Merge pull request #50301 from kwondh5217

* fix/50246-sni-fallback:
  Polish "Fall back to default SSL provider for unmapped SNI hostnames"
  Fall back to default SSL provider for unmapped SNI hostnames

Closes gh-50301

Author: snicoll

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/netty/SslServerCustomizer.java

@@ -75,11 +75,13 @@ public HttpServer apply(HttpServer server) {
 	}
 
 	private void applySecurity(SslContextSpec spec) {
-		spec.sslContext(this.sslProvider.getSslContext()).setSniAsyncMappings((serverName, promise) -> {
-			SslProvider provider = (serverName != null) ? this.serverNameSslProviders.get(serverName)
-					: this.sslProvider;
-			return promise.setSuccess(provider);
-		});
+		spec.sslContext(this.sslProvider.getSslContext())
+			.setSniAsyncMappings((serverName, promise) -> promise.setSuccess(getSslProvider(serverName)));
+	}
+
+	SslProvider getSslProvider(String serverName) {
+		return (serverName != null) ? this.serverNameSslProviders.getOrDefault(serverName, this.sslProvider)
+				: this.sslProvider;
 	}
 
 	void updateSslBundle(String serverName, SslBundle sslBundle) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/netty/SslServerCustomizerTests.java

@@ -0,0 +1,75 @@
+/*
+ * 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.embedded.netty;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import reactor.netty.tcp.SslProvider;
+
+import org.springframework.boot.ssl.SslBundle;
+import org.springframework.boot.ssl.pem.PemSslStoreBundle;
+import org.springframework.boot.ssl.pem.PemSslStoreDetails;
+import org.springframework.boot.testsupport.classpath.resources.WithPackageResources;
+import org.springframework.boot.web.server.Ssl;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link SslServerCustomizer}.
+ *
+ * @author Daeho Kwon
+ */
+class SslServerCustomizerTests {
+
+	@Test
+	@WithPackageResources({ "1.key", "1.crt", "2.key", "2.crt" })
+	void getSslProviderReturnsMappedProviderForKnownServerName() {
+		SslBundle defaultBundle = createBundle("1.key", "1.crt");
+		SslBundle mappedBundle = createBundle("2.key", "2.crt");
+		SslServerCustomizer customizer = new SslServerCustomizer(null, Ssl.ClientAuth.NONE, defaultBundle,
+				Map.of("mapped.example", mappedBundle));
+		SslProvider mapped = customizer.getSslProvider("mapped.example");
+		assertThat(mapped).isNotNull().isNotSameAs(customizer.getSslProvider(null));
+	}
+
+	@Test
+	@WithPackageResources({ "1.key", "1.crt", "2.key", "2.crt" })
+	void getSslProviderFallsBackToDefaultWhenServerNameIsUnmapped() {
+		SslBundle defaultBundle = createBundle("1.key", "1.crt");
+		SslBundle mappedBundle = createBundle("2.key", "2.crt");
+		SslServerCustomizer customizer = new SslServerCustomizer(null, Ssl.ClientAuth.NONE, defaultBundle,
+				Map.of("mapped.example", mappedBundle));
+		assertThat(customizer.getSslProvider("unmapped.example")).isSameAs(customizer.getSslProvider(null));
+	}
+
+	@Test
+	@WithPackageResources({ "1.key", "1.crt" })
+	void getSslProviderReturnsDefaultWhenServerNameIsNull() {
+		SslBundle defaultBundle = createBundle("1.key", "1.crt");
+		SslServerCustomizer customizer = new SslServerCustomizer(null, Ssl.ClientAuth.NONE, defaultBundle,
+				Collections.emptyMap());
+		assertThat(customizer.getSslProvider(null)).isNotNull();
+	}
+
+	private static SslBundle createBundle(String key, String certificate) {
+		return SslBundle.of(new PemSslStoreBundle(
+				new PemSslStoreDetails(null, "classpath:" + certificate, "classpath:" + key), null));
+	}
+
+}