Fix wrong last modify time (#32102) (#32104)

Backport #32102 by @lunny

Fix #31930 and more places which use `http.TimeFormat` wrongly.
`http.TimeFormat` requires a UTC time. refer to
https://pkg.go.dev/net/http#TimeFormat

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/httpcache/httpcache.go

@@ -75,7 +75,8 @@ func HandleGenericETagTimeCache(req *http.Request, w http.ResponseWriter, etag s
 		w.Header().Set("Etag", etag)
 	}
 	if lastModified != nil && !lastModified.IsZero() {
-		w.Header().Set("Last-Modified", lastModified.Format(http.TimeFormat))
+		// http.TimeFormat required a UTC time, refer to https://pkg.go.dev/net/http#TimeFormat
+		w.Header().Set("Last-Modified", lastModified.UTC().Format(http.TimeFormat))
 	}
 
 	if len(etag) > 0 {

modules/httplib/serve.go

@@ -79,6 +79,7 @@ func ServeSetHeaders(w http.ResponseWriter, opts *ServeHeaderOptions) {
 	httpcache.SetCacheControlInHeader(header, duration)
 
 	if !opts.LastModified.IsZero() {
+		// http.TimeFormat required a UTC time, refer to https://pkg.go.dev/net/http#TimeFormat
 		header.Set("Last-Modified", opts.LastModified.UTC().Format(http.TimeFormat))
 	}
 }

routers/api/packages/maven/maven.go

@@ -115,7 +115,9 @@ func serveMavenMetadata(ctx *context.Context, params parameters) {
 	xmlMetadataWithHeader := append([]byte(xml