The primary bug here is in the streaming subsystem that makes the overall v1/health/service/:service request behave incorrectly when servicing a blocking request with a filter provided.
There is a secondary non-streaming bug being fixed here that is much less obvious related to when to update the `reply` variable in a `blockingQuery` evaluation. It is unlikely that it is triggerable in practical environments and I could not actually get the bug to manifest, but I fixed it anyway while investigating the original issue.
Simple reproduction (streaming):
1. Register a service with a tag.
curl -sL --request PUT 'http://localhost:8500/v1/agent/service/register' \
--header 'Content-Type: application/json' \
--data-raw '{ "ID": "ID1", "Name": "test", "Tags":[ "a" ], "EnableTagOverride": true }'
2. Do an initial filter query that matches on the tag.
curl -sLi --get 'http://localhost:8500/v1/health/service/test' --data-urlencode 'filter=a in Service.Tags'
3. Note you get one result. Use the `X-Consul-Index` header to establish
a blocking query in another terminal, this should not return yet.
curl -sLi --get 'http://localhost:8500/v1/health/service/test?index=$INDEX' --data-urlencode 'filter=a in Service.Tags'
4. Re-register that service with a different tag.
curl -sL --request PUT 'http://localhost:8500/v1/agent/service/register' \
--header 'Content-Type: application/json' \
--data-raw '{ "ID": "ID1", "Name": "test", "Tags":[ "b" ], "EnableTagOverride": true }'
5. Your blocking query from (3) should return with a header
`X-Consul-Query-Backend: streaming` and empty results if it works
correctly `[]`.
Attempts to reproduce with non-streaming failed (where you add `&near=_agent` to the read queries and ensure `X-Consul-Query-Backend: blocking-query` shows up in the results).
R.B. Boyer