 				.to(factory::setUseForwardHeaders);
 		propertyMapper.from(properties::getMaxHttpHeaderSize).whenNonNull()
-				.asInt(DataSize::toBytes)
+				.asInt(DataSize::toBytes).when(this::isPositive)
 				.to((maxHttpHeaderSize) -> customizeMaxHttpHeaderSize(factory,
 						maxHttpHeaderSize));
 		propertyMapper.from(undertowProperties::getMaxHttpPostSize)

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/embedded/JettyWebServerFactoryCustomizerTests.java

@@ -18,6 +18,8 @@ package org.springframework.boot.autoconfigure.web.embedded;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Locale;
 import java.util.TimeZone;
 
@@ -38,6 +40,7 @@ import org.springframework.boot.web.embedded.jetty.JettyServletWebServerFactory;
 import org.springframework.boot.web.embedded.jetty.JettyWebServer;
 import org.springframework.mock.env.MockEnvironment;
 import org.springframework.test.context.support.TestPropertySourceUtils;
+import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
@@ -147,15 +150,40 @@ public class JettyWebServerFactoryCustomizerTests {
 	public void customizeMaxHttpHeaderSize() {
 		bind("server.max-http-header-size=2048");
 		JettyWebServer server = customizeAndGetServer();
-		for (Connector connector : server.getServer().getConnectors()) {
+		List<Integer> requestHeaderSizes = getRequestHeaderSizes(server);
+		assertThat(requestHeaderSizes).containsOnly(2048);
+	}
+
+	@Test
+	public void customMaxHttpHeaderSizeIgnoredIfNegative() {
+		bind("server.max-http-header-size=-1");
+		JettyWebServer server = customizeAndGetServer();
+		List<Integer> requestHeaderSizes = getRequestHeaderSizes(server);
+		assertThat(requestHeaderSizes).containsOnly(8192);
+	}
+
+	@Test
+	public void customMaxHttpHeaderSizeIgnoredIfZero() {
+		bind("server.max-http-header-size=0");
+		JettyWebServer server = customizeAndGetServer();
+		List<Integer> requestHeaderSizes = getRequestHeaderSizes(server);
+		assertThat(requestHeaderSizes).containsOnly(8192);
+	}
+
+	private List<Integer> getRequestHeaderSizes(JettyWebServer server) {
+		List<Integer> requestHeaderSizes = new ArrayList<>();
+		Connector[] connectors = (Connector[]) ReflectionTestUtils.getField(server,
+				"connectors");
+		for (Connector connector : connectors) {
 			connector.getConnectionFactories().stream()
 					.filter((factory) -> factory instanceof ConnectionFactory)
 					.forEach((cf) -> {
 						ConnectionFactory factory = (ConnectionFactory) cf;
 						HttpConfiguration configuration = factory.getHttpConfiguration();
-						assertThat(configuration.getRequestHeaderSize()).isEqualTo(2048);
+						requestHeaderSizes.add(configuration.getRequestHeaderSize());
 					});
 		}
+		return requestHeaderSizes;
 	}
 
 	private void bind(String... inlinedProperties) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/embedded/UndertowWebServerFactoryCustomizerTests.java

@@ -17,18 +17,28 @@
 package org.springframework.boot.autoconfigure.web.embedded;
 
 import java.io.File;
+import java.util.Arrays;
 
+import io.undertow.Undertow;
+import io.undertow.Undertow.Builder;
+import io.undertow.UndertowOptions;
 import org.junit.Before;
 import org.junit.Test;
+import org.xnio.OptionMap;
 
 import org.springframework.boot.autoconfigure.web.ServerProperties;
 import org.springframework.boot.context.properties.bind.Bindable;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySources;
 import org.springframework.boot.web.embedded.undertow.ConfigurableUndertowWebServerFactory;
+import org.springframework.boot.web.embedded.undertow.UndertowBuilderCustomizer;
 import org.springframework.mock.env.MockEnvironment;
 import org.springframework.test.context.support.TestPropertySourceUtils;
+import org.springframework.test.util.ReflectionTestUtils;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.BDDMockito.willAnswer;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 
@@ -100,6 +110,54 @@ public class UndertowWebServerFactoryCustomizerTests {
 		verify(factory).setUseForwardHeaders(true);
 	}
 
+	@Test
+	public void customizeMaxHttpHeaderSize() {
+		bind("server.max-http-header-size=2048");
+		Builder builder = Undertow.builder();
+		ConfigurableUndertowWebServerFactory factory = mockFactory(builder);
+		this.customizer.customize(factory);
+		OptionMap map = ((OptionMap.Builder) ReflectionTestUtils.getField(builder,
+				"serverOptions")).getMap();
+		assertThat(map.get(UndertowOptions.MAX_HEADER_SIZE).intValue()).isEqualTo(2048);
+	}
+
+	@Test
+	public void customMaxHttpHeaderSizeIgnoredIfNegative() {
+		bind("server.max-http-header-size=-1");
+		Builder builder = Undertow.builder();
+		ConfigurableUndertowWebServerFactory factory = mockFactory(builder);
+		this.customizer.customize(factory);
+		OptionMap map = ((OptionMap.Builder) ReflectionTestUtils.getField(builder,
+				"serverOptions")).getMap();
+		assertThat(map.contains(UndertowOptions.MAX_HEADER_SIZE)).isFalse();
+	}
+
+	@Test
+	public void customMaxHttpHeaderSizeIgnoredIfZero() {
+		bind("server.max-http-header-size=0");
+		Builder builder = Undertow.builder();
+		ConfigurableUndertowWebServerFactory factory = mockFactory(builder);
+		this.customizer.customize(factory);
+		OptionMap map = ((OptionMap.Builder) ReflectionTestUtils.getField(builder,
+				"serverOptions")).getMap();
+		assertThat(map.contains(UndertowOptions.MAX_HEADER_SIZE)).isFalse();
+	}
+
+	private ConfigurableUndertowWebServerFactory mockFactory(Builder builder) {
+		ConfigurableUndertowWebServerFactory factory = mock(
+				ConfigurableUndertowWebServerFactory.class);
+		willAnswer((invocation) -> {
+			Object argument = invocation.getArgument(0);
+			Arrays.stream((argument instanceof UndertowBuilderCustomizer)
+					? new UndertowBuilderCustomizer[] {
+							(UndertowBuilderCustomizer) argument }
+					: (UndertowBuilderCustomizer[]) argument)
+					.forEach((customizer) -> customizer.customize(builder));
+			return null;
+		}).given(factory).addBuilderCustomizers(any());
+		return factory;
+	}
+
 	private void bind(String... inlinedProperties) {
 		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.environment,
 				inlinedProperties);