Introduce `BaseUrl` and `BaseUrlProvider`

Add the concept of a `BaseUrl` to the core `spring-boot-test`
module for use when making test HTTP calls. The web server module
provides `BaseUrlProvider` implementations that provide the actual
base URL (usually `https://localhost:<local-server-port>`).

Test utilities will be able to use `BaseUrlProviders` to find the
`BaseUrl`.

See gh-46356

core/spring-boot-test/src/main/java/org/springframework/boot/test/http/server/BaseUrl.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.http.server;
+
+import java.util.function.Supplier;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+
+/**
+ * A base URL that can be used to connect to the running server.
+ *
+ * @author Phillip Webb
+ * @since 4.0.0
+ */
+public interface BaseUrl {
+
+	/**
+	 * Default base URL suitable for mock environments.
+	 */
+	BaseUrl DEFAULT = BaseUrl.of("http://localhost");
+
+	/**
+	 * Return if the URL will ultimately resolve to an HTTPS address.
+	 * @return if the URL is HTTPS
+	 */
+	boolean isHttps();
+
+	/**
+	 * Resolve the URL to a string. This method is called as late as possible to ensure
+	 * that an local port information is available.
+	 * @param path the path to append
+	 * @return the resolved base URL
+	 */
+	default String resolve(@Nullable String path) {
+		String resolved = resolve();
+		if (StringUtils.hasLength(path)) {
+			if (resolved.endsWith("/") && path.startsWith("/")) {
+				path = path.substring(1);
+			}
+			resolved += (resolved.endsWith("/") || path.startsWith("/")) ? "" : "/";
+			resolved += path;
+		}
+		return resolved;
+	}
+
+	/**
+	 * Resolve the URL to a string. This method is called as late as possible to ensure
+	 * that an local port information is available.
+	 * @return the resolved base URL
+	 */
+	String resolve();
+
+	/**
+	 * Factory method to create a new {@link BaseUrl}.
+	 * @param url the URL to use
+	 * @return a new {@link BaseUrl} instance
+	 */
+	static BaseUrl of(String url) {
+		Assert.notNull(url, "'url' must not be null");
+		return of(StringUtils.startsWithIgnoreCase(url, "https"), () -> url);
+	}
+
+	/**
+	 * Factory method to create a new {@link BaseUrl}.
+	 * @param https whether the base URL is https
+	 * @param resolver the resolver used to supply the actual URL
+	 * @return a new {@link BaseUrl} instance
+	 */
+	static BaseUrl of(boolean https, Supplier<String> resolver) {
+		Assert.notNull(resolver, "'resolver' must not be null");
+		return new BaseUrl() {
+
+			@Override
+			public boolean isHttps() {
+				return https;
+			}
+
+			@Override
+			public String resolve() {
+				return resolver.get();
+			}
+
+		};
+	}
+
+}

core/spring-boot-test/src/main/java/org/springframework/boot/test/http/server/BaseUrlProvider.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.http.server;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.context.ApplicationContext;
+
+/**
+ * Strategy used to provide the base URL that can be used to connect to the running
+ * server. Implementations can be registered in {@code spring.factories} and may accept an
+ * {@link ApplicationContext} constructor argument.
+ *
+ * @author Phillip Webb
+ * @since 4.0.0
+ */
+@FunctionalInterface
+public interface BaseUrlProvider {
+
+	/**
+	 * Return the base URL that can be used to connect to the running server.
+	 * @return the base URL or {@code null}
+	 */
+	@Nullable BaseUrl getBaseUrl();
+
+}

