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https://issues.apache.org/jira/browse/AVRO-3240?focusedWorklogId=669889&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-669889
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ASF GitHub Bot logged work on AVRO-3240:
----------------------------------------
Author: ASF GitHub Bot
Created on: 26/Oct/21 05:04
Start Date: 26/Oct/21 05:04
Worklog Time Spent: 10m
Work Description: martin-g commented on pull request #1379:
URL: https://github.com/apache/avro/pull/1379#issuecomment-951563363
You understood it correctly! With `Read` you consumed the bytes on the first
read. On the second attempt it returns EOF and thus the `None`.
https://doc.rust-lang.org/std/io/trait.Read.html#impl-Read-2 says
```
Read is implemented for &[u8] by copying from the slice.
Note that reading updates the slice to point to the yet unread part. The
slice will be empty when EOF is reached.
```
If you want to `read` the same data twice you need to `reset` the source.
This is what the `Seek` trait gives you.
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Issue Time Tracking
-------------------
Worklog Id: (was: 669889)
Time Spent: 1h 40m (was: 1.5h)
> 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: 1h 40m
> 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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