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// Copyright 2024 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package promsafe provides safe labeling - strongly typed labels in prometheus metrics.
// Enjoy promsafe as you wish!
package promsafe
import (
"fmt"
"reflect"
"strings"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
)
//
// promsafe configuration: promauto-compatibility, etc
//
// factory stands for a global promauto.Factory to be used (if any)
var factory *promauto.Factory
// SetupGlobalPromauto sets a global promauto.Factory to be used for all promsafe metrics.
// This means that each promsafe.New* call will use this promauto.Factory.
func SetupGlobalPromauto(factoryArg ...promauto.Factory) {
if len(factoryArg) == 0 {
f := promauto.With(prometheus.DefaultRegisterer)
factory = &f
} else {
f := factoryArg[0]
factory = &f
}
}
// CustomLabelsProvider is an interface that allows to convert anything to a prometheus.Labels
// It allows to provide your own FAST implementation of Struct->prometheus.Labels conversion
// without using reflection.
type CustomLabelsProvider interface {
ToPrometheusLabels() prometheus.Labels
}
// CustomLabelNamesProvider is an interface that allows to convert anything to an order list of label names
// Result of it is considered to be when registering new metric. As we need proper ORDERED list of label names
// It allows to provide your own FAST implementation of Struct->[]string conversion without any reflection
type CustomLabelNamesProvider interface {
ToLabelNames() []string
}
// promsafeTag is the tag name used for promsafe labels inside structs.
// The tag is optional, as if not present, field is used with snake_cased FieldName.
// It's useful to use a tag when you want to override the default naming or exclude a field from the metric.
var promsafeTag = "promsafe"
// SetPromsafeTag sets the tag name used for promsafe labels inside structs.
func SetPromsafeTag(tag string) {
promsafeTag = tag
}
// labelsProviderMarker is a marker interface for enforcing type-safety of StructLabelProvider.
type labelsProviderMarker interface {
labelsProviderMarker()
}
// StructLabelProvider should be embedded in any struct that serves as a label provider.
type StructLabelProvider struct{}
var _ labelsProviderMarker = (*StructLabelProvider)(nil)
func (s StructLabelProvider) labelsProviderMarker() {
panic("labelsProviderMarker interface method should never be called")
}
// newEmptyLabels creates a new empty labels instance of type T
// It's a bit tricky as we want to support both structs and pointers to structs
// e.g. &MyLabels{StructLabelProvider} or MyLabels{StructLabelProvider}
func newEmptyLabels[T labelsProviderMarker]() T {
var emptyLabels T
// Let's Support both Structs or Pointer to Structs given as T
val := reflect.ValueOf(&emptyLabels).Elem()
if val.Kind() == reflect.Ptr {
val.Set(reflect.New(val.Type().Elem()))
}
return emptyLabels
}
// NewCounterVecT creates a new CounterVecT with type-safe labels.
func NewCounterVecT[T labelsProviderMarker](opts prometheus.CounterOpts) *CounterVecT[T] {
emptyLabels := newEmptyLabels[T]()
var inner *prometheus.CounterVec
if factory != nil {
inner = factory.NewCounterVec(opts, extractLabelNames(emptyLabels))
} else {
inner = prometheus.NewCounterVec(opts, extractLabelNames(emptyLabels))
}
return &CounterVecT[T]{inner: inner}
}
// CounterVecT is a wrapper around prometheus.CounterVec that allows type-safe labels.
type CounterVecT[T labelsProviderMarker] struct {
inner *prometheus.CounterVec
}
// GetMetricWithLabelValues covers prometheus.CounterVec.GetMetricWithLabelValues
// Deprecated: Use GetMetricWith() instead. We can't provide a []string safe implementation in promsafe
func (c *CounterVecT[T]) GetMetricWithLabelValues(lvs ...string) (prometheus.Counter, error) {
panic("There can't be a SAFE GetMetricWithLabelValues(). Use GetMetricWith() instead")
}
// GetMetricWith behaves like prometheus.CounterVec.GetMetricWith but with type-safe labels.
func (c *CounterVecT[T]) GetMetricWith(labels T) (prometheus.Counter, error) {
return c.inner.GetMetricWith(extractLabelsWithValues(labels))
}
// WithLabelValues covers like prometheus.CounterVec.WithLabelValues.
// Deprecated: Use With() instead. We can't provide a []string safe implementation in promsafe
func (c *CounterVecT[T]) WithLabelValues(lvs ...string) prometheus.Counter {
panic("There can't be a SAFE WithLabelValues(). Use With() instead")
}
// With behaves like prometheus.CounterVec.With but with type-safe labels.
func (c *CounterVecT[T]) With(labels T) prometheus.Counter {
return c.inner.With(extractLabelsWithValues(labels))
}
// CurryWith behaves like prometheus.CounterVec.CurryWith but with type-safe labels.
