Preencode attribute keys into utf8 bytes. (#3576)

* Use constants for AttributeKeys in JMH

* Preencode attribute keys into utf8 bytes.

* Spot

* Ignore

* Be lazy

* Boil

api/all/src/main/java/io/opentelemetry/api/common/AttributeKey.java

@@ -5,6 +5,7 @@
 
 package io.opentelemetry.api.common;
 
+import io.opentelemetry.api.internal.InternalAttributeKeyImpl;
 import java.util.List;
 import javax.annotation.concurrent.Immutable;
 
@@ -27,41 +28,41 @@ public interface AttributeKey<T> {
 
   /** Returns a new AttributeKey for String valued attributes. */
   static AttributeKey<String> stringKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.STRING);
+    return InternalAttributeKeyImpl.create(key, AttributeType.STRING);
   }
 
   /** Returns a new AttributeKey for Boolean valued attributes. */
   static AttributeKey<Boolean> booleanKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.BOOLEAN);
+    return InternalAttributeKeyImpl.create(key, AttributeType.BOOLEAN);
   }
 
   /** Returns a new AttributeKey for Long valued attributes. */
   static AttributeKey<Long> longKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.LONG);
+    return InternalAttributeKeyImpl.create(key, AttributeType.LONG);
   }
 
   /** Returns a new AttributeKey for Double valued attributes. */
   static AttributeKey<Double> doubleKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.DOUBLE);
+    return InternalAttributeKeyImpl.create(key, AttributeType.DOUBLE);
   }
 
   /** Returns a new AttributeKey for List&lt;String&gt; valued attributes. */
   static AttributeKey<List<String>> stringArrayKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.STRING_ARRAY);
+    return InternalAttributeKeyImpl.create(key, AttributeType.STRING_ARRAY);
   }
 
   /** Returns a new AttributeKey for List&lt;Boolean&gt; valued attributes. */
   static AttributeKey<List<Boolean>> booleanArrayKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.BOOLEAN_ARRAY);
+    return InternalAttributeKeyImpl.create(key, AttributeType.BOOLEAN_ARRAY);
   }
 
   /** Returns a new AttributeKey for List&lt;Long&gt; valued attributes. */
   static AttributeKey<List<Long>> longArrayKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.LONG_ARRAY);
+    return InternalAttributeKeyImpl.create(key, AttributeType.LONG_ARRAY);
   }
 
   /** Returns a new AttributeKey for List&lt;Double&gt; valued attributes. */
   static AttributeKey<List<Double>> doubleArrayKey(String key) {
-    return AttributeKeyImpl.create(key, AttributeType.DOUBLE_ARRAY);
+    return InternalAttributeKeyImpl.create(key, AttributeType.DOUBLE_ARRAY);
   }
 }

api/all/src/main/java/io/opentelemetry/api/internal/InternalAttributeKeyImpl.java

@@ -3,18 +3,28 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-package io.opentelemetry.api.common;
+package io.opentelemetry.api.internal;
 
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.AttributeType;
+import java.nio.charset.StandardCharsets;
 import javax.annotation.Nullable;
 
-@SuppressWarnings("rawtypes")
-final class AttributeKeyImpl<T> implements AttributeKey<T> {
+/**
+ * Default AttributeKey implementation which preencodes to UTF8 for OTLP export.
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+public final class InternalAttributeKeyImpl<T> implements AttributeKey<T> {
 
   private final AttributeType type;
   private final String key;
   private final int hashCode;
 
-  private AttributeKeyImpl(AttributeType type, String key) {
+  private byte[] keyUtf8;
+
+  private InternalAttributeKeyImpl(AttributeType type, String key) {
     if (type == null) {
       throw new NullPointerException("Null type");
     }
@@ -38,8 +48,8 @@ final class AttributeKeyImpl<T> implements AttributeKey<T> {
   // the class loader automatically resolves its super classes (interfaces), which in this case is
   // Context, which would be the same class (interface) being instrumented at that time,
   // which would lead to the JVM throwing a LinkageError "attempted duplicate interface definition"
-  static <T> AttributeKey<T> create(@Nullable String key, AttributeType type) {
-    return new AttributeKeyImpl<>(type, key != null ? key : "");
+  public static <T> AttributeKey<T> create(@Nullable String key, AttributeType type) {
+    return new InternalAttributeKeyImpl<>(type, key != null ? key : "");
   }
 
