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/*
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 (
// nolint:gosec
"crypto/sha1"
"encoding/hex"
"fmt"
"io"
"net/http"
"path"
"strings"
"time"
"github.com/gin-gonic/gin"
"github.com/superseriousbusiness/gotosocial/internal/log"
)
type eTagCacheEntry struct {
eTag string
fileLastModified time.Time
}
// generateEtag generates a strong (byte-for-byte) etag using
// the entirety of the provided reader.
func generateEtag(r io.Reader) (string, error) {
// nolint:gosec
hash := sha1.New()
if _, err := io.Copy(hash, r); err != nil {
return "", err
}
b := make([]byte, 0, sha1.Size)
b = hash.Sum(b)
return `"` + hex.EncodeToString(b) + `"`, nil
}
// getAssetFileInfo tries to fetch the ETag for the given filePath from the module's
// assetsETagCache. If it can't be found there, it uses the provided http.FileSystem
// to generate a new ETag to go in the cache, which it then returns.
func (m *Module) getAssetETag(filePath string, fs http.FileSystem) (string, error) {
file, err := fs.Open(filePath)
if err != nil {
return "", fmt.Errorf("error opening %s: %s", filePath, err)
}
defer file.Close()
fileInfo, err := file.Stat()
if err != nil {
return "", fmt.Errorf("error statting %s: %s", filePath, err)
}
fileLastModified := fileInfo.ModTime()
if cachedETag, ok := m.assetsETagCache.Get(filePath); ok && !fileLastModified.After(cachedETag.fileLastModified) {
// only return our cached etag if the file wasn't
// modified since last time, otherwise generate a
// new one; eat fresh!
return cachedETag.eTag, nil
}
eTag, err := generateEtag(file)
if err != nil {
return "", fmt.Errorf("error generating etag: %s", err)
}
// put new entry in cache before we return
m.assetsETagCache.Set(filePath, eTagCacheEntry{
eTag: eTag,
fileLastModified: fileLastModified,
})
return eTag, nil
}
// cacheControlMiddleware implements Cache-Control header setting, and checks for
// files inside the given http.FileSystem.
//
// The middleware checks if the file has been modified using If-None-Match etag,
// if present. If the file hasn't been modified, the middleware returns 304.
//
// See: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-None-Match
// and: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
func (m *Module) cacheControlMiddleware(fs http.FileSystem) gin.HandlerFunc {
return func(c *gin.Context) {
// no-cache prevents clients using default caching or heuristic caching,
// and also ensures that clients will validate their cached version against
// the version stored on the server to keep up to date.
c.Header("Cache-Control", "no-cache")
ifNoneMatch := c.Request.Header.Get("If-None-Match")
// derive the path of the requested asset inside the provided filesystem
upath := c.Request.URL.Path
if !strings.HasPrefix(upath, "/") {
upath = "/" + upath
}
assetFilePath := strings.TrimPrefix(path.Clean(upath), assetsPathPrefix)
// either fetch etag from ttlcache or generate it
eTag, err := m.getAssetETag(assetFilePath, fs)
if err != nil {
log.Errorf("error getting ETag for %s: %s", assetFilePath, err)
return
}
// Regardless of what happens further down, set the etag header
// so that the client has the up-to-date version.
c.Header("Etag", eTag)
// If client already has latest version of the asset, 304 + bail.
if ifNoneMatch == eTag {
c.AbortWithStatus(http.StatusNotModified)
return
}
// else let the rest of the request be processed normally
}
}
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