chore: Update java-genai header merging logic to handle vertex-genai-modules case

PiperOrigin-RevId: 914364665

Author: matthew29tang

src/main/java/com/google/genai/ApiClient.java

@@ -714,6 +714,37 @@ private Optional<Map<String, String>> getTimeoutHeader(HttpOptions httpOptionsTo
     return Optional.empty();
   }
 
+  /**
+   * Merges two user agent values, handling a special case for vertex-genai-modules.
+   *
+   * <p>Example:
+   * <li>val1 = google-genai-sdk/1.42.0 gl-java/22.0.2
+   * <li>val2 = vertex-genai-modules/1.2.3
+   * <li>Result: google-genai-sdk/1.42.0+vertex-genai-modules/1.2.3 gl-java/22.0.2
+   *
+   * @param val1 The first value.
+   * @param val2 The second value.
+   * @return The merged user agent value.
+   */
+  private String mergeUserAgentValues(String val1, String val2) {
+    String extensionRegex = "^vertex-genai-modules/[^ ]+.*";
+    boolean val1Matches = val1.matches(extensionRegex);
+    boolean val2Matches = val2.matches(extensionRegex);
+
+    if (val1Matches || val2Matches) {
+      String extensionHeader = val1Matches ? val1 : val2;
+      String baseHeader = val1Matches ? val2 : val1;
+
+      // Find google-genai-sdk/x.y.z in baseHeader
+      if (baseHeader.contains("google-genai-sdk/")) {
+        // $1 refers to the matched (google-genai-sdk/[^ ]+) group
+        return baseHeader.replaceFirst("(google-genai-sdk/[^ ]+)", "$1+" + extensionHeader);
+      }
+    }
+
+    return val1 + " " + val2;
+  }
+
   /**
    * Merges the http options to the client's http options.
    *
@@ -752,7 +783,7 @@ HttpOptions mergeHttpOptions(HttpOptions httpOptionsToApply) {
                   (val1, val2) -> {
                     if (entry.getKey().equals("user-agent")
                         || entry.getKey().equals("x-goog-api-client")) {
-                      return val1 + " " + val2;
+                      return mergeUserAgentValues(val1, val2);
                     }
                     return val2;
                   }));

src/test/java/com/google/genai/HttpApiClientTest.java

@@ -605,6 +605,26 @@ public void testInitHttpClientCustomUserAgent() throws Exception {
             + "' does not match the expected format.");
   }
 
+  @Test
+  public void testInitHttpClientExtensionsUserAgentMerge() throws Exception {
+    String vertexHeader = "vertex-genai-modules/1.2.3";
+    ImmutableMap<String, String> trackingHeaders =
+        ImmutableMap.of(
+            "x-goog-api-client", vertexHeader,
+            "user-agent", vertexHeader);
+    HttpOptions httpOptions = HttpOptions.builder().headers(trackingHeaders).build();
+    HttpApiClient client =
+        new HttpApiClient(Optional.of(API_KEY), Optional.of(httpOptions), Optional.empty());
+
+    String userAgent = client.httpOptions.headers().get().get("user-agent");
+    String apiClient = client.httpOptions.headers().get().get("x-goog-api-client");
+
+    String expectedRegex = "^google-genai-sdk/[^ ]+vertex-genai-modules/1.2.3 gl-java/[^ ]+$";
+
+    assertTrue(userAgent.matches(expectedRegex), "User-Agent did not match: " + userAgent);
+    assertTrue(apiClient.matches(expectedRegex), "x-goog-api-client did not match: " + apiClient);
+  }
+
   @Test
   public void testInitHttpClientMldev() throws Exception {
     HttpOptions httpOptions =