revproxy: better handling of memory cache size and expiration

Use a typed cache, and keep track of the size of the data payload instead of
just the number of elements.

Author: creachadair

go.mod

@@ -1,6 +1,6 @@
 module github.com/tailscale/go-cache-plugin
 
-go 1.23.0
+go 1.23.1
 
 require (
 	github.com/aws/aws-sdk-go-v2/config v1.27.28
@@ -9,11 +9,11 @@ require (
 	github.com/creachadair/command v0.1.14
 	github.com/creachadair/flax v0.0.1
 	github.com/creachadair/gocache v0.0.0-20240904225701-6c4617815112
-	github.com/creachadair/mds v0.18.1
+	github.com/creachadair/mds v0.19.2
 	github.com/creachadair/mhttp v0.0.0-20240904023549-156b88d21c62
+	github.com/creachadair/scheddle v0.0.0-20240907053453-f3bdd9f33c58
 	github.com/creachadair/taskgroup v0.9.1
 	github.com/creachadair/tlsutil v0.0.0-20240901051800-c769f173a559
-	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da
 	github.com/goproxy/goproxy v0.17.2
 	golang.org/x/sync v0.8.0
 	golang.org/x/sys v0.22.0
@@ -41,6 +41,7 @@ require (
 	github.com/aws/smithy-go v1.20.4 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.2.0 // indirect
+	github.com/creachadair/msync v0.2.1 // indirect
 	github.com/go-json-experiment/json v0.0.0-20231102232822-2e55bd4e08b0 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/prometheus/client_golang v1.19.1 // indirect

go.sum

@@ -48,10 +48,14 @@ github.com/creachadair/flax v0.0.1 h1:it+joEf9aEUalaV7XWll/pk6zA4/FbNvMImW9q/lS8
 github.com/creachadair/flax v0.0.1/go.mod h1:K8bFvn8hMdAljQkaKNc7I3os5Wk36JxkyCkfdZ7S8d4=
 github.com/creachadair/gocache v0.0.0-20240904225701-6c4617815112 h1:FSlFO2eztBGGzp67D2z/eeNe5U+AZyj4g/CjKf0AHbo=
 github.com/creachadair/gocache v0.0.0-20240904225701-6c4617815112/go.mod h1:vkGW73GdzBPQZJdFlPBZVzFcG7lTxIgDY0+U30mp3xs=
-github.com/creachadair/mds v0.18.1 h1:lq2JufNm5Vfkdolf9Z+2shiw7r8XJgLSZniLHUFYJcI=
-github.com/creachadair/mds v0.18.1/go.mod h1:4b//mUiL8YldH6TImXjmW45myzTLNS1LLjOmrk888eg=
+github.com/creachadair/mds v0.19.2 h1:I5OdjsrG2jqGklMcyv50Iqo6gTrwUSIpIJVSnlVw85c=
+github.com/creachadair/mds v0.19.2/go.mod h1:4b//mUiL8YldH6TImXjmW45myzTLNS1LLjOmrk888eg=
 github.com/creachadair/mhttp v0.0.0-20240904023549-156b88d21c62 h1:6OEfFAgnbvhEDAR83DBUbvImn68DH2NpqcXrwID9Vbs=
 github.com/creachadair/mhttp v0.0.0-20240904023549-156b88d21c62/go.mod h1:Vito16r0HqXVEcwjz5Z9PLdFEbX016lCOV6iVgH06tc=
+github.com/creachadair/msync v0.2.1 h1:nBrUkGnk+vhEO+fe6fEMcT6Reo/C9Oc4s62bL4Bj/Wo=
+github.com/creachadair/msync v0.2.1/go.mod h1:fMAB2Ihnsojvz5nRxqzEEUmHgW2/CEKY64VPP4VskSY=
+github.com/creachadair/scheddle v0.0.0-20240907053453-f3bdd9f33c58 h1:ZH2lplzOAJitYaaf427wVWo8tijhPZedhvbNXGwnTAs=
+github.com/creachadair/scheddle v0.0.0-20240907053453-f3bdd9f33c58/go.mod h1:/IRMmOFNVSrAMzgcOYcdGOFJf4RU4UurRHvMykHEzJc=
 github.com/creachadair/taskgroup v0.9.1 h1:oam4POtt6PpmUr4us+ycUUfb2mPWc0RmIycte2oWoWw=
 github.com/creachadair/taskgroup v0.9.1/go.mod h1:9oDDPt/5QPS4iylvPMC81GRlj+1je8AFDbjUh4zaQWo=
 github.com/creachadair/tlsutil v0.0.0-20240901051800-c769f173a559 h1:8hlU8ebt2lI//6sFj6ICE6mN6c6Uvj4588XilSqpmu8=
@@ -64,8 +68,6 @@ github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHk
 github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
 github.com/go-json-experiment/json v0.0.0-20231102232822-2e55bd4e08b0 h1:ymLjT4f35nQbASLnvxEde4XOBL+Sn7rFuV+FOJqkljg=
 github.com/go-json-experiment/json v0.0.0-20231102232822-2e55bd4e08b0/go.mod h1:6daplAwHHGbUGib4990V3Il26O0OC4aRyvewaaAihaA=
-github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da h1:oI5xCqsCo564l8iNU+DwB5epxmsaqB+rhGL0m5jtYqE=
-github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=