core/spring-boot-test/src/main/java/org/springframework/boot/test/http/server/BaseUrlProviders.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.http.server;
+
+import java.util.List;
+import java.util.Objects;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.core.io.support.SpringFactoriesLoader;
+import org.springframework.core.io.support.SpringFactoriesLoader.ArgumentResolver;
+import org.springframework.lang.Contract;
+import org.springframework.util.Assert;
+
+/**
+ * A collection of {@link BaseUrlProvider} instances loaded from {@code spring.factories}.
+ *
+ * @author Phillip Webb
+ * @since 4.0.0
+ */
+public class BaseUrlProviders {
+
+	private List<BaseUrlProvider> providers;
+
+	public BaseUrlProviders(ApplicationContext applicationContext) {
+		Assert.notNull(applicationContext, "'applicationContext' must not be null");
+		this.providers = SpringFactoriesLoader.forDefaultResourceLocation(applicationContext.getClassLoader())
+			.load(BaseUrlProvider.class, ArgumentResolver.of(ApplicationContext.class, applicationContext));
+	}
+
+	BaseUrlProviders(List<BaseUrlProvider> providers) {
+		this.providers = providers;
+	}
+
+	/**
+	 * Return the provided {@link BaseUrl} or {@link BaseUrl#DEFAULT}.
+	 * @return the base URL
+	 */
+	public BaseUrl getBaseUrlOrDefault() {
+		return getBaseUrl(BaseUrl.DEFAULT);
+	}
+
+	/**
+	 * Return the provided {@link BaseUrl} or {@code null}.
+	 * @return the base URL or {@code null}
+	 */
+	public @Nullable BaseUrl getBaseUrl() {
+		return getBaseUrl(null);
+	}
+
+	/**
+	 * Return the provided {@link BaseUrl} or the given fallback.
+	 * @param fallback the fallback
+	 * @return the base URL or the fallback
+	 */
+	@Contract("!null -> !null")
+	public @Nullable BaseUrl getBaseUrl(@Nullable BaseUrl fallback) {
+		return this.providers.stream()
+			.map(BaseUrlProvider::getBaseUrl)
+			.filter(Objects::nonNull)
+			.findFirst()
+			.orElse(fallback);
+
+	}
+
+}

core/spring-boot-test/src/main/java/org/springframework/boot/test/http/server/package-info.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Support for HTTP server testing.
+ */
+@NullMarked
+package org.springframework.boot.test.http.server;
+
+import org.jspecify.annotations.NullMarked;

core/spring-boot-test/src/test/java/org/springframework/boot/test/http/server/BaseUrlProvidersTests.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.http.server;
+
+import java.util.Collections;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.BDDMockito.then;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Tests for {@link BaseUrlProviders}.
+ *
+ * @author Phillip Webb
+ */
+class BaseUrlProvidersTests {
+
+	@Test
+	void getBaseUrlOrDefaultWhenNoProvidedBaseUrlReturnsDefault() {
+		assertThat(new BaseUrlProviders(Collections.emptyList()).getBaseUrlOrDefault()).isSameAs(BaseUrl.DEFAULT);
+	}
+
+	@Test
+	void getBaseUrlWhenNoProvidedBaseUrlReturnsNull() {
+		assertThat(new BaseUrlProviders(Collections.emptyList()).getBaseUrl()).isNull();
+	}
+
+	@Test
+	void getBaseUrlWithFallbackWhenNoProvidedBaseUrlReturnsFallback() {
+		BaseUrl fallback = BaseUrl.of("https://example.com");
+		assertThat(new BaseUrlProviders(Collections.emptyList()).getBaseUrl(fallback)).isSameAs(fallback);
+	}
+
+	@Test
+	void getBaseUrlReturnsFirstProvidedBaseUrl() {
+		BaseUrlProvider p1 = mock();
+		BaseUrlProvider p2 = mock();
+		BaseUrl baseUrl = BaseUrl.of("https://example.com");
+		given(p1.getBaseUrl()).willReturn(baseUrl);
+		assertThat(new BaseUrlProviders(List.of(p1, p2)).getBaseUrl()).isSameAs(baseUrl);
+		then(p2).shouldHaveNoInteractions();
+	}
+
+}

