adding allow list metric view configration and adding cardinality support

Author: thugrock7

otel-extensions/src/main/java/org/hypertrace/agent/otel/extensions/MetricViewConfiguration.java

@@ -17,45 +17,113 @@
 package org.hypertrace.agent.otel.extensions;
 
 import io.opentelemetry.sdk.metrics.View;
+import java.lang.reflect.Field;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 public class MetricViewConfiguration {
+  private static final Logger logger = Logger.getLogger(MetricViewConfiguration.class.getName());
 
+  // OpenTelemetry's cardinality limit property
+  private static final String OTEL_CARDINALITY_LIMIT =
+      "otel.experimental.metrics.cardinality.limit";
+
+  // Default HTTP attributes to include
+  private static final Set<String> KEYS_TO_RETAIN =
+      new HashSet<>(
+          Arrays.asList(
+              "http.method",
+              "http.status_code",
+              "http.scheme",
+              "http.route",
+              "rpc.method",
+              "rpc.grpc.status_code",
+              "rpc.service"));
+
+  /**
+   * Creates a View with HTTP attribute filtering and cardinality limit based on OpenTelemetry
+   * configuration.
+   *
+   * <p>The cardinality limit is set from the OpenTelemetry system property or environment variable:
+   *
+   * <ul>
+   *   <li>System property: otel.experimental.metrics.cardinality.limit
+   *   <li>Environment variable: OTEL_EXPERIMENTAL_METRICS_CARDINALITY_LIMIT
+   * </ul>
+   *
+   * @return a configured View with HTTP attribute filtering and cardinality limit
+   */
   public static View createView() {
-    // Attributes to exclude
-    Set<String> excludedAttributes =
-        new HashSet<>(
-            Arrays.asList(
-                "net.sock.peer.addr",
-                "net.sock.host.addr",
-                "net.sock.peer.port",
-                "net.sock.host.port",
-                "net.host.name",
-                "net.host.port",
-                "net.protocol.name",
-                "net.protocol.version",
-                "http.user_agent",
-                "enduser.id",
-                "http.client_ip",
-                "http.route",
-                "http.target",
-                "http.request_content_length",
-                "http.response_content_length",
-                "user_agent.original"));
-
-    // Build the view
-    return View.builder()
-        .setAttributeFilter(
-            attributes -> {
-              for (String attribute : excludedAttributes) {
-                if (attributes.contains(attribute)) {
+    // Build the view with our attribute filter
+    View view =
+        View.builder()
+            .setAttributeFilter(
+                attributes -> {
+                  for (String attribute : KEYS_TO_RETAIN) {
+                    if (attributes.contains(attribute)) {
+                      return true;
+                    }
+                  }
                   return false;
-                }
-              }
-              return true;
-            })
-        .build();
+                })
+            .build();
+
+    Integer cardinalityLimit = getCardinalityLimit();
+
+    /* Only apply cardinality limit if it's explicitly configured
+       The global cardinality configuration field 'otel.experimental.metrics.cardinality.limit' does not apply for custom views
+       Also the view builder, does not have a setter for cardinality limit in 1.33.0 SDK we use.
+       So using reflection to set the cardinality limit
+    */
+    if (cardinalityLimit != null) {
+      try {
+        // Get the View class
+        Class<?> viewClass = view.getClass();
+
+        // Get the cardinalityLimit field
+        Field cardinalityLimitField = viewClass.getDeclaredField("cardinalityLimit");
+        cardinalityLimitField.setAccessible(true);
+
+        // Set the cardinality limit
+        cardinalityLimitField.set(view, cardinalityLimit);
+
+      } catch (Exception e) {
+        logger.log(Level.WARNING, "Failed to set cardinality limit using reflection", e);
+      }
+    }
+
+    return view;
+  }
+
+  /**
+   * Gets the cardinality limit from OpenTelemetry's system property or environment variable.
+   *
+   * @return the configured cardinality limit, or null if not configured
+   */
+  private static Integer getCardinalityLimit() {
+    String limitValue = getProperty(OTEL_CARDINALITY_LIMIT);
+
+    if (limitValue != null && !limitValue.isEmpty()) {
+      try {
+        return Integer.parseInt(limitValue);
+      } catch (NumberFormatException e) {
+        logger.log(Level.WARNING, "Invalid cardinality limit value: " + limitValue, e);
+      }
+    }
+
+    return null; // No explicit configuration
+  }
+
+  /**
+   * Gets a property from system properties or environment variables.
+   *
+   * @param name the property name
+   * @return the property value, or null if not set
+   */
+  private static String getProperty(String name) {
+    return System.getProperty(name, System.getenv(name.replaceAll("\\.", "_").toUpperCase()));
   }
 }