From 9c2ad91230d72fe6d661450cc78300ea223ae2bc Mon Sep 17 00:00:00 2001
From: Vidhu Kant Sharma <bokuwakanojogahoshii@yahoo.com>
Date: Mon, 19 Oct 2020 11:05:36 +0530
Subject: make it better

---
 vendor/github.com/heroku/x/hmetrics/hmetrics.go | 169 ++++++++++++++++++++++++
 1 file changed, 169 insertions(+)
 create mode 100644 vendor/github.com/heroku/x/hmetrics/hmetrics.go

(limited to 'vendor/github.com/heroku/x/hmetrics/hmetrics.go')

diff --git a/vendor/github.com/heroku/x/hmetrics/hmetrics.go b/vendor/github.com/heroku/x/hmetrics/hmetrics.go
new file mode 100644
index 0000000..4ae88f6
--- /dev/null
+++ b/vendor/github.com/heroku/x/hmetrics/hmetrics.go
@@ -0,0 +1,169 @@
+package hmetrics
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"runtime"
+	"sync"
+	"time"
+)
+
+const (
+	metricWaitTime = 20 * time.Second
+)
+
+var (
+	DefaultEndpoint string
+)
+
+func init() {
+	DefaultEndpoint = os.Getenv("HEROKU_METRICS_URL")
+}
+
+type AlreadyStarted struct{}
+
+func (as AlreadyStarted) Error() string {
+	return "already started"
+}
+
+func (as AlreadyStarted) Fatal() bool {
+	return false
+}
+
+type HerokuMetricsURLUnset struct{}
+
+func (e HerokuMetricsURLUnset) Error() string {
+	return "cannot report metrics because HEROKU_METRICS_URL is unset"
+}
+
+func (e HerokuMetricsURLUnset) Fatal() bool {
+	return true
+}
+
+var (
+	mu      sync.Mutex
+	started bool
+)
+
+// ErrHandler receives any errors encountered during collection or reporting of metrics to Heroku. Processing of metrics
+// continues if the ErrHandler returns nil, but aborts if the ErrHandler itself returns an error.
+type ErrHandler func(err error) error
+
+func Report(ctx context.Context, ef ErrHandler) error {
+	mu.Lock()
+	defer mu.Unlock()
+	if started {
+		return AlreadyStarted{}
+	}
+	endpoint := DefaultEndpoint
+	if endpoint == "" {
+		return HerokuMetricsURLUnset{}
+	}
+	if ef == nil {
+		ef = func(_ error) error { return nil }
+	}
+	go report(ctx, endpoint, ef)
+	started = true
+	return nil
+}
+
+// The only thing that should come after an exit() is a return.
+// Best to use in a function that can defer it.
+func exit() {
+	mu.Lock()
+	defer mu.Unlock()
+	started = false
+}
+
+func report(ctx context.Context, endpoint string, ef ErrHandler) {
+	defer exit()
+
+	t := time.NewTicker(metricWaitTime)
+	defer t.Stop()
+
+	for {
+		select {
+		case <-t.C:
+		case <-ctx.Done():
+			return
+		}
+
+		if err := gatherMetrics(); err != nil {
+			if err := ef(err); err != nil {
+				return
+			}
+			continue
+		}
+		if err := submitPayload(ctx, endpoint); err != nil {
+			if err := ef(err); err != nil {
+				return
+			}
+			continue
+		}
+	}
+}
+
+var (
+	lastGCPause uint64
+	lastNumGC   uint32
+	buf         bytes.Buffer
+)
+
+// TODO: If we ever have high frequency charts HeapIdle minus HeapReleased could be interesting.
+func gatherMetrics() error {
+	var stats runtime.MemStats
+	runtime.ReadMemStats(&stats)
+
+	// cribbed from https://github.com/codahale/metrics/blob/master/runtime/memstats.go
+
+	pauseNS := stats.PauseTotalNs - lastGCPause
+	lastGCPause = stats.PauseTotalNs
+
+	numGC := stats.NumGC - lastNumGC
+	lastNumGC = stats.NumGC
+
+	result := struct {
+		Counters map[string]float64 `json:"counters"`
+		Gauges   map[string]float64 `json:"gauges"`
+	}{
+		Counters: map[string]float64{
+			"go.gc.collections": float64(numGC),
+			"go.gc.pause.ns":    float64(pauseNS),
+		},
+		Gauges: map[string]float64{
+			"go.memory.heap.bytes":   float64(stats.Alloc),
+			"go.memory.stack.bytes":  float64(stats.StackInuse),
+			"go.memory.heap.objects": float64(stats.Mallocs - stats.Frees), // Number of "live" objects.
+			"go.gc.goal":             float64(stats.NextGC),                // Goal heap size for next GC.
+			"go.routines":            float64(runtime.NumGoroutine()),      // Current number of goroutines.
+		},
+	}
+
+	buf.Reset()
+	return json.NewEncoder(&buf).Encode(result)
+}
+
+func submitPayload(ctx context.Context, where string) error {
+	req, err := http.NewRequest("POST", where, &buf)
+	if err != nil {
+		return err
+	}
+	req = req.WithContext(ctx)
+	req.Header.Add("Content-Type", "application/json")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("expected %v (http.StatusOK) but got %s", http.StatusOK, resp.Status)
+	}
+
+	return nil
+}
-- 
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