fix: protobuf version not always getting set in headers

gax-java/gax/src/main/java/com/google/api/gax/core/GaxProperties.java

@@ -49,7 +49,7 @@ public class GaxProperties {
   private static final String GAX_VERSION = getLibraryVersion(GaxProperties.class, "version.gax");
   private static final String JAVA_VERSION = getRuntimeVersion();
   private static final String PROTOBUF_VERSION =
-      getBundleVersion(Any.class).orElse(DEFAULT_VERSION);
+      getProtobufVersion(Any.class, "com.google.protobuf.RuntimeVersion");;
 
   private GaxProperties() {}
 
@@ -148,4 +148,28 @@ static Optional<String> getBundleVersion(Class<?> clazz) {
       return Optional.empty();
     }
   }
+
+  /**
+   * Returns the Protobuf runtime version as reported by com.google.protobuf.RuntimeVersion, if
+   * class is available, otherwise by reading from MANIFEST file. If niether option is available
+   * defaults to protobuf version 3 as RuntimeVersion class is available in protobuf version 4+
+   */
+  @VisibleForTesting
+  static String getProtobufVersion(Class clazz, String protobufRuntimeVersionClassName) {
+    try {
+      Class<?> protobufRuntimeVersionClass = Class.forName(protobufRuntimeVersionClassName);
+      return protobufRuntimeVersionClass.getField("MAJOR").get(null)
+          + "."
+          + protobufRuntimeVersionClass.getField("MINOR").get(null)
+          + "."
+          + protobufRuntimeVersionClass.getField("PATCH").get(null);
+    } catch (ClassNotFoundException
+        | NoSuchFieldException
+        | IllegalAccessException
+        | SecurityException e) {
+      // If manifest file is not available default to protobuf generic version 3 as we know
+      // RuntimeVersion class is available in protobuf jar 4+.
+      return getBundleVersion(clazz).orElse("3");
+    }
+  }
 }

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

@@ -88,7 +88,7 @@ private static String checkAndAppendProtobufVersionIfNecessary(
     // TODO(b/366417603): appending protobuf version to existing client library token until resolved
     Pattern pattern = Pattern.compile("(gccl|gapic)\\S*");
     Matcher matcher = pattern.matcher(apiClientHeaderValue);
-    if (matcher.find()) {
+    if (matcher.find() && GaxProperties.getProtobufVersion() != null) {
       return apiClientHeaderValue.substring(0, matcher.end())
           + "--"
           + PROTOBUF_HEADER_VERSION_KEY

gax-java/gax/src/main/resources/META-INF/native-image/com.google.api/gax/reflect-config.json

@@ -0,0 +1,10 @@
+[
+  {
+    "name": "com.google.protobuf.RuntimeVersion",
+    "fields" : [
+      { "name" : "MAJOR" },
+      { "name" : "MINOR" },
+      { "name" : "PATCH" }
+    ]
+  }
+]

gax-java/gax/src/test/java/com/google/api/gax/core/GaxPropertiesTest.java

@@ -35,6 +35,7 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.common.base.Strings;
+import com.google.protobuf.Any;
 import java.io.IOException;
 import java.util.Optional;
 import java.util.regex.Pattern;
@@ -160,12 +161,8 @@ void testGetJavaRuntimeInfo_nullJavaVersion() {
 
   @Test
   public void testGetProtobufVersion() throws IOException {
-    Version version = readVersion(GaxProperties.getProtobufVersion());
-
-    assertTrue(version.major >= 3);
-    if (version.major == 3) {
-      assertTrue(version.minor >= 25);
-    }
+    assertTrue(
+        Pattern.compile("^\\d+\\.\\d+\\.\\d+").matcher(GaxProperties.getProtobufVersion()).find());
   }
 
   @Test
@@ -175,6 +172,34 @@ public void testGetBundleVersion_noManifestFile() throws IOException {
     assertFalse(version.isPresent());
   }
 
+  @Test
+  void testGetProtobufVersion_success() {
+    String version = GaxProperties.getProtobufVersion(Any.class, "com.google.protobuf.Any");
+
+    assertTrue(Pattern.compile("^\\d+\\.\\d+\\.\\d+").matcher(version).find());
+  }
+
+  @Test
+  void testGetProtobufVersion_classNotFoundException() throws Exception {
+    String version = GaxProperties.getProtobufVersion(Any.class, "foo.NonExistantClass");
+
+    assertTrue(Pattern.compile("^\\d+\\.\\d+\\.\\d+").matcher(version).find());
+  }
+
+  @Test
+  void testgetProtobufVersion_noSuchFieldException() throws Exception {
+    String version = GaxProperties.getProtobufVersion(Any.class, "java.lang.Class");
+
+    assertTrue(Pattern.compile("^\\d+\\.\\d+\\.\\d+").matcher(version).find());
+  }
+
+  @Test
+  void testGetProtobufVersion_noManifest() throws Exception {
+    String version = GaxProperties.getProtobufVersion(GaxProperties.class, "foo.NonExistantClass");
+
+    assertEquals("3", version);
+  }
+
   private Version readVersion(String version) {
     assertTrue(Pattern.compile("^\\d+\\.\\d+\\.\\d+").matcher(version).find());
     String[] versionComponents = version.split("\\.");

showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/it/ITVersionHeaders.java

@@ -241,7 +241,7 @@ void testHttpJsonCompliance_userApiVersionSetSuccess() throws IOException {
   @Test
   void testGrpcCall_sendsCorrectApiClientHeader() {
     Pattern defautlGrpcHeaderPattern =
-        Pattern.compile("gl-java/.* gapic/.*?--protobuf-.* gax/.* grpc/.* protobuf/.*");
+        Pattern.compile("gl-java/.* gapic/.*?--protobuf-\\d.* gax/.* grpc/.* protobuf/\\d.*");
     grpcClient.echo(EchoRequest.newBuilder().build());
     String headerValue = grpcInterceptor.metadata.get(API_CLIENT_HEADER_KEY);
     assertTrue(defautlGrpcHeaderPattern.matcher(headerValue).matches());
@@ -250,7 +250,7 @@ void testGrpcCall_sendsCorrectApiClientHeader() {
   @Test
   void testHttpJson_sendsCorrectApiClientHeader() {
     Pattern defautlHttpHeaderPattern =
-        Pattern.compile("gl-java/.* gapic/.*?--protobuf-.* gax/.* rest/ protobuf/.*");
+        Pattern.compile("gl-java/.* gapic/.*?--protobuf-\\d.* gax/.* rest/ protobuf/\\d.*");
     httpJsonClient.echo(EchoRequest.newBuilder().build());
     ArrayList<String> headerValues =
         (ArrayList<String>)