// It still returns a CounterVecT, but it's inner prometheus.CounterVec is curried.
func (c *CounterVecT[T]) CurryWith(labels T) (*CounterVecT[T], error) {
curriedInner, err := c.inner.CurryWith(extractLabelsWithValues(labels))
if err != nil {
return nil, err
}
c.inner = curriedInner
return c, nil
}
// MustCurryWith behaves like prometheus.CounterVec.MustCurryWith but with type-safe labels.
// It still returns a CounterVecT, but it's inner prometheus.CounterVec is curried.
func (c *CounterVecT[T]) MustCurryWith(labels T) *CounterVecT[T] {
c.inner = c.inner.MustCurryWith(extractLabelsWithValues(labels))
return c
}
// Unsafe returns the underlying prometheus.CounterVec
// it's used to call any other method of prometheus.CounterVec that doesn't require type-safe labels
func (c *CounterVecT[T]) Unsafe() *prometheus.CounterVec {
return c.inner
}
// NewCounterT simply creates a new prometheus.Counter.
// As it doesn't have any labels, it's already type-safe.
// We keep this method just for consistency and interface fulfillment.
func NewCounterT(opts prometheus.CounterOpts) prometheus.Counter {
return prometheus.NewCounter(opts)
}
// NewCounterFuncT simply creates a new prometheus.CounterFunc.
// As it doesn't have any labels, it's already type-safe.
// We keep this method just for consistency and interface fulfillment.
func NewCounterFuncT(opts prometheus.CounterOpts, function func() float64) prometheus.CounterFunc {
return prometheus.NewCounterFunc(opts, function)
}
//
// Shorthand for Metrics with a single label
//
// NewCounterVecT1 creates a new CounterVecT with the only single label
func NewCounterVecT1(opts prometheus.CounterOpts, labelName string) *CounterVecT1 {
var inner *prometheus.CounterVec
if factory != nil {
inner = factory.NewCounterVec(opts, []string{labelName})
} else {
inner = prometheus.NewCounterVec(opts, []string{labelName})
}
return &CounterVecT1{inner: inner, labelName: labelName}
}
// CounterVecT1 is a wrapper around prometheus.CounterVec that allows a single type-safe label.
type CounterVecT1 struct {
labelName string
inner *prometheus.CounterVec
}
// GetMetricWithLabelValues behaves like prometheus.CounterVec.GetMetricWithLabelValues but with type-safe labels.
func (c *CounterVecT1) GetMetricWithLabelValues(labelValue string) (prometheus.Counter, error) {
return c.inner.GetMetricWithLabelValues(labelValue)
}
// GetMetricWith behaves like prometheus.CounterVec.GetMetricWith but with type-safe labels.
// We keep this function for consistency. Actually is useless and it's the same as GetMetricWithLabelValues
func (c *CounterVecT1) GetMetricWith(labelValue string) (prometheus.Counter, error) {
return c.inner.GetMetricWith(prometheus.Labels{c.labelName: labelValue})
}
// WithLabelValues behaves like prometheus.CounterVec.WithLabelValues but with type-safe labels.
func (c *CounterVecT1) WithLabelValues(labelValue string) prometheus.Counter {
return c.inner.WithLabelValues(labelValue)
}
// With behaves like prometheus.CounterVec.With but with type-safe labels.
// We keep this function for consistency. Actually is useless and it's the same as WithLabelValues
func (c *CounterVecT1) With(labelValue string) prometheus.Counter {
return c.inner.With(prometheus.Labels{c.labelName: labelValue})
}
// CurryWith behaves like prometheus.CounterVec.CurryWith but with type-safe labels.
// It still returns a CounterVecT, but it's inner prometheus.CounterVec is curried.
func (c *CounterVecT1) CurryWith(labelValue string) (*CounterVecT1, error) {
curriedInner, err := c.inner.CurryWith(prometheus.Labels{c.labelName: labelValue})
if err != nil {
return nil, err
}
c.inner = curriedInner
return c, nil
}
// MustCurryWith behaves like prometheus.CounterVec.MustCurryWith but with type-safe labels.
// It still returns a CounterVecT, but it's inner prometheus.CounterVec is curried.
func (c *CounterVecT1) MustCurryWith(labelValue string) *CounterVecT1 {
c.inner = c.inner.MustCurryWith(prometheus.Labels{c.labelName: labelValue})
return c
}
// Unsafe returns the underlying prometheus.CounterVec
// it's used to call any other method of prometheus.CounterVec that doesn't require type-safe labels
func (c *CounterVecT1) Unsafe() *prometheus.CounterVec {
return c.inner
}
//
// Promauto compatibility
//
// Factory is a promauto-like factory that allows type-safe labels.
