MM-10417 Add local image proxy and enable by default (#9967)

* MM-10417 Add local image proxy and enable by default

* Remove unused function

* Add dependencies for willnorris/imageproxy

* Fixed compilation errors

* Lock to the master version of willnorris/imageproxy

* Fix atmos/camo proxy when no SiteURL is specified

* Re-add default values for deprecated settings

* Fix unit tests added by merge

* Pass imageproxy to App struct

* Remove unneeded locking when creating the image proxy

* Remove empty test file

services/imageproxy/atmos_camo.go

@@ -0,0 +1,70 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package imageproxy
+
+import (
+	"crypto/hmac"
+	"crypto/sha1"
+	"encoding/hex"
+	"net/http"
+	"strings"
+)
+
+type AtmosCamoBackend struct {
+	proxy *ImageProxy
+}
+
+func makeAtmosCamoBackend(proxy *ImageProxy) *AtmosCamoBackend {
+	return &AtmosCamoBackend{
+		proxy: proxy,
+	}
+}
+
+func (backend *AtmosCamoBackend) GetImage(w http.ResponseWriter, r *http.Request, imageURL string) {
+	http.Redirect(w, r, backend.GetProxiedImageURL(imageURL), http.StatusFound)
+}
+
+func (backend *AtmosCamoBackend) GetProxiedImageURL(imageURL string) string {
+	cfg := *backend.proxy.ConfigService.Config()
+	siteURL := *cfg.ServiceSettings.SiteURL
+	proxyURL := *cfg.ImageProxySettings.RemoteImageProxyURL
+	options := *cfg.ImageProxySettings.RemoteImageProxyOptions
+
+	return getAtmosCamoImageURL(imageURL, siteURL, proxyURL, options)
+}
+
+func getAtmosCamoImageURL(imageURL, siteURL, proxyURL, options string) string {
+	// Don't proxy blank images, relative URLs, absolute URLs on this server, or URLs that are already going through the proxy
+	if imageURL == "" || imageURL[0] == '/' || (siteURL != "" && strings.HasPrefix(imageURL, siteURL)) || strings.HasPrefix(imageURL, proxyURL) {
+		return imageURL
+	}
+
+	mac := hmac.New(sha1.New, []byte(options))
+	mac.Write([]byte(imageURL))
+	digest := hex.EncodeToString(mac.Sum(nil))
+
+	return proxyURL + "/" + digest + "/" + hex.EncodeToString([]byte(imageURL))
+}
+
+func (backend *AtmosCamoBackend) GetUnproxiedImageURL(proxiedURL string) string {
+	proxyURL := *backend.proxy.ConfigService.Config().ImageProxySettings.RemoteImageProxyURL + "/"
+
+	if !strings.HasPrefix(proxiedURL, proxyURL) {
+		return proxiedURL
+	}
+
+	path := proxiedURL[len(proxyURL):]
+
+	slash := strings.IndexByte(path, '/')
+	if slash == -1 {
+		return proxiedURL
+	}
+
+	decoded, err := hex.DecodeString(path[slash+1:])
+	if err != nil {
+		return proxiedURL
+	}
+
+	return string(decoded)
+}