fix: improve warnings for Direct Path xDS set via env (#3019)

Fixes #2427

### Context
If `GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS` is set in the environment
aiming to enable Direct Path xDS in another client, we want to just warn
the user that _if this is intended_, it can be a misconfiguration and
that the gRPCLB Direct Path setting should be enabled as well.

### Approach
As said in the context, we will _warn_ the user that it _could_ be a
misconfiguration _if_ the env var setting was meant for the client in
question. Other warn cases remain the same.

### Coverage
Due to the fact that part of the method in question is tested via a
special env var test (not detected by SonarCloud), it will show as
uncovered. See this screenshot for coverage of all tests combined

![image](https://github.com/googleapis/sdk-platform-java/assets/22083784/af24e721-6495-4030-8804-c013b14679d7)

---------

Co-authored-by: Lawrence Qiu <[email protected]>

Author: diegomarquezp

.github/workflows/ci.yaml

@@ -30,6 +30,7 @@ jobs:
         # Set the Env Var for this step only
         env:
           GOOGLE_CLOUD_UNIVERSE_DOMAIN: random.com
+          GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS: true
       - run: bazelisk version
       - name: Install Maven modules
         run: |
@@ -80,6 +81,7 @@ jobs:
         # Set the Env Var for this step only
         env:
           GOOGLE_CLOUD_UNIVERSE_DOMAIN: random.com
+          GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS: true
       - run: bazelisk version
       - name: Install Maven modules
         run: |
@@ -130,6 +132,7 @@ jobs:
         # Set the Env Var for this step only
         env:
           GOOGLE_CLOUD_UNIVERSE_DOMAIN: random.com
+          GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS: true
 
   build-java8-gapic-generator-java:
     name: "build(8) for gapic-generator-java"

gax-java/gax-grpc/pom.xml

@@ -128,6 +128,30 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <configuration>
+          <!-- These tests require an Env Var to be set. Use -PenvVarTest to ONLY run these tests -->
+          <test>!InstantiatingGrpcChannelProviderTest#testLogDirectPathMisconfig_AttemptDirectPathNotSetAndAttemptDirectPathXdsSetViaEnv_warns</test>
+        </configuration>
+      </plugin>
     </plugins>
   </build>
+  <profiles>
+    <profile>
+      <id>envVarTest</id>
+      <build>
+        <plugins>
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-surefire-plugin</artifactId>
+            <configuration>
+              <test>InstantiatingGrpcChannelProviderTest#testLogDirectPathMisconfig_AttemptDirectPathNotSetAndAttemptDirectPathXdsSetViaEnv_warns</test>
+            </configuration>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
+  </profiles>
 </project>

gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java

@@ -92,7 +92,10 @@ public final class InstantiatingGrpcChannelProvider implements TransportChannelP
   static final Logger LOG = Logger.getLogger(InstantiatingGrpcChannelProvider.class.getName());
 
   static final String DIRECT_PATH_ENV_DISABLE_DIRECT_PATH = "GOOGLE_CLOUD_DISABLE_DIRECT_PATH";
-  private static final String DIRECT_PATH_ENV_ENABLE_XDS = "GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS";
+
+  @VisibleForTesting
+  static final String DIRECT_PATH_ENV_ENABLE_XDS = "GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS";
+
   static final long DIRECT_PATH_KEEP_ALIVE_TIME_SECONDS = 3600;
   static final long DIRECT_PATH_KEEP_ALIVE_TIMEOUT_SECONDS = 20;
   static final String GCE_PRODUCTION_NAME_PRIOR_2016 = "Google";
@@ -273,42 +276,63 @@ private boolean isDirectPathEnabled() {
     return false;
   }
 
+  private boolean isDirectPathXdsEnabledViaBuilderOption() {
+    return Boolean.TRUE.equals(attemptDirectPathXds);
+  }
+
+  private boolean isDirectPathXdsEnabledViaEnv() {
+    String directPathXdsEnv = envProvider.getenv(DIRECT_PATH_ENV_ENABLE_XDS);
+    return Boolean.parseBoolean(directPathXdsEnv);
+  }
+
+  /**
+   * This method tells if Direct Path xDS was enabled. There are two ways of enabling it: via
+   * environment variable (by setting GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS=true) or when building
+   * this channel provider (via the {@link Builder#setAttemptDirectPathXds()} method).
+   *
+   * @return true if Direct Path xDS was either enabled via env var or via builder option
+   */
   @InternalApi
   public boolean isDirectPathXdsEnabled() {
-    // Method 1: Enable DirectPath xDS by option.
-    if (Boolean.TRUE.equals(attemptDirectPathXds)) {
-      return true;
-    }
-    // Method 2: Enable DirectPath xDS by env.
-    String directPathXdsEnv = envProvider.getenv(DIRECT_PATH_ENV_ENABLE_XDS);
-    boolean isDirectPathXdsEnv = Boolean.parseBoolean(directPathXdsEnv);
-    if (isDirectPathXdsEnv) {
-      return true;
-    }
-    return false;
+    return isDirectPathXdsEnabledViaEnv() || isDirectPathXdsEnabledViaBuilderOption();
   }
 
