Refactor collectors

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

pkg/perflib/unmarshal.go

@@ -0,0 +1,111 @@
+package perflib
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+)
+
+// Conversion factors
+const (
+	TicksToSecondScaleFactor = 1 / 1e7
+	WindowsEpoch             = 116444736000000000
+)
+
+func UnmarshalObject(obj *PerfObject, vs interface{}, logger log.Logger) error {
+	if obj == nil {
+		return fmt.Errorf("counter not found")
+	}
+	rv := reflect.ValueOf(vs)
+	if rv.Kind() != reflect.Ptr || rv.IsNil() {
+		return fmt.Errorf("%v is nil or not a pointer to slice", reflect.TypeOf(vs))
+	}
+	ev := rv.Elem()
+	if ev.Kind() != reflect.Slice {
+		return fmt.Errorf("%v is not slice", reflect.TypeOf(vs))
+	}
+
+	// Ensure sufficient length
+	if ev.Cap() < len(obj.Instances) {
+		nvs := reflect.MakeSlice(ev.Type(), len(obj.Instances), len(obj.Instances))
+		ev.Set(nvs)
+	}
+
+	for idx, instance := range obj.Instances {
+		target := ev.Index(idx)
+		rt := target.Type()
+
+		counters := make(map[string]*PerfCounter, len(instance.Counters))
+		for _, ctr := range instance.Counters {
+			if ctr.Def.IsBaseValue && !ctr.Def.IsNanosecondCounter {
+				counters[ctr.Def.Name+"_Base"] = ctr
+			} else {
+				counters[ctr.Def.Name] = ctr
+			}
+		}
+
+		for i := 0; i < target.NumField(); i++ {
+			f := rt.Field(i)
+			tag := f.Tag.Get("perflib")
+			if tag == "" {
+				continue
+			}
+			secondValue := false
+
+			st := strings.Split(tag, ",")
+			tag = st[0]
+
+			for _, t := range st {
+				if t == "secondvalue" {
+					secondValue = true
+				}
+			}
+
+			ctr, found := counters[tag]
+			if !found {
+				_ = level.Debug(logger).Log("msg", fmt.Sprintf("missing counter %q, have %v", tag, counterMapKeys(counters)))
+				continue
+			}
+			if !target.Field(i).CanSet() {
+				return fmt.Errorf("tagged field %v cannot be written to", f.Name)
+			}
+			if fieldType := target.Field(i).Type(); fieldType != reflect.TypeOf((*float64)(nil)).Elem() {
+				return fmt.Errorf("tagged field %v has wrong type %v, must be float64", f.Name, fieldType)
+			}
+
+			if secondValue {
+				if !ctr.Def.HasSecondValue {
+					return fmt.Errorf("tagged field %v expected a SecondValue, which was not present", f.Name)
+				}
+				target.Field(i).SetFloat(float64(ctr.SecondValue))
+				continue
+			}
+
+			switch ctr.Def.CounterType {
+			case PERF_ELAPSED_TIME:
+				target.Field(i).SetFloat(float64(ctr.Value-WindowsEpoch) / float64(obj.Frequency))
+			case PERF_100NSEC_TIMER, PERF_PRECISION_100NS_TIMER:
+				target.Field(i).SetFloat(float64(ctr.Value) * TicksToSecondScaleFactor)
+			default:
+				target.Field(i).SetFloat(float64(ctr.Value))
+			}
+		}
+
+		if instance.Name != "" && target.FieldByName("Name").CanSet() {
+			target.FieldByName("Name").SetString(instance.Name)
+		}
+	}
+
+	return nil
+}
+
+func counterMapKeys(m map[string]*PerfCounter) []string {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	return keys
+}