// We have to duplicate promauto.Factory logic here, because promauto.Factory's registry is private.
type Factory[T labelsProviderMarker] struct {
r prometheus.Registerer
}
// WithAuto is a helper function that allows to use promauto.With with promsafe.With
func WithAuto[T labelsProviderMarker](r prometheus.Registerer) Factory[T] {
return Factory[T]{r: r}
}
// NewCounterVecT works like promauto.NewCounterVec but with type-safe labels
func (f Factory[T]) NewCounterVecT(opts prometheus.CounterOpts) *CounterVecT[T] {
c := NewCounterVecT[T](opts)
if f.r != nil {
f.r.MustRegister(c.inner)
}
return c
}
// NewCounterT wraps promauto.NewCounter.
// As it doesn't require any labels, it's already type-safe, and we keep it for consistency.
func (f Factory[T]) NewCounterT(opts prometheus.CounterOpts) prometheus.Counter {
return promauto.With(f.r).NewCounter(opts)
}
// NewCounterFuncT wraps promauto.NewCounterFunc.
// As it doesn't require any labels, it's already type-safe, and we keep it for consistency.
func (f Factory[T]) NewCounterFuncT(opts prometheus.CounterOpts, function func() float64) prometheus.CounterFunc {
return promauto.With(f.r).NewCounterFunc(opts, function)
}
// TODO: we can't use Factory with NewCounterT1. If we need, then we need a new type-less Factory
//
// Helpers
//
// extractLabelsWithValues extracts labels names+values from a given labelsProviderMarker (parent instance of a StructLabelProvider)
func extractLabelsWithValues(labelProvider labelsProviderMarker) prometheus.Labels {
if any(labelProvider) == nil {
return nil
}
if clp, ok := labelProvider.(CustomLabelsProvider); ok {
return clp.ToPrometheusLabels()
}
// Here, then, it can be only a struct, that is a parent of StructLabelProvider
return extractLabelFromStruct(labelProvider)
}
// extractLabelNames extracts labels names from a given labelsProviderMarker (parent instance of aStructLabelProvider)
func extractLabelNames(labelProvider labelsProviderMarker) []string {
if any(labelProvider) == nil {
return nil
}
// If custom implementation is done, just do it
if clp, ok := labelProvider.(CustomLabelNamesProvider); ok {
return clp.ToLabelNames()
}
// Fallback to slow implementation via reflect
// We'll return label values in order of fields in the struct
val := reflect.Indirect(reflect.ValueOf(labelProvider))
typ := val.Type()
labelNames := make([]string, 0, typ.NumField())
for i := 0; i < typ.NumField(); i++ {
field := typ.Field(i)
if field.Anonymous {
continue
}
var fieldName string
if ourTag := field.Tag.Get(promsafeTag); ourTag == "-" {
continue
} else if ourTag != "" {
fieldName = ourTag
} else {
fieldName = toSnakeCase(field.Name)
}
labelNames = append(labelNames, fieldName)
}
return labelNames
}
// extractLabelFromStruct extracts labels names+values from a given StructLabelProvider
func extractLabelFromStruct(structWithLabels any) prometheus.Labels {
labels := prometheus.Labels{}
val := reflect.Indirect(reflect.ValueOf(structWithLabels))
typ := val.Type()
for i := 0; i < typ.NumField(); i++ {
field := typ.Field(i)
if field.Anonymous {
continue
}
var labelName string
if ourTag := field.Tag.Get(promsafeTag); ourTag != "" {
if ourTag == "-" { // tag="-" means "skip this field"
continue
}
labelName = ourTag
} else {
labelName = toSnakeCase(field.Name)
}
labels[labelName] = stringifyLabelValue(val.Field(i))
}
return labels
}
// stringifyLabelValue makes up a valid string value from a given field's value
// It's used ONLY in fallback reflect mode
// Field value might be a pointer, that's why we do reflect.Indirect()
// Note: in future we can handle default values here as well
func stringifyLabelValue(v reflect.Value) string {
return fmt.Sprintf("%v", reflect.Indirect(v).Interface())
}
// Convert struct field names to snake_case for Prometheus label compliance.
func toSnakeCase(s string) string {
s = strings.TrimSpace(s)
var result []rune
for i, r := range s {
if i > 0 && r >= 'A' && r <= 'Z' {
result = append(result, '_')
}
result = append(result, r)
}
return strings.ToLower(string(result))
}

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// Copyright 2024 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package promsafe_test
import (
"log"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
"github.com/prometheus/client_golang/prometheus/promsafe"
)
// Important: This is not a test file. These are only examples!
