fix: protobuf version not always getting set in headers (#3322)

In order to maximize amount of times protobuf version is logged we have
updated logic as follows:

1) First try to use protbuf RuntimeVersion which is available in
protobuf 4.x
2) if not available try to read using manifest file
3) if manifest file doesn't not exist then default to "3" as we know
runtime < 4

Also updated showcase test to fail in the case protobuf version is
missing

Tested: 
1) maven build using client library directly and overriding protobuf
2) spring boot started project + google cloud storage client client lib,
validated that protobuf header was sent

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 +148,29 @@ 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
+        | NullPointerException 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 +172,36 @@ public void testGetBundleVersion_noManifestFile() throws IOException {
     assertFalse(version.isPresent());
   }
 
+  @Test
+  void testGetProtobufVersion_success() {
+    String version =
+        GaxProperties.getProtobufVersion(
+            Any.class, "com.google.api.gax.core.GaxPropertiesTest$RuntimeVersion");
+
+    assertEquals("3.13.6", version);
+  }
+
+  @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("\\.");
@@ -194,4 +221,11 @@ public Version(int major, int minor) {
       this.minor = minor;
     }
   }
+
+  // Test class that emulates com.google.protobuf.RuntimeVersion for reflection lookup of fields
+  class RuntimeVersion {
+    public static final int MAJOR = 3;
+    public static final int MINOR = 13;
+    public static final int PATCH = 6;
+  }
 }

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>)