feat: Allow user-agents to be specified by both internal headers and …

…user headers (#1190)

* feat: Allow user-agents to be specified by both internal headers and user headers

This is primarily meant to address the googleapis/java-bigtable#404 (review). Where both the hbase adapter and the core client needs to set the UserAgent. To reconcile the conflict this PR takes grpc's approach and concatenates the values. The reason this needs to happen now is that for DirectPath we need to ship clients that send a UserAgent, however Bigtable needs to keep stats to differentiate client usage.

* remove stale code

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

@@ -42,10 +42,13 @@
 import com.google.auto.value.AutoValue;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Sets;
 import java.io.IOException;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
@@ -222,27 +225,33 @@ public static ClientContext create(StubSettings settings) throws IOException {
    * Project Id.
    */
   private static Map<String, String> getHeadersFromSettings(StubSettings settings) {
-    ImmutableMap.Builder<String, String> headersBuilder = ImmutableMap.builder();
-    if (settings.getQuotaProjectId() != null) {
-      headersBuilder.put(QUOTA_PROJECT_ID_HEADER_KEY, settings.getQuotaProjectId());
-      for (Map.Entry<String, String> entry : settings.getHeaderProvider().getHeaders().entrySet()) {
-        if (entry.getKey().equals(QUOTA_PROJECT_ID_HEADER_KEY)) {
-          continue;
-        }
-        headersBuilder.put(entry);
+    // Resolve conflicts when merging headers from multiple sources
+    Map<String, String> userHeaders = settings.getHeaderProvider().getHeaders();
+    Map<String, String> internalHeaders = settings.getInternalHeaderProvider().getHeaders();
+    Map<String, String> conflictResolution = new HashMap<>();
+
+    Set<String> conflicts = Sets.intersection(userHeaders.keySet(), internalHeaders.keySet());
+    for (String key : conflicts) {
+      if ("user-agent".equals(key)) {
+        conflictResolution.put(key, userHeaders.get(key) + " " + internalHeaders.get(key));
+        continue;
       }
-      for (Map.Entry<String, String> entry :
-          settings.getInternalHeaderProvider().getHeaders().entrySet()) {
-        if (entry.getKey().equals(QUOTA_PROJECT_ID_HEADER_KEY)) {
-          continue;
-        }
-        headersBuilder.put(entry);
+      // Backwards compat: quota project id can conflict if its overriden in settings
+      if (QUOTA_PROJECT_ID_HEADER_KEY.equals(key) && settings.getQuotaProjectId() != null) {
+        continue;
       }
-    } else {
-      headersBuilder.putAll(settings.getHeaderProvider().getHeaders());
-      headersBuilder.putAll(settings.getInternalHeaderProvider().getHeaders());
+      throw new IllegalArgumentException("Header provider can't override the header: " + key);
+    }
+    if (settings.getQuotaProjectId() != null) {
+      conflictResolution.put(QUOTA_PROJECT_ID_HEADER_KEY, settings.getQuotaProjectId());
     }
-    return headersBuilder.build();
+
+    Map<String, String> effectiveHeaders = new HashMap<>();
+    effectiveHeaders.putAll(internalHeaders);
+    effectiveHeaders.putAll(userHeaders);
+    effectiveHeaders.putAll(conflictResolution);
+
+    return ImmutableMap.copyOf(effectiveHeaders);
   }
 
   @AutoValue.Builder

gax/src/test/java/com/google/api/gax/rpc/ClientContextTest.java

@@ -36,6 +36,7 @@
 import com.google.api.gax.core.CredentialsProvider;
 import com.google.api.gax.core.ExecutorProvider;
 import com.google.api.gax.core.FixedCredentialsProvider;
+import com.google.api.gax.core.FixedExecutorProvider;
 import com.google.api.gax.rpc.testing.FakeChannel;
 import com.google.api.gax.rpc.testing.FakeClientSettings;
 import com.google.api.gax.rpc.testing.FakeTransportChannel;
@@ -526,4 +527,75 @@ public Credentials getCredentials() throws IOException {
     ClientContext clientContext = ClientContext.create(builder.build());
     assertThat(clientContext.getCredentials().getRequestMetadata(null)).isEqualTo(metaData);
   }
+
+  @Test
+  public void testUserAgentInternalOnly() throws Exception {
+    TransportChannelProvider transportChannelProvider =
+        new FakeTransportProvider(
+            FakeTransportChannel.create(new FakeChannel()), null, true, null, null);
+
+    ClientSettings.Builder builder =
+        new FakeClientSettings.Builder()
+            .setExecutorProvider(
+                FixedExecutorProvider.create(Mockito.mock(ScheduledExecutorService.class)))
+            .setTransportChannelProvider(transportChannelProvider)
+            .setCredentialsProvider(
+                FixedCredentialsProvider.create(Mockito.mock(GoogleCredentials.class)));
+
+    builder.setInternalHeaderProvider(FixedHeaderProvider.create("user-agent", "internal-agent"));
+
+    ClientContext clientContext = ClientContext.create(builder.build());
+    FakeTransportChannel transportChannel =
+        (FakeTransportChannel) clientContext.getTransportChannel();
+
+    assertThat(transportChannel.getHeaders()).containsEntry("user-agent", "internal-agent");
+  }
+
+  @Test
+  public void testUserAgentExternalOnly() throws Exception {
+    TransportChannelProvider transportChannelProvider =
+        new FakeTransportProvider(
+            FakeTransportChannel.create(new FakeChannel()), null, true, null, null);
+
+    ClientSettings.Builder builder =
+        new FakeClientSettings.Builder()
+            .setExecutorProvider(
+                FixedExecutorProvider.create(Mockito.mock(ScheduledExecutorService.class)))
+            .setTransportChannelProvider(transportChannelProvider)
+            .setCredentialsProvider(
+                FixedCredentialsProvider.create(Mockito.mock(GoogleCredentials.class)));
+
+    builder.setHeaderProvider(FixedHeaderProvider.create("user-agent", "user-supplied-agent"));
+
+    ClientContext clientContext = ClientContext.create(builder.build());
+    FakeTransportChannel transportChannel =
+        (FakeTransportChannel) clientContext.getTransportChannel();
+
+    assertThat(transportChannel.getHeaders()).containsEntry("user-agent", "user-supplied-agent");
+  }
+
+  @Test
+  public void testUserAgentConcat() throws Exception {
+    TransportChannelProvider transportChannelProvider =
+        new FakeTransportProvider(
+            FakeTransportChannel.create(new FakeChannel()), null, true, null, null);
+
+    ClientSettings.Builder builder =
+        new FakeClientSettings.Builder()
+            .setExecutorProvider(
+                FixedExecutorProvider.create(Mockito.mock(ScheduledExecutorService.class)))
+            .setTransportChannelProvider(transportChannelProvider)
+            .setCredentialsProvider(
+                FixedCredentialsProvider.create(Mockito.mock(GoogleCredentials.class)));
+
+    builder.setHeaderProvider(FixedHeaderProvider.create("user-agent", "user-supplied-agent"));
+    builder.setInternalHeaderProvider(FixedHeaderProvider.create("user-agent", "internal-agent"));
+
+    ClientContext clientContext = ClientContext.create(builder.build());
+    FakeTransportChannel transportChannel =
+        (FakeTransportChannel) clientContext.getTransportChannel();
+
+    assertThat(transportChannel.getHeaders())
+        .containsEntry("user-agent", "user-supplied-agent internal-agent");
+  }
 }