metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

metrics/librato/client.go

@@ -0,0 +1,102 @@
+package librato
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+)
+
+const Operations = "operations"
+const OperationsShort = "ops"
+
+type LibratoClient struct {
+	Email, Token string
+}
+
+// property strings
+const (
+	// display attributes
+	Color             = "color"
+	DisplayMax        = "display_max"
+	DisplayMin        = "display_min"
+	DisplayUnitsLong  = "display_units_long"
+	DisplayUnitsShort = "display_units_short"
+	DisplayStacked    = "display_stacked"
+	DisplayTransform  = "display_transform"
+	// special gauge display attributes
+	SummarizeFunction = "summarize_function"
+	Aggregate         = "aggregate"
+
+	// metric keys
+	Name        = "name"
+	Period      = "period"
+	Description = "description"
+	DisplayName = "display_name"
+	Attributes  = "attributes"
+
+	// measurement keys
+	MeasureTime = "measure_time"
+	Source      = "source"
+	Value       = "value"
+
+	// special gauge keys
+	Count      = "count"
+	Sum        = "sum"
+	Max        = "max"
+	Min        = "min"
+	SumSquares = "sum_squares"
+
+	// batch keys
+	Counters = "counters"
+	Gauges   = "gauges"
+
+	MetricsPostUrl = "https://metrics-api.librato.com/v1/metrics"
+)
+
+type Measurement map[string]interface{}
+type Metric map[string]interface{}
+
+type Batch struct {
+	Gauges      []Measurement `json:"gauges,omitempty"`
+	Counters    []Measurement `json:"counters,omitempty"`
+	MeasureTime int64         `json:"measure_time"`
+	Source      string        `json:"source"`
+}
+
+func (self *LibratoClient) PostMetrics(batch Batch) (err error) {
+	var (
+		js   []byte
+		req  *http.Request
+		resp *http.Response
+	)
+
+	if len(batch.Counters) == 0 && len(batch.Gauges) == 0 {
+		return nil
+	}
+
+	if js, err = json.Marshal(batch); err != nil {
+		return
+	}
+
+	if req, err = http.NewRequest("POST", MetricsPostUrl, bytes.NewBuffer(js)); err != nil {
+		return
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+	req.SetBasicAuth(self.Email, self.Token)
+
+	if resp, err = http.DefaultClient.Do(req); err != nil {
+		return
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		var body []byte
+		if body, err = ioutil.ReadAll(resp.Body); err != nil {
+			body = []byte(fmt.Sprintf("(could not fetch response body for error: %s)", err))
+		}
+		err = fmt.Errorf("Unable to post to Librato: %d %s %s", resp.StatusCode, resp.Status, string(body))
+	}
+	return
+}