From fb905ad53caac427e16a3fe6bb56748070ea69ad Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sat, 21 May 2022 10:04:50 -0600
Subject: Add in-memory cache to GET requests, purges on successful POSTs

---
 srv/src/http/middleware.go | 99 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 90 insertions(+), 9 deletions(-)

(limited to 'srv/src/http/middleware.go')

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()
+			}
+		})
+	}
+}
-- 
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