Use minimal fallback managed channel when none is specified

exporters/otlp/all/src/jmh/java/io/opentelemetry/exporter/otlp/trace/OltpExporterBenchmark.java

@@ -85,6 +85,7 @@ public void setUp() {
             "span",
             new UpstreamGrpcSender<>(
                 MarshalerTraceServiceGrpc.newFutureStub(defaultGrpcChannel, null),
+                /* shutdownChannel= */ false,
                 10,
                 Collections::emptyMap),
             MeterProvider::noop);

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/AbstractGrpcTelemetryExporterTest.java

@@ -5,6 +5,7 @@
 
 package io.opentelemetry.exporter.otlp.testing.internal;
 
+import static org.assertj.core.api.Assertions.as;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
@@ -23,8 +24,10 @@
 import com.linecorp.armeria.testing.junit5.server.SelfSignedCertificateExtension;
 import com.linecorp.armeria.testing.junit5.server.ServerExtension;
 import io.github.netmikey.logunit.api.LogCapturer;
+import io.grpc.ManagedChannel;
 import io.opentelemetry.exporter.internal.TlsUtil;
 import io.opentelemetry.exporter.internal.grpc.GrpcExporter;
+import io.opentelemetry.exporter.internal.grpc.MarshalerServiceStub;
 import io.opentelemetry.exporter.internal.marshal.Marshaler;
 import io.opentelemetry.internal.testing.slf4j.SuppressLogger;
 import io.opentelemetry.proto.collector.logs.v1.ExportLogsServiceRequest;
@@ -61,6 +64,7 @@
 import javax.net.ssl.TrustManager;
 import javax.net.ssl.X509KeyManager;
 import javax.net.ssl.X509TrustManager;
+import org.assertj.core.api.InstanceOfAssertFactories;
 import org.assertj.core.api.iterable.ThrowingExtractor;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
@@ -215,6 +219,23 @@ void reset() {
     httpRequests.clear();
   }
 
+  @Test
+  void minimalChannel() {
+    // Test that UpstreamGrpcSender uses minimal fallback managed channel, so skip for
+    // OkHttpGrpcSender
+    assumeThat(exporter.unwrap())
+        .extracting("delegate.grpcSender")
+        .matches(sender -> sender.getClass().getSimpleName().equals("UpstreamGrpcSender"));
+    // When no channel is explicitly set, should fall back to a minimally configured managed channel
+    TelemetryExporter<?> exporter = exporterBuilder().build();
+    assertThat(exporter.shutdown().join(10, TimeUnit.SECONDS).isSuccess()).isTrue();
+    assertThat(exporter.unwrap())
+        .extracting(
+            "delegate.grpcSender.stub",
+            as(InstanceOfAssertFactories.type(MarshalerServiceStub.class)))
+        .satisfies(stub -> assertThat(((ManagedChannel) stub.getChannel()).isShutdown()).isTrue());
+  }
+
   @Test
   void export() {
     List<T> telemetry = Collections.singletonList(generateFakeTelemetry());

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/ManagedChannelTelemetryExporterBuilder.java

@@ -22,7 +22,9 @@
 import java.time.Duration;
 import java.util.Collection;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 import javax.annotation.Nullable;
 import javax.net.ssl.SSLContext;
@@ -158,16 +160,19 @@ public TelemetryExporterBuilder<T> setChannel(Object channel) {
 
   @Override
   public TelemetryExporter<T> build() {
-    requireNonNull(channelBuilder, "channel");
+    AtomicReference<Runnable> shutdownCallbackRef = new AtomicReference<>(() -> {});
+    if (channelBuilder != null) {
+      try {
+        setSslContext(channelBuilder, tlsConfigHelper);
+      } catch (SSLException e) {
+        throw new IllegalStateException(e);
+      }
 
-    try {
-      setSslContext(channelBuilder, tlsConfigHelper);
-    } catch (SSLException e) {
-      throw new IllegalStateException(e);
+      ManagedChannel channel = channelBuilder.build();
+      delegate.setChannel(channel);
+      shutdownCallbackRef.set(channel::shutdownNow);
     }
 
-    ManagedChannel channel = channelBuilder.build();
-    delegate.setChannel(channel);
     TelemetryExporter<T> delegateExporter = delegate.build();
     return new TelemetryExporter<T>() {
       @Override
@@ -182,7 +187,7 @@ public CompletableResultCode export(Collection<T> items) {
 
