From d218062aa1447eb6f85e871f08c3122c859e0b5e Mon Sep 17 00:00:00 2001
From: Adrien Kunysz <adrien@kunysz.be>
Date: Thu, 14 Nov 2013 22:08:46 +0100
Subject: [PATCH 3/4] Unspaghettify the call graph

fetchImageFromServer() now doesn't return anything useful,
it just updates the cache and we always get (meta)data with
fetchImageFromCache(). This will allow to do more fancy stuff
with the headers from the upstream server without making the
call graph even worse.

Also, previously, when fetching an outdated image, we would still
try to get it from the cache while updating it asynchronously.
Now, we update the cache before returning. This means requests that
trigger a cache miss can be a bit slower but at least they get the
correct answer now.
---
 img.go |   45 +++++++++++++++++++++------------------------
 1 files changed, 21 insertions(+), 24 deletions(-)

diff --git a/img.go b/img.go
index f587653..8fe139f 100644
--- a/img.go
+++ b/img.go
@@ -162,11 +162,19 @@ func resetCacheTimer(uri string) {
 }
 
 // Fetch image from cache
-func fetchImageFromCache(uri string, behaviour Behaviour) (headers Headers, body []byte, ok bool) {
-	ok = false
+func fetchImageFromCache(uri string, behaviour Behaviour) (headers Headers, body []byte, err error) {
+	err = nil
+
+	exists := connection.Exists("img/updated/" + uri)
+	if exists.Err() != nil || !exists.Val() {
+		err = fetchImageFromServer(uri, behaviour)
+		if err != nil {
+			return
+		}
+	}
 
 	hget := connection.HGet("img/"+uri, "type")
-	if err := hget.Err(); err != nil {
+	if err = hget.Err(); err != nil {
 		return
 	}
 	contentType := hget.Val()
@@ -181,23 +189,15 @@ func fetchImageFromCache(uri string, behaviour Behaviour) (headers Headers, body
 	headers.lastModified = lastModified
 
 	body, err = ioutil.ReadFile(filename)
-	ok = err == nil
-
-	exists := connection.Exists("img/updated/" + uri)
-	if err := exists.Err(); err == nil {
-		if present := exists.Val(); !present {
-			go fetchImageFromServer(uri, behaviour)
-		}
-	}
 
 	return
 }
 
 // Save the body and the content-type header in cache
-func saveImageInCache(uri string, headers Headers, body []byte) {
+func saveImageInCache(uri string, contentType string, body []byte) (err error) {
 	checksum := generateChecksumForCache(body)
 	hget := connection.HGet("img/"+uri, "checksum")
-	if err := hget.Err(); err == nil {
+	if err = hget.Err(); err == nil {
 		if was := hget.Val(); checksum == was {
 			resetCacheTimer(uri)
 			return
@@ -206,7 +206,7 @@ func saveImageInCache(uri string, headers Headers, body []byte) {
 
 	filename := generateKeyForCache(uri)
 	dirname := path.Dir(filename)
-	err := os.MkdirAll(dirname, 0755)
+	err = os.MkdirAll(dirname, 0755)
 	if err != nil {
 		return
 	}
@@ -219,9 +219,11 @@ func saveImageInCache(uri string, headers Headers, body []byte) {
 	}
 
 	// And other infos in redis
-	connection.HSet("img/"+uri, "type", headers.contentType)
+	connection.HSet("img/"+uri, "type", contentType)
 	connection.HSet("img/"+uri, "checksum", checksum)
 	resetCacheTimer(uri)
+
+	return
 }
 
 // Save the error in redis for 10 minutes
@@ -233,7 +235,7 @@ func saveErrorInCache(uri string, err error) {
 }
 
 // Fetch the image from the distant server
-func fetchImageFromServer(uri string, behaviour Behaviour) (headers Headers, body []byte, err error) {
+func fetchImageFromServer(uri string, behaviour Behaviour) (err error) {
 	// Accepts any certificate in HTTPS
 	cfg := &tls.Config{InsecureSkipVerify: true}
 	tr := &http.Transport{TLSClientConfig: cfg}
@@ -266,7 +268,7 @@ func fetchImageFromServer(uri string, behaviour Behaviour) (headers Headers, bod
 	}
 	log.Printf("Fetch %s (%s)\n", uri, contentType)
 
-	body, err = ioutil.ReadAll(res.Body)
+	body, err := ioutil.ReadAll(res.Body)
 	if err != nil {
 		log.Printf("Error on ioutil.ReadAll for %s: %s\n", uri, err)
 		return
@@ -274,10 +276,8 @@ func fetchImageFromServer(uri string, behaviour Behaviour) (headers Headers, bod
 
 	body = behaviour.Manipulate(body)
 
-	headers.contentType = contentType
-	headers.lastModified = time.Now().Format(time.RFC1123)
 	if urlStatus(uri) == nil {
-		go saveImageInCache(uri, headers, body)
+		err = saveImageInCache(uri, contentType, body)
 	}
 	return
 }
@@ -289,10 +289,7 @@ func fetchImage(uri string, behaviour Behaviour) (headers Headers, body []byte,
 		return
 	}
 
-	headers, body, ok := fetchImageFromCache(uri, behaviour)
-	if !ok {
-		headers, body, err = fetchImageFromServer(uri, behaviour)
-	}
+	headers, body, err = fetchImageFromCache(uri, behaviour)
 	headers.cacheControl = fmt.Sprintf("public, max-age=%d", CacheRefreshInterval)
 
 	return
-- 
1.7.2.5