feat: include User agent

google-cloud-spanner/src/main/java/com/google/cloud/spanner/spi/v1/GapicSpannerRpc.java

@@ -152,6 +152,7 @@
 import java.net.URLDecoder;
 import java.nio.charset.StandardCharsets;
 import java.util.Comparator;
+import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -338,7 +339,20 @@ public GapicSpannerRpc(final SpannerOptions options) {
                             options.getInterceptorProvider(),
                             SpannerInterceptorProvider.createDefault()))
                     .withEncoding(compressorName))
-            .setHeaderProvider(mergedHeaderProvider);
+            .setHeaderProvider(mergedHeaderProvider)
+
+            // Inject client library version to `user-agent`
+            .setHeaderProvider(
+                new HeaderProvider() {
+                  @Override
+                  public Map<String, String> getHeaders() {
+                    final HashMap<String, String> headers = new HashMap<>();
+                    headers.put(
+                        "user-agent",
+                        "spanner-java/" + GaxProperties.getLibraryVersion(GapicSpannerRpc.class));
+                    return headers;
+                  }
+                });
 
     // TODO(weiranf): Set to true by default once DirectPath goes to public beta.
     if (shouldAttemptDirectPath()) {
@@ -478,8 +492,10 @@ private static void checkEmulatorConnection(
         throw SpannerExceptionFactory.newSpannerException(
             ErrorCode.UNAVAILABLE,
             String.format(
-                "The environment variable SPANNER_EMULATOR_HOST has been set to %s, but no running emulator could be found at that address.\n"
-                    + "Did you forget to start the emulator, or to unset the environment variable?",
+                "The environment variable SPANNER_EMULATOR_HOST has been set to %s, but no running"
+                    + " emulator could be found at that address.\n"
+                    + "Did you forget to start the emulator, or to unset the environment"
+                    + " variable?",
                 emulatorHost));
       }
     }