From 832f3655e886b42eaf017c27c3a8c6f3cf523318 Mon Sep 17 00:00:00 2001
From: Martin Polden <mpolden@mpolden.no>
Date: Fri, 11 Sep 2020 21:55:09 +0200
Subject: [PATCH] http, cache: Track evictions

---
 http/cache.go      | 21 +++++++++++++--------
 http/cache_test.go | 21 ++++++++++++++++-----
 http/http.go       |  6 ++++--
 http/http_test.go  |  2 +-
 4 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/http/cache.go b/http/cache.go
index 6d61b20..5568d7a 100644
--- a/http/cache.go
+++ b/http/cache.go
@@ -9,15 +9,17 @@ import (
 )
 
 type Cache struct {
-	capacity int
-	mu       sync.RWMutex
-	entries  map[uint64]*list.Element
-	values   *list.List
+	capacity  int
+	mu        sync.RWMutex
+	entries   map[uint64]*list.Element
+	values    *list.List
+	evictions uint64
 }
 
 type CacheStats struct {
-	Capacity int
-	Size     int
+	Capacity  int
+	Size      int
+	Evictions uint64
 }
 
 func NewCache(capacity int) *Cache {
@@ -55,6 +57,7 @@ func (c *Cache) Set(ip net.IP, resp Response) {
 			el = next
 			evicted++
 		}
+		c.evictions += uint64(evicted)
 	}
 	current, ok := c.entries[k]
 	if ok {
@@ -81,6 +84,7 @@ func (c *Cache) Resize(capacity int) error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.capacity = capacity
+	c.evictions = 0
 	return nil
 }
 
@@ -88,7 +92,8 @@ func (c *Cache) Stats() CacheStats {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 	return CacheStats{
-		Size:     len(c.entries),
-		Capacity: c.capacity,
+		Size:      len(c.entries),
+		Capacity:  c.capacity,
+		Evictions: c.evictions,
 	}
 }
diff --git a/http/cache_test.go b/http/cache_test.go
index 0867958..e99d480 100644
--- a/http/cache_test.go
+++ b/http/cache_test.go
@@ -9,11 +9,13 @@ import (
 func TestCacheCapacity(t *testing.T) {
 	var tests = []struct {
 		addCount, capacity, size int
+		evictions                uint64
 	}{
-		{1, 0, 0},
-		{1, 2, 1},
-		{2, 2, 2},
-		{3, 2, 2},
+		{1, 0, 0, 0},
+		{1, 2, 1, 0},
+		{2, 2, 2, 0},
+		{3, 2, 2, 1},
+		{10, 5, 5, 5},
 	}
 	for i, tt := range tests {
 		c := NewCache(tt.capacity)
@@ -27,6 +29,9 @@ func TestCacheCapacity(t *testing.T) {
 		if got := len(c.entries); got != tt.size {
 			t.Errorf("#%d: len(entries) = %d, want %d", i, got, tt.size)
 		}
+		if got := c.evictions; got != tt.evictions {
+			t.Errorf("#%d: evictions = %d, want %d", i, got, tt.evictions)
+		}
 		if tt.capacity > 0 && tt.addCount > tt.capacity && tt.capacity == tt.size {
 			lastAdded := responses[tt.addCount-1]
 			if _, ok := c.Get(lastAdded.IP); !ok {
@@ -57,7 +62,7 @@ func TestCacheDuplicate(t *testing.T) {
 
 func TestCacheResize(t *testing.T) {
 	c := NewCache(10)
-	for i := 1; i <= 10; i++ {
+	for i := 1; i <= 20; i++ {
 		ip := net.ParseIP(fmt.Sprintf("192.0.2.%d", i))
 		r := Response{IP: ip}
 		c.Set(ip, r)
@@ -65,9 +70,15 @@ func TestCacheResize(t *testing.T) {
 	if got, want := len(c.entries), 10; got != want {
 		t.Errorf("want %d entries, got %d", want, got)
 	}
+	if got, want := c.evictions, uint64(10); got != want {
+		t.Errorf("want %d evictions, got %d", want, got)
+	}
 	if err := c.Resize(5); err != nil {
 		t.Fatal(err)
 	}
+	if got, want := c.evictions, uint64(0); got != want {
+		t.Errorf("want %d evictions, got %d", want, got)
+	}
 	r := Response{IP: net.ParseIP("192.0.2.42")}
 	c.Set(r.IP, r)
 	if got, want := len(c.entries), 5; got != want {
diff --git a/http/http.go b/http/http.go
index 29295b5..1054b3b 100644
--- a/http/http.go
+++ b/http/http.go
@@ -299,11 +299,13 @@ func (s *Server) cacheResizeHandler(w http.ResponseWriter, r *http.Request) *app
 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"`
+		Size      int    `json:"size"`
+		Capacity  int    `json:"capacity"`
+		Evictions uint64 `json:"evictions"`
 	}{
 		cacheStats.Size,
 		cacheStats.Capacity,
+		cacheStats.Evictions,
 	}
 	b, err := json.Marshal(data)
 	if err != nil {
diff --git a/http/http_test.go b/http/http_test.go
index b7ee568..f96ba12 100644
--- a/http/http_test.go
+++ b/http/http_test.go
@@ -187,7 +187,7 @@ func TestCacheHandler(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	want := `{"size":0,"capacity":100}`
+	want := `{"size":0,"capacity":100,"evictions":0}`
 	if got != want {
 		t.Errorf("got %q, want %q", got, want)
 	}