Format Referer header on X-Dashboard-Title and X-Panel-Title

[velom]

The plugin can forward HTTP headers.
Unfortunately, ClickHouse stores only Referer header in the system.query_log.
This PR adds additional header Referer based on X-Dashboard-Title and X-Panel-Title.

Examle of how it looks in the query_log:

    ┌─http_referer────────────────────────────────────────────────┐
 1. │ Explorer                                                    │
 2. │ Dashboard title: "New dashboard", pannel title: "New panel" │
    └─────────────────────────────────────────────────────────────┘

[CLAassistant]

All committers have signed the CLA.

[velom]

Hi @adamyeats, any ETA here?

[SpencerTorres]

I like this, but is it possible to use the array-like behavior of the headers to add more data? I want to make it easier to fetch this out of the query log. The string formatting works, but I'm wondering if we can make it more HTTP-compliant

What I mean is, is it possible where the header can have multiple entries? I forgot the interface in Go, but there should be a way to do that

[velom]

There is one global problem: Grafana doesn't pass most of headers to the datasource plugin, only few number of them, and there are no common HTTP headers.
As far as I understand, there could be this set of headers: https://github.com/grafana/grafana/blob/5694d6371ee9989409f7259295b1cf821cd1f022/pkg/services/query/query.go#L34-L42

I can adjust the header handler and make it configurable:

1. Header format string
2. Array of headers to pass to the string

E.g. instead of "Dashboard title: %q, panel title: %q" some users may want to have:

1. "%q (%q) from %q (%q)"
2. [X-Panel-Title, X-Panel-Id, X-Dashboard-Title, X-Dashboard-Uid]

What do you think?

[SpencerTorres]

I suppose this is better than what we have now, I just wish we had a better way to attach metadata to queries. This doesn't apply to TCP connections does it?

[aangelisc]

This is technically untrue; the query could also come from alerting. You should be able to validate this by checking the uname from the plugin context for grafana_scheduler.

[aangelisc]

Generally this LGTM. I wonder if we should have this configurable - I'm not sure all users would want this enabled, wdyt?

[velom]

Sure, sounds reasonable.
Let me make it more flexible like described above, there will be a way to disable it at all.

[aangelisc]

Hi @velom 😊 sorry for the delay here. Are you able to update this PR based on my feedback? I believe this should be configurable to allow users to disable it if they wish. I think this should be disabled by default. Also, we should correctly identify alerting queries.