Hoist UTF-8 selection and specialize Timestamp/Duration typed accessors; add regression test and perf baseline

buff-json-tests/src/test/java/io/suboptimal/buffjson/BuffJsonEncodingRegressionTest.java

@@ -10,6 +10,7 @@
 import com.alibaba.fastjson2.JSON;
 import com.alibaba.fastjson2.JSONWriter;
 import com.google.protobuf.*;
+import com.google.protobuf_test_messages.proto3.TestMessagesProto3.TestAllTypesProto3;
 import com.google.protobuf.util.JsonFormat;
 
 import org.junit.jupiter.api.Test;
@@ -109,6 +110,20 @@ void wellKnownTypesMatchForConcreteAndDynamicMessages() throws Exception {
 		}
 	}
 
+	@Test
+	void repeatedTimestampAndDurationMatchAcrossAllPaths() throws Exception {
+		var original = TestAllTypesProto3.newBuilder()
+				.addRepeatedTimestamp(Timestamp.newBuilder().setSeconds(-1).setNanos(123456789))
+				.addRepeatedTimestamp(Timestamp.newBuilder().setSeconds(1711627200).setNanos(123000000))
+				.addRepeatedDuration(Duration.newBuilder().setSeconds(-2).setNanos(-123456789))
+				.addRepeatedDuration(Duration.newBuilder().setSeconds(3).setNanos(250000000)).build();
+		String expected = PRINTER.print(original);
+		for (var encoder : encoders()) {
+			assertEquals(expected, encoder.encode(original));
+			assertEquals(expected, new String(encoder.encodeToBytes(original), StandardCharsets.UTF_8));
+		}
+	}
+
 	@Test
 	void booleanMapKeysStayBooleanNamesWithNumericBooleanFeature() throws Exception {
 		var message = TestMaps.newBuilder().putBoolToString(true, "yes").putBoolToString(false, "no").build();

buff-json/src/main/java/io/suboptimal/buffjson/internal/WellKnownTypes.java

@@ -50,7 +50,8 @@
  * For Timestamp and Duration, {@code writeTimestampDirect()} and
  * {@code writeDurationDirect()} accept primitive seconds/nanos directly,
  * bypassing descriptor lookup and {@code message.getField()} reflection. These
- * are used by generated encoders that know the field type at generation time.
+ * are used by generated encoders and pre-specialized typed runtime accessors
+ * that know the field type before entering the hot write loop.
  *
  * <p>
  * Timestamp formatting uses Howard Hinnant's civil calendar algorithm to

buff-json/src/main/java/io/suboptimal/buffjson/internal/typed/FieldName.java

@@ -6,8 +6,9 @@
 import com.alibaba.fastjson2.JSONWriter;
 
 /**
- * Pre-encoded field name in both UTF-16 (char[]) and UTF-8 (byte[]) forms.
- * Dispatches to the optimal variant based on the JSONWriter type.
+ * Pre-encoded field name in both UTF-16 (char[]) and UTF-8 (byte[]) forms. The
+ * caller hoists the JSONWriter encoding check once per message and passes the
+ * selected form to {@link #writeTo(JSONWriter, boolean)}.
  */
 public record FieldName(char[] chars, byte[] utf8) {
 
@@ -28,8 +29,8 @@ public static FieldName of(String jsonName) {
 		}
 	}
 
-	public void writeTo(JSONWriter jw) {
-		if (jw.isUTF8())
+	public void writeTo(JSONWriter jw, boolean isUtf8) {
+		if (isUtf8)
 			jw.writeNameRaw(utf8);
 		else
 			jw.writeNameRaw(chars);