Issue decoding fixed decimal field into *big.Rat

[cdrexle]

When encoding a fixed decimal field, the source data type is required to be *big.Rat (see https://github.com/hamba/avro/blob/v2.23.0/codec_fixed.go#L76), but when decoding, only big.Rat is supported (see https://github.com/hamba/avro/blob/v2.23.0/codec_fixed.go#L40).

This causes an issue when trying to encode and decode using the same struct, as it will be incompatible and not have the ability to decode into the same type that it encoded from.

The tests that cover this scenario (here https://github.com/hamba/avro/blob/v2.23.0/decoder_fixed_test.go#L43) don't correctly pass in the destination object, since Decode requires a pointer to where we want to store the data. Since we want to store in a *big.Rat (as that's what we encoded from), we need to pass in a **big.Rat.

[nrwiersma]

I have seen the oddness around big.Rat but was not aware it actually manifested a bug. Thanks for catching this.

[nrwiersma]

Would it be possible for you to test this branch: https://github.com/hamba/avro/tree/fix-big-rat

[cdrexle]

Thanks for the quick response! Yes that fixed the issue 👍 I was working on a PR myself that was pretty much what you have here

[nrwiersma]

Out of interest, is this being testing in a production like workload or in a Go test setup?

[cdrexle]

Thanks for merging this in! Any idea when a new tag will be cut?

This is being tested in a go test setup, that writes an ocf file and immediately reads it out, using the same struct type for both read and write.

[nrwiersma]

More than likely early next week some time.