feat: Adds structure for gRPC client metrics instrumentation (#1021)

* added a new grpc client metric `grpc.client.attempt.started`

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/metrics/MetricsClientInstruments.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2016-2023 The gRPC-Spring 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
+ *
+ *     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 net.devh.boot.grpc.client.metrics;
+
+import io.micrometer.core.instrument.Counter;
+import io.micrometer.core.instrument.MeterRegistry;
+
+/*
+ * The instruments used to record metrics on client.
+ */
+public final class MetricsClientInstruments {
+
+    private MetricsClientInstruments() {}
+
+    /*
+     * This is a client side metric defined in gRFC <a
+     * href="https://github.com/grpc/proposal/blob/master/A66-otel-stats.md">A66</a>. Please note that this is the name
+     * used for instrumentation and can be changed by exporters in an unpredictable manner depending on the destination.
+     */
+    private static final String CLIENT_ATTEMPT_STARTED = "grpc.client.attempt.started";
+
+    static MetricsMeters newClientMetricsMeters(MeterRegistry registry) {
+        MetricsMeters.Builder builder = MetricsMeters.newBuilder();
+
+        builder.setAttemptCounter(Counter.builder(CLIENT_ATTEMPT_STARTED)
+                .description(
+                        "The total number of RPC attempts started from the client side, including "
+                                + "those that have not completed.")
+                .baseUnit("attempt")
+                .withRegistry(registry));
+        return builder.build();
+    }
+
+}

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/metrics/MetricsClientInterceptor.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2016-2023 The gRPC-Spring 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
+ *
+ *     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 net.devh.boot.grpc.client.metrics;
+
+import io.grpc.CallOptions;
+import io.grpc.Channel;
+import io.grpc.ClientCall;
+import io.grpc.ClientInterceptor;
+import io.grpc.ForwardingClientCall.SimpleForwardingClientCall;
+import io.grpc.ForwardingClientCallListener.SimpleForwardingClientCallListener;
+import io.grpc.Metadata;
+import io.grpc.MethodDescriptor;
+import io.grpc.Status;
+import io.micrometer.core.instrument.MeterRegistry;
+
+/**
+ * A gRPC client interceptor that collects gRPC metrics.
+ *
+ * <b>Note:</b> This class uses experimental grpc-java-API features.
+ */
+public class MetricsClientInterceptor implements ClientInterceptor {
+
+    private final MetricsMeters metricsMeters;
+
+    /**
+     * Creates a new gRPC client interceptor that collects metrics into the given
+     * {@link io.micrometer.core.instrument.MeterRegistry}.
+     *
+     * @param registry The MeterRegistry to use.
+     */
+    public MetricsClientInterceptor(MeterRegistry registry) {
+        this.metricsMeters = MetricsClientInstruments.newClientMetricsMeters(registry);
+    }
+
+    @Override
+    public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
+            MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
+
+        /*
+         * This is a per call ClientStreamTracer.Factory which creates a new stream tracer for each attempt under the
+         * same call. Each call needs a dedicated factory as they share the same method descriptor.
+         */
+        final MetricsClientStreamTracers.CallAttemptsTracerFactory tracerFactory =
+                new MetricsClientStreamTracers.CallAttemptsTracerFactory(method.getFullMethodName(),
+                        metricsMeters);
+
+        ClientCall<ReqT, RespT> call =
+                next.newCall(method, callOptions.withStreamTracerFactory(tracerFactory));
+
+        // TODO(dnvindhya): Collect the actual response/error in the SimpleForwardingClientCall
+        return new SimpleForwardingClientCall<ReqT, RespT>(call) {
+            @Override
+            public void start(Listener<RespT> responseListener, Metadata headers) {
+                delegate().start(
+                        new SimpleForwardingClientCallListener<RespT>(responseListener) {
+                            @Override
+                            public void onClose(Status status, Metadata trailers) {
+                                super.onClose(status, trailers);
+                            }
+                        },
+                        headers);
+            }
+        };
+    }
+}

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/metrics/MetricsClientStreamTracers.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2016-2023 The gRPC-Spring 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
+ *
+ *     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 net.devh.boot.grpc.client.metrics;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import io.grpc.ClientStreamTracer;
+import io.grpc.ClientStreamTracer.StreamInfo;
+import io.grpc.Metadata;
+import io.micrometer.core.instrument.Tags;
+
+/**
+ * Provides factories for {@link io.grpc.StreamTracer} that records metrics.
+ *
+ * <p>
+ * On the client-side, a factory is created for each call, and the factory creates a stream tracer for each attempt.
+ *
+ * <b>Note:</b> This class uses experimental grpc-java-API features.
+ */
+public final class MetricsClientStreamTracers {
+
+    private MetricsClientStreamTracers() {}
+
+    private static final class ClientTracer extends ClientStreamTracer {
+        private final CallAttemptsTracerFactory attemptsState;
+        private final StreamInfo info;
+        private final String fullMethodName;
+
+        ClientTracer(CallAttemptsTracerFactory attemptsState, StreamInfo info, String fullMethodName) {
+            this.attemptsState = attemptsState;
+            this.info = info;
+            this.fullMethodName = fullMethodName;
+        }
+
+    }
+
+    static final class CallAttemptsTracerFactory extends ClientStreamTracer.Factory {
+        private final String fullMethodName;
+        private final MetricsMeters metricsMeters;
+        private boolean attemptRecorded;
+
+        CallAttemptsTracerFactory(String fullMethodName, MetricsMeters metricsMeters) {
+            this.fullMethodName = checkNotNull(fullMethodName, "fullMethodName");
+            this.metricsMeters = checkNotNull(metricsMeters, "metricsMeters");
+
+            // Record here in case newClientStreamTracer() would never be called.
+            this.metricsMeters.getAttemptCounter()
+                    .withTags(Tags.of("grpc.method", fullMethodName))
+                    .increment();
+            this.attemptRecorded = true;
+        }
+
+        @Override
+        public ClientStreamTracer newClientStreamTracer(StreamInfo info, Metadata metadata) {
+            if (!this.attemptRecorded) {
+                this.metricsMeters.getAttemptCounter()
+                        .withTags((Tags.of("grpc.method", fullMethodName)))
+                        .increment();
+            } else {
+                this.attemptRecorded = false;
+            }
+            return new ClientTracer(this, info, fullMethodName);
+        }
+
+    }
+}

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/metrics/MetricsMeters.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2016-2023 The gRPC-Spring 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
+ *
+ *     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 net.devh.boot.grpc.client.metrics;
+
+import io.micrometer.core.instrument.Counter;
+import io.micrometer.core.instrument.Meter.MeterProvider;
+
+/*
+ * Collection of metrics meters.
+ */
+public class MetricsMeters {
+
+    private MeterProvider<Counter> attemptCounter;
+
+    private MetricsMeters(Builder builder) {
+        this.attemptCounter = builder.attemptCounter;
+    }
+
+    public MeterProvider<Counter> getAttemptCounter() {
+        return this.attemptCounter;
+    }
+
+    public static Builder newBuilder() {
+        return new Builder();
+    }
+
+    static class Builder {
+
+        private MeterProvider<Counter> attemptCounter;
+
+        private Builder() {}
+
+        public Builder setAttemptCounter(MeterProvider<Counter> counter) {
+            this.attemptCounter = counter;
+            return this;
+        }
+
+        public MetricsMeters build() {
+            return new MetricsMeters(this);
+        }
+    }
+}

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/metrics/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * A package containing client side classes for grpc metric collection.
+ */
+
+package net.devh.boot.grpc.client.metrics;