fix: correct event serializer mapper usage

nostr-java-base/src/main/java/nostr/base/json/EventJsonMapper.java

@@ -0,0 +1,23 @@
+package nostr.base.json;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+import com.fasterxml.jackson.module.blackbird.BlackbirdModule;
+import lombok.AccessLevel;
+import lombok.NoArgsConstructor;
+
+/**
+ * Provides access to the shared {@link ObjectMapper} configured for canonical Nostr event
+ * serialization and deserialization.
+ */
+@NoArgsConstructor(access = AccessLevel.PRIVATE)
+public final class EventJsonMapper {
+
+  private static final ObjectMapper MAPPER =
+      JsonMapper.builder().addModule(new BlackbirdModule()).build();
+
+  /** Returns the shared {@link ObjectMapper} instance for Nostr events. */
+  public static ObjectMapper mapper() {
+    return MAPPER;
+  }
+}

nostr-java-event/src/main/java/nostr/event/serializer/EventSerializer.java

@@ -0,0 +1,48 @@
+package nostr.event.serializer;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+import java.nio.charset.StandardCharsets;
+import java.util.Optional;
+import lombok.NonNull;
+import lombok.experimental.UtilityClass;
+import nostr.base.json.EventJsonMapper;
+import nostr.event.impl.GenericEvent;
+import nostr.util.NostrException;
+
+/** Utility methods for producing canonical NIP-01 event payloads. */
+@UtilityClass
+public class EventSerializer {
+
+  private static final ObjectMapper MAPPER = EventJsonMapper.mapper();
+
+  /**
+   * Serializes the provided {@link GenericEvent} to its canonical JSON representation following
+   * NIP-01.
+   *
+   * @param event the event to serialize
+   * @return the canonical JSON array representation as a string
+   * @throws NostrException if the event cannot be serialized
+   */
+  public static String serializeToJson(@NonNull GenericEvent event) throws NostrException {
+    ArrayNode arrayNode = MAPPER.createArrayNode();
+    arrayNode.add(0);
+    arrayNode.add(Optional.ofNullable(event.getPubKey()).map(Object::toString).orElse(null));
+    arrayNode.add(event.getCreatedAt());
+    arrayNode.add(event.getKind());
+    arrayNode.add(MAPPER.valueToTree(event.getTags()));
+    arrayNode.add(event.getContent());
+
+    try {
+      return MAPPER.writeValueAsString(arrayNode);
+    } catch (JsonProcessingException e) {
+      throw new NostrException(e);
+    }
+  }
+
+  /** Serializes the provided event to UTF-8 encoded bytes of the canonical JSON payload. */
+  public static byte[] serializeToBytes(@NonNull GenericEvent event) throws NostrException {
+    return serializeToJson(event).getBytes(StandardCharsets.UTF_8);
+  }
+}