[feature] Implement cache-control and etags for static assets (#711)

* start working on etag stuff

* add + use cache middleware

* generate etags on the fly

* remove unused field

* clean up filepath

* add license headers to cache files

* add attachgroup function to router interface

* move cache into web module

* rename a couple things

* remove attachStaticFS function from router

* rename + tidy up a few things

* mount assets filesystem

* create assetsFileInfoCache

* update comment

* simplify hash

* fix string fmt

* skip last mod chk, prefer strong etags w/long cache

* move base handler to its own file
this matches the modules in the api folder

* generate new etag if file was modified

* wrap strong etag in quotation marks as per spec

* clarify logic in avatar search

* make hashing a little niftier

internal/web/web.go

@@ -0,0 +1,159 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package web
+
+import (
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"codeberg.org/gruf/go-cache/v2"
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/api"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/processing"
+	"github.com/superseriousbusiness/gotosocial/internal/router"
+	"github.com/superseriousbusiness/gotosocial/internal/uris"
+)
+
+const (
+	confirmEmailPath = "/" + uris.ConfirmEmailPath
+	profilePath      = "/@:" + usernameKey
+	statusPath       = profilePath + "/statuses/:" + statusIDKey
+	adminPanelPath   = "/admin"
+	userPanelpath    = "/user"
+	assetsPath       = "/assets"
+
+	tokenParam  = "token"
+	usernameKey = "username"
+	statusIDKey = "status"
+)
+
+// Module implements the api.ClientModule interface for web pages.
+type Module struct {
+	processor            processing.Processor
+	webAssetsAbsFilePath string
+	assetsETagCache      cache.Cache[string, eTagCacheEntry]
+	defaultAvatars       []string
+}
+
+// New returns a new api.ClientModule for web pages.
+func New(processor processing.Processor) (api.ClientModule, error) {
+	webAssetsBaseDir := config.GetWebAssetBaseDir()
+	if webAssetsBaseDir == "" {
+		return nil, fmt.Errorf("%s cannot be empty and must be a relative or absolute path", config.WebAssetBaseDirFlag())
+	}
+
+	webAssetsAbsFilePath, err := filepath.Abs(webAssetsBaseDir)
+	if err != nil {
+		return nil, fmt.Errorf("error getting absolute path of %s: %s", webAssetsBaseDir, err)
+	}
+
+	defaultAvatarsAbsFilePath := filepath.Join(webAssetsAbsFilePath, "default_avatars")
+	defaultAvatarFiles, err := ioutil.ReadDir(defaultAvatarsAbsFilePath)
+	if err != nil {
+		return nil, fmt.Errorf("error reading default avatars at %s: %s", defaultAvatarsAbsFilePath, err)
+	}
+
+	defaultAvatars := []string{}
+	for _, f := range defaultAvatarFiles {
+		// ignore directories
+		if f.IsDir() {
+			continue
+		}
+
+		// ignore files bigger than 50kb
+		if f.Size() > 50000 {
+			continue
+		}
+
+		// get the name of the file, eg avatar.jpeg
+		fileName := f.Name()
+
+		// get just the .jpeg, for example, from avatar.jpeg
+		extensionWithDot := filepath.Ext(fileName)
+
+		// remove the leading . to just get, eg, jpeg
+		extension := strings.TrimPrefix(extensionWithDot, ".")
+
+		// take only files with simple extensions
+		// that we know will work OK as avatars
+		switch strings.ToLower(extension) {
+		case "svg", "jpeg", "jpg", "gif", "png":
+			avatar := fmt.Sprintf("%s/default_avatars/%s", assetsPath, f.Name())
+			defaultAvatars = append(defaultAvatars, avatar)
+		default:
+			continue
+		}
+	}
+
+	assetsETagCache := cache.New[string, eTagCacheEntry]()
+	assetsETagCache.SetTTL(time.Hour, false)
+	assetsETagCache.Start(time.Minute)
+
+	return &Module{
+		processor:            processor,
+		webAssetsAbsFilePath: webAssetsAbsFilePath,
+		assetsETagCache:      assetsETagCache,
+		defaultAvatars:       defaultAvatars,
+	}, nil
+}
+
+// Route satisfies the RESTAPIModule interface
+func (m *Module) Route(s router.Router) error {
+	// serve static files from assets dir at /assets
+	assetsGroup := s.AttachGroup(assetsPath)
+	m.mountAssetsFilesystem(assetsGroup)
+
+	s.AttachHandler(http.MethodGet, adminPanelPath, m.AdminPanelHandler)
+	// redirect /admin/ to /admin
+	s.AttachHandler(http.MethodGet, adminPanelPath+"/", func(c *gin.Context) {
+		c.Redirect(http.StatusMovedPermanently, adminPanelPath)
+	})
+
+	s.AttachHandler(http.MethodGet, userPanelpath, m.UserPanelHandler)
+	// redirect /settings/ to /settings
+	s.AttachHandler(http.MethodGet, userPanelpath+"/", func(c *gin.Context) {
+		c.Redirect(http.StatusMovedPermanently, userPanelpath)
+	})
+
+	// serve front-page
+	s.AttachHandler(http.MethodGet, "/", m.baseHandler)
+
+	// serve profile pages at /@username
+	s.AttachHandler(http.MethodGet, profilePath, m.profileGETHandler)
+
+	// serve statuses
+	s.AttachHandler(http.MethodGet, statusPath, m.threadGETHandler)
+
+	// serve email confirmation page at /confirm_email?token=whatever
+	s.AttachHandler(http.MethodGet, confirmEmailPath, m.confirmEmailGETHandler)
+
+	// 404 handler
+	s.AttachNoRouteHandler(func(c *gin.Context) {
+		api.ErrorHandler(c, gtserror.NewErrorNotFound(errors.New(http.StatusText(http.StatusNotFound))), m.processor.InstanceGet)
+	})
+
+	return nil
+}