AVRO-4332: [java] Add support for enum default values in IDL serialization

lang/java/idl/src/main/java/org/apache/avro/idl/IdlUtils.java

@@ -84,7 +84,7 @@ public void serialize(JsonProperties.Null value, JsonGenerator gen, SerializerPr
     module.addSerializer(new StdSerializer<byte[]>(byte[].class) {
       @Override
       public void serialize(byte[] value, JsonGenerator gen, SerializerProvider provider) throws IOException {
-        MAPPER.writeValueAsString(new String(value, StandardCharsets.ISO_8859_1));
+        gen.writeString(new String(value, StandardCharsets.ISO_8859_1));
       }
     });
 
@@ -285,7 +285,12 @@ private static void writeSchema(Schema schema, boolean insideProtocol, Writer wr
       } else {
         throw new AvroRuntimeException("Enum schema must have at least a symbol " + schema);
       }
-      writer.append(NEWLINE).append(indent).append("}").append(NEWLINE);
+      writer.append(NEWLINE).append(indent).append("}");
+      String enumDefault = schema.getEnumDefault();
+      if (enumDefault != null) {
+        writer.append(" = ").append(enumDefault).append(";");
+      }
+      writer.append(NEWLINE);
     } else /* (type == Schema.Type.FIXED) */ {
       writer.append(indent).append("fixed ").append(schemaName).append('(')
           .append(Integer.toString(schema.getFixedSize())).append(");").append(NEWLINE);

lang/java/idl/src/test/java/org/apache/avro/idl/IdlUtilsTest.java → lang/java/idl/src/test/java/org/apache/avro/idl/TestIdlUtils.java

@@ -17,6 +17,7 @@
  */
 package org.apache.avro.idl;
 
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
@@ -26,20 +27,24 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 
-import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.JsonProcessingException;
 import org.apache.avro.AvroRuntimeException;
 import org.apache.avro.JsonProperties;
 import org.apache.avro.Protocol;
 import org.apache.avro.Schema;
 import org.junit.jupiter.api.Test;
 
+import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
 import static java.util.Objects.requireNonNull;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
-public class IdlUtilsTest {
+public class TestIdlUtils {
   @Test
   public void idlUtilsUtilitiesThrowRuntimeExceptionsOnProgrammerError() {
     assertThrows(IllegalStateException.class, () -> IdlUtils.getField(Object.class, "noSuchField"), "Programmer error");
@@ -92,7 +97,7 @@ public void validateHappyFlowForSingleSchema() throws IOException {
     Schema mainSchema = idlFile.getMainSchema();
 
     StringWriter buffer = new StringWriter();
-    IdlUtils.writeIdlSchema(buffer, mainSchema.getTypes().iterator().next());
+    IdlUtils.writeIdlSchema(buffer, mainSchema);
 
     assertEquals(getResourceAsString("idl_utils_test_schema.avdl"), buffer.toString());
   }
@@ -103,6 +108,56 @@ public void cannotWriteProtocolWithUnnamedTypes() {
         () -> IdlUtils.writeIdlProtocol(new StringWriter(), Schema.create(Schema.Type.STRING)));
   }
 
+  @Test
+  public void enumDefaultIsWrittenToIdl() throws IOException {
+    Schema withDefault = Schema.createEnum("Status", null, "naming", asList("ACTIVE", "INACTIVE"), "ACTIVE");
+    Schema withoutDefault = Schema.createEnum("Status", null, "naming", asList("ACTIVE", "INACTIVE"));
+
+    StringWriter withDefaultWriter = new StringWriter();
+    IdlUtils.writeIdlProtocol(withDefaultWriter, withDefault);
+    StringWriter withoutDefaultWriter = new StringWriter();
+    IdlUtils.writeIdlProtocol(withoutDefaultWriter, withoutDefault);
+
+    assertTrue(withDefaultWriter.toString().contains("} = ACTIVE;"),
+        "Enum with default should serialize default value");
+    assertFalse(withoutDefaultWriter.toString().contains("="), "Enum without default should not serialize a default");
+  }
+
+  @Test
+  public void enumDefaultSurvivesWriteThenParse() throws IOException {
+    Schema withDefault = Schema.createEnum("Status", null, "naming", asList("ACTIVE", "INACTIVE"), "ACTIVE");
+
+    StringWriter withDefaultWriter = new StringWriter();
+    IdlUtils.writeIdlProtocol(withDefaultWriter, withDefault);
+
+    // The written IDL must parse back into an equivalent schema: this is the bug
+    // that was reported.
+    IdlReader reader = new IdlReader();
+    Schema roundTripped;
+    try (InputStream in = new ByteArrayInputStream(withDefaultWriter.toString().getBytes(StandardCharsets.UTF_8))) {
+      roundTripped = reader.parse(in).getNamedSchemas().get("naming.Status");
+    }
+    assertEquals("ACTIVE", roundTripped.getEnumDefault());
+  }
+
+  @Test
+  public void enumDefaultIsReadFromIdlFile() throws IOException {
+    Protocol protocol = parseIdlResource("idl_utils_test_enum_default.avdl").getProtocol();
+
+    assertEquals("ACTIVE", protocol.getType("naming.Status").getEnumDefault());
+    assertNull(protocol.getType("naming.Color").getEnumDefault());
+  }
+
+  @Test
+  public void idlFileWithEnumDefaultIsWrittenBackUnchanged() throws IOException {
+    Protocol protocol = parseIdlResource("idl_utils_test_enum_default.avdl").getProtocol();
+
+    StringWriter buffer = new StringWriter();
+    IdlUtils.writeIdlProtocol(buffer, protocol);
+
+    assertEquals(getResourceAsString("idl_utils_test_enum_default.avdl"), buffer.toString());
+  }
+
   @Test
   public void cannotWriteEmptyEnums() {
     assertThrows(AvroRuntimeException.class,
@@ -126,12 +181,12 @@ public void validateMapToJson() throws IOException {
     Map<String, Object> data = new LinkedHashMap<>();
     data.put("key", "name");
     data.put("value", 81763);
-    assertEquals("{\"key\":\"name\",\"value\":81763}", callToJson(data));
+    assertEquals("{\"key\":\"name\", \"value\":81763}", callToJson(data));
   }
 