   // This method should be called once per client initialization, hence can not be called in the
   // builder or createSingleChannel, only in getTransportChannel which creates the first channel
   // for a client.
   private void logDirectPathMisconfig() {
     if (isDirectPathXdsEnabled()) {
-      // Case 1: does not enable DirectPath
       if (!isDirectPathEnabled()) {
-        LOG.log(
-            Level.WARNING,
-            "DirectPath is misconfigured. Please set the attemptDirectPath option along with the"
-                + " attemptDirectPathXds option.");
+        // This misconfiguration occurs when Direct Path xDS is enabled, but Direct Path is not
+        // Direct Path xDS can be enabled two ways: via environment variable or via builder.
+        // Case 1: Direct Path is only enabled via xDS env var. We will _warn_ the user that this is
+        // a misconfiguration if they intended to set the env var.
+        if (isDirectPathXdsEnabledViaEnv()) {
+          LOG.log(
+              Level.WARNING,
+              "Env var "
+                  + DIRECT_PATH_ENV_ENABLE_XDS
+                  + " was found and set to TRUE, but DirectPath was not enabled for this client. If this is intended for "
+                  + "this client, please note that this is a misconfiguration and set the attemptDirectPath option as well.");
+        }
+        // Case 2: Direct Path xDS was enabled via Builder. Direct Path Traffic Director must be set
+        // (enabled with `setAttemptDirectPath(true)`) along with xDS.
+        // Here we warn the user about this.
+        else if (isDirectPathXdsEnabledViaBuilderOption()) {
+          LOG.log(
+              Level.WARNING,
+              "DirectPath is misconfigured. The DirectPath XDS option was set, but the attemptDirectPath option was not. Please set both the attemptDirectPath and attemptDirectPathXds options.");
+        }
       } else {
-        // Case 2: credential is not correctly set
+        // Case 3: credential is not correctly set
         if (!isCredentialDirectPathCompatible()) {
           LOG.log(
               Level.WARNING,
               "DirectPath is misconfigured. Please make sure the credential is an instance of "
                   + ComputeEngineCredentials.class.getName()
                   + " .");
         }
-        // Case 3: not running on GCE
+        // Case 4: not running on GCE
         if (!isOnComputeEngine()) {
           LOG.log(
               Level.WARNING,

gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProviderTest.java

@@ -594,28 +594,50 @@ protected Object getMtlsObjectFromTransportChannel(MtlsProvider provider)
     return channelProvider.createMtlsChannelCredentials();
   }
 
+  private InstantiatingGrpcChannelProvider.Builder
+      createChannelProviderBuilderForDirectPathLogTests() {
+    return InstantiatingGrpcChannelProvider.newBuilder()
+        .setHeaderProvider(Mockito.mock(HeaderProvider.class))
+        .setExecutor(Mockito.mock(Executor.class))
+        .setEndpoint("localhost:8080");
+  }
+
+  private void createAndCloseTransportChannel(InstantiatingGrpcChannelProvider provider)
+      throws Exception {
+    TransportChannel transportChannel = provider.getTransportChannel();
+    transportChannel.close();
+    transportChannel.awaitTermination(10, TimeUnit.SECONDS);
+  }
+
   @Test
-  void testLogDirectPathMisconfigAttrempDirectPathNotSet() throws Exception {
+  void
+      testLogDirectPathMisconfig_AttemptDirectPathNotSetAndAttemptDirectPathXdsSetViaBuilder_warns()
+          throws Exception {
     FakeLogHandler logHandler = new FakeLogHandler();
     InstantiatingGrpcChannelProvider.LOG.addHandler(logHandler);
     InstantiatingGrpcChannelProvider provider =
-        InstantiatingGrpcChannelProvider.newBuilder()
-            .setAttemptDirectPathXds()
-            .setHeaderProvider(Mockito.mock(HeaderProvider.class))
-            .setExecutor(Mockito.mock(Executor.class))
-            .setEndpoint("localhost:8080")
-            .build();
+        createChannelProviderBuilderForDirectPathLogTests().setAttemptDirectPathXds().build();
+    createAndCloseTransportChannel(provider);
+    assertThat(logHandler.getAllMessages())
+        .contains(
+            "DirectPath is misconfigured. The DirectPath XDS option was set, but the attemptDirectPath option was not. Please set both the attemptDirectPath and attemptDirectPathXds options.");
+    InstantiatingGrpcChannelProvider.LOG.removeHandler(logHandler);
+  }
 
-    TransportChannel transportChannel = provider.getTransportChannel();
+  @Test
+  void testLogDirectPathMisconfig_AttemptDirectPathNotSetAndAttemptDirectPathXdsSetViaEnv_warns()
+      throws Exception {
+    FakeLogHandler logHandler = new FakeLogHandler();
+    InstantiatingGrpcChannelProvider.LOG.addHandler(logHandler);
 
+    InstantiatingGrpcChannelProvider provider =
+        createChannelProviderBuilderForDirectPathLogTests().build();
+    createAndCloseTransportChannel(provider);
     assertThat(logHandler.getAllMessages())
         .contains(
-            "DirectPath is misconfigured. Please set the attemptDirectPath option along with the"
-                + " attemptDirectPathXds option.");
+            "Env var GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS was found and set to TRUE, but DirectPath was not enabled for this client. If this is intended for "
+                + "this client, please note that this is a misconfiguration and set the attemptDirectPath option as well.");
     InstantiatingGrpcChannelProvider.LOG.removeHandler(logHandler);
-
-    transportChannel.close();
-    transportChannel.awaitTermination(10, TimeUnit.SECONDS);
   }
 
   @Test