Feat: Add CounterVec type.

Also, fix comments and staticcheck warnings.

context.go

@@ -2,9 +2,9 @@ package metrics
 
 import "context"
 
-type ctxScopeKey struct{}
+type CtxScopeKey struct{}
 
-var CtxScopeKey = ctxScopeKey{}
+const CtxScopeKey = ctxScopeKey
 
 func CtxGetScope(ctx context.Context) string {
 	s := ctx.Value(CtxScopeKey)

ctor.go

@@ -9,13 +9,12 @@ var ErrImplemented = errors.New("there is implemenation already injected")
 
 var ctorImpl InternalNew = nil
 
-// name is dot spearated path
-// must be uniqe, use system naming, and unit postfix, examples:
+// New returns a Creator. Name is a dot separated path which must be unique.
+// Examples:
+// ipfs.blockstore.bloomcache.bloom.miss.total
+// ipfs.routing.dht.notresuingstream.total
 //
-//	ipfs.blockstore.bloomcache.bloom.miss.total
-//	ipfs.routing.dht.notresuingstream.total
-//
-// both arguemnts are obligatory
+// Both arguemnts are mandatory.
 func New(name, helptext string) Creator {
 	if ctorImpl == nil {
 		return &noop{}
@@ -24,6 +23,8 @@ func New(name, helptext string) Creator {
 	}
 }
 
+// NewCtx is like New but obtains the metric scope from the given
+// context.
 func NewCtx(ctx context.Context, name, helptext string) Creator {
 	return New(CtxGetScope(ctx)+"."+name, helptext)
 }

interface.go

@@ -1,16 +1,24 @@
+// Package metrics provides a unified interface for different metrics
+// backends (prometheus etc.).
 package metrics
 
 import (
 	"time"
 )
 
-// Increment only metric
+// Counter is a metric that can only be incremented.
 type Counter interface {
 	Inc()
 	Add(float64) // Only positive
 }
 
-// Increse and decrese metric
+// CounterVec is a counter with tags.
+type CounterVec interface {
+	IncWithLabelValues(labels ...string)
+	AddWithLabelValues(n float64, labels ...string)
+}
+
+// Gauge is a metric that can be increased and decreased.
 type Gauge interface {
 	Set(float64) // Introduced discontinuity
 	Inc()
@@ -19,6 +27,7 @@ type Gauge interface {
 	Sub(float64)
 }
 
+// Histogram metric.
 type Histogram interface {
 	Observe(float64) // Adds observation to Histogram
 }
@@ -27,16 +36,18 @@ type Summary interface {
 	Observe(float64) // Adds observation to Summary
 }
 
-// Consult http://godoc.org/github.com/prometheus/client_golang/prometheus#SummaryOpts
+// SummaryOpts allow specifying options for Summary. See: http://godoc.org/github.com/prometheus/client_golang/prometheus#SummaryOpts .
 type SummaryOpts struct {
 	Objectives map[float64]float64
 	MaxAge     time.Duration
 	AgeBuckets uint32
 	BufCap     uint32
 }
 
+// Creator can be used to create different types of metrics.
 type Creator interface {
 	Counter() Counter
+	CounterVec() CounterVec
 	Gauge() Gauge
 	Histogram(buckets []float64) Histogram
 

noop.go

@@ -1,6 +1,6 @@
 package metrics
 
-// Also implements the Counter interface
+// Also implements the Counter and CounterVec interfaces
 type noop struct{}
 
 func (g *noop) Set(v float64) {
@@ -27,12 +27,24 @@ func (g *noop) Observe(v float64) {
 	// Noop
 }
 
+func (g *noop) IncWithLabelValues(labels ...string) {
+	// Noop
+}
+
+func (g *noop) AddWithLabelValues(v float64, labels ...string) {
+	// Noop
+}
+
 // Creator functions
 
 func (g *noop) Counter() Counter {
 	return g
 }
 
+func (g *noop) CounterVec() CounterVec {
+	return g
+}
+
 func (g *noop) Gauge() Gauge {
 	return g
 }

noop_test.go

@@ -1,6 +1,7 @@
 package metrics
 
 var _ Counter = (*noop)(nil)
+var _ CounterVec = (*noop)(nil)
 var _ Gauge = (*noop)(nil)
 var _ Histogram = (*noop)(nil)
 var _ Summary = (*noop)(nil)