feat(observability): introduce minimal tracing implementation

gax-java/dependencies.properties

@@ -40,6 +40,7 @@ maven.com_google_api_grpc_grpc_google_common_protos=com.google.api.grpc:grpc-goo
 maven.com_google_auth_google_auth_library_oauth2_http=com.google.auth:google-auth-library-oauth2-http:1.42.1
 maven.com_google_auth_google_auth_library_credentials=com.google.auth:google-auth-library-credentials:1.42.1
 maven.io_opentelemetry_opentelemetry_api=io.opentelemetry:opentelemetry-api:1.47.0
+maven.io_opentelemetry_opentelemetry_context=io.opentelemetry:opentelemetry-context:1.47.0
 maven.io_opencensus_opencensus_api=io.opencensus:opencensus-api:0.31.1
 maven.io_opencensus_opencensus_contrib_grpc_metrics=io.opencensus:opencensus-contrib-grpc-metrics:0.31.1
 maven.io_opencensus_opencensus_contrib_http_util=io.opencensus:opencensus-contrib-http-util:0.31.1

gax-java/gax/BUILD.bazel

@@ -19,6 +19,7 @@ _COMPILE_DEPS = [
     "@com_google_errorprone_error_prone_annotations//jar",
     "@com_google_guava_guava//jar",
     "@io_opentelemetry_opentelemetry_api//jar",
+    "@io_opentelemetry_opentelemetry_context//jar",
     "@io_opencensus_opencensus_api//jar",
     "@io_opencensus_opencensus_contrib_http_util//jar",
     "@io_grpc_grpc_java//context:context",

gax-java/gax/src/main/java/com/google/api/gax/rpc/ClientContext.java

@@ -41,6 +41,7 @@
 import com.google.api.gax.core.ExecutorAsBackgroundResource;
 import com.google.api.gax.core.ExecutorProvider;
 import com.google.api.gax.rpc.internal.QuotaProjectIdHidingCredentials;
+import com.google.api.gax.tracing.ApiTracerContext;
 import com.google.api.gax.tracing.ApiTracerFactory;
 import com.google.api.gax.tracing.BaseApiTracerFactory;
 import com.google.auth.ApiKeyCredentials;
@@ -269,6 +270,11 @@ public static ClientContext create(StubSettings settings) throws IOException {
     if (watchdogProvider != null && watchdogProvider.shouldAutoClose()) {
       backgroundResources.add(watchdog);
     }
+    ApiTracerContext apiTracerContext =
+        ApiTracerContext.newBuilder()
+            .setServerAddress(endpointContext.resolvedServerAddress())
+            .build();
+    ApiTracerFactory apiTracerFactory = settings.getTracerFactory().withContext(apiTracerContext);
 
     return newBuilder()
         .setBackgroundResources(backgroundResources.build())
@@ -284,7 +290,7 @@ public static ClientContext create(StubSettings settings) throws IOException {
         .setQuotaProjectId(settings.getQuotaProjectId())
         .setStreamWatchdog(watchdog)
         .setStreamWatchdogCheckIntervalDuration(settings.getStreamWatchdogCheckIntervalDuration())
-        .setTracerFactory(settings.getTracerFactory())
+        .setTracerFactory(apiTracerFactory)
         .setEndpointContext(endpointContext)
         .build();
   }

gax-java/gax/src/main/java/com/google/api/gax/rpc/EndpointContext.java

@@ -40,6 +40,7 @@
 import com.google.auto.value.AutoValue;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Strings;
+import com.google.common.net.HostAndPort;
 import java.io.IOException;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -133,6 +134,8 @@ public static EndpointContext getDefaultInstance() {
 
   public abstract String resolvedEndpoint();
 
+  public abstract String resolvedServerAddress();
+
   public abstract Builder toBuilder();
 
   public static Builder newBuilder() {
@@ -228,6 +231,8 @@ public abstract static class Builder {
 
     public abstract Builder setResolvedEndpoint(String resolvedEndpoint);
 
+    public abstract Builder setResolvedServerAddress(String serverAddress);
+
     public abstract Builder setResolvedUniverseDomain(String resolvedUniverseDomain);
 
     abstract Builder setUseS2A(boolean useS2A);
@@ -382,6 +387,23 @@ boolean shouldUseS2A() {
       return mtlsEndpoint().contains(Credentials.GOOGLE_DEFAULT_UNIVERSE);
     }
 