   @Override
@@ -52,13 +62,23 @@ final class AttributeKeyImpl<T> implements AttributeKey<T> {
     return key;
   }
 
+  /** Returns the key, encoded as UTF-8 bytes. */
+  public byte[] getKeyUtf8() {
+    byte[] keyUtf8 = this.keyUtf8;
+    if (keyUtf8 == null) {
+      keyUtf8 = key.getBytes(StandardCharsets.UTF_8);
+      this.keyUtf8 = keyUtf8;
+    }
+    return keyUtf8;
+  }
+
   @Override
   public boolean equals(@Nullable Object o) {
     if (o == this) {
       return true;
     }
-    if (o instanceof AttributeKeyImpl) {
-      AttributeKeyImpl<?> that = (AttributeKeyImpl<?>) o;
+    if (o instanceof InternalAttributeKeyImpl) {
+      InternalAttributeKeyImpl<?> that = (InternalAttributeKeyImpl<?>) o;
       return this.type.equals(that.getType()) && this.key.equals(that.getKey());
     }
     return false;

api/all/src/test/java/io/opentelemetry/api/common/AttributeKeyTest.java

@@ -7,6 +7,7 @@ package io.opentelemetry.api.common;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import io.opentelemetry.api.internal.InternalAttributeKeyImpl;
 import nl.jqno.equalsverifier.EqualsVerifier;
 import org.junit.jupiter.api.Test;
 
@@ -14,9 +15,12 @@ class AttributeKeyTest {
 
   @Test
   void equalsVerifier() {
-    EqualsVerifier.forClass(AttributeKeyImpl.class)
+    EqualsVerifier.forClass(InternalAttributeKeyImpl.class)
+        .withIgnoredFields("keyUtf8")
         .withCachedHashCode(
-            "hashCode", "buildHashCode", (AttributeKeyImpl<?>) AttributeKey.stringKey("test"))
+            "hashCode",
+            "buildHashCode",
+            (InternalAttributeKeyImpl<?>) AttributeKey.stringKey("test"))
         .verify();
   }
 

exporters/otlp/common/src/main/java/io/opentelemetry/exporter/otlp/internal/KeyValueMarshaler.java

@@ -7,6 +7,7 @@ package io.opentelemetry.exporter.otlp.internal;
 
 import io.opentelemetry.api.common.AttributeKey;
 import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.internal.InternalAttributeKeyImpl;
 import io.opentelemetry.proto.common.v1.internal.AnyValue;
 import io.opentelemetry.proto.common.v1.internal.ArrayValue;
 import io.opentelemetry.proto.common.v1.internal.KeyValue;
@@ -41,7 +42,14 @@ final class KeyValueMarshaler extends MarshalerWithSize {
 
   @SuppressWarnings("unchecked")
   static KeyValueMarshaler create(AttributeKey<?> attributeKey, Object value) {
-    byte[] keyUtf8 = MarshalerUtil.toBytes(attributeKey.getKey());
+    final byte[] keyUtf8;
+    if (attributeKey.getKey().isEmpty()) {
+      keyUtf8 = MarshalerUtil.EMPTY_BYTES;
+    } else if (attributeKey instanceof InternalAttributeKeyImpl) {
+      keyUtf8 = ((InternalAttributeKeyImpl<?>) attributeKey).getKeyUtf8();
+    } else {
+      keyUtf8 = attributeKey.getKey().getBytes(StandardCharsets.UTF_8);
+    }
     switch (attributeKey.getType()) {
       case STRING:
         return new KeyValueMarshaler(