feat: etag cache fingerprinting (#4)

* feat: etag cache fingerprinting

* fix: logrus sirupsen package dependency

cache/content/constructor.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/foomo/neosproxy/cache/content/store"
 	"github.com/foomo/neosproxy/client/cms"
+	"golang.org/x/sync/singleflight"
 )
 
 // New will return a newly created content cache
@@ -15,7 +16,8 @@ func New(cacheLifetime time.Duration, store store.CacheStore, loader cms.Content
 		store:    store,
 
 		// invalidationChannel: make(chan InvalidationRequest),
-		lifetime: cacheLifetime,
+		invalidationRequestGroup: &singleflight.Group{},
+		lifetime:                 cacheLifetime,
 	}
 	return c
 }

cache/content/getter.go

@@ -26,3 +26,11 @@ func (c *Cache) Len() int {
 	}
 	return counter
 }
+
+func (c *Cache) GetAllEtags(workspace string) (etags map[string]string) {
+	return c.store.GetAllEtags(workspace)
+}
+
+func (c *Cache) GetEtag(hash string) (etag string, e error) {
+	return c.store.GetEtag(hash)
+}

cache/content/invalidator.go

@@ -1,6 +1,7 @@
 package content
 
 import (
+	"strings"
 	"time"
 
 	"github.com/foomo/neosproxy/cache/content/store"
@@ -11,8 +12,7 @@ func (c *Cache) RemoveAll() (err error) {
 	return c.store.RemoveAll()
 }
 
-// Invalidate cache item
-func (c *Cache) Invalidate(id, dimension, workspace string) (item store.CacheItem, err error) {
+func (c *Cache) invalidator(id, dimension, workspace string) (item store.CacheItem, err error) {
 
 	// timer
 	start := time.Now()
@@ -40,7 +40,23 @@ func (c *Cache) Invalidate(id, dimension, workspace string) (item store.CacheIte
 		Duration: time.Since(start),
 	})
 
-	// done
+	return
+}
+
+// Invalidate cache item
+func (c *Cache) Invalidate(id, dimension, workspace string) (item store.CacheItem, err error) {
+
+	groupName := strings.Join([]string{"invalidate", id, dimension, workspace}, "-")
+	itemInterfaced, errThrottled, _ := c.invalidationRequestGroup.Do(groupName, func() (i interface{}, e error) {
+		return c.invalidator(id, dimension, workspace)
+	})
+
+	if errThrottled != nil {
+		err = errThrottled
+		return
+	}
+
+	item = itemInterfaced.(store.CacheItem)
 	return
 }
 

cache/content/store/cache.go

@@ -7,6 +7,9 @@ type CacheStore interface {
 	Get(hash string) (item CacheItem, e error)
 	GetAll() (item []CacheItem, e error)
 
+	GetEtag(hash string) (etag string, e error)
+	GetAllEtags(workspace string) (etags map[string]string)
+
 	Count() (int, error)
 
 	Remove(hash string) (e error)

cache/content/store/fs/filesystem.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/foomo/neosproxy/cache/content"
 	"github.com/foomo/neosproxy/cache/content/store"
@@ -23,6 +24,9 @@ type fsCacheStore struct {
 	lock sync.Mutex
 	rw   map[string]*sync.RWMutex
 	l    logging.Entry
+
+	lockEtags sync.RWMutex
+	etags     map[string]string
 }
 
 //------------------------------------------------------------------
@@ -38,14 +42,21 @@ func NewCacheStore(cacheDir string) store.CacheStore {
 		l.WithError(err).Fatal("failed creating cache directory")
 	}
 
-	s := &fsCacheStore{
+	f := &fsCacheStore{
 		CacheDir: cacheDir,
-		lock:     sync.Mutex{},
-		rw:       make(map[string]*sync.RWMutex),
-		l:        l,
+
+		l: l,
+
+		lock: sync.Mutex{},
+		rw:   make(map[string]*sync.RWMutex),
+
+		lockEtags: sync.RWMutex{},
+		etags:     make(map[string]string),
 	}
 
-	return s
+	go f.initEtagCache()
+
+	return f
 }
 
 //------------------------------------------------------------------
@@ -56,6 +67,11 @@ func (f *fsCacheStore) Upsert(item store.CacheItem) (e error) {
 	// key
 	key := f.getItemKey(item)
 