// These can be considered smoke tests, but nothing more.
// TODO: Write real tests
func ExampleNewCounterVecT_multiple_labels_manual() {
// Manually registering with multiple labels
type MyCounterLabels struct {
promsafe.StructLabelProvider
EventType string
Success bool
Position uint8 // yes, it's a number, but be careful with high-cardinality labels
ShouldNotBeUsed string `promsafe:"-"`
}
c := promsafe.NewCounterVecT[MyCounterLabels](prometheus.CounterOpts{
Name: "items_counted_detailed",
})
// Manually register the counter
if err := prometheus.Register(c.Unsafe()); err != nil {
log.Fatal("could not register: ", err.Error())
}
// and now, because of generics we can call Inc() with filled struct of labels:
counter := c.With(MyCounterLabels{
EventType: "reservation", Success: true, Position: 1,
})
counter.Inc()
// Output:
}
func ExampleNewCounterVecT_promauto_migrated() {
// Examples on how to migrate from promauto to promsafe
// When promauto was using a custom factory with custom registry
myReg := prometheus.NewRegistry()
counterOpts := prometheus.CounterOpts{
Name: "items_counted_detailed_auto",
}
// Old unsafe code
// promauto.With(myReg).NewCounterVec(counterOpts, []string{"event_type", "source"})
// becomes:
type MyLabels struct {
promsafe.StructLabelProvider
EventType string
Source string
}
c := promsafe.WithAuto[MyLabels](myReg).NewCounterVecT(counterOpts)
c.With(MyLabels{
EventType: "reservation", Source: "source1",
}).Inc()
// Output:
}
func ExampleNewCounterVecT_promauto_global_migrated() {
// Examples on how to migrate from promauto to promsafe
// when promauto public API was used (with default registry)
// Setup so every NewCounter* call will use default registry
// like promauto does
// Note: it actually accepts other registry to become a default one
promsafe.SetupGlobalPromauto()
defer func() {
// cleanup for other examples
promsafe.SetupGlobalPromauto(promauto.With(nil))
}()
counterOpts := prometheus.CounterOpts{
Name: "items_counted_detailed_auto_global",
}
// Old code:
//c := promauto.NewCounterVec(counterOpts, []string{"status", "source"})
//c.With(prometheus.Labels{
// "status": "active",
// "source": "source1",
//}).Inc()
// becomes:
type MyLabels struct {
promsafe.StructLabelProvider
Status string
Source string
}
c := promsafe.NewCounterVecT[*MyLabels](counterOpts)
c.With(&MyLabels{
Status: "active", Source: "source1",
}).Inc()
// Output:
}
func ExampleNewCounterVecT_pointer_to_labels_promauto() {
// It's possible to use pointer to labels struct
myReg := prometheus.NewRegistry()
counterOpts := prometheus.CounterOpts{
Name: "items_counted_detailed_ptr",
}
type MyLabels struct {
promsafe.StructLabelProvider
EventType string
Source string
}
c := promsafe.WithAuto[*MyLabels](myReg).NewCounterVecT(counterOpts)
c.With(&MyLabels{
EventType: "reservation", Source: "source1",
}).Inc()
// Output:
}
// FastMyLabels is a struct that will have a custom method that converts to prometheus.Labels
type FastMyLabels struct {
promsafe.StructLabelProvider
EventType string
Source string
}
// ToPrometheusLabels does a superfast conversion to labels. So no reflection is involved.
func (f FastMyLabels) ToPrometheusLabels() prometheus.Labels {
return prometheus.Labels{"event_type": f.EventType, "source": f.Source}
}
// ToLabelNames does a superfast label names list. So no reflection is involved.
func (f FastMyLabels) ToLabelNames() []string {
return []string{"event_type", "source"}
}
func ExampleNewCounterVecT_fast_safe_labels_provider() {
// It's possible to use pointer to labels struct
myReg := prometheus.NewRegistry()
counterOpts := prometheus.CounterOpts{
Name: "items_counted_fast",
}
c := promsafe.WithAuto[FastMyLabels](myReg).NewCounterVecT(counterOpts)
c.With(FastMyLabels{
EventType: "reservation", Source: "source1",
}).Inc()
// Output:
}
func ExampleNewCounterVecT_single_label_manual() {
// Manually registering with a single label
// Example of usage of shorthand: no structs no generics, but one string only
c := promsafe.NewCounterVecT1(prometheus.CounterOpts{
Name: "items_counted_by_status",
}, "status")
// Manually register the counter
if err := prometheus.Register(c.Unsafe()); err != nil {
log.Fatal("could not register: ", err.Error())
}
c.With("active").Inc()
// Output:
}