chore: Add client_hash metric attribute (#3357)

* chore: Add client_hash metric attribute

* review comments

google-cloud-spanner/src/main/java/com/google/cloud/spanner/BuiltInOpenTelemetryMetricsProvider.java

@@ -28,6 +28,8 @@
 import com.google.cloud.opentelemetry.detection.AttributeKeys;
 import com.google.cloud.opentelemetry.detection.DetectedPlatform;
 import com.google.cloud.opentelemetry.detection.GCPPlatformDetector;
+import com.google.common.hash.HashFunction;
+import com.google.common.hash.Hashing;
 import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.sdk.OpenTelemetrySdk;
 import io.opentelemetry.sdk.metrics.SdkMeterProvider;
@@ -83,11 +85,40 @@ Map<String, String> createClientAttributes(String projectId, String client_name)
     // TODO: Replace this with real value.
     clientAttributes.put(INSTANCE_CONFIG_ID_KEY.getKey(), "unknown");
     clientAttributes.put(CLIENT_NAME_KEY.getKey(), client_name);
-    clientAttributes.put(CLIENT_UID_KEY.getKey(), getDefaultTaskValue());
-    clientAttributes.put(CLIENT_HASH_KEY.getKey(), "cloud_spanner_client_raw_metrics");
+    String clientUid = getDefaultTaskValue();
+    clientAttributes.put(CLIENT_UID_KEY.getKey(), clientUid);
+    clientAttributes.put(CLIENT_HASH_KEY.getKey(), generateClientHash(clientUid));
     return clientAttributes;
   }
 
+  /**
+   * Generates a 6-digit zero-padded all lower case hexadecimal representation of hash of the
+   * accounting group. The hash utilizes the 10 most significant bits of the value returned by
+   * `Hashing.goodFastHash(64).hashBytes()`, so effectively the returned values are uniformly
+   * distributed in the range [000000, 0003ff].
+   *
+   * <p>The primary purpose of this function is to generate a hash value for the `client_hash`
+   * resource label using `client_uid` metric field. The range of values is chosen to be small
+   * enough to keep the cardinality of the Resource targets under control. Note: If at later time
+   * the range needs to be increased, it can be done by increasing the value of `kPrefixLength` to
+   * up to 24 bits without changing the format of the returned value.
+   *
+   * @return Returns a 6-digit zero-padded all lower case hexadecimal representation of hash of the
+   *     accounting group.
+   */
+  static String generateClientHash(String clientUid) {
+    if (clientUid == null) {
+      return "000000";
+    }
+
+    HashFunction hashFunction = Hashing.goodFastHash(64);
+    Long hash = hashFunction.hashBytes(clientUid.getBytes()).asLong();
+    // Don't change this value without reading above comment
+    int kPrefixLength = 10;
+    long shiftedValue = hash >>> (64 - kPrefixLength);
+    return String.format("%06x", shiftedValue);
+  }
+
   static String detectClientLocation() {
     GCPPlatformDetector detector = GCPPlatformDetector.DEFAULT_INSTANCE;
     DetectedPlatform detectedPlatform = detector.detectPlatform();

google-cloud-spanner/src/test/java/com/google/cloud/spanner/BuiltInOpenTelemetryMetricsProviderTest.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.spanner;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class BuiltInOpenTelemetryMetricsProviderTest {
+
+  @Test
+  public void testGenerateClientHashWithSimpleUid() {
+    String clientUid = "testClient";
+    verifyHash(BuiltInOpenTelemetryMetricsProvider.generateClientHash(clientUid));
+  }
+
+  @Test
+  public void testGenerateClientHashWithEmptyUid() {
+    String clientUid = "";
+    verifyHash(BuiltInOpenTelemetryMetricsProvider.generateClientHash(clientUid));
+  }
+
+  @Test
+  public void testGenerateClientHashWithNullUid() {
+    String clientUid = null;
+    verifyHash(BuiltInOpenTelemetryMetricsProvider.generateClientHash(clientUid));
+  }
+
+  @Test
+  public void testGenerateClientHashWithLongUid() {
+    String clientUid = "aVeryLongUniqueClientIdentifierThatIsUnusuallyLong";
+    verifyHash(BuiltInOpenTelemetryMetricsProvider.generateClientHash(clientUid));
+  }
+
+  @Test
+  public void testGenerateClientHashWithSpecialCharacters() {
+    String clientUid = "273d60f2-5604-42f1-b687-f5f1b975fd07@2316645@test#";
+    verifyHash(BuiltInOpenTelemetryMetricsProvider.generateClientHash(clientUid));
+  }
+
+  private void verifyHash(String hash) {
+    // Check if the hash length is 6
+    assertEquals(hash.length(), 6);
+    // Check if the hash is in the range [000000, 0003ff]
+    long hashValue = Long.parseLong(hash, 16); // Convert hash from hex to decimal
+    assertTrue(hashValue >= 0 && hashValue <= 0x3FF);
+  }
+}

google-cloud-spanner/src/test/java/com/google/cloud/spanner/OpenTelemetryBuiltInMetricsTracerTest.java

@@ -99,7 +99,7 @@ public static void setup() {
                 BuiltInOpenTelemetryMetricsProvider.detectClientLocation())
             .put(BuiltInMetricsConstant.CLIENT_NAME_KEY, client_name)
             .put(BuiltInMetricsConstant.CLIENT_UID_KEY, attributes.get("client_uid"))
-            .put(BuiltInMetricsConstant.CLIENT_HASH_KEY, "cloud_spanner_client_raw_metrics")
+            .put(BuiltInMetricsConstant.CLIENT_HASH_KEY, attributes.get("client_hash"))
             .build();
   }