move relabeling functionality to its own package

also remove the returned error as it was always nil

notifier/notifier.go

@@ -30,7 +30,7 @@ import (
 	"golang.org/x/net/context/ctxhttp"
 
 	"github.com/prometheus/prometheus/config"
-	"github.com/prometheus/prometheus/retrieval"
+	"github.com/prometheus/prometheus/relabel"
 )
 
 const (
@@ -239,7 +239,7 @@ func (n *Notifier) Send(alerts ...*model.Alert) {
 func (n *Notifier) relabelAlerts(alerts []*model.Alert) []*model.Alert {
 	var relabeledAlerts []*model.Alert
 	for _, alert := range alerts {
-		labels, _ := retrieval.Relabel(alert.Labels, n.opts.RelabelConfigs...)
+		labels := relabel.Process(alert.Labels, n.opts.RelabelConfigs...)
 		if labels != nil {
 			alert.Labels = labels
 			relabeledAlerts = append(relabeledAlerts, alert)

relabel/relabel.go

@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package retrieval
+package relabel
 
 import (
 	"crypto/md5"
@@ -23,27 +23,23 @@ import (
 	"github.com/prometheus/prometheus/config"
 )
 
-// Relabel returns a relabeled copy of the given label set. The relabel configurations
+// Process returns a relabeled copy of the given label set. The relabel configurations
 // are applied in order of input.
 // If a label set is dropped, nil is returned.
-func Relabel(labels model.LabelSet, cfgs ...*config.RelabelConfig) (model.LabelSet, error) {
+func Process(labels model.LabelSet, cfgs ...*config.RelabelConfig) model.LabelSet {
 	out := model.LabelSet{}
 	for ln, lv := range labels {
 		out[ln] = lv
 	}
-	var err error
 	for _, cfg := range cfgs {
-		if out, err = relabel(out, cfg); err != nil {
-			return nil, err
-		}
-		if out == nil {
-			return nil, nil
+		if out = relabel(out, cfg); out == nil {
+			return nil
 		}
 	}
-	return out, nil
+	return out
 }
 
-func relabel(labels model.LabelSet, cfg *config.RelabelConfig) (model.LabelSet, error) {
+func relabel(labels model.LabelSet, cfg *config.RelabelConfig) model.LabelSet {
 	values := make([]string, 0, len(cfg.SourceLabels))
 	for _, ln := range cfg.SourceLabels {
 		values = append(values, string(labels[ln]))
@@ -53,11 +49,11 @@ func relabel(labels model.LabelSet, cfg *config.RelabelConfig) (model.LabelSet,
 	switch cfg.Action {
 	case config.RelabelDrop:
 		if cfg.Regex.MatchString(val) {
-			return nil, nil
+			return nil
 		}
 	case config.RelabelKeep:
 		if !cfg.Regex.MatchString(val) {
-			return nil, nil
+			return nil
 		}
 	case config.RelabelReplace:
 		indexes := cfg.Regex.FindStringSubmatchIndex(val)
@@ -90,7 +86,7 @@ func relabel(labels model.LabelSet, cfg *config.RelabelConfig) (model.LabelSet,
 	default:
 		panic(fmt.Errorf("retrieval.relabel: unknown relabel action type %q", cfg.Action))
 	}
-	return labels, nil
+	return labels
 }
 
 // sum64 sums the md5 hash to an uint64.

relabel/relabel_test.go

@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package retrieval
+package relabel
 
 import (
 	"reflect"
@@ -280,10 +280,7 @@ func TestRelabel(t *testing.T) {
 	}
 
 	for i, test := range tests {
-		res, err := Relabel(test.input, test.relabel...)
-		if err != nil {
-			t.Errorf("Test %d: error relabeling: %s", i+1, err)
-		}
+		res := Process(test.input, test.relabel...)
 
 		if !reflect.DeepEqual(res, test.output) {
 			t.Errorf("Test %d: relabel output mismatch: expected %#v, got %#v", i+1, test.output, res)

retrieval/target.go

@@ -26,6 +26,7 @@ import (
 	"github.com/prometheus/common/model"
 
 	"github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/relabel"
 	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/util/httputil"
 )
@@ -275,10 +276,8 @@ type relabelAppender struct {
 }
 
 func (app relabelAppender) Append(s *model.Sample) error {
-	labels, err := Relabel(model.LabelSet(s.Metric), app.relabelings...)
-	if err != nil {
-		return fmt.Errorf("metric relabeling error %s: %s", s.Metric, err)
-	}
+	labels := relabel.Process(model.LabelSet(s.Metric), app.relabelings...)
+
 	// Check if the timeseries was dropped.
 	if labels == nil {
 		return nil

retrieval/targetmanager.go

@@ -25,6 +25,7 @@ import (
 	"golang.org/x/net/context"
 
 	"github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/relabel"
 	"github.com/prometheus/prometheus/retrieval/discovery"
 	"github.com/prometheus/prometheus/storage"
 )
@@ -448,10 +449,8 @@ func targetsFromGroup(tg *config.TargetGroup, cfg *config.ScrapeConfig) ([]*Targ
 
 		preRelabelLabels := labels
 
-		labels, err := Relabel(labels, cfg.RelabelConfigs...)
-		if err != nil {
-			return nil, fmt.Errorf("error while relabeling instance %d in target group %s: %s", i, tg, err)
-		}
+		labels := relabel.Process(labels, cfg.RelabelConfigs...)
+
 		// Check if the target was dropped.
 		if labels == nil {
 			continue
@@ -469,7 +468,7 @@ func targetsFromGroup(tg *config.TargetGroup, cfg *config.ScrapeConfig) ([]*Targ
 			}
 			labels[model.AddressLabel] = model.LabelValue(addr)
 		}
-		if err = config.CheckTargetAddress(labels[model.AddressLabel]); err != nil {
+		if err := config.CheckTargetAddress(labels[model.AddressLabel]); err != nil {
 			return nil, err
 		}