[jira] [Created] (KAFKA-8013) Avoid buffer underflow when reading a Struct from a partially correct buffer

["Konstantine Karantasis (JIRA)" <ji...@apache.org>]

Konstantine Karantasis created KAFKA-8013:
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             Summary: Avoid buffer underflow when reading a Struct from a partially correct buffer
                 Key: KAFKA-8013
                 URL: https://issues.apache.org/jira/browse/KAFKA-8013
             Project: Kafka
          Issue Type: Bug
            Reporter: Konstantine Karantasis
            Assignee: Konstantine Karantasis
             Fix For: 2.3.0


Protocol compatibility can be facilitated if a {{Struct}}, that has been defined as an extension of a previous {{Struct}} by adding fields at the end of the older version, can read an older version by ignoring the absence of the missing new fields. Of course this has to be allowed by the definition of these fields (they have to be {{nullable}}). 

For example, this should work: 
{code:java}
Schema oldSchema = new Schema(new Field("field1", Type.NULLABLE_STRING));
Schema newSchema = new Schema(new Field("field1", Type.NULLABLE_STRING), new Field("field2" , Type.NULLABLE_STRING));
String value = "foo bar baz";
Struct oldFormat = new Struct(oldSchema).set("field1", value);
ByteBuffer buffer = ByteBuffer.allocate(oldSchema.sizeOf(oldFormat));
oldFormat.writeTo(buffer);
buffer.flip();
Struct newFormat = newSchema.read(buffer);
assertEquals(value, newFormat.get("field1"));
assertEquals(null, newFormat.get("field2"));
{code}
Currently it does not. 

A fix to the above is considered safe, because depending on buffer underflow to detect missing data at the end of a {{Struct}} is not an appropriate check. 



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