Add in-memory cache to GET requests, purges on successful POSTs

4 files changed, 103 insertions, 13 deletions

diff --git a/srv/src/go.mod b/srv/src/go.mod
index dd6509d..f65034f 100644
--- a/srv/src/go.mod
+++ b/srv/src/go.mod
@@ -10,6 +10,7 @@ require (
 	github.com/google/uuid v1.3.0
 	github.com/gorilla/feeds v1.1.1 // indirect
 	github.com/gorilla/websocket v1.4.2
+	github.com/hashicorp/golang-lru v0.5.4 // indirect
 	github.com/mattn/go-sqlite3 v1.14.8
 	github.com/mediocregopher/mediocre-go-lib/v2 v2.0.0-beta.0.0.20220506011745-cbeee71cb1ee
 	github.com/mediocregopher/radix/v4 v4.0.0-beta.1.0.20210726230805-d62fa1b2e3cb
diff --git a/srv/src/go.sum b/srv/src/go.sum
index f5bd1fe..d8139cc 100644
--- a/srv/src/go.sum
+++ b/srv/src/go.sum
@@ -75,6 +75,8 @@ github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0/go.mod h1:8NvIoxWQoOIhqOTXgf
 github.com/grpc-ecosystem/grpc-gateway v1.9.0/go.mod h1:vNeuVxBJEsws4ogUvrchl83t/GYV9WGTSLVdBhOQFDY=
 github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-multierror v1.0.0/go.mod h1:dHtQlpGsu+cZNNAkkCN/P3hoUDHhCYQXV3UM06sGGrk=
+github.com/hashicorp/golang-lru v0.5.4 h1:YDjusn29QI/Das2iO9M0BHnIbxPeyuCHsjMW+lJfyTc=
+github.com/hashicorp/golang-lru v0.5.4/go.mod h1:iADmTwqILo4mZ8BN3D2Q6+9jd8WM5uGBxy+E8yxSoD4=
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
 github.com/huandu/xstrings v1.3.2/go.mod h1:y5/lhBue+AyNmUVz9RLU9xbLR0o4KIIExikq4ovT0aE=
 github.com/imdario/mergo v0.3.11/go.mod h1:jmQim1M+e3UYxmgPu/WyfjB3N3VflVyUjjjwH0dnCYA=
diff --git a/srv/src/http/api.go b/srv/src/http/api.go
index 11d092d..ebc1de2 100644
--- a/srv/src/http/api.go
+++ b/srv/src/http/api.go
@@ -15,6 +15,7 @@ import (
 	"strings"
 	"time"
 
+	lru "github.com/hashicorp/golang-lru"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/cfg"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/chat"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
@@ -162,8 +163,11 @@ func (a *api) Shutdown(ctx context.Context) error {
 
 func (a *api) handler() http.Handler {
 
-	requirePow := func(h http.Handler) http.Handler {
-		return a.requirePowMiddleware(h)
+	cache, err := lru.New(5000)
+
+	// instantiating the lru cache can't realistically fail
+	if err != nil {
+		panic(err)
 	}
 
 	mux := http.NewServeMux()
@@ -172,12 +176,12 @@ func (a *api) handler() http.Handler {
 		apiMux := http.NewServeMux()
 		apiMux.Handle("/pow/challenge", a.newPowChallengeHandler())
 		apiMux.Handle("/pow/check",
-			requirePow(
+			a.requirePowMiddleware(
 				http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {}),
 			),
 		)
 
-		apiMux.Handle("/mailinglist/subscribe", requirePow(a.mailingListSubscribeHandler()))
+		apiMux.Handle("/mailinglist/subscribe", a.requirePowMiddleware(a.mailingListSubscribeHandler()))
 		apiMux.Handle("/mailinglist/finalize", a.mailingListFinalizeHandler())
 		apiMux.Handle("/mailinglist/unsubscribe", a.mailingListUnsubscribeHandler())
 
@@ -222,10 +226,12 @@ func (a *api) handler() http.Handler {
 		"GET": applyMiddlewares(
 			globalHandler,
 			logReqMiddleware,
+			cacheMiddleware(cache),
 			setCSRFMiddleware,
 		),
 		"*": applyMiddlewares(
 			globalHandler,
+			purgeCacheOnOKMiddleware(cache),
 			authMiddleware(a.auther),
 			checkCSRFMiddleware,
 			addResponseHeadersMiddleware(map[string]string{
diff --git a/srv/src/http/middleware.go b/srv/src/http/middleware.go
index 02d156b..7296a35 100644
--- a/srv/src/http/middleware.go
+++ b/srv/src/http/middleware.go
@@ -1,10 +1,14 @@
 package http
 
 import (
+	"bytes"
 	"net"
 	"net/http"
+	"path/filepath"
+	"sync"
 	"time"
 
