Getting avro message metadata

[ryosagisu]

In my system I need to get Schema from Avro message, and I notice we could get Schema by calling (*OCFReader).Metadata(). But when generating new OCFReader it has to generate new codec, and I see this is quite expensive to do. Ref: https://github.com/linkedin/goavro/blob/master/ocf.go#L114-L171

So, I propose to create function that will return Avro metadata when called, without creating new OCFReader. This is what I used now:

func readAvroHeader(ctx context.Context, ior io.Reader) (map[string][]byte, error) {
	span, ctx := tracer.StartSpanFromContext(ctx)
	defer span.Finish()

	//
	// magic bytes
	//
	magic := make([]byte, 4)
	_, err := io.ReadFull(ior, magic)
	if err != nil {
		return nil, fmt.Errorf("cannot read OCF header magic bytes: %s", err)
	}
	
	if !bytes.Equal(magic, ocfMagicBytes) {
		return nil, fmt.Errorf("cannot read OCF header with invalid magic bytes: %#q", magic)
	}

	//
	// metadata
	//
	metadata, err := metadataBinaryReader(ctx, ior)
	if err != nil {
		return nil, fmt.Errorf("cannot read OCF header metadata: %s", err)
	}
	return metadata, nil
}

What do you guys think?

[karrick]

in the middle of playing with this on branch https://github.com/linkedin/goavro/tree/145

[karrick]

While the above branch passes all the included tests, there are some overlap and redundancy between some of the data types, and I'd like to refactor a bit more before I merge it back in.

I'd be happy to have some feedback if you're interested in providing it.

[ryosagisu]

Sure, I've seen your code and it's much cleaner than what I've done. I'll try to play it later, when I got some times. Thanks

[ryosagisu]

hello, any help needed to merge branch https://github.com/linkedin/goavro/tree/145?