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https://issues.apache.org/jira/browse/AVRO-3240?focusedWorklogId=669777&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-669777
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ASF GitHub Bot logged work on AVRO-3240:
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Author: ASF GitHub Bot
Created on: 25/Oct/21 20:23
Start Date: 25/Oct/21 20:23
Worklog Time Spent: 10m
Work Description: ultrabug commented on pull request #1379:
URL: https://github.com/apache/avro/pull/1379#issuecomment-951287832
> This is expected. You try to unwrap a None the second time.
I'm sorry but I'm not sure I'm following you here. Calling the same function
twice with the same parameters is an expected failure?
My understanding is that Rust's Array &[u8] does implement the `Read` trait
but there's no mean to `seek` its position back to 0, which means that the
second time we use it, we are indeed at the end position of the array reader.
For instance, using a `Cursor` + forcing its position with `set_position(0)`
between the two `from_avro_datum` makes the test above work just fine.
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Issue Time Tracking
-------------------
Worklog Id: (was: 669777)
Time Spent: 1.5h (was: 1h 20m)
> 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
> Priority: Critical
> Labels: pull-request-available
> Time Spent: 1.5h
> 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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