   @Test
   public void validateCollectionToJson() throws IOException {
-    assertEquals("[123,\"abc\"]", callToJson(Arrays.asList(123, "abc")));
+    assertEquals("[123, \"abc\"]", callToJson(Arrays.asList(123, "abc")));
   }
 
   @Test
@@ -179,12 +234,12 @@ public void validateUnknownCannotBeWrittenAsJson() {
     assertThrows(AvroRuntimeException.class, () -> callToJson(new Object()));
   }
 
-  private String callToJson(Object datum) throws IOException {
-    StringWriter buffer = new StringWriter();
-    try (JsonGenerator generator = IdlUtils.MAPPER.createGenerator(buffer)) {
-      IdlUtils.MAPPER.writeValueAsString(datum);
+  private String callToJson(Object datum) {
+    try {
+      return IdlUtils.MAPPER.writeValueAsString(datum);
+    } catch (JsonProcessingException e) {
+      throw new AvroRuntimeException(e);
     }
-    return buffer.toString();
   }
 
   private enum SingleValue {

lang/java/idl/src/test/resources/org/apache/avro/idl/idl_utils_test_enum_default.avdl

@@ -0,0 +1,10 @@
+@namespace("naming")
+protocol EnumDefaults {
+    enum Status {
+        ACTIVE, INACTIVE
+    } = ACTIVE;
+
+    enum Color {
+        RED, GREEN
+    }
+}

lang/java/idl/src/test/resources/org/apache/avro/util/idl_utils_test_protocol.avdl → lang/java/idl/src/test/resources/org/apache/avro/idl/idl_utils_test_protocol.avdl

@@ -6,7 +6,7 @@ protocol HappyFlow {
     @aliases(["naming.OldMessage"])
     record NewMessage {
         string @generator("uuid-type1") id;
-        @my-key("my-value") string? @aliases(["text","msg"]) message = null;
+        @my-key("my-value") string? @aliases(["text", "msg"]) message = null;
         @my-key("my-value") map<common.Flag> @order("DESCENDING") flags;
         Counter mainCounter;
         /** A list of counters. */
@@ -20,7 +20,9 @@ protocol HappyFlow {
     }
 
     @namespace("common")
-    enum Flag {ON, OFF, CANARY}
+    enum Flag {
+        ON, OFF, CANARY
+    }
 
     record Counter {
         string name;

lang/java/idl/src/test/resources/org/apache/avro/idl/idl_utils_test_schema.avdl

@@ -0,0 +1,35 @@
+namespace naming;
+
+schema NewMessage;
+
+/** A sample record type. */
+@version(2)
+@aliases(["naming.OldMessage"])
+record NewMessage {
+    string @generator("uuid-type1") id;
+    @my-key("my-value") string? @aliases(["text", "msg"]) message = null;
+    @my-key("my-value") map<common.Flag> @order("DESCENDING") flags;
+    Counter mainCounter;
+    /** A list of counters. */
+    union{null, @my-key("my-value") array<Counter>} otherCounters = null;
+    Nonce nonce;
+    date my_date;
+    time_ms my_time;
+    timestamp_ms my_timestamp;
+    decimal(12,3) my_number;
+    @logicalType("time-micros") long my_dummy;
+}
+
+@namespace("common")
+enum Flag {
+    ON, OFF, CANARY
+}
+
+record Counter {
+    string name;
+    int count;
+    /** Because the Flag field is defined earlier in NewMessage, it's already defined and does not need repeating below. */
+    common.Flag flag;
+}
+
+fixed Nonce(8);