Fix json repeated string parsing.

exporters/common/src/main/java/io/opentelemetry/exporter/internal/marshal/JsonSerializer.java

@@ -122,6 +122,22 @@ public void writeString(
     generator.writeString(string);
   }
 
+  @Override
+  public void writeRepeatedString(ProtoFieldInfo field, byte[][] utf8Bytes) throws IOException {
+    generator.writeArrayFieldStart(field.getJsonName());
+    for (byte[] value : utf8Bytes) {
+      // Marshalers encoded String into UTF-8 bytes to optimize for binary serialization where
+      // we are able to avoid the encoding process happening twice, one for size computation and one
+      // for actual writing. JsonGenerator actually has a writeUTF8String that would be able to
+      // accept
+      // this, but it only works when writing to an OutputStream, but not to a String like we do for
+      // writing to logs. It's wasteful to take a String, convert it to bytes, and convert back to
+      // the same String but we can see if this can be improved in the future.
+      generator.writeString(new String(value, StandardCharsets.UTF_8));
+    }
+    generator.writeEndArray();
+  }
+
   @Override
   public void writeBytes(ProtoFieldInfo field, byte[] value) throws IOException {
     generator.writeBinaryField(field.getJsonName(), value);

exporters/common/src/main/java/io/opentelemetry/exporter/internal/marshal/ProtoSerializer.java

@@ -163,6 +163,13 @@ public void writeString(
     StatelessMarshalerUtil.writeUtf8(output, string, utf8Length, context);
   }
 
+  @Override
+  public void writeRepeatedString(ProtoFieldInfo field, byte[][] utf8Bytes) throws IOException {
+    for (byte[] value : utf8Bytes) {
+      writeString(field, value);
+    }
+  }
+
   @Override
   public void writeBytes(ProtoFieldInfo field, byte[] value) throws IOException {
     output.writeUInt32NoTag(field.getTag());

exporters/common/src/main/java/io/opentelemetry/exporter/internal/marshal/Serializer.java

@@ -220,6 +220,18 @@ public void serializeString(ProtoFieldInfo field, byte[] utf8Bytes) throws IOExc
     writeString(field, utf8Bytes);
   }
 
+  /**
+   * Serializes a protobuf {@code repeated string} field. {@code utf8Bytes} is the UTF8 encoded
+   * bytes of the strings to serialize.
+   */
+  @SuppressWarnings("AvoidObjectArrays")
+  public void serializeRepeatedString(ProtoFieldInfo field, byte[][] utf8Bytes) throws IOException {
+    if (utf8Bytes.length == 0) {
+      return;
+    }
+    writeRepeatedString(field, utf8Bytes);
+  }
+
   /**
    * Serializes a protobuf {@code string} field. {@code string} is the value to be serialized and
    * {@code utf8Length} is the length of the string after it is encoded in UTF8. This method reads
@@ -246,6 +258,11 @@ public abstract void writeString(
       ProtoFieldInfo field, String string, int utf8Length, MarshalerContext context)
       throws IOException;
 
+  /** Writes a protobuf {@code repeated string} field, even if it matches the default value. */
+  @SuppressWarnings("AvoidObjectArrays")
+  public abstract void writeRepeatedString(ProtoFieldInfo field, byte[][] utf8Bytes)
+      throws IOException;
+
   /** Serializes a protobuf {@code bytes} field. */
   public void serializeBytes(ProtoFieldInfo field, byte[] value) throws IOException {
     if (value.length == 0) {

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

@@ -33,12 +33,10 @@ protected void writeTo(Serializer output) throws IOException {
       output.writeString(ResourceEntityRefExperimental.SCHEMA_URL, schemaUrlUtf8);
     }
     output.writeString(ResourceEntityRefExperimental.TYPE, typeUtf8);
-    for (byte[] keyUtf8 : identityAttributeKeysUtf8) {
-      output.serializeString(ResourceEntityRefExperimental.IDENTITY_ATTRIBUTES, keyUtf8);
-    }
-    for (byte[] keyUtf8 : descriptiveAttributeKeysUtf8) {
-      output.serializeString(ResourceEntityRefExperimental.DESCRIPTION_ATTRIBUTES, keyUtf8);
-    }
+    output.writeRepeatedString(
+        ResourceEntityRefExperimental.IDENTITY_ATTRIBUTES, identityAttributeKeysUtf8);
+    output.writeRepeatedString(
+        ResourceEntityRefExperimental.DESCRIPTION_ATTRIBUTES, descriptiveAttributeKeysUtf8);
   }
 
   public static ResourceEntityRefMarshaler createForEntity(Entity e) {
@@ -81,6 +79,7 @@ private static int calculateSize(
       size += MarshalerUtil.sizeBytes(ResourceEntityRefExperimental.SCHEMA_URL, schemaUrlUtf8);
     }
     size += MarshalerUtil.sizeBytes(ResourceEntityRefExperimental.TYPE, typeUtf8);
+    // TODO - we need repeated string support.
     for (byte[] keyUtf8 : identityAttributeKeysUtf8) {
       size += MarshalerUtil.sizeBytes(ResourceEntityRefExperimental.IDENTITY_ATTRIBUTES, keyUtf8);
     }

exporters/otlp/common/src/test/java/io/opentelemetry/exporter/internal/otlp/ResourceEntityTest.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.internal.otlp;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.opentelemetry.sdk.resources.Entity;
+import io.opentelemetry.sdk.resources.Resource;
+import java.io.ByteArrayOutputStream;
+import java.nio.charset.StandardCharsets;
+import org.junit.jupiter.api.Test;
+
+public class ResourceEntityTest {
+  @Test
+  void toJsonResourceWithEntity() throws Exception {
+    Resource resource =
+        Resource.builder()
+            .add(
+                Entity.builder()
+                    .setSchemaUrl("http://example.com/1.0")
+                    .setEntityType("test")
+                    .withIdentifying(attr -> attr.put("test.id", 1))
+                    .withDescriptive(attr -> attr.put("test.name", "one"))
+                    .build())
+            .build();
+
+    ByteArrayOutputStream out = new ByteArrayOutputStream();
+    try {
+      ResourceMarshaler.create(resource).writeJsonTo(out);
+    } finally {
+      out.close();
+    }
+
+    String json = new String(out.toByteArray(), StandardCharsets.UTF_8);
+    assertThat(json)
+        .isEqualTo(
+            "{\"attributes\":[{\"key\":\"test.id\",\"value\":{\"intValue\":\"1\"}},{\"key\":\"test.name\",\"value\":{\"stringValue\":\"one\"}}],"
+                + "\"entityRefs\":[{\"schemaUrl\":\"http://example.com/1.0\",\"type\":\"test\",\"idAttrKeys\":[\"test.id\"],\"descrAttrKeys\":[\"test.name\"]}]}");
+  }
+}