+    private String parseServerAddress(String endpoint) {
+      if (Strings.isNullOrEmpty(endpoint)) {
+        return endpoint;
+      }
+      String hostPort = endpoint;
+      if (hostPort.contains("://")) {
+        // Strip the scheme if present. HostAndPort doesn't support schemes.
+        hostPort = hostPort.substring(hostPort.indexOf("://") + 3);
+      }
+      try {
+        return HostAndPort.fromString(hostPort).getHost();
+      } catch (IllegalArgumentException e) {
+        // Fallback for cases HostAndPort can't handle.
+        return hostPort;
+      }
+    }
+
     // Default to port 443 for HTTPS. Using HTTP requires explicitly setting the endpoint
     private String buildEndpointTemplate(String serviceName, String resolvedUniverseDomain) {
       return serviceName + "." + resolvedUniverseDomain + ":443";
@@ -416,7 +438,9 @@ String mtlsEndpointResolver(
     public EndpointContext build() throws IOException {
       // The Universe Domain is used to resolve the Endpoint. It should be resolved first
       setResolvedUniverseDomain(determineUniverseDomain());
-      setResolvedEndpoint(determineEndpoint());
+      String endpoint = determineEndpoint();
+      setResolvedEndpoint(endpoint);
+      setResolvedServerAddress(parseServerAddress(endpoint));
       setUseS2A(shouldUseS2A());
       return autoBuild();
     }

gax-java/gax/src/main/java/com/google/api/gax/tracing/ApiTracerContext.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.api.gax.tracing;
+
+import com.google.api.core.InternalApi;
+import com.google.auto.value.AutoValue;
+import javax.annotation.Nullable;
+
+/**
+ * A context object that contains information used to infer attributes that are common for all
+ * {@link ApiTracer}s.
+ *
+ * <p>For internal use only.
+ */
+@InternalApi
+@AutoValue
+public abstract class ApiTracerContext {
+
+  @Nullable
+  public abstract String getServerAddress();
+
+  public static Builder newBuilder() {
+    return new AutoValue_ApiTracerContext.Builder();
+  }
+
+  @AutoValue.Builder
+  public abstract static class Builder {
+    public abstract Builder setServerAddress(String serverAddress);
+
+    public abstract ApiTracerContext build();
+  }
+}

gax-java/gax/src/main/java/com/google/api/gax/tracing/ApiTracerFactory.java

@@ -61,4 +61,15 @@ enum OperationType {
    * @param operationType the type of operation that the tracer will trace
    */
   ApiTracer newTracer(ApiTracer parent, SpanName spanName, OperationType operationType);
+
+  /**
+   * Returns a new {@link ApiTracerFactory} that will use the provided context to infer attributes
+   * for all tracers created by the factory.
+   *
+   * @param context an {@link ApiTracerContext} object containing information to construct
+   *     attributes
+   */
+  default ApiTracerFactory withContext(ApiTracerContext context) {
+    return this;
+  }
 }

gax-java/gax/src/main/java/com/google/api/gax/tracing/AppCentricTracer.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.api.gax.tracing;
+
+import com.google.api.core.BetaApi;
+import com.google.api.core.InternalApi;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * An implementation of {@link ApiTracer} that uses a {@link TraceRecorder} to record traces. This
+ * implementation is agnostic to the specific {@link TraceRecorder} in order to allow extensions
+ * that interact with other backends.
+ */
+@BetaApi
+@InternalApi
+public class AppCentricTracer extends BaseApiTracer {
+  public static final String SERVER_ADDRESS_ATTRIBUTE = "server.address";
+  public static final String LANGUAGE_ATTRIBUTE = "gcp.client.language";
+
+  public static final String DEFAULT_LANGUAGE = "Java";
+
+  private final TraceRecorder recorder;
+  private final Map<String, String> attemptAttributes;
+  private final String attemptSpanName;
+  private final TraceRecorder.TraceSpan operationHandle;
+  private TraceRecorder.TraceSpan attemptHandle;
+
+  /**
+   * Creates a new instance of {@code AppCentricTracer}.
+   *
+   * @param recorder the {@link TraceRecorder} to use for recording spans
+   * @param operationSpanName the name of the long-lived operation span
+   * @param attemptSpanName the name of the individual attempt spans
+   * @param operationAttributes attributes to be added to the operation span
+   * @param attemptAttributes attributes to be added to each attempt span
+   */
+  public AppCentricTracer(
+      TraceRecorder recorder,
+      String operationSpanName,
+      String attemptSpanName,
+      Map<String, String> operationAttributes,
+      Map<String, String> attemptAttributes) {
+    this.recorder = recorder;
+    this.attemptSpanName = attemptSpanName;
+    this.attemptAttributes = new HashMap<>(attemptAttributes);
+    this.attemptAttributes.put(LANGUAGE_ATTRIBUTE, DEFAULT_LANGUAGE);
+
+    // Start the long-lived operation span.
+    this.operationHandle = recorder.createSpan(operationSpanName, operationAttributes);
+  }
+
+  @Override
+  public void attemptStarted(Object request, int attemptNumber) {
+    Map<String, String> attemptAttributes = new HashMap<>(this.attemptAttributes);
+    // Start the specific attempt span with the operation span as parent
+    this.attemptHandle = recorder.createSpan(attemptSpanName, attemptAttributes, operationHandle);
+  }
+
+  @Override
+  public void attemptSucceeded() {
+    endAttempt();
+  }
+
+  private void endAttempt() {
+    if (attemptHandle != null) {
+      attemptHandle.end();
+      attemptHandle = null;
+    }
+  }
+
+  @Override
+  public void operationSucceeded() {
+    operationHandle.end();
+  }
+}

