Implements support for client gRPC channel injections

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()));
+    }
+}