Alerting: Send information about alert rule to data source in headers (#90344)

* add support of metadata to condition and adding it to request headers
* support for additional metadata when condition is built
* add additionall context to conditions: source and folder title
* add version
* use percent-encoding for header values

pkg/services/ngalert/eval/eval.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net/url"
 	"runtime/debug"
 	"sort"
 	"strconv"
@@ -43,13 +44,18 @@ type ConditionEvaluator interface {
 	Evaluate(ctx context.Context, now time.Time) (Results, error)
 }
 
-type expressionService interface {
+type expressionExecutor interface {
 	ExecutePipeline(ctx context.Context, now time.Time, pipeline expr.DataPipeline) (*backend.QueryDataResponse, error)
 }
 
+type expressionBuilder interface {
+	expressionExecutor
+	BuildPipeline(req *expr.Request) (expr.DataPipeline, error)
+}
+
 type conditionEvaluator struct {
 	pipeline          expr.DataPipeline
-	expressionService expressionService
+	expressionService expressionExecutor
 	condition         models.Condition
 	evalTimeout       time.Duration
 	evalResultLimit   int
@@ -105,7 +111,7 @@ type evaluatorImpl struct {
 	evaluationTimeout     time.Duration
 	evaluationResultLimit int
 	dataSourceCache       datasources.CacheService
-	expressionService     *expr.Service
+	expressionService     expressionBuilder
 	pluginsStore          pluginstore.Store
 }
 
@@ -324,22 +330,24 @@ func ParseStateString(repr string) (State, error) {
 	}
 }
 
-func buildDatasourceHeaders(ctx context.Context) map[string]string {
-	headers := map[string]string{
-		// Many data sources check this in query method as sometimes alerting needs special considerations.
-		// Several existing systems also compare against the value of this header. Altering this constitutes a breaking change.
-		//
-		// Note: The spelling of this headers is intentionally degenerate from the others for compatibility reasons.
-		// When sent over a network, the key of this header is canonicalized to "Fromalert".
-		// However, some datasources still compare against the string "FromAlert".
-		models.FromAlertHeaderName: "true",
+func buildDatasourceHeaders(ctx context.Context, metadata map[string]string) map[string]string {
+	headers := make(map[string]string, len(metadata)+3)
 
-		models.CacheSkipHeaderName: "true",
+	for key, value := range metadata {
+		headers[fmt.Sprintf("X-Rule-%s", key)] = url.QueryEscape(value)
 	}
 
+	// Many data sources check this in query method as sometimes alerting needs special considerations.
+	// Several existing systems also compare against the value of this header. Altering this constitutes a breaking change.
+	//
+	// Note: The spelling of this headers is intentionally degenerate from the others for compatibility reasons.
+	// When sent over a network, the key of this header is canonicalized to "Fromalert".
+	// However, some datasources still compare against the string "FromAlert".
+	headers[models.FromAlertHeaderName] = "true"
+	headers[models.CacheSkipHeaderName] = "true"
+
 	key, ok := models.RuleKeyFromContext(ctx)
 	if ok {
-		headers["X-Rule-Uid"] = key.UID
 		headers["X-Grafana-Org-Id"] = strconv.FormatInt(key.OrgID, 10)
 	}
 
@@ -350,7 +358,7 @@ func buildDatasourceHeaders(ctx context.Context) map[string]string {
 func getExprRequest(ctx EvaluationContext, condition models.Condition, dsCacheService datasources.CacheService, reader AlertingResultsReader) (*expr.Request, error) {
 	req := &expr.Request{
 		OrgId:   ctx.User.GetOrgID(),
-		Headers: buildDatasourceHeaders(ctx.Ctx),
+		Headers: buildDatasourceHeaders(ctx.Ctx, condition.Metadata),
 		User:    ctx.User,
 	}
 	datasources := make(map[string]*datasources.DataSource, len(condition.Data))