carbonserver: adds /admin/info endpoint for returning internal info

cache/cache.go

@@ -378,3 +378,15 @@ func (c *Cache) GetRecentNewMetrics() []map[string]struct{} {
 func (c *Cache) SetThrottle(throttle func(ps *points.Points, inCache bool) bool) {
 	c.throttle = throttle
 }
+
+func (c *Cache) GetInfo() map[string]interface{} {
+	s, ok := c.settings.Load().(*cacheSettings)
+	if !ok {
+		return map[string]interface{}{}
+	}
+
+	return map[string]interface{}{
+		"size":  c.stat.size,
+		"limit": s.maxSize,
+	}
+}

carbon/app.go

@@ -537,6 +537,8 @@ func (app *App) Start(version string) (err error) {
 			return
 		}
 
+		carbonserver.RegisterInternalInfoHandler("cache", core.GetInfo)
+
 		app.Carbonserver = carbonserver
 	}
 	/* CARBONSERVER end */

carbonserver/carbonserver.go

@@ -21,6 +21,7 @@ import (
 	"compress/gzip"
 	"context"
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"math"
@@ -258,6 +259,8 @@ type CarbonserverListener struct {
 	estimateSize              func(metric string) (size, dataPoints int64)
 	quotaAndUsageMetrics      chan []points.Points
 	quotaUsageReportFrequency time.Duration
+
+	interfalInfoCallbacks map[string]func() map[string]interface{}
 }
 
 type prometheus struct {
@@ -1569,6 +1572,16 @@ func (listener *CarbonserverListener) Listen(listen string) error {
 
 		fidx.trieIdx.getQuotaTree(w)
 	})
+	carbonserverMux.HandleFunc("/admin/info", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Add("Content-Type", "application/json")
+
+		infos := map[string]map[string]interface{}{}
+		for name, f := range listener.interfalInfoCallbacks {
+			infos[name] = f()
+		}
+
+		json.NewEncoder(w).Encode(infos)
+	})
 
 	carbonserverMux.HandleFunc("/robots.txt", func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintln(w, "User-agent: *\nDisallow: /")
@@ -1773,3 +1786,10 @@ func (flc *fileListCache) close() error {
 
 	return nil
 }
+
+func (listener *CarbonserverListener) RegisterInternalInfoHandler(name string, f func() map[string]interface{}) {
+	if listener.interfalInfoCallbacks == nil {
+		listener.interfalInfoCallbacks = map[string]func() map[string]interface{}{}
+	}
+	listener.interfalInfoCallbacks[name] = f
+}