+	// validate etag
+	if item.Etag == "" {
+		item.Etag = item.GetEtag()
+	}
+
 	// serialize
 	bytes, errMarshall := json.Marshal(item)
 	if errMarshall != nil {
@@ -64,10 +80,54 @@ func (f *fsCacheStore) Upsert(item store.CacheItem) (e error) {
 
 	// lock
 	cacheFile := f.Lock(key)
-	defer f.Unlock(key)
 
 	// write to file
-	return ioutil.WriteFile(cacheFile, bytes, 0644)
+	errWrite := ioutil.WriteFile(cacheFile, bytes, 0644)
+	if errWrite != nil {
+		f.Unlock(key)
+		e = errWrite
+		return
+	}
+	f.Unlock(key)
+
+	// update etag
+	f.upsertEtag(item.Hash, item.Etag)
+
+	return nil
+}
+
+func (f *fsCacheStore) GetAllEtags(workspace string) (etags map[string]string) {
+	f.lockEtags.RLock()
+	etags = make(map[string]string)
+	for hash, etag := range f.etags {
+		if !strings.HasPrefix(hash, workspace) {
+			continue
+		}
+		etags[hash] = etag
+	}
+	f.lockEtags.RUnlock()
+	return
+}
+
+func (f *fsCacheStore) GetEtag(hash string) (etag string, e error) {
+	f.lockEtags.RLock()
+	if value, ok := f.etags[hash]; ok {
+		etag = value
+		f.lockEtags.RUnlock()
+		return
+	}
+	f.lockEtags.RUnlock()
+
+	item, errGet := f.Get(hash)
+	if errGet != nil {
+		e = errGet
+		return
+	}
+
+	etag = item.GetEtag()
+	f.upsertEtag(hash, etag)
+
+	return
 }
 
 func (f *fsCacheStore) Get(hash string) (item store.CacheItem, e error) {
@@ -146,7 +206,17 @@ func (f *fsCacheStore) Remove(hash string) (e error) {
 	cacheFile := f.Lock(key)
 	defer f.Unlock(key)
 
-	return os.Remove(cacheFile)
+	errRemove := os.Remove(cacheFile)
+	if errRemove != nil {
+		e = errRemove
+		return
+	}
+
+	f.lockEtags.Lock()
+	delete(f.etags, hash)
+	f.lockEtags.Unlock()
+
+	return nil
 }
 
 func (f *fsCacheStore) createCacheDir() error {
@@ -163,6 +233,10 @@ func (f *fsCacheStore) RemoveAll() (e error) {
 		return errRemoveAll
 	}
 
+	f.lockEtags.Lock()
+	f.etags = make(map[string]string)
+	f.lockEtags.Unlock()
+
 	errCreateCache := f.createCacheDir()
 	if errCreateCache != nil {
 		f.l.WithError(errCreateCache).Error("unable to re-create cache directory")
@@ -176,6 +250,44 @@ func (f *fsCacheStore) RemoveAll() (e error) {
 // ~ PRIVATE METHODS
 //------------------------------------------------------------------
 
+func (f *fsCacheStore) initEtagCache() {
+	start := time.Now()
+	l := f.l.WithField(logging.FieldFunction, "initEtagCache")
+	files, errReadDir := ioutil.ReadDir(f.CacheDir)
+	if errReadDir != nil {
+		l.WithError(errReadDir).Error("failed reading cache dir")
+		return
+	}
+
+	l.Debug("init etag cache")
+	counter := 0
+	for _, file := range files {
+		if !file.IsDir() {
+			filename := file.Name()
+			index := strings.Index(filename, ".")
+			if index >= 0 {
+				filename = filename[0:index]
+			}
+			item, errGet := f.Get(filename)
+			if errGet != nil {
+				l.WithError(errGet).Warn("could not load cache item")
+				continue
+			}
+			counter++
+			f.upsertEtag(item.Hash, item.GetEtag())
+		}
+	}
+	l.WithField("len", counter).WithDuration(start).Debug("etag cache initialized")
+
+	return
+}
+
+func (f *fsCacheStore) upsertEtag(hash, etag string) {
+	f.lockEtags.Lock()
+	f.etags[hash] = etag
+	f.lockEtags.Unlock()
+}
+
 func (f *fsCacheStore) getItemKey(item store.CacheItem) string {
 	return f.getKey(item.Hash)
 }

cache/content/store/vo.go

@@ -1,6 +1,8 @@
 package store
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"strings"
 	"time"
 )
@@ -19,6 +21,7 @@ type CacheItem struct {
 	validUntil time.Time
 
