Fix static file caching (#2975)

Replaces #2972

Fixes #2483

Removed etag header as etag is used incorrectly, it should be based on
content not startup time and we don't handle it from request headers
anyway.

server/web/web.go

@@ -16,9 +16,7 @@ package web
 
 import (
 	"bytes"
-	"crypto/md5"
 	"errors"
-	"fmt"
 	"io"
 	"io/fs"
 	"net/http"
@@ -32,12 +30,7 @@ import (
 	"go.woodpecker-ci.org/woodpecker/v2/web"
 )
 
-// etag is an identifier for a resource version
-// it lets caches determine if resource is still the same and not send it again
-var (
-	etag      = fmt.Sprintf("%x", md5.Sum([]byte(time.Now().String())))
-	indexHTML []byte
-)
+var indexHTML []byte
 
 type prefixFS struct {
 	fs     http.FileSystem
@@ -53,8 +46,6 @@ func New() (*gin.Engine, error) {
 	e := gin.New()
 	indexHTML = parseIndex()
 
-	e.Use(setupCache)
-
 	rootPath := server.Config.Server.RootPath
 
 	httpFS, err := web.HTTPFS()
@@ -121,6 +112,8 @@ func serveFile(f *prefixFS) func(ctx *gin.Context) {
 			mime = "image/svg"
 		}
 		ctx.Status(http.StatusOK)
+		ctx.Writer.Header().Set("Cache-Control", "public, max-age=31536000")
+		ctx.Writer.Header().Del("Expires")
 		ctx.Writer.Header().Set("Content-Type", mime)
 		if _, err := ctx.Writer.Write(replaceBytes(data)); err != nil {
 			log.Error().Err(err).Msgf("can not write %s", ctx.Request.URL.Path)
@@ -142,6 +135,7 @@ func redirect(location string, status ...int) func(ctx *gin.Context) {
 
 func handleIndex(c *gin.Context) {
 	rw := c.Writer
+	rw.Header().Set("Cache-Control", "no-cache")
 	rw.Header().Set("Content-Type", "text/html; charset=UTF-8")
 	rw.WriteHeader(http.StatusOK)
 	if _, err := rw.Write(indexHTML); err != nil {
@@ -171,9 +165,3 @@ func parseIndex() []byte {
 	data = bytes.ReplaceAll(data, []byte("/assets/custom.js"), []byte(server.Config.Server.RootPath+"/assets/custom.js"))
 	return data
 }
-
-func setupCache(c *gin.Context) {
-	c.Writer.Header().Set("Cache-Control", "public, max-age=31536000")
-	c.Writer.Header().Del("Expires")
-	c.Writer.Header().Set("ETag", etag)
-}