core/spring-boot-test/src/test/java/org/springframework/boot/test/http/server/BaseUrlTests.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.http.server;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link BaseUrl}.
+ *
+ * @author Phillip Webb
+ */
+class BaseUrlTests {
+
+	@Test
+	void resolveWithString() {
+		assertThat(BaseUrl.of("http://localhost").resolve(null)).isEqualTo("http://localhost");
+		assertThat(BaseUrl.of("http://localhost").resolve("")).isEqualTo("http://localhost");
+		assertThat(BaseUrl.of("http://localhost").resolve("path")).isEqualTo("http://localhost/path");
+		assertThat(BaseUrl.of("http://localhost").resolve("/path")).isEqualTo("http://localhost/path");
+		assertThat(BaseUrl.of("http://localhost/").resolve("path")).isEqualTo("http://localhost/path");
+		assertThat(BaseUrl.of("http://localhost/").resolve("/path")).isEqualTo("http://localhost/path");
+	}
+
+	@Test
+	void ofWhenHttp() {
+		BaseUrl baseUrl = BaseUrl.of("http://localhost:8080/context");
+		assertThat(baseUrl.isHttps()).isFalse();
+		assertThat(baseUrl.resolve()).isEqualTo("http://localhost:8080/context");
+	}
+
+	@Test
+	void ofWhenHttps() {
+		BaseUrl baseUrl = BaseUrl.of("https://localhost:8080/context");
+		assertThat(baseUrl.isHttps()).isTrue();
+		assertThat(baseUrl.resolve()).isEqualTo("https://localhost:8080/context");
+	}
+
+	@Test
+	void ofWhenUppercaseHttps() {
+		BaseUrl baseUrl = BaseUrl.of("HTTPS://localhost:8080/context");
+		assertThat(baseUrl.isHttps()).isTrue();
+		assertThat(baseUrl.resolve()).isEqualTo("HTTPS://localhost:8080/context");
+	}
+
+	@Test
+	void ofWhenUrlIssNull() {
+		assertThatIllegalArgumentException().isThrownBy(() -> BaseUrl.of(null)).withMessage("'url' must not be null");
+	}
+
+	@Test
+	void of() {
+		AtomicInteger atomicInteger = new AtomicInteger();
+		BaseUrl baseUrl = BaseUrl.of(true, () -> String.valueOf(atomicInteger.incrementAndGet()));
+		assertThat(atomicInteger.get()).isZero();
+		assertThat(baseUrl.isHttps()).isTrue();
+		assertThat(baseUrl.resolve()).isEqualTo("1");
+		assertThat(baseUrl.resolve()).isEqualTo("2");
+	}
+
+	@Test
+	void ofWhenResolverIsNull() {
+		assertThatIllegalArgumentException().isThrownBy(() -> BaseUrl.of(true, null))
+			.withMessage("'resolver' must not be null");
+	}
+
+}

module/spring-boot-web-server/src/main/java/org/springframework/boot/web/server/reactive/context/ReactiveWebServerApplicationContextBaseUrlProvider.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.server.reactive.context;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.boot.test.http.server.BaseUrl;
+import org.springframework.boot.test.http.server.BaseUrlProvider;
+import org.springframework.boot.web.server.AbstractConfigurableWebServerFactory;
+import org.springframework.boot.web.server.reactive.AbstractReactiveWebServerFactory;
+import org.springframework.context.ApplicationContext;
+
+/**
+ * {@link BaseUrlProvider} for a {@link ReactiveWebServerApplicationContext}.
+ *
+ * @author Phillip Webb
+ */
+class ReactiveWebServerApplicationContextBaseUrlProvider implements BaseUrlProvider {
+
+	private final @Nullable ReactiveWebServerApplicationContext context;
+
+	ReactiveWebServerApplicationContextBaseUrlProvider(ApplicationContext context) {
+		this.context = getWebServerApplicationContextIfPossible(context);
+	}
+
+	static @Nullable ReactiveWebServerApplicationContext getWebServerApplicationContextIfPossible(
+			ApplicationContext context) {
+		try {
+			return (ReactiveWebServerApplicationContext) context;
+		}
+		catch (NoClassDefFoundError | ClassCastException ex) {
+			return null;
+		}
+	}
+
+	@Override
+	public @Nullable BaseUrl getBaseUrl() {
+		if (this.context == null) {
+			return null;
+		}
+		boolean sslEnabled = isSslEnabled(this.context);
+		return BaseUrl.of(sslEnabled, () -> {
+			String scheme = (sslEnabled) ? "https" : "http";
+			String port = this.context.getEnvironment().getProperty("local.server.port", "8080");
+			String path = this.context.getEnvironment().getProperty("spring.webflux.base-path", "");
+			return scheme + "://localhost:" + port + path;
+		});
+	}
+
+	private boolean isSslEnabled(ReactiveWebServerApplicationContext context) {
+		try {
+			AbstractConfigurableWebServerFactory webServerFactory = context
+				.getBean(AbstractReactiveWebServerFactory.class);
+			return webServerFactory.getSsl() != null && webServerFactory.getSsl().isEnabled();
+		}
+		catch (NoSuchBeanDefinitionException ex) {
+			return false;
+		}
+	}
+
+}