       @Override
       public CompletableResultCode shutdown() {
-        channel.shutdownNow();
+        Optional.ofNullable(shutdownCallbackRef.get()).ifPresent(Runnable::run);
         return delegateExporter.shutdown();
       }
     };

exporters/sender/grpc-managed-channel/src/main/java/io/opentelemetry/exporter/sender/grpc/managedchannel/internal/UpstreamGrpcSender.java

@@ -8,6 +8,7 @@
 import com.google.common.util.concurrent.FutureCallback;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.MoreExecutors;
+import io.grpc.ManagedChannel;
 import io.grpc.Metadata;
 import io.grpc.Status;
 import io.grpc.stub.MetadataUtils;
@@ -32,16 +33,19 @@
 public final class UpstreamGrpcSender<T extends Marshaler> implements GrpcSender<T> {
 
   private final MarshalerServiceStub<T, ?, ?> stub;
+  private final boolean shutdownChannel;
   private final long timeoutNanos;
   private final Supplier<Map<String, List<String>>> headersSupplier;
 
   /** Creates a new {@link UpstreamGrpcSender}. */
   public UpstreamGrpcSender(
       MarshalerServiceStub<T, ?, ?> stub,
+      boolean shutdownChannel,
       long timeoutNanos,
       Supplier<Map<String, List<String>>> headersSupplier) {
-    this.timeoutNanos = timeoutNanos;
     this.stub = stub;
+    this.shutdownChannel = shutdownChannel;
+    this.timeoutNanos = timeoutNanos;
     this.headersSupplier = headersSupplier;
   }
 
@@ -82,6 +86,10 @@ public void onFailure(Throwable t) {
 
   @Override
   public CompletableResultCode shutdown() {
+    if (shutdownChannel) {
+      ManagedChannel channel = (ManagedChannel) stub.getChannel();
+      channel.shutdownNow();
+    }
     return CompletableResultCode.ofSuccess();
   }
 }

exporters/sender/grpc-managed-channel/src/main/java/io/opentelemetry/exporter/sender/grpc/managedchannel/internal/UpstreamGrpcSenderProvider.java

@@ -7,6 +7,8 @@
 
 import io.grpc.Channel;
 import io.grpc.Codec;
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
 import io.opentelemetry.exporter.internal.grpc.GrpcSender;
 import io.opentelemetry.exporter.internal.grpc.GrpcSenderProvider;
 import io.opentelemetry.exporter.internal.grpc.MarshalerServiceStub;
@@ -41,6 +43,13 @@ public <T extends Marshaler> GrpcSender<T> createSender(
       @Nullable RetryPolicy retryPolicy,
       @Nullable SSLContext sslContext,
       @Nullable X509TrustManager trustManager) {
+    boolean shutdownChannel = false;
+    if (managedChannel == null) {
+      // Shutdown the channel as part of the exporter shutdown sequence if
+      shutdownChannel = true;
+      managedChannel = minimalFallbackManagedChannel(endpoint);
+    }
+
     String authorityOverride = null;
     Map<String, List<String>> headers = headersSupplier.get();
     if (headers != null) {
@@ -58,6 +67,27 @@ public <T extends Marshaler> GrpcSender<T> createSender(
             .apply((Channel) managedChannel, authorityOverride)
             .withCompression(codec.getMessageEncoding());
 
-    return new UpstreamGrpcSender<>(stub, timeoutNanos, headersSupplier);
+    return new UpstreamGrpcSender<>(stub, shutdownChannel, timeoutNanos, headersSupplier);
+  }
+
+  /**
+   * If {@link ManagedChannel} is not explicitly set, provide a minimally configured fallback
+   * channel to avoid failing initialization.
+   *
+   * <p>This is required to accommodate autoconfigure with {@code
+   * opentelemetry-exporter-sender-grpc-managed-channel} which will always fail to initialize
+   * without a fallback channel since there isn't an opportunity to explicitly set the channel.
+   *
+   * <p>This only incorporates the target address, port, and whether to use plain text. All
+   * additional settings are intentionally ignored and must be configured with an explicitly set
+   * {@link ManagedChannel}.
+   */
+  private static ManagedChannel minimalFallbackManagedChannel(URI endpoint) {
+    ManagedChannelBuilder<?> channelBuilder =
+        ManagedChannelBuilder.forAddress(endpoint.getHost(), endpoint.getPort());
+    if (!endpoint.getScheme().equals("https")) {
+      channelBuilder.usePlaintext();
+    }
+    return channelBuilder.build();
   }
 }