feat: Add ApiVersion Support

google-api-client/src/main/java/com/google/api/client/googleapis/services/AbstractGoogleClientRequest.java

@@ -37,6 +37,7 @@
 import com.google.api.client.http.UriTemplate;
 import com.google.api.client.util.GenericData;
 import com.google.api.client.util.Preconditions;
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Joiner;
 import java.io.IOException;
 import java.io.InputStream;
@@ -62,7 +63,13 @@ public abstract class AbstractGoogleClientRequest<T> extends GenericData {
    */
   public static final String USER_AGENT_SUFFIX = "Google-API-Java-Client";
 
-  private static final String API_VERSION_HEADER = "X-Goog-Api-Client";
+  private static final String API_CLIENT_HEADER = "X-Goog-Api-Client";
+
+  /**
+   * The generated request class will pass this constant as part of the header if the RPC supports
+   * ApiVersion.
+   */
+  protected static final String API_VERSION_HEADER = "X-Google-Api-Version";
 
   /** Google client. */
   private final AbstractGoogleClient abstractGoogleClient;
@@ -133,7 +140,7 @@ protected AbstractGoogleClientRequest(
       requestHeaders.setUserAgent(USER_AGENT_SUFFIX + "/" + GoogleUtils.VERSION);
     }
     // Set the header for the Api Client version (Java and OS version)
-    requestHeaders.set(API_VERSION_HEADER, ApiClientVersion.DEFAULT_VERSION);
+    requestHeaders.set(API_CLIENT_HEADER, ApiClientVersion.DEFAULT_VERSION);
   }
 
   /**
@@ -312,6 +319,12 @@ public AbstractGoogleClientRequest<T> setRequestHeaders(HttpHeaders headers) {
     return this;
   }
 
+  /** Returns the ApiVersion set in the headers. If ApiVersion is not set, null is returned. */
+  @VisibleForTesting
+  String getApiVersionHeader() {
+    return (String) requestHeaders.get(API_VERSION_HEADER);
+  }
+
   /**
    * Returns the HTTP headers of the last response or {@code null} before request has been executed.
    */

google-api-client/src/main/java/com/google/api/client/googleapis/testing/services/MockGoogleClientRequest.java

@@ -18,6 +18,7 @@
 import com.google.api.client.http.HttpHeaders;
 import com.google.api.client.http.UriTemplate;
 import com.google.api.client.util.Beta;
+import com.google.common.base.Strings;
 
 /**
  * {@link Beta} <br>
@@ -46,7 +47,32 @@ public MockGoogleClientRequest(
       String uriTemplate,
       HttpContent content,
       Class<T> responseClass) {
+    this(client, method, uriTemplate, content, responseClass, null);
+  }
+
+  /**
+   * @param client Google client
+   * @param method HTTP Method
+   * @param uriTemplate URI template for the path relative to the base URL. If it starts with a "/"
+   *     the base path from the base URL will be stripped out. The URI template can also be a full
+   *     URL. URI template expansion is done using {@link UriTemplate#expand(String, String, Object,
+   *     boolean)}
+   * @param content HTTP content or {@code null} for none
+   * @param responseClass response class to parse into
+   * @param apiVersion ApiVersion to be passed to the header
+   */
+  public MockGoogleClientRequest(
+      AbstractGoogleClient client,
+      String method,
+      String uriTemplate,
+      HttpContent content,
+      Class<T> responseClass,
+      String apiVersion) {
     super(client, method, uriTemplate, content, responseClass);
+    // Matches generator code: Null or Empty String is not set to the header
+    if (!Strings.isNullOrEmpty(apiVersion)) {
+      getRequestHeaders().set(API_VERSION_HEADER, apiVersion);
+    }
   }
 
   @Override

google-api-client/src/test/java/com/google/api/client/googleapis/services/AbstractGoogleClientRequestTest.java

@@ -242,6 +242,49 @@ public void testUserAgent() throws IOException {
     request.executeUnparsed();
   }
 
+  public void testSetsApiVersionHeader_apiVersionSet() {
+    String apiVersion = "testVersion";
+    HttpTransport transport = new MockHttpTransport();
+    MockGoogleClient client =
+        new MockGoogleClient.Builder(transport, ROOT_URL, SERVICE_PATH, JSON_OBJECT_PARSER, null)
+            .build();
+    AbstractGoogleClientRequest<Void> request =
+        new MockGoogleClientRequest<>(
+            client, HttpMethods.GET, URI_TEMPLATE, null, Void.class, apiVersion);
+    assertEquals(apiVersion, request.getApiVersionHeader());
+  }
+
+  public void testDoesNotSetsApiVersionHeader_noApiVersionSet() {
+    HttpTransport transport = new MockHttpTransport();
+    MockGoogleClient client =
+        new MockGoogleClient.Builder(transport, ROOT_URL, SERVICE_PATH, JSON_OBJECT_PARSER, null)
+            .build();
+    AbstractGoogleClientRequest<Void> request =
+        new MockGoogleClientRequest<>(client, HttpMethods.GET, URI_TEMPLATE, null, Void.class);
+    assertNull(request.getApiVersionHeader());
+  }
+
+  public void testNullApiVersionHeader_noApiVersionSet() {
+    HttpTransport transport = new MockHttpTransport();
+    MockGoogleClient client =
+        new MockGoogleClient.Builder(transport, ROOT_URL, SERVICE_PATH, JSON_OBJECT_PARSER, null)
+            .build();
+    final AbstractGoogleClientRequest<Void> request =
+        new MockGoogleClientRequest<>(
+            client, HttpMethods.GET, URI_TEMPLATE, null, Void.class, null);
+    assertNull(request.getApiVersionHeader());
+  }
+
+  public void testEmptyStringApiVersionHeader_noApiVersionSet() {
+    HttpTransport transport = new MockHttpTransport();
+    MockGoogleClient client =
+        new MockGoogleClient.Builder(transport, ROOT_URL, SERVICE_PATH, JSON_OBJECT_PARSER, null)
+            .build();
+    final AbstractGoogleClientRequest<Void> request =
+        new MockGoogleClientRequest<>(client, HttpMethods.GET, URI_TEMPLATE, null, Void.class, "");
+    assertNull(request.getApiVersionHeader());
+  }
+
   public void testSetsApiClientHeader() throws IOException {
     HttpTransport transport =
         new AssertHeaderTransport("X-Goog-Api-Client", "gl-java/\\d+\\.\\d+\\.\\d+.*");