Add ConditionalOnGrpcClientEnabled flag

This adds a coarse-grained conditional guard that will disable the
client autoconfiguration if `spring.grpc.client.enabled` is set to
false or the `io.grpc:grpc-stub` module is not on the classpath.

Signed-off-by: Chris Bono <chris.bono@gmail.com>

spring-grpc-docs/src/main/antora/modules/ROOT/partials/_configprops.adoc

@@ -18,6 +18,7 @@
 |spring.grpc.client.default-channel.ssl.bundle |  | SSL bundle name.
 |spring.grpc.client.default-channel.ssl.enabled |  | Whether to enable SSL support. Enabled automatically if "bundle" is provided unless specified otherwise.
 |spring.grpc.client.default-channel.user-agent |  | The custom User-Agent for the channel.
+|spring.grpc.client.enabled | `+++true+++` | Whether to enable client autoconfiguration.
 |spring.grpc.client.observations.enabled | `+++true+++` | Whether to enable Observations on the client.
 |spring.grpc.server.address |  | The address to bind to. could be a host:port combination or a pseudo URL like static://host:port. Can not be set if host or port are set independently.
 |spring.grpc.server.exception-handling.enabled | `+++true+++` | Whether to enable user-defined global exception handling on the gRPC server.

spring-grpc-spring-boot-autoconfigure/src/main/java/org/springframework/grpc/autoconfigure/client/ConditionalOnGrpcClientEnabled.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2023-2024 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.
+ * 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.grpc.autoconfigure.client;
+
+import io.grpc.stub.AbstractStub;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.context.annotation.Conditional;
+
+/**
+ * {@link Conditional @Conditional} that only matches when the {@code io.grpc:grpc-stub}
+ * module is in the classpath and the {@code spring.grpc.client.enabled} property is not
+ * explicitly set to {@code false}.
+ *
+ * @author Freeman
+ * @author Chris Bono
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.TYPE, ElementType.METHOD })
+@ConditionalOnClass(AbstractStub.class)
+@ConditionalOnProperty(prefix = "spring.grpc.client", name = "enabled", matchIfMissing = true)
+public @interface ConditionalOnGrpcClientEnabled {
+
+}

spring-grpc-spring-boot-autoconfigure/src/main/java/org/springframework/grpc/autoconfigure/client/GrpcClientAutoConfiguration.java

@@ -32,6 +32,7 @@ import io.grpc.DecompressorRegistry;
 import io.grpc.ManagedChannelBuilder;
 
 @AutoConfiguration
+@ConditionalOnGrpcClientEnabled
 @EnableConfigurationProperties(GrpcClientProperties.class)
 @Import({ GrpcCodecConfiguration.class, ClientInterceptorsConfiguration.class,
 		GrpcChannelFactoryConfigurations.ShadedNettyChannelFactoryConfiguration.class,

spring-grpc-spring-boot-autoconfigure/src/main/java/org/springframework/grpc/autoconfigure/client/GrpcClientObservationAutoConfiguration.java

@@ -26,6 +26,7 @@ import org.springframework.grpc.client.GlobalClientInterceptor;
 
 @AutoConfiguration(
 		afterName = "org.springframework.boot.actuate.autoconfigure.observation.ObservationAutoConfiguration")
+@ConditionalOnGrpcClientEnabled
 @ConditionalOnClass({ ObservationRegistry.class, ObservationGrpcClientInterceptor.class })
 @ConditionalOnBean(ObservationRegistry.class)
 @ConditionalOnProperty(name = "spring.grpc.client.observation.enabled", havingValue = "true", matchIfMissing = true)

spring-grpc-spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -35,6 +35,12 @@
       "description": "Whether to enable Observations on the server.",
       "defaultValue": true
     },
+    {
+      "name": "spring.grpc.client.enabled",
+      "type": "java.lang.Boolean",
+      "description": "Whether to enable client autoconfiguration.",
+      "defaultValue": true
+    },
     {
       "name": "spring.grpc.client.observations.enabled",
       "type": "java.lang.Boolean",

spring-grpc-spring-boot-autoconfigure/src/test/java/org/springframework/grpc/autoconfigure/client/GrpcClientAutoConfigurationTests.java

