This is my new blog CMS https://jlelse.blog
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package main
import (
"bytes"
"crypto/sha256"
"encoding/binary"
"fmt"
"io"
"net/http"
"net/http/httptest"
"net/url"
"strconv"
"strings"
"time"
"unsafe"
"github.com/araddon/dateparse"
"github.com/dgraph-io/ristretto"
servertiming "github.com/mitchellh/go-server-timing"
"golang.org/x/sync/singleflight"
)
const (
cacheInternalExpirationHeader = "GoBlog-Expire"
)
var (
cacheGroup singleflight.Group
cacheR *ristretto.Cache
)
func initCache() (err error) {
cacheR, err = ristretto.NewCache(&ristretto.Config{
NumCounters: 5000,
MaxCost: 20000000, // 20 MB
BufferItems: 16,
Cost: func(value interface{}) (cost int64) {
if cacheItem, ok := value.(*cacheItem); ok {
cost = int64(binary.Size(cacheItem.body)) // Byte size of body
for h, hv := range cacheItem.header {
cost += int64(binary.Size([]byte(h))) // Byte size of header name
for _, hvi := range hv {
cost += int64(binary.Size([]byte(hvi))) // byte size of each header value item
}
}
} else {
cost = int64(unsafe.Sizeof(cacheItem))
}
return cost
},
})
return
}
func cacheMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// Do checks
if !appConfig.Cache.Enable {
next.ServeHTTP(w, r)
return
}
if !(r.Method == http.MethodGet || r.Method == http.MethodHead) {
next.ServeHTTP(w, r)
return
}
if r.URL.Query().Get("cache") == "0" || r.URL.Query().Get("cache") == "false" {
next.ServeHTTP(w, r)
return
}
if loggedIn, ok := r.Context().Value(loggedInKey).(bool); ok && loggedIn {
next.ServeHTTP(w, r)
return
}
// Search and serve cache
key := cacheKey(r)
// Get cache or render it
cacheInterface, _, _ := cacheGroup.Do(key, func() (interface{}, error) {
return getCache(key, next, r), nil
})
cache := cacheInterface.(*cacheItem)
// copy cached headers
for k, v := range cache.header {
w.Header()[k] = v
}
setCacheHeaders(w, cache)
// check conditional request
if ifNoneMatchHeader := r.Header.Get("If-None-Match"); ifNoneMatchHeader != "" && ifNoneMatchHeader == cache.eTag {
// send 304
w.WriteHeader(http.StatusNotModified)
return
}
if ifModifiedSinceHeader := r.Header.Get("If-Modified-Since"); ifModifiedSinceHeader != "" {
if t, err := dateparse.ParseAny(ifModifiedSinceHeader); err == nil && t.After(cache.creationTime) {
// send 304
w.WriteHeader(http.StatusNotModified)
return
}
}
// set status code
w.WriteHeader(cache.code)
// write cached body
_, _ = w.Write(cache.body)
})
}
func cacheKey(r *http.Request) string {
def := cacheURLString(r.URL)
// Special cases
if asRequest, ok := r.Context().Value(asRequestKey).(bool); ok && asRequest {
return "as-" + def
}
// Default
return def
}
func cacheURLString(u *url.URL) string {
var buf strings.Builder
_, _ = buf.WriteString(u.EscapedPath())
if q := u.Query(); len(q) > 0 {
_ = buf.WriteByte('?')
_, _ = buf.WriteString(q.Encode())
}
return buf.String()
}
func setCacheHeaders(w http.ResponseWriter, cache *cacheItem) {
w.Header().Set("ETag", cache.eTag)
w.Header().Set("Last-Modified", cache.creationTime.UTC().Format(http.TimeFormat))
if w.Header().Get("Cache-Control") == "" {
if cache.expiration != 0 {
w.Header().Set("Cache-Control", fmt.Sprintf("public,max-age=%d,stale-while-revalidate=%d", cache.expiration, cache.expiration))
} else {
w.Header().Set("Cache-Control", fmt.Sprintf("public,max-age=%d,s-max-age=%d,stale-while-revalidate=%d", appConfig.Cache.Expiration, appConfig.Cache.Expiration/3, appConfig.Cache.Expiration))
}
}
}
type cacheItem struct {
expiration int
creationTime time.Time
eTag string
code int
header http.Header
body []byte
}
func getCache(key string, next http.Handler, r *http.Request) (item *cacheItem) {
if rItem, ok := cacheR.Get(key); ok {
item = rItem.(*cacheItem)
}
if item == nil {
// No cache available
servertiming.FromContext(r.Context()).NewMetric("cm")
// Remove problematic headers
r.Header.Del("If-Modified-Since")
r.Header.Del("If-Unmodified-Since")
r.Header.Del("If-None-Match")
r.Header.Del("If-Match")
r.Header.Del("If-Range")
r.Header.Del("Range")
// Record request
recorder := httptest.NewRecorder()
next.ServeHTTP(recorder, r)
// Cache values from recorder
result := recorder.Result()
body, _ := io.ReadAll(result.Body)
_ = result.Body.Close()
eTag := result.Header.Get("ETag")
if eTag == "" {
h := sha256.New()
_, _ = io.Copy(h, bytes.NewReader(body))
eTag = fmt.Sprintf("%x", h.Sum(nil))
}
lastMod := time.Now()
if lm := result.Header.Get("Last-Modified"); lm != "" {
if parsedTime, te := dateparse.ParseLocal(lm); te == nil {
lastMod = parsedTime
}
}
exp, _ := strconv.Atoi(result.Header.Get(cacheInternalExpirationHeader))
// Remove problematic headers
result.Header.Del(cacheInternalExpirationHeader)
result.Header.Del("Accept-Ranges")
result.Header.Del("ETag")
result.Header.Del("Last-Modified")
result.Header.Del("Server-Timing")
// Create cache item
item = &cacheItem{
expiration: exp,
creationTime: lastMod,
eTag: eTag,
code: result.StatusCode,
header: result.Header,
body: body,
}
// Save cache
if cch := item.header.Get("Cache-Control"); !strings.Contains(cch, "no-store") && !strings.Contains(cch, "private") && !strings.Contains(cch, "no-cache") {
if exp == 0 {
cacheR.Set(key, item, 0)
} else {
ttl := time.Duration(exp) * time.Second
cacheR.SetWithTTL(key, item, 0, ttl)
}
}
} else {
servertiming.FromContext(r.Context()).NewMetric("c")
}
return item
}
func purgeCache() {
cacheR.Clear()
}
func setInternalCacheExpirationHeader(w http.ResponseWriter, expiration int) {
w.Header().Set(cacheInternalExpirationHeader, strconv.Itoa(expiration))
}