Added support for logging metrics as single line json instead of printing on separate lines

json.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"io"
 	"time"
+	"fmt"
 )
 
 // MarshalJSON returns a byte slice containing a JSON representation of all
@@ -68,6 +69,72 @@ func (r *StandardRegistry) MarshalJSON() ([]byte, error) {
 	return json.Marshal(data)
 }
 
+
+// MarshalJSONStringified returns a byte slice containing a JSON representation of all
+// the metrics in the Registry with values stringified.
+func (r *StandardRegistry) MarshalJSONStringified(scale time.Duration) ([]byte, error) {
+	du := float64(scale)
+	duSuffix := scale.String()[1:]
+
+	data := make(map[string]map[string]interface{})
+	r.Each(func(name string, i interface{}) {
+		values := make(map[string]interface{})
+		switch metric := i.(type) {
+		case Counter:
+			values["count"] = fmt.Sprintf("%9d", metric.Count())
+		case Gauge:
+			values["value"] = fmt.Sprintf("%9d", metric.Value())
+		case GaugeFloat64:
+			values["value"] = fmt.Sprintf("%f", metric.Value())
+		case Healthcheck:
+			values["error"] = nil
+			metric.Check()
+			if err := metric.Error(); nil != err {
+				values["error"] = metric.Error().Error()
+			}
+		case Histogram:
+			h := metric.Snapshot()
+			ps := h.Percentiles([]float64{0.5, 0.75, 0.95, 0.99, 0.999})
+			values["count"] =  fmt.Sprintf("%9d", h.Count())
+			values["min"] =    fmt.Sprintf("%9d", h.Min())
+			values["max"] =    fmt.Sprintf("%9d", h.Max())
+			values["mean"] =   fmt.Sprintf("%12.2f", h.Mean())
+			values["stddev"] = fmt.Sprintf("%12.2f", h.StdDev())
+			values["median"] = fmt.Sprintf("%12.2f", ps[0])
+			values["75%"] =    fmt.Sprintf("%12.2f", ps[1])
+			values["95%"] =    fmt.Sprintf("%12.2f", ps[2])
+			values["99%"] =    fmt.Sprintf("%12.2f", ps[3])
+			values["99.9%"] =  fmt.Sprintf("%12.2f", ps[4])
+		case Meter:
+			m := metric.Snapshot()
+			values["count"] =     fmt.Sprintf("%9d", m.Count())
+			values["1m.rate"] =   fmt.Sprintf("%12.2f", m.Rate1())
+			values["5m.rate"] =   fmt.Sprintf("%12.2f", m.Rate5())
+			values["15m.rate"] =  fmt.Sprintf("%12.2f", m.Rate15())
+			values["mean.rate"] = fmt.Sprintf("%12.2f", m.RateMean())
+		case Timer:
+			t := metric.Snapshot()
+			ps := t.Percentiles([]float64{0.5, 0.75, 0.95, 0.99, 0.999})
+			values["count"] =     fmt.Sprintf("%9d", t.Count())
+			values["min"] =       fmt.Sprintf("%12.2f%s", float64(t.Min())/du, duSuffix)
+			values["max"] =       fmt.Sprintf("%12.2f%s", float64(t.Max())/du, duSuffix)
+			values["mean"] =      fmt.Sprintf("%12.2f%s", t.Mean()/du, duSuffix)
+			values["stddev"] =    fmt.Sprintf("%12.2f%s", t.StdDev()/du, duSuffix)
+			values["median"] =    fmt.Sprintf("%12.2f%s", ps[0]/du, duSuffix)
+			values["75%"] =       fmt.Sprintf("%12.2f%s", ps[1]/du, duSuffix)
+			values["95%"] =       fmt.Sprintf("%12.2f%s", ps[2]/du, duSuffix)
+			values["99%"] =       fmt.Sprintf("%12.2f%s", ps[3]/du, duSuffix)
+			values["99.9%"] =     fmt.Sprintf("%12.2f%s", ps[4]/du, duSuffix)
+			values["1m.rate"] =   fmt.Sprintf("%12.2f", t.Rate1())
+			values["5m.rate"] =   fmt.Sprintf("%12.2f", t.Rate5())
+			values["15m.rate"] =  fmt.Sprintf("%12.2f", t.Rate15())
+			values["mean.rate"] = fmt.Sprintf("%12.2f", t.RateMean())
+		}
+		data[name] = values
+	})
+	return json.Marshal(data)
+}
+
 // WriteJSON writes metrics from the given registry  periodically to the
 // specified io.Writer as JSON.
 func WriteJSON(r Registry, d time.Duration, w io.Writer) {

log.go

@@ -12,6 +12,10 @@ func Log(r Registry, freq time.Duration, l Logger) {
 	LogScaled(r, freq, time.Nanosecond, l)
 }
 
+func LogJSON(r Registry, freq time.Duration, l Logger) {
+	LogJSONScaled(r, freq, time.Nanosecond, l)
+}
+
 // Output each metric in the given registry periodically using the given
 // logger. Print timings in `scale` units (eg time.Millisecond) rather than nanos.
 func LogScaled(r Registry, freq time.Duration, scale time.Duration, l Logger) {
@@ -78,3 +82,18 @@ func LogScaled(r Registry, freq time.Duration, scale time.Duration, l Logger) {
 		})
 	}
 }
+
+// Output each metric in the given registry periodically, in JSON format using the given logger.
+// Timings are converted into `scale` units (eg time.Millisecond) rather than nanos when the JSON is marshaled.
+func LogJSONScaled(r Registry, freq time.Duration, scale time.Duration, l Logger) {
+
+	for _ = range time.Tick(freq) {
+		sr, ok := r.(*StandardRegistry)
+		if ok {
+			jsonMetrics, err := sr.MarshalJSONStringified(scale)
+			if err == nil {
+				l.Printf("%s\n", jsonMetrics)
+			}
+		}
+	}
+}