Datasource: Add custom headers on alerting queries

[weeco]

Reference issue #15381

Which issue(s) this PR fixes:

Fixes #15381

I am not sure whether this pull request fixes the problem for all datasources, but it does fix the Problem for the Prometheus datasource. Thus I have omitted the keyword which automatically closes the referenced issue.

Special notes for your reviewer:

This PR does not add any further tests, as I wasn't sure how I can implement the tests for the custom headers. Additionally this breaks the existing datasource_cache.test as it is testing the TLS configuration.

What's the best way to handle this? Maintainers' changes obviously welcome.

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[marefr]

@weeco thanks.

First of all you have some linting errors:

# github.com/grafana/grafana/pkg/models [github.com/grafana/grafana/pkg/models.test]
pkg/models/datasource_cache_test.go:34:9: t1.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:37:13: t1.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:40:9: t1.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:65:9: t1.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:68:13: t1.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:71:9: t1.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:82:9: t2.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:113:9: tr.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:116:13: tr.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:142:9: tr.TLSClientConfig undefined (type http.RoundTripper has no field or method TLSClientConfig)
pkg/models/datasource_cache_test.go:142:9: too many errors
make: *** [Makefile:111: go-vet] Error 2
Exited with code 2

Then you have some nil-pointer errors: https://circleci.com/gh/grafana/grafana/159848?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-checks-link

[weeco]

@marefr Exactly I meant these linting errors and I am not sure how you want me to handle these. Since I return the http.RoundTripper in the GetHttpTransport method, the TLSClientConfig can not be accessed anymore.

What do you recommend here? I'll take a look at the failing test in the meantime.

[marefr]

Oh right. I think you have to return something else than http.RoundTripper, like a new struct. Maybe something along the lines of this?

type cachedTransport struct {
	updated time.Time

	*dataSourceTransport
}

type dataSourceTransport struct {
	roundTripper    http.RoundTripper
	transport *http.Transport
}

...

func (ds *DataSource) GetHttpTransport() (*dataSourceTransport, error) {

...

// RoundTrip implements http.RoundTripper.
func (dst *dataSourceTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	return dst.roundTripper.RoundTrip(req)
}

[weeco]

@marefr I think you can give this another look now.

[rjmasikome]

Any update?

[marefr]

Sorry it took some time for me to get back to this. Great work 👍 Some test-related changes left before we can merge to make sure that we have some additional test-coverage for the future in case we change/put in additional logic around round trippers. See comment for detail.

Have verified that it's working as expected using Prometheus:

Have verified that it's working as expected using Elasticsearch:

[marefr]

Perfect 👍 Great work!

[marefr]

@weeco Thank you for contributing to Grafana!