+	lru "github.com/hashicorp/golang-lru"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mlog"
@@ -52,33 +56,33 @@ func setLoggerMiddleware(logger *mlog.Logger) middleware {
 	}
 }
 
-type logResponseWriter struct {
+type wrappedResponseWriter struct {
 	http.ResponseWriter
 	http.Hijacker
 	statusCode int
 }
 
-func newLogResponseWriter(rw http.ResponseWriter) *logResponseWriter {
+func newWrappedResponseWriter(rw http.ResponseWriter) *wrappedResponseWriter {
 	h, _ := rw.(http.Hijacker)
-	return &logResponseWriter{
+	return &wrappedResponseWriter{
 		ResponseWriter: rw,
 		Hijacker:       h,
 		statusCode:     200,
 	}
 }
 
-func (lrw *logResponseWriter) WriteHeader(statusCode int) {
-	lrw.statusCode = statusCode
-	lrw.ResponseWriter.WriteHeader(statusCode)
+func (rw *wrappedResponseWriter) WriteHeader(statusCode int) {
+	rw.statusCode = statusCode
+	rw.ResponseWriter.WriteHeader(statusCode)
 }
 
 func logReqMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 
-		lrw := newLogResponseWriter(rw)
+		wrw := newWrappedResponseWriter(rw)
 
 		started := time.Now()
-		h.ServeHTTP(lrw, r)
+		h.ServeHTTP(wrw, r)
 		took := time.Since(started)
 
 		type logCtxKey string
@@ -86,7 +90,7 @@ func logReqMiddleware(h http.Handler) http.Handler {
 		ctx := r.Context()
 		ctx = mctx.Annotate(ctx,
 			logCtxKey("took"), took.String(),
-			logCtxKey("response_code"), lrw.statusCode,
+			logCtxKey("response_code"), wrw.statusCode,
 		)
 
 		apiutil.GetRequestLogger(r).Info(ctx, "handled HTTP request")
@@ -106,3 +110,80 @@ func disallowGetMiddleware(h http.Handler) http.Handler {
 		rw.WriteHeader(405)
 	})
 }
+
+type cacheResponseWriter struct {
+	*wrappedResponseWriter
+	buf *bytes.Buffer
+}
+
+func newCacheResponseWriter(rw http.ResponseWriter) *cacheResponseWriter {
+	return &cacheResponseWriter{
+		wrappedResponseWriter: newWrappedResponseWriter(rw),
+		buf:                   new(bytes.Buffer),
+	}
+}
+
+func (rw *cacheResponseWriter) Write(b []byte) (int, error) {
+	if _, err := rw.buf.Write(b); err != nil {
+		panic(err)
+	}
+	return rw.wrappedResponseWriter.Write(b)
+}
+
+func cacheMiddleware(cache *lru.Cache) middleware {
+
+	type entry struct {
+		body      []byte
+		createdAt time.Time
+	}
+
+	pool := sync.Pool{
+		New: func() interface{} { return new(bytes.Reader) },
+	}
+
+	return func(h http.Handler) http.Handler {
+		return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+
+			id := r.URL.RequestURI()
+
+			if val, ok := cache.Get(id); ok {
+
+				entry := val.(entry)
+
+				reader := pool.Get().(*bytes.Reader)
+				defer pool.Put(reader)
+
+				reader.Reset(entry.body)
+
+				http.ServeContent(
+					rw, r, filepath.Base(r.URL.Path), entry.createdAt, reader,
+				)
+				return
+			}
+
+			cacheRW := newCacheResponseWriter(rw)
+			h.ServeHTTP(cacheRW, r)
+
+			if cacheRW.statusCode == 200 {
+				cache.Add(id, entry{
+					body:      cacheRW.buf.Bytes(),
+					createdAt: time.Now(),
+				})
+			}
+		})
+	}
+}
+
+func purgeCacheOnOKMiddleware(cache *lru.Cache) middleware {
+	return func(h http.Handler) http.Handler {
+		return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+
+			wrw := newWrappedResponseWriter(rw)
+			h.ServeHTTP(wrw, r)
+
+			if wrw.statusCode == 200 {
+				cache.Purge()
+			}
+		})
+	}
+}