@@ -51,6 +51,7 @@ import io.grpc.CompressorRegistry;
 import io.grpc.DecompressorRegistry;
 import io.grpc.ManagedChannelBuilder;
 import io.grpc.netty.NettyChannelBuilder;
+import io.grpc.stub.AbstractStub;
 
 /**
  * Tests for {@link GrpcClientAutoConfiguration}.
@@ -65,6 +66,32 @@ class GrpcClientAutoConfigurationTests {
 			.withConfiguration(AutoConfigurations.of(GrpcClientAutoConfiguration.class, SslAutoConfiguration.class));
 	}
 
+	@Test
+	void whenGrpcStubNotOnClasspathThenAutoConfigurationIsSkipped() {
+		this.contextRunner()
+			.withClassLoader(new FilteredClassLoader(AbstractStub.class))
+			.run((context) -> assertThat(context).doesNotHaveBean(GrpcClientAutoConfiguration.class));
+	}
+
+	@Test
+	void whenClientEnabledPropertySetFalseThenAutoConfigurationIsSkipped() {
+		this.contextRunner()
+			.withPropertyValues("spring.grpc.client.enabled=false")
+			.run((context) -> assertThat(context).doesNotHaveBean(GrpcClientAutoConfiguration.class));
+	}
+
+	@Test
+	void whenClientEnabledPropertyNotSetThenAutoConfigurationIsNotSkipped() {
+		this.contextRunner().run((context) -> assertThat(context).hasSingleBean(GrpcClientAutoConfiguration.class));
+	}
+
+	@Test
+	void whenClientEnabledPropertySetTrueThenAutoConfigurationIsNotSkipped() {
+		this.contextRunner()
+			.withPropertyValues("spring.grpc.client.enabled=true")
+			.run((context) -> assertThat(context).hasSingleBean(GrpcClientAutoConfiguration.class));
+	}
+
 	@Test
 	void whenHasUserDefinedCredentialsProviderDoesNotAutoConfigureBean() {
 		ChannelCredentialsProvider customCredentialsProvider = mock(ChannelCredentialsProvider.class);

spring-grpc-spring-boot-autoconfigure/src/test/java/org/springframework/grpc/autoconfigure/client/GrpcClientObservationAutoConfigurationTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.grpc.autoconfigure.client;
 
+import io.grpc.stub.AbstractStub;
 import io.micrometer.core.instrument.binder.grpc.ObservationGrpcClientInterceptor;
 import io.micrometer.observation.ObservationRegistry;
 import org.junit.jupiter.api.Test;
@@ -75,6 +76,33 @@ class GrpcClientObservationAutoConfigurationTests {
 			.run(context -> assertThat(context).doesNotHaveBean(GrpcClientObservationAutoConfiguration.class));
 	}
 
+	@Test
+	void whenClientEnabledPropertyNotSetThenAutoConfigNotSkipped() {
+		this.validContextRunner()
+			.run(context -> assertThat(context).hasSingleBean(GrpcClientObservationAutoConfiguration.class));
+	}
+
+	@Test
+	void whenClientEnabledPropertySetTrueThenAutoConfigIsNotSkipped() {
+		this.validContextRunner()
+			.withPropertyValues("spring.grpc.client.enabled=true")
+			.run(context -> assertThat(context).hasSingleBean(GrpcClientObservationAutoConfiguration.class));
+	}
+
+	@Test
+	void whenClientEnabledPropertySetFalseThenAutoConfigIsSkipped() {
+		this.validContextRunner()
+			.withPropertyValues("spring.grpc.client.enabled=false")
+			.run(context -> assertThat(context).doesNotHaveBean(GrpcClientObservationAutoConfiguration.class));
+	}
+
+	@Test
+	void whenGrpcStubNotOnClasspathThenAutoConfigIsSkipped() {
+		this.validContextRunner()
+			.withClassLoader(new FilteredClassLoader(AbstractStub.class))
+			.run(context -> assertThat(context).doesNotHaveBean(GrpcClientObservationAutoConfiguration.class));
+	}
+
 	@Test
 	void whenAllConditionsAreMetThenInterceptorConfiguredAsExpected() {
 		this.validContextRunner().run((context) -> {
@@ -86,4 +114,4 @@ class GrpcClientObservationAutoConfigurationTests {
 		});
 	}
 
-}
+}