 	HTML string
+	Etag string // hashed fingerprint of html content
 }
 
 // NewCacheItem will create a new cache item
@@ -31,10 +34,25 @@ func NewCacheItem(id string, dimension string, workspace string, html string, va
 		created:    time.Now(),
 		validUntil: validUntil,
 		HTML:       html,
+		Etag:       generateFingerprint(html),
 	}
 }
 
+// GetEtag returns an etag
+func (item *CacheItem) GetEtag() string {
+	if item.Etag != "" {
+		return item.Etag
+	}
+	return generateFingerprint(item.HTML)
+}
+
 // GetHash will return a cache item hash
 func GetHash(id, dimension, workspace string) string {
 	return strings.Join([]string{workspace, dimension, id}, "_")
 }
+
+func generateFingerprint(data string) string {
+	sha := sha256.New()
+	sha.Write([]byte(data))
+	return hex.EncodeToString(sha.Sum(nil))
+}

cache/content/vo.go

@@ -5,14 +5,16 @@ import (
 
 	"github.com/foomo/neosproxy/cache/content/store"
 	"github.com/foomo/neosproxy/client/cms"
+	"golang.org/x/sync/singleflight"
 )
 
 // Cache workspace items
 type Cache struct {
-	observer            Observer
-	loader              cms.ContentLoader
-	store               store.CacheStore
-	invalidationChannel chan InvalidationRequest
+	observer                 Observer
+	loader                   cms.ContentLoader
+	store                    store.CacheStore
+	invalidationChannel      chan InvalidationRequest
+	invalidationRequestGroup *singleflight.Group
 
 	lifetime time.Duration // time until an item must be re-invalidated (< 0 === never)
 }

cache/invalidator.go

@@ -5,9 +5,9 @@ import (
 	"os"
 	"time"
 
-	"github.com/Sirupsen/logrus"
 	"github.com/cloudfoundry/bytefmt"
 	"github.com/foomo/neosproxy/logging"
+	"github.com/sirupsen/logrus"
 )
 
 // Invalidate cache maybe invalidates cache, but skips requests if invalidation queue is already full

cmd/neosproxy/main.go

@@ -5,7 +5,7 @@ import (
 	"path/filepath"
 	"time"
 
-	"github.com/Sirupsen/logrus"
+	"github.com/sirupsen/logrus"
 	"github.com/foomo/neosproxy/cache/content/store/fs"
 	"github.com/foomo/neosproxy/client/cms"
 	"github.com/foomo/neosproxy/config"

glide.lock

@@ -1,54 +0,0 @@
-hash: c8774276cbc27688b992f05c04cf2e330655e27c5a22bc9b3cad5dae8fd66b60
-updated: 2018-12-24T02:41:18.010901+01:00
-imports:
-- name: github.com/auth0/go-jwt-middleware
-  version: 5493cabe49f7bfa6e2ec444a09d334d90cd4e2bd
-- name: github.com/cloudfoundry/bytefmt
-  version: 2aa6f33b730c79971cfc3c742f279195b0abc627
-- name: github.com/dgrijalva/jwt-go
-  version: 06ea1031745cb8b3dab3f6a236daf2b0aa468b7e
-- name: github.com/foomo/shop
-  version: e55de455dd26d50c2033008174da3bff0125e218
-  subpackages:
-  - persistence
-- name: github.com/gorilla/context
-  version: 51ce91d2eaddeca0ef29a71d766bb3634dadf729
-- name: github.com/gorilla/mux
-  version: e3702bed27f0d39777b0b37b664b6280e8ef8fbf
-- name: github.com/konsorten/go-windows-terminal-sequences
-  version: 5c8c8bd35d3832f5d134ae1e1e375b69a4d25242
-- name: github.com/pkg/errors
-  version: 059132a15dd08d6704c67711dae0cf35ab991756
-- name: github.com/Sirupsen/logrus
-  version: bcd833dfe83d3cebad139e4a29ed79cb2318bf95
-- name: github.com/stretchr/testify
-  version: f35b8ab0b5a2cef36673838d662e249dd9c94686
-  subpackages:
-  - assert
-- name: golang.org/x/crypto
-  version: 81e90905daefcd6fd217b62423c0908922eadb30
-  subpackages:
-  - ssh/terminal
-- name: golang.org/x/sys
-  version: b05ddf57801d2239d6ab0ee35f9d981e0420f4ac
-  subpackages:
-  - unix
-  - windows
-- name: gopkg.in/mgo.v2
-  version: 9856a29383ce1c59f308dd1cf0363a79b5bef6b5
-  subpackages:
-  - bson
-  - internal/json
-  - internal/sasl
-  - internal/scram
-- name: gopkg.in/yaml.v2
-  version: 51d6538a90f86fe93ac480b35f37b2be17fef232
-testImports:
-- name: github.com/davecgh/go-spew
-  version: d8f796af33cc11cb798c1aaeb27a4ebc5099927d
-  subpackages:
-  - spew
-- name: github.com/pmezard/go-difflib
-  version: 792786c7400a136282c1664665ae0a8db921c6c2
-  subpackages:
-  - difflib

