[jira] [Assigned] (AVRO-3240) Schema deserialization is not backwards compatible

["Martin Tzvetanov Grigorov (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/AVRO-3240?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Martin Tzvetanov Grigorov reassigned AVRO-3240:
-----------------------------------------------

    Assignee: Martin Tzvetanov Grigorov

> Schema deserialization is not backwards compatible
> --------------------------------------------------
>
>                 Key: AVRO-3240
>                 URL: https://issues.apache.org/jira/browse/AVRO-3240
>             Project: Apache Avro
>          Issue Type: Bug
>          Components: rust
>            Reporter: Ultrabug
>            Assignee: Martin Tzvetanov Grigorov
>            Priority: Critical
>              Labels: pull-request-available
>             Fix For: 1.12.0
>
>          Time Spent: 2h 50m
>  Remaining Estimate: 0h
>
> Hello,
>  
> When providing your own schema to `from_avro_datum`, the deserialization is not backward compatible with messages containing a previous schema even if the schemas are created to be backward compatible.
> This is due to the `decode_variable` function in `utils` returning `Error::ReadVariableIntegerBytes` when the reader object is smaller than expected when reading a message with previous schema version (which is indeed smaller) and trying to decode it with a backward compatible schema.
> I have fixed the issue locally with the following patch which I will submit as a PR
>  
> ```
> diff --git a/lang/rust/src/util.rs b/lang/rust/src/util.rs
> index f9daf285..3538399e 100644
> --- a/lang/rust/src/util.rs
> +++ b/lang/rust/src/util.rs
> @@ -96,7 +96,7 @@ fn decode_variable<R: Read>(reader: &mut R) -> AvroResult<u64> {
>  }
>  reader
>  .read_exact(&mut buf[..])
> - .map_err(Error::ReadVariableIntegerBytes)?;
> + .or(Ok(()))?; // return nullable to support avro schemas backward compatibility
>  i |= (u64::from(buf[0] & 0x7F)) << (j * 7);
>  if (buf[0] >> 7) == 0 {
>  break;
> ```



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