Backwards compatible - Optional fields

[Gabriel Ki]

Hi all,

I had an impression that reader works with older version object as long as
the new fields are optional.  Is that true?  If not,
what would you recommend?  Thanks a lot in advance.

For example:

{
  "namespace": "org.apache.avro.examples",
  "protocol": "MyProtocol",

  "types": [
    { "name": "Metadata", "type": "record", "fields": [
      {"name": "S1", "type": "string"}
    ]},

    { "name": "Metadatav2", "type": "record", "fields": [
      {"name": "S1", "type": "string"},
      {"name": "S2", "type": ["string", "null"]}      // optional field in
the new version
    ]}
  ]
}

    public static <A extends SpecificRecordBase> A parseAvroObject(final A
a, final byte[] bb)
    throws IOException {
        if (bb == null) {
            return null;
        }
        ByteArrayInputStream bais = new ByteArrayInputStream(bb);
        DatumReader<A> dr = new SpecificDatumReader<A>(a.getSchema());
        Decoder d = DecoderFactory.get().binaryDecoder(bais, null);
        return dr.read(a, d);
    }


public static void main(String[] args) throws IOException {

        Metadata.Builder mb = Metadata.newBuilder();
        mb.setS1("S1 value");
        byte[] bs = toBytes(mb.build());

        Metadata m = parseAvroObject(new Metadata(), bs);
        System.out.println("parse as Metadata " + m);

        // This I thought it worked with older avro
        Metadatav2 m2 = parseAvroObject(new Metadatav2(), bs);
        System.out.println("parse as Metadatav2 " + m2);
     }


Exception in thread "main" java.io.EOFException
    at org.apache.avro.io.BinaryDecoder.readInt(BinaryDecoder.java:145)
    at org.apache.avro.io.BinaryDecoder.readIndex(BinaryDecoder.java:405)
    at
org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:229)
    at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
    at
org.apache.avro.io.ResolvingDecoder.readIndex(ResolvingDecoder.java:206)
    at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:142)
    at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:166)
    at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:138)
    at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:129)


Thanks
-gabe