Streaming expressions allow for users to pass in any arbitrary URL params in the search streaming source. I'm looking to add the ability for certain streaming functions, maybe just "search()" but possibly more, to extract the extra URL params passed along in the streaming request.
For example sending a request: http://localhost:8983/solr/example/stream?expr=search(collection1, q="*:*", fl="id", sort="id")& *shards.preference=shards.preference=replica.location:local* would be equivalent to: http://localhost:8983/solr/example/stream?expr=search(collection1, q="*:*", fl="id", sort="id", *shards.preference="shards.preference=replica.location:local"*) The beauty of URL params is that they can easily be overridden and checked, for example in a proxy between the user and solr. It is harder to do this with streaming expressions as the proxy would need to parse the expression and know the logic of the functions and sources. I'm open to discussion on whether the params able to be captured by the streaming function would need to be white-listed or black-listed. My idea is that this would be generically implemented through something like the StreamContext, so that any streaming function that wants to add this functionality is able to do so. Another option is to add a URL parameter such as *&expr.override.search.shards.preference=replica.location:local* ( *expr.override.<function>.<parameter>=<value>*). That way it's explicit that the user is trying to send options to the streaming expression, and extraneous URL params aren't accidentally captured when they were included for a different purpose. Anyways this would really help us for some uses cases, especially the replica routing options used in the example above. Really interested to see opinions on either of these options. - Houston Putman
