Prometheus: Migrate metadata queries to use resource calls (#49921)

* Sent resource calls for metadata to the backend

* moved resource calls to the backend

* code review feedback

* fixed post with body

* statuscode >= 300

* cleanup

* fixed tests

* fixed datasource tests

* code review feedback

* force some other endpoints to only GET

* fix linting errors

* fixed tests

* was able to remove section of redundant code

* cleanup and code review feedback

* moved query_exemplars to get request

* fixed return on error

* went back to resource calls, but using the backendsrv directly

* moved to a resource call with fallback

* fixed tests

* check for proper messages

* proper check for invalid calls

* code review changes

pkg/tsdb/prometheus/client/client.go

@@ -42,7 +42,7 @@ func (c *Client) QueryRange(ctx context.Context, q *models.Query) (*http.Respons
 	qs.Set("end", formatTime(tr.End))
 	qs.Set("step", strconv.FormatFloat(tr.Step.Seconds(), 'f', -1, 64))
 
-	return c.fetch(ctx, u, qs)
+	return c.fetch(ctx, c.method, u, qs)
 }
 
 func (c *Client) QueryInstant(ctx context.Context, q *models.Query) (*http.Response, error) {
@@ -60,7 +60,7 @@ func (c *Client) QueryInstant(ctx context.Context, q *models.Query) (*http.Respo
 		qs.Set("time", formatTime(tr.End))
 	}
 
-	return c.fetch(ctx, u, qs)
+	return c.fetch(ctx, c.method, u, qs)
 }
 
 func (c *Client) QueryExemplars(ctx context.Context, q *models.Query) (*http.Response, error) {
@@ -77,20 +77,31 @@ func (c *Client) QueryExemplars(ctx context.Context, q *models.Query) (*http.Res
 	qs.Set("start", formatTime(tr.Start))
 	qs.Set("end", formatTime(tr.End))
 
-	return c.fetch(ctx, u, qs)
+	return c.fetch(ctx, c.method, u, qs)
 }
 
-func (c *Client) fetch(ctx context.Context, u *url.URL, qs url.Values) (*http.Response, error) {
-	if strings.ToUpper(c.method) == http.MethodGet {
-		u.RawQuery = qs.Encode()
-	}
-
-	r, err := http.NewRequestWithContext(ctx, c.method, u.String(), nil)
+func (c *Client) QueryResource(ctx context.Context, method string, p string, qs url.Values) (*http.Response, error) {
+	u, err := url.ParseRequestURI(c.baseUrl)
 	if err != nil {
 		return nil, err
 	}
 
-	if strings.ToUpper(c.method) == http.MethodPost {
+	u.Path = path.Join(u.Path, p)
+
+	return c.fetch(ctx, method, u, qs)
+}
+
+func (c *Client) fetch(ctx context.Context, method string, u *url.URL, qs url.Values) (*http.Response, error) {
+	if strings.ToUpper(method) == http.MethodGet {
+		u.RawQuery = qs.Encode()
+	}
+
+	r, err := http.NewRequestWithContext(ctx, method, u.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+
+	if strings.ToUpper(method) == http.MethodPost {
 		r.Body = ioutil.NopCloser(strings.NewReader(qs.Encode()))
 		r.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 	}

pkg/tsdb/prometheus/prometheus.go

@@ -16,6 +16,7 @@ import (
 	"github.com/grafana/grafana/pkg/setting"
 	"github.com/grafana/grafana/pkg/tsdb/prometheus/buffered"
 	"github.com/grafana/grafana/pkg/tsdb/prometheus/querydata"
+	"github.com/grafana/grafana/pkg/tsdb/prometheus/resource"
 	apiv1 "github.com/prometheus/client_golang/api/prometheus/v1"
 )
 
@@ -29,6 +30,7 @@ type Service struct {
 type instance struct {
 	buffered  *buffered.Buffered
 	queryData *querydata.QueryData
+	resource  *resource.Resource
 }
 
 func ProvideService(httpClientProvider httpclient.Provider, cfg *setting.Cfg, features featuremgmt.FeatureToggles, tracer tracing.Tracer) *Service {
@@ -57,9 +59,15 @@ func newInstanceSettings(httpClientProvider httpclient.Provider, cfg *setting.Cf
 			return nil, err
 		}
 