module/spring-boot-web-server/src/main/java/org/springframework/boot/web/server/servlet/context/ServletWebServerApplicationContextBaseUrlProvider.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.server.servlet.context;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.boot.test.http.server.BaseUrl;
+import org.springframework.boot.test.http.server.BaseUrlProvider;
+import org.springframework.boot.web.server.AbstractConfigurableWebServerFactory;
+import org.springframework.boot.web.server.reactive.AbstractReactiveWebServerFactory;
+import org.springframework.context.ApplicationContext;
+
+/**
+ * {@link BaseUrlProvider} for a {@link ServletWebServerApplicationContext}.
+ *
+ * @author Phillip Webb
+ */
+class ServletWebServerApplicationContextBaseUrlProvider implements BaseUrlProvider {
+
+	private final @Nullable ServletWebServerApplicationContext context;
+
+	ServletWebServerApplicationContextBaseUrlProvider(ApplicationContext context) {
+		this.context = getWebServerApplicationContextIfPossible(context);
+	}
+
+	static @Nullable ServletWebServerApplicationContext getWebServerApplicationContextIfPossible(
+			ApplicationContext context) {
+		try {
+			return (ServletWebServerApplicationContext) context;
+		}
+		catch (NoClassDefFoundError | ClassCastException ex) {
+			return null;
+		}
+	}
+
+	@Override
+	public @Nullable BaseUrl getBaseUrl() {
+		if (this.context == null) {
+			return null;
+		}
+		boolean sslEnabled = isSslEnabled(this.context);
+		return BaseUrl.of(sslEnabled, () -> {
+			String scheme = (sslEnabled) ? "https" : "http";
+			String port = this.context.getEnvironment().getProperty("local.server.port", "8080");
+			String path = this.context.getEnvironment().getProperty("server.servlet.context-path", "");
+			return scheme + "://localhost:" + port + path;
+		});
+	}
+
+	private boolean isSslEnabled(ServletWebServerApplicationContext context) {
+		try {
+			AbstractConfigurableWebServerFactory webServerFactory = context
+				.getBean(AbstractReactiveWebServerFactory.class);
+			return webServerFactory.getSsl() != null && webServerFactory.getSsl().isEnabled();
+		}
+		catch (NoSuchBeanDefinitionException ex) {
+			return false;
+		}
+	}
+
+}

module/spring-boot-web-server/src/main/resources/META-INF/spring.factories

@@ -11,3 +11,8 @@ org.springframework.boot.web.server.context.ServerPortInfoApplicationContextInit
 org.springframework.boot.diagnostics.FailureAnalyzer=\
 org.springframework.boot.web.server.PortInUseFailureAnalyzer,\
 org.springframework.boot.web.server.context.MissingWebServerFactoryBeanFailureAnalyzer
+
+# HTTP Server Test Base URL Providers
+org.springframework.boot.test.http.server.BaseUrlProvider=\
+org.springframework.boot.web.server.reactive.context.ReactiveWebServerApplicationContextBaseUrlProvider,\
+org.springframework.boot.web.server.servlet.context.ServletWebServerApplicationContextBaseUrlProvider