lib/revproxy/cache.go

@@ -17,6 +17,7 @@ import (
 	"time"
 
 	"github.com/creachadair/atomicfile"
+	"github.com/creachadair/scheddle"
 	"github.com/creachadair/taskgroup"
 )
 
@@ -75,29 +76,22 @@ func (s *Server) cacheStoreS3(hash string, hdr http.Header, body []byte) taskgro
 
 // cacheLoadMemory reads cached headers and body from the memory cache.
 func (s *Server) cacheLoadMemory(hash string) ([]byte, http.Header, error) {
-	s.mcacheMu.Lock()
-	defer s.mcacheMu.Unlock()
-	v, ok := s.mcache.Get(hash)
+	e, ok := s.mcache.Get(hash)
 	if !ok {
 		return nil, nil, fs.ErrNotExist
 	}
-	entry := v.(memCacheEntry)
-	if time.Now().After(entry.expires) {
-		s.mcache.Remove(hash)
-		return nil, nil, errors.New("entry expired")
-	}
-	return entry.body, entry.header, nil
+	return e.body, e.header, nil
 }
 
 // cacheStoreMemory writes the contents of body to the memory cache.
 func (s *Server) cacheStoreMemory(hash string, maxAge time.Duration, hdr http.Header, body []byte) {
-	s.mcacheMu.Lock()
-	defer s.mcacheMu.Unlock()
-	s.mcache.Add(hash, memCacheEntry{
-		header:  trimCacheHeader(hdr),
-		body:    body,
-		expires: time.Now().Add(maxAge),
+	s.mcache.Put(hash, memCacheEntry{
+		header: trimCacheHeader(hdr),
+		body:   body,
 	})
+	s.expire.After(maxAge, scheddle.Run(func() {
+		s.mcache.Remove(hash)
+	}))
 }
 
 var keepHeader = []string{
@@ -158,7 +152,6 @@ func setXCacheInfo(h http.Header, result, hash string) {
 
 // memCacheEntry is the format of entries in the memory cache.
 type memCacheEntry struct {
-	header  http.Header
-	body    []byte
-	expires time.Time
+	header http.Header
+	body   []byte
 }

lib/revproxy/revproxy.go

@@ -31,8 +31,9 @@ import (
 	"sync"
 	"time"
 
+	"github.com/creachadair/mds/cache"
+	"github.com/creachadair/scheddle"
 	"github.com/creachadair/taskgroup"
-	"github.com/golang/groupcache/lru"
 	"github.com/tailscale/go-cache-plugin/lib/s3util"
 )
 
@@ -89,9 +90,8 @@ type Server struct {
 	initOnce sync.Once
 	tasks    *taskgroup.Group
 	start    func(taskgroup.Task) *taskgroup.Group
-
-	mcacheMu sync.Mutex // protects mcache
-	mcache   *lru.Cache // short-lived mutable objects
+	mcache   *cache.Cache[string, memCacheEntry] // short-lived mutable objects
+	expire   *scheddle.Queue                     // cache expirations
 
 	reqReceived  expvar.Int // total requests received
 	reqMemoryHit expvar.Int // hit in memory cache (volatile)
@@ -114,7 +114,14 @@ func (s *Server) init() {
 	s.initOnce.Do(func() {
 		nt := runtime.NumCPU()
 		s.tasks, s.start = taskgroup.New(nil).Limit(nt)
-		s.mcache = lru.New(1 << 16)
+		s.mcache = cache.New(cache.Config[string, memCacheEntry]{
+			Limit: 10 << 20,
+			Store: cache.LRU[string, memCacheEntry](),
+			Size: func(e memCacheEntry) int64 {
+				return int64(len(e.body))
+			},
+		})
+		s.expire = scheddle.NewQueue(nil)
 	})
 }