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/imageproxy.go

@@ -0,0 +1,123 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package imageproxy
+
+import (
+	"net/http"
+	"sync"
+
+	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/services/configservice"
+	"github.com/mattermost/mattermost-server/services/httpservice"
+)
+
+// An ImageProxy is the public interface for Mattermost's image proxy. An instance of ImageProxy should be created
+// using MakeImageProxy which requires a configService and an HTTPService provided by the server.
+type ImageProxy struct {
+	ConfigService    configservice.ConfigService
+	configListenerId string
+
+	HTTPService httpservice.HTTPService
+
+	lock    sync.RWMutex
+	backend ImageProxyBackend
+}
+
+// An ImageProxyBackend provides the functionality for different types of image proxies. An ImageProxy will construct
+// the required backend depending on the ImageProxySettings provided by the ConfigService.
+type ImageProxyBackend interface {
+	// GetImage provides a proxied image in response to an HTTP request.
+	GetImage(w http.ResponseWriter, r *http.Request, imageURL string)
+
+	// GetProxiedImageURL returns the URL to access a given image through the image proxy, whether the image proxy is
+	// running externally or as part of the Mattermost server itself.
+	GetProxiedImageURL(imageURL string) string
+
+	// GetUnproxiedImageURL returns the original URL of an image from one that has been directed at the image proxy.
+	GetUnproxiedImageURL(proxiedURL string) string
+}
+
+func MakeImageProxy(configService configservice.ConfigService, httpService httpservice.HTTPService) *ImageProxy {
+	proxy := &ImageProxy{
+		ConfigService: configService,
+		HTTPService:   httpService,
+	}
+
+	proxy.configListenerId = proxy.ConfigService.AddConfigListener(proxy.OnConfigChange)
+
+	config := proxy.ConfigService.Config()
+	proxy.backend = proxy.makeBackend(*config.ImageProxySettings.Enable, *config.ImageProxySettings.ImageProxyType)
+
+	return proxy
+}
+
+func (proxy *ImageProxy) makeBackend(enable bool, proxyType string) ImageProxyBackend {
+	if !enable {
+		return nil
+	}
+
+	switch proxyType {
+	case model.IMAGE_PROXY_TYPE_LOCAL:
+		return makeLocalBackend(proxy)
+	case model.IMAGE_PROXY_TYPE_ATMOS_CAMO:
+		return makeAtmosCamoBackend(proxy)
+	default:
+		return nil
+	}
+}
+
+func (proxy *ImageProxy) Close() {
+	proxy.lock.Lock()
+	defer proxy.lock.Unlock()
+
+	proxy.ConfigService.RemoveConfigListener(proxy.configListenerId)
+}
+
+func (proxy *ImageProxy) OnConfigChange(oldConfig, newConfig *model.Config) {
+	if *oldConfig.ImageProxySettings.Enable != *newConfig.ImageProxySettings.Enable ||
+		*oldConfig.ImageProxySettings.ImageProxyType != *newConfig.ImageProxySettings.ImageProxyType {
+		proxy.lock.Lock()
+		defer proxy.lock.Unlock()
+
+		proxy.backend = proxy.makeBackend(*newConfig.ImageProxySettings.Enable, *newConfig.ImageProxySettings.ImageProxyType)
+	}
+}
+
+// GetImage takes an HTTP request for an image and requests that image using the image proxy.
+func (proxy *ImageProxy) GetImage(w http.ResponseWriter, r *http.Request, imageURL string) {
+	proxy.lock.RLock()
+	defer proxy.lock.RUnlock()
+
+	if proxy.backend == nil {
+		w.WriteHeader(http.StatusNotImplemented)
+		return
+	}
+
+	proxy.backend.GetImage(w, r, imageURL)
+}
+
+// GetProxiedImageURL takes the URL of an image and returns a URL that can be used to view that image through the
+// image proxy.
+func (proxy *ImageProxy) GetProxiedImageURL(imageURL string) string {
+	proxy.lock.RLock()
+	defer proxy.lock.RUnlock()
+
+	if proxy.backend == nil {
+		return imageURL
+	}
+
+	return proxy.backend.GetProxiedImageURL(imageURL)
+}
+
+// GetUnproxiedImageURL takes the URL of an image on the image proxy and returns the original URL of the image.
+func (proxy *ImageProxy) GetUnproxiedImageURL(proxiedURL string) string {
+	proxy.lock.RLock()
+	defer proxy.lock.RUnlock()
+
+	if proxy.backend == nil {
+		return proxiedURL
+	}
+
+	return proxy.backend.GetUnproxiedImageURL(proxiedURL)
+}