From ceaff84709dfd014ec73a6e7bb0dd6ef48d2b19e Mon Sep 17 00:00:00 2001
From: Martin Polden <mpolden@mpolden.no>
Date: Fri, 11 Sep 2020 20:52:35 +0200
Subject: [PATCH] http, cache: Expose cache stats

---
 http/cache.go     | 15 +++++++++++++++
 http/http.go      | 19 +++++++++++++++++++
 http/http_test.go | 15 +++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/http/cache.go b/http/cache.go
index 8ea55de..97aac30 100644
--- a/http/cache.go
+++ b/http/cache.go
@@ -2,6 +2,7 @@ package http
 
 import (
 	"container/list"
+	"fmt"
 	"hash/fnv"
 	"net"
 	"sync"
@@ -14,6 +15,11 @@ type Cache struct {
 	values   *list.List
 }
 
+type CacheStats struct {
+	Capacity int
+	Size     int
+}
+
 func NewCache(capacity int) *Cache {
 	if capacity < 0 {
 		capacity = 0
@@ -63,3 +69,12 @@ func (c *Cache) Get(ip net.IP) (Response, bool) {
 	}
 	return r.Value.(Response), true
 }
+
+func (c *Cache) Stats() CacheStats {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return CacheStats{
+		Size:     len(c.entries),
+		Capacity: c.capacity,
+	}
+}
diff --git a/http/http.go b/http/http.go
index c41ef65..940684f 100644
--- a/http/http.go
+++ b/http/http.go
@@ -271,6 +271,24 @@ func (s *Server) PortHandler(w http.ResponseWriter, r *http.Request) *appError {
 	return nil
 }
 
+func (s *Server) cacheHandler(w http.ResponseWriter, r *http.Request) *appError {
+	cacheStats := s.cache.Stats()
+	var data = struct {
+		Size     int `json:"size"`
+		Capacity int `json:"capacity"`
+	}{
+		cacheStats.Size,
+		cacheStats.Capacity,
+	}
+	b, err := json.Marshal(data)
+	if err != nil {
+		return internalServerError(err).AsJSON()
+	}
+	w.Header().Set("Content-Type", jsonMediaType)
+	w.Write(b)
+	return nil
+}
+
 func (s *Server) DefaultHandler(w http.ResponseWriter, r *http.Request) *appError {
 	response, err := s.newResponse(r)
 	if err != nil {
@@ -391,6 +409,7 @@ func (s *Server) Handler() http.Handler {
 
 	// Profiling
 	if s.profile {
+		r.Route("GET", "/debug/cache/", s.cacheHandler)
 		r.Route("GET", "/debug/pprof/cmdline", wrapHandlerFunc(pprof.Cmdline))
 		r.Route("GET", "/debug/pprof/profile", wrapHandlerFunc(pprof.Profile))
 		r.Route("GET", "/debug/pprof/symbol", wrapHandlerFunc(pprof.Symbol))
diff --git a/http/http_test.go b/http/http_test.go
index 61c1d72..f081510 100644
--- a/http/http_test.go
+++ b/http/http_test.go
@@ -160,6 +160,21 @@ func TestJSONHandlers(t *testing.T) {
 	}
 }
 
+func TestCacheHandler(t *testing.T) {
+	log.SetOutput(ioutil.Discard)
+	srv := testServer()
+	srv.profile = true
+	s := httptest.NewServer(srv.Handler())
+	got, _, err := httpGet(s.URL+"/debug/cache/", jsonMediaType, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := `{"size":0,"capacity":100}`
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}
+
 func TestIPFromRequest(t *testing.T) {
 	var tests = []struct {
 		remoteAddr     string