Implements support for client gRPC channel injections (#9155)

* Implements support for client gRPC channel injections. Does not use CDI qualifiers for forward compatibility with our declarative API (annotations will be reused). New test that shows field and constructor injection.

* Updates documentation with a new section.

Signed-off-by: Santiago Pericas-Geertsen <[email protected]>

---------

Signed-off-by: Santiago Pericas-Geertsen <[email protected]>

docs/src/main/asciidoc/mp/grpc/client.adoc

@@ -35,6 +35,7 @@ include::{rootdir}/includes/mp.adoc[]
 - <<Usage, Usage>>
 ** <<Defining a Client Interface, Defining a Client Interface>>
 ** <<Injecting Client Proxies, Injecting Client Proxies>>
+** <<Injecting Channels, Injecting Channels>>
 - <<Examples, Examples>>
 
 == Overview
@@ -133,7 +134,7 @@ include::{sourcedir}/mp/grpc/GrpcSnippets.java[tag=snippet_5, indent=0]
 service when it differs from the interface name, as it is the case in this example.
 <2> The `@Grpc.GrpcChannel` annotation is the qualifier that supplies the channel name.
 This is the same name as used in the channel configuration in the examples provided in
-the <<Configuration, Configuration Section>>.
+the <<Configuration, Configuration section>>.
 
 There is no need to write any code to implement the client. The Helidon MP gRPC API will
 create a dynamic proxy for the interface using the information from the annotations and
@@ -162,14 +163,33 @@ include::{sourcedir}/mp/grpc/GrpcSnippets.java[tag=snippet_7, indent=0]
 
 <1> The `@Inject` annotation tells CDI to inject the client implementation.
 <2> The `@Grpc.GrpcProxy` annotation is used by the CDI container to match the injection point to
-the gRPC MP APIs provider.
+the gRPC MP API provider.
 
 When the CDI container instantiates `MyAppBean`, it will inject a dynamic proxy into
 the `stringServiceClient` field, and then provide the necessary logic for the proxy
 methods to convert a method call into a gRPC call.
 
 In the example above, there is no need to use a channel directly. The correct channel is added to
-the dynamic client proxy internally by the Helidon MP gRPC APIs.
+the dynamic client proxy internally by the Helidon MP gRPC API.
+
+=== Injecting Channels
+
+Channels can also be directly injected into application bean instances.
+The Helidon gRPC client API has CDI producers to inject `io.grpc.Channel` instances.
+
+For example, a class might have an injectable `io.grpc.Channel` field as follows:
+
+[source,java]
+----
+include::{sourcedir}/mp/grpc/GrpcSnippets.java[tag=snippet_8, indent=4]
+----
+
+<1> The `@Inject` annotation tells CDI to inject the channel.
+<2> The `@Grpc.GrpcChannel` annotation supplies the channel name.
+This is the same name as used in the channel configuration in the examples provided in
+the <<Configuration, Configuration section>>.
+
+An injected channel can be used, for example, when directly instantiating `protoc` generated stubs.
 
 == Examples
 

docs/src/main/java/io/helidon/docs/mp/grpc/GrpcSnippets.java

@@ -136,4 +136,13 @@ public class MyAppBean {
         }
         // end::snippet_7[]
     }
+
+    class Snippet8 {
+
+        // tag::snippet_8[]
+        @Inject  // <1>
+        @Grpc.GrpcChannel("string-channel")  // <2>
+        private Channel channel;
+        // end::snippet_8[]
+    }
 }

grpc/api/src/main/java/io/helidon/grpc/api/Grpc.java

@@ -275,7 +275,7 @@ public interface Grpc {
     }
 
     /**
-     * An annotation to indicate the response type of a gRPC method.
+     * An annotation to indicate the response type of gRPC method.
      */
     @Target(ElementType.METHOD)
     @Retention(RetentionPolicy.RUNTIME)
@@ -293,7 +293,7 @@ public interface Grpc {
     /**
      * An annotation that can be used to specify the name of a configured gRPC channel.
      */
-    @Target({ElementType.TYPE, ElementType.METHOD})
+    @Target({ElementType.TYPE, ElementType.METHOD, ElementType.CONSTRUCTOR, ElementType.FIELD, ElementType.PARAMETER})
     @Retention(RetentionPolicy.RUNTIME)
     @interface GrpcChannel {
 

microprofile/grpc/client/src/main/java/io/helidon/microprofile/grpc/client/ChannelProducer.java

@@ -57,9 +57,8 @@ public class ChannelProducer {
      * @return a gRPC {@link io.grpc.Channel}
      */
     @Produces
-    @Grpc.GrpcChannel(GrpcChannelsProvider.DEFAULT_CHANNEL_NAME)
     public Channel get(InjectionPoint injectionPoint) {
-        Grpc.GrpcChannel qualifier = injectionPoint.getQualifiers()
+        Grpc.GrpcChannel qualifier = injectionPoint.getAnnotated().getAnnotations()
                 .stream()
                 .filter(q -> q.annotationType().equals(Grpc.GrpcChannel.class))
                 .map(q -> (Grpc.GrpcChannel) q)
@@ -70,16 +69,6 @@ public Channel get(InjectionPoint injectionPoint) {
         return findChannel(name);
     }
 
-    /**
-     * Produces the default gRPC {@link io.grpc.Channel}.
-     *
-     * @return the default gRPC {@link io.grpc.Channel}
-     */
-    @Produces
-    public Channel getDefaultChannel() {
-        return findChannel(GrpcChannelsProvider.DEFAULT_CHANNEL_NAME);
-    }
-
     /**
      * Obtain the named {@link io.grpc.Channel}.
      *

microprofile/grpc/client/src/test/java/io/helidon/microprofile/grpc/client/ChannelInjectionTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2024 Oracle and/or its affiliates.
+ *
+ * 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
+ *
+ *     http://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 io.helidon.microprofile.grpc.client;
+
+import io.helidon.grpc.api.Grpc;
+import io.helidon.microprofile.testing.junit5.HelidonTest;
+
+import io.grpc.Channel;
+import jakarta.inject.Inject;
+import org.junit.jupiter.api.Test;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+@HelidonTest
+class ChannelInjectionTest {
+
+    @Inject
+    @Grpc.GrpcChannel("echo-channel")
+    private Channel echoChannel1;
+
+    private final Channel echoChannel2;
+
+    @Inject
+    ChannelInjectionTest(@Grpc.GrpcChannel("echo-channel") Channel echoChannel2) {
+        this.echoChannel2 = echoChannel2;
+    }
+
+    @Test
+    void testInjection() {
+        assertThat(echoChannel1, notNullValue());
+        assertThat(echoChannel2, notNullValue());
+        assertThat(echoChannel1.getClass(), equalTo(echoChannel2.getClass()));
+        assertThat(echoChannel1.authority(), equalTo(echoChannel2.authority()));
+    }
+}