feat: add custom histograms (#70)

* feat: add custom histograms

* fix linter

* test: improve coverage

README.md

@@ -21,8 +21,9 @@ Inspired by [github.com/zsais/go-gin-prometheus](https://github.com/zsais/go-gin
 - [Differences with go-gin-prometheus](#differences-with-go-gin-prometheus)
 - [Usage](#usage)
 - [Options](#options)
-	- [Custom Counters](#custom-counters)
+	- [Custom counters](#custom-counters)
 	- [Custom gauges](#custom-gauges)
+	- [Custom histograms](#custom-histograms)
 	- [Path](#path)
 	- [Namespace](#namespace)
 	- [Subsystem](#subsystem)
@@ -76,7 +77,7 @@ func main() {
 
 ## Options
 
-### Custom Counters
+### Custom counters
 
 Add custom counters to add own values to the metrics
 
@@ -113,6 +114,23 @@ Save `p` and use the following functions:
 - DecrementGaugeValue
 - SetGaugeValue
 
+### Custom histograms
+
+Add custom histograms to add own values to the metrics
+
+```go
+r := gin.New()
+p := ginprom.New(
+  ginprom.Engine(r),
+)
+p.AddCustomHistogram("internal_request_latency", "Duration of internal HTTP requests", []string{"url", "method", "status"})
+r.Use(p.Instrument())
+```
+
+Save `p` and use the following functions:
+
+- AddCustomHistogramValue
+
 ### Path
 
 Override the default path (`/metrics`) on which the metrics can be accessed:

prom.go

@@ -51,6 +51,11 @@ type pmapCounter struct {
 	values map[string]prometheus.CounterVec
 }
 
+type pmapHistogram struct {
+	sync.RWMutex
+	values map[string]prometheus.HistogramVec
+}
+
 // Prometheus contains the metrics gathered by the instance and its path.
 type Prometheus struct {
 	reqCnt       *prometheus.CounterVec
@@ -61,6 +66,7 @@ type Prometheus struct {
 	customCounters              pmapCounter
 	customCounterLabelsProvider func(c *gin.Context) map[string]string
 	customCounterLabels         []string
+	customHistograms            pmapHistogram
 
 	MetricsPath     string
 	Namespace       string
@@ -201,6 +207,33 @@ func (p *Prometheus) AddCustomCounter(name, help string, labels []string) {
 	p.mustRegister(g)
 }
 
+// AddCustomHistogramValue adds value to custom counter.
+func (p *Prometheus) AddCustomHistogramValue(name string, labelValues []string, value float64) error {
+	p.customHistograms.RLock()
+	defer p.customHistograms.RUnlock()
+
+	if g, ok := p.customHistograms.values[name]; ok {
+		g.WithLabelValues(labelValues...).Observe(value)
+	} else {
+		return ErrCustomCounter
+	}
+	return nil
+}
+
+// AddCustomCounter adds a custom counter and registers it.
+func (p *Prometheus) AddCustomHistogram(name, help string, labels []string) {
+	p.customHistograms.Lock()
+	defer p.customHistograms.Unlock()
+	g := prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: p.Namespace,
+		Subsystem: p.Subsystem,
+		Name:      name,
+		Help:      help,
+	}, labels)
+	p.customHistograms.values[name] = *g
+	p.mustRegister(g)
+}
+
 func (p *Prometheus) mustRegister(c ...prometheus.Collector) {
 	registerer, _ := p.getRegistererAndGatherer()
 	registerer.MustRegister(c...)
@@ -225,6 +258,7 @@ func New(options ...PrometheusOption) *Prometheus {
 	p.customGauges.values = make(map[string]prometheus.GaugeVec)
 	p.customCounters.values = make(map[string]prometheus.CounterVec)
 	p.customCounterLabels = make([]string, 0)
+	p.customHistograms.values = make(map[string]prometheus.HistogramVec)
 
 	p.Ignored.values = make(map[string]bool)
 	for _, option := range options {

prom_test.go

@@ -424,6 +424,77 @@ func TestCustomCounterMetrics(t *testing.T) {
 	unregister(p)
 }
 
+func TestCustomHistogram(t *testing.T) {
+	r := gin.New()
+	p := New(Engine(r), Registry(prometheus.NewRegistry()))
+	p.AddCustomHistogram("request_latency", "test histogram", []string{"url", "method"})
+	r.Use(p.Instrument())
+	defer unregister(p)
+
+	r.GET("/ping", func(c *gin.Context) {
+		err := p.AddCustomHistogramValue("request_latency", []string{"http://example.com/status", "GET"}, 0.45)
+		assert.NoError(t, err)
+		c.JSON(http.StatusOK, gin.H{"status": "ok"})
+	})
+	r.GET("/pong", func(c *gin.Context) {
+		err := p.AddCustomHistogramValue("request_latency", []string{"http://example.com/status", "GET"}, 9.56)
+		assert.NoError(t, err)
+		c.JSON(http.StatusOK, gin.H{"status": "ok"})
+	})
+	r.GET("/error", func(c *gin.Context) {
+		// Metric not found
+		err := p.AddCustomHistogramValue("invalid", []string{}, 9.56)
+		assert.Error(t, err)
+		c.JSON(http.StatusOK, gin.H{"status": "ok"})
+	})
+
+	expectedLines := []string{
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.005"} 0`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.01"} 0`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.025"} 0`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.05"} 0`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.1"} 0`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.25"} 0`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="0.5"} 1`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="1"} 1`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="2.5"} 1`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="5"} 1`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="10"} 2`,
+		`gin_gonic_request_latency_bucket{method="GET",url="http://example.com/status",le="+Inf"} 2`,
+		`gin_gonic_request_latency_sum{method="GET",url="http://example.com/status"} 10.01`,
+		`gin_gonic_request_latency_count{method="GET",url="http://example.com/status"} 2`,
+	}
+
+	g := gofight.New()
+	g.GET(p.MetricsPath).Run(r, func(r gofight.HTTPResponse, rq gofight.HTTPRequest) {
+		assert.Equal(t, http.StatusOK, r.Code)
+		assert.NotContains(t, r.Body.String(), prometheus.BuildFQName(p.Namespace, p.Subsystem, "request_latency"))
+
+		for _, line := range expectedLines {
+			assert.NotContains(t, r.Body.String(), line)
+		}
+	})
+
+	g.GET("/ping").Run(r, func(r gofight.HTTPResponse, rq gofight.HTTPRequest) {
+		assert.Equal(t, http.StatusOK, r.Code)
+	})
+	g.GET("/pong").Run(r, func(r gofight.HTTPResponse, rq gofight.HTTPRequest) {
+		assert.Equal(t, http.StatusOK, r.Code)
+	})
+	g.GET("/error").Run(r, func(r gofight.HTTPResponse, rq gofight.HTTPRequest) {
+		assert.Equal(t, http.StatusOK, r.Code)
+	})
+
+	g.GET(p.MetricsPath).Run(r, func(r gofight.HTTPResponse, rq gofight.HTTPRequest) {
+		assert.Equal(t, http.StatusOK, r.Code)
+		assert.Contains(t, r.Body.String(), prometheus.BuildFQName(p.Namespace, p.Subsystem, "request_latency"))
+
+		for _, line := range expectedLines {
+			assert.Contains(t, r.Body.String(), line)
+		}
+	})
+}
+
 func TestIgnore(t *testing.T) {
 	r := gin.New()
 	ipath := "/ping"