+		r, err := resource.New(httpClientProvider, cfg, features, settings, plog)
+		if err != nil {
+			return nil, err
+		}
+
 		return instance{
 			buffered:  b,
 			queryData: qd,
+			resource:  r,
 		}, nil
 	}
 }
@@ -81,6 +89,27 @@ func (s *Service) QueryData(ctx context.Context, req *backend.QueryDataRequest)
 	return i.buffered.ExecuteTimeSeriesQuery(ctx, req)
 }
 
+func (s *Service) CallResource(ctx context.Context, req *backend.CallResourceRequest, sender backend.CallResourceResponseSender) error {
+	i, err := s.getInstance(req.PluginContext)
+	if err != nil {
+		return err
+	}
+
+	statusCode, bytes, err := i.resource.Execute(ctx, req)
+	body := bytes
+	if err != nil {
+		body = []byte(err.Error())
+	}
+
+	return sender.Send(&backend.CallResourceResponse{
+		Status: statusCode,
+		Headers: map[string][]string{
+			"content-type": {"application/json"},
+		},
+		Body: body,
+	})
+}
+
 func (s *Service) getInstance(pluginCtx backend.PluginContext) (*instance, error) {
 	i, err := s.im.Get(pluginCtx)
 	if err != nil {

pkg/tsdb/prometheus/resource/resource.go

@@ -0,0 +1,85 @@
+package resource
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/url"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana/pkg/infra/httpclient"
+	"github.com/grafana/grafana/pkg/infra/log"
+	"github.com/grafana/grafana/pkg/services/featuremgmt"
+	"github.com/grafana/grafana/pkg/setting"
+	"github.com/grafana/grafana/pkg/tsdb/prometheus/client"
+)
+
+type Resource struct {
+	provider *client.Provider
+	log      log.Logger
+}
+
+func New(
+	httpClientProvider httpclient.Provider,
+	cfg *setting.Cfg,
+	features featuremgmt.FeatureToggles,
+	settings backend.DataSourceInstanceSettings,
+	plog log.Logger,
+) (*Resource, error) {
+	var jsonData map[string]interface{}
+	if err := json.Unmarshal(settings.JSONData, &jsonData); err != nil {
+		return nil, fmt.Errorf("error reading settings: %w", err)
+	}
+
+	p := client.NewProvider(settings, jsonData, httpClientProvider, cfg, features, plog)
+
+	return &Resource{
+		log:      plog,
+		provider: p,
+	}, nil
+}
+
+func (r *Resource) Execute(ctx context.Context, req *backend.CallResourceRequest) (int, []byte, error) {
+	client, err := r.provider.GetClient(reqHeaders(req.Headers))
+	if err != nil {
+		return 500, nil, err
+	}
+
+	return r.fetch(ctx, client, req)
+}
+
+func (r *Resource) fetch(ctx context.Context, client *client.Client, req *backend.CallResourceRequest) (int, []byte, error) {
+	r.log.Debug("Sending resource query", "URL", req.URL)
+	u, err := url.Parse(req.URL)
+	if err != nil {
+		return 500, nil, err
+	}
+
+	resp, err := client.QueryResource(ctx, req.Method, u.Path, u.Query())
+	if err != nil {
+		return resp.StatusCode, nil, err
+	}
+
+	defer resp.Body.Close() //nolint (we don't care about the error being returned by resp.Body.Close())
+
+	data, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return 500, nil, err
+	}
+
+	return resp.StatusCode, data, err
+}
+
+func reqHeaders(headers map[string][]string) map[string]string {
+	// Keep only the authorization header, incase downstream the authorization header is required.
+	// Strip all the others out as appropriate headers will be applied to speak with prometheus.
+	h := make(map[string]string)
+	accessValues := headers["Authorization"]
+
+	if len(accessValues) > 0 {
+		h["Authorization"] = accessValues[0]
+	}
+
+	return h
+}