gax-java/gax/src/main/java/com/google/api/gax/tracing/AppCentricTracerFactory.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.api.gax.tracing;
+
+import com.google.api.core.BetaApi;
+import com.google.api.core.InternalApi;
+import com.google.common.annotations.VisibleForTesting;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A {@link ApiTracerFactory} to build instances of {@link AppCentricTracer}.
+ *
+ * <p>This class wraps the {@link TraceRecorder} and pass it to {@link AppCentricTracer}. It will be
+ * used to record traces in {@link AppCentricTracer}.
+ *
+ * <p>This class is expected to be initialized once during client initialization.
+ */
+@BetaApi
+@InternalApi
+public class AppCentricTracerFactory implements ApiTracerFactory {
+  private final TraceRecorder traceRecorder;
+
+  /** Mapping of client attributes that are set for every AppCentricTracer at operation level */
+  private final Map<String, String> operationAttributes;
+
+  /** Mapping of client attributes that are set for every AppCentricTracer at attempt level */
+  private final Map<String, String> attemptAttributes;
+
+  /** Creates a AppCentricTracerFactory */
+  public AppCentricTracerFactory(TraceRecorder traceRecorder) {
+    this(traceRecorder, new HashMap<>(), new HashMap<>());
+  }
+
+  /**
+   * Pass in a Map of client level attributes which will be added to every single AppCentricTracer
+   * created from the ApiTracerFactory. This is package private since span attributes are determined
+   * internally.
+   */
+  @VisibleForTesting
+  AppCentricTracerFactory(
+      TraceRecorder traceRecorder,
+      Map<String, String> operationAttributes,
+      Map<String, String> attemptAttributes) {
+    this.traceRecorder = traceRecorder;
+
+    this.operationAttributes = new HashMap<>(operationAttributes);
+    this.attemptAttributes = new HashMap<>(attemptAttributes);
+  }
+
+  @Override
+  public ApiTracer newTracer(ApiTracer parent, SpanName spanName, OperationType operationType) {
+    // TODO(diegomarquezp): these are placeholders for span names and will be adjusted as the
+    // feature is developed.
+    String operationSpanName =
+        spanName.getClientName() + "." + spanName.getMethodName() + "/operation";
+    String attemptSpanName = spanName.getClientName() + "/" + spanName.getMethodName() + "/attempt";
+
+    AppCentricTracer appCentricTracer =
+        new AppCentricTracer(
+            traceRecorder,
+            operationSpanName,
+            attemptSpanName,
+            this.operationAttributes,
+            this.attemptAttributes);
+    return appCentricTracer;
+  }
+
+  @Override
+  public ApiTracerFactory withContext(ApiTracerContext context) {
+    Map<String, String> newAttemptAttributes = new HashMap<>(this.attemptAttributes);
+    if (context.getServerAddress() != null) {
+      newAttemptAttributes.put(
+          AppCentricTracer.SERVER_ADDRESS_ATTRIBUTE, context.getServerAddress());
+    }
+    return new AppCentricTracerFactory(traceRecorder, operationAttributes, newAttemptAttributes);
+  }
+}