Prefixes are lost when piping data

[jeswr]

Issue type:

• 🐛 Bug

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Description:

comunica/packages/actor-rdf-serialize-n3/lib/ActorRdfSerializeN3.ts

Lines 40 to 42 in e5a1f63

	// Prefer piping if possible, to maintain backpressure
	action.quadStream.on('error', error => writer.emit('error', error));
	data = (<any> action.quadStream).pipe(writer);

The above code to have the following between line 41 and 42 otherwise results are never serialized with prefixes when the pipe method is available on the quadStream.

action.quadStream.on('prefix', (prefix, iri) => writer._writer.addPrefix(prefix, iri));

Not opening a PR immediately as tests should be added at the same time.

A similar addition is probably also required for the jsonld serializer.

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Environment:

Crash log:

[github-actions]

Thanks for reporting!

[rubensworks]

The 'prefix' event is not part of the RDF/JS streams spec, it's a N3-specific thing.

I'm definitely ok with adding the line you suggest, but we can not rely on it as a standard, since other parsers and serializers might not handle it, or use a different approach.
For example, the JSON-LD parser does not emit a prefix event, but a context event.