glide.yaml

@@ -1,22 +0,0 @@
-package: github.com/foomo/neosproxy
-import:
-- package: github.com/Sirupsen/logrus
-  version: ~1.2.0
-- package: gopkg.in/yaml.v2
-  version: ~2.2.2
-- package: golang.org/x/crypto
-  subpackages:
-  - ssh/terminal
-- package: golang.org/x/sys
-  subpackages:
-  - unix
-- package: github.com/stretchr/testify
-  version: ~1.2.2
-  subpackages:
-  - assert
-- package: github.com/gorilla/mux
-  version: ~1.6.2
-- package: github.com/auth0/go-jwt-middleware
-- package: github.com/dgrijalva/jwt-go
-  version: ~3.2.0
-- package: github.com/cloudfoundry/bytefmt

go.mod

@@ -0,0 +1,19 @@
+module github.com/foomo/neosproxy
+
+go 1.12
+
+require (
+	github.com/auth0/go-jwt-middleware v0.0.0-20170425171159-5493cabe49f7
+	github.com/cloudfoundry/bytefmt v0.0.0-20180906201452-2aa6f33b730c
+	github.com/dgrijalva/jwt-go v3.2.0+incompatible
+	github.com/foomo/shop v0.0.0-20190306093145-644b0b683ba1
+	github.com/gorilla/mux v1.6.2
+	github.com/pkg/errors v0.0.0-20181023235946-059132a15dd0
+	github.com/sirupsen/logrus v1.2.0
+	github.com/stretchr/testify v1.2.2
+	golang.org/x/crypto v0.0.0-20190103213133-ff983b9c42bc
+	golang.org/x/sync v0.0.0-20170517211232-f52d1811a629
+	golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33
+	gopkg.in/mgo.v2 v2.0.0-20180705113604-9856a29383ce
+	gopkg.in/yaml.v2 v2.2.2
+)

go.sum

@@ -0,0 +1,30 @@
+github.com/auth0/go-jwt-middleware v0.0.0-20170425171159-5493cabe49f7 h1:irR1cO6eek3n5uquIVaRAsQmZnlsfPuHNz31cXo4eyk=
+github.com/auth0/go-jwt-middleware v0.0.0-20170425171159-5493cabe49f7/go.mod h1:LWMyo4iOLWXHGdBki7NIht1kHru/0wM179h+d3g8ATM=
+github.com/cloudfoundry/bytefmt v0.0.0-20180906201452-2aa6f33b730c h1:zE9z4EZZwJTjOi9Q9WYM/81BuwOKyjhHagiNUDhDdnI=
+github.com/cloudfoundry/bytefmt v0.0.0-20180906201452-2aa6f33b730c/go.mod h1:4oo6ExqTPaBVBwSm814h6UO5Fels1kN2KvpNscaCcS0=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumCAMpl/TFQ4/5kLM=
+github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
+github.com/foomo/shop v0.0.0-20190306093145-644b0b683ba1/go.mod h1:+Y2nUdyvktarq9+F2B0tvk/BM7y+jwNJI1CW/KgM7as=
+github.com/gorilla/mux v1.6.2 h1:Pgr17XVTNXAk3q/r4CpKzC5xBM/qW1uVLV+IhRZpIIk=
+github.com/gorilla/mux v1.6.2/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2zaAs=
+github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
+github.com/pkg/errors v0.0.0-20181023235946-059132a15dd0 h1:R+lX9nKwNd1n7UE5SQAyoorREvRn3aLF6ZndXBoIWqY=
+github.com/pkg/errors v0.0.0-20181023235946-059132a15dd0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.2.0 h1:juTguoYk5qI21pwyTXY3B3Y5cOTH3ZUyZCg1v/mihuo=
+github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
+github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/crypto v0.0.0-20190103213133-ff983b9c42bc h1:F5tKCVGp+MUAHhKp5MZtGqAlGX3+oCsiL1Q629FL90M=
+golang.org/x/crypto v0.0.0-20190103213133-ff983b9c42bc/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/sync v0.0.0-20170517211232-f52d1811a629 h1:wqoYUzeICxRnvJCvfHTh0OY0VQ6xern7nYq+ccc19e4=
+golang.org/x/sync v0.0.0-20170517211232-f52d1811a629/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20171031081856-95c657629925/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33 h1:I6FyU15t786LL7oL/hn43zqTuEGr4PN7F4XJ1p4E3Y8=
+golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/mgo.v2 v2.0.0-20180705113604-9856a29383ce/go.mod h1:yeKp02qBN3iKW1OzL3MGk2IdtZzaj7SFntXj72NppTA=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

logging/entry.go

@@ -5,7 +5,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/Sirupsen/logrus"
+	"github.com/sirupsen/logrus"
 	"github.com/pkg/errors"
 )
 

logging/getter.go

@@ -3,7 +3,7 @@ package logging
 import (
 	"errors"
 
-	"github.com/Sirupsen/logrus"
+	"github.com/sirupsen/logrus"
 )
 
 func GetDefaultLogEntry() Entry {

logging/logger.go

@@ -9,7 +9,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/Sirupsen/logrus"
+	"github.com/sirupsen/logrus"
 )
 
 var Logger *logrus.Logger

notifier/broker.go

@@ -3,7 +3,7 @@ package notifier
 import (
 	"sync"
 
-	"github.com/Sirupsen/logrus"
+	"github.com/sirupsen/logrus"
 	"github.com/foomo/neosproxy/cache"
 	"github.com/foomo/neosproxy/logging"
 

proxy/api.go

@@ -7,7 +7,9 @@ import (
 	"strings"
 	"time"
 
-	"github.com/Sirupsen/logrus"
+	"github.com/foomo/neosproxy/cache/content/store"
+
+	"github.com/sirupsen/logrus"
 	"github.com/cloudfoundry/bytefmt"
 	"github.com/foomo/neosproxy/cache"
 	"github.com/foomo/neosproxy/client/cms"
@@ -50,6 +52,17 @@ func (p *Proxy) getContent(w http.ResponseWriter, r *http.Request) {
 		logging.FieldID:        id,
 	})
 
+	// etag cache handling
+	headerEtag := r.Header.Get("ETag")
+	if headerEtag != "" {
+		etag, errEtag := p.contentCache.GetEtag(store.GetHash(id, dimension, workspace))
+		if errEtag == nil && etag != "" && etag == headerEtag {
+			w.WriteHeader(http.StatusNotModified)
+			log.WithDuration(start).Debug("content not modified")
+			return
+		}
+	}
+
 	// try cache hit, invalidate in case of item not found
 	item, errCacheGet := p.contentCache.Get(id, dimension, workspace)
 	if errCacheGet != nil {
@@ -78,6 +91,8 @@ func (p *Proxy) getContent(w http.ResponseWriter, r *http.Request) {
 		HTML: item.HTML,
 	}
 
+	w.Header().Set("ETag", item.GetEtag())
+
 	// stream json response
 	encoder := json.NewEncoder(w)
 	errEncode := encoder.Encode(data)
@@ -88,7 +103,7 @@ func (p *Proxy) getContent(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// done
-	log.WithDuration(start).Debug("served content")
+	log.WithDuration(start).Debug("content served")
 	return
 }
 
@@ -241,12 +256,87 @@ func (p *Proxy) streamStatus(w http.ResponseWriter, r *http.Request) {
 	// error handling
 	if errEncode != nil {
 		log.WithError(errEncode).WithField("content-negotiation", contentNegotioation).Error("failed streaming status")
-		w.WriteHeader(http.StatusInternalServerError)
+		http.Error(w, "failed streaming status", http.StatusInternalServerError)
 		return
 	}
 
 }
 
+func (p *Proxy) getAllEtags(w http.ResponseWriter, r *http.Request) {
+
+	// extract request data
+	workspace := strings.TrimSpace(strings.ToLower(r.URL.Query().Get("workspace")))
+
+	// validate workspace
+	if workspace == "" {
+		workspace = cms.WorkspaceLive
+	}
+
+	// logger
+	log := p.setupLogger(r, "getAllEtags").WithField(logging.FieldWorkspace, workspace)
+
+	etags := p.contentCache.GetAllEtags(workspace)
+
+	w.Header().Set("Content-Type", string(mimeApplicationJSON))
+	encoder := json.NewEncoder(w)
+	errEncode := encoder.Encode(etags)
+
+	// error handling
+	if errEncode != nil {
+		log.WithError(errEncode).Error("failed encoding etags")
+		http.Error(w, "failed encoding etags", http.StatusInternalServerError)
+		return
+	}
+
+	return
+}
+
+func (p *Proxy) getEtag(w http.ResponseWriter, r *http.Request, hash string) {
+	// logger
+	log := p.setupLogger(r, "getEtag").WithField(logging.FieldID, hash)
+
+	etag, errEtag := p.contentCache.GetEtag(hash)
+
+	// error handling
+	if errEtag != nil {
+		log.WithError(errEtag).Error("failed getting etag")
+		http.Error(w, "failed getting etag", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", string(mimeTextPlain))
+	w.Header().Set("ETag", etag)
+	w.Write([]byte(etag))
+
+	return
+}
+
+func (p *Proxy) getEtagByID(w http.ResponseWriter, r *http.Request) {
+	// extract request data
+	workspace := strings.TrimSpace(strings.ToLower(r.URL.Query().Get("workspace")))
+
+	// validate workspace
+	if workspace == "" {
+		workspace = cms.WorkspaceLive
+	}
+
+	// extract request data
+	id := getRequestParameter(r, "id")
+	dimension := getRequestParameter(r, "dimension")
+
+	hash := store.GetHash(id, dimension, workspace)
+
+	p.getEtag(w, r, hash)
+}
+
+func (p *Proxy) getEtagByHash(w http.ResponseWriter, r *http.Request) {
+
+	// extract request data
+	hash := getRequestParameter(r, "hash")
+
+	p.getEtag(w, r, hash)
+}
+
 // ------------------------------------------------------------------------------------------------
 // ~ Private methods
 // ------------------------------------------------------------------------------------------------

proxy/routes.go

@@ -16,12 +16,25 @@ const routeContentServerExport = "/contentserver/export"
 func (p *Proxy) setupRoutes() {
 
 	// hijack content server export routes
+
+	// content tree / sitemap
 	p.router.HandleFunc(routeContentServerExport, p.streamCachedNeosContentServerExport)
 	p.router.HandleFunc(routeContentServerExport, p.streamCachedNeosContentServerExport).Queries("workspace", "{workspace}")
 
-	// /contentserver/export/de/571fd1ae-c8e4-4d91-a708-d97025fb015c?workspace=stage
-	p.router.HandleFunc(routeContentServerExport+"/{dimension}/{id}", p.getContent)
-	p.router.HandleFunc(routeContentServerExport+"/{dimension}/{id}", p.getContent).Queries("workspace", "{workspace}")
+	// etag
+	p.router.HandleFunc(routeContentServerExport+"/etag/{dimension}/{id}", p.getEtagByID).Methods(http.MethodGet)
+	p.router.HandleFunc(routeContentServerExport+"/etag/{dimension}/{id}", p.getEtagByID).Methods(http.MethodGet).Queries("workspace", "{workspace}")
+	p.router.HandleFunc(routeContentServerExport+"/etag/{hash}", p.getEtagByHash).Methods(http.MethodGet)
+
+	p.router.HandleFunc(routeContentServerExport+"/etags", p.getAllEtags).Methods(http.MethodGet)
+	p.router.HandleFunc(routeContentServerExport+"/etags", p.getAllEtags).Methods(http.MethodGet).Queries("workspace", "{workspace}")
+
+	// documents => /contentserver/export/de/571fd1ae-c8e4-4d91-a708-d97025fb015c?workspace=stage
+	p.router.HandleFunc(routeContentServerExport+"/{dimension}/{id}", p.getContent).Methods(http.MethodGet)
+	p.router.HandleFunc(routeContentServerExport+"/{dimension}/{id}", p.getContent).Methods(http.MethodGet).Queries("workspace", "{workspace}")
+
+	p.router.HandleFunc(routeContentServerExport+"/{dimension}/{id}", p.getEtagByID).Methods(http.MethodHead)
+	p.router.HandleFunc(routeContentServerExport+"/{dimension}/{id}", p.getEtagByID).Methods(http.MethodHead).Queries("workspace", "{workspace}")
 
 	// api
 	// neosproxy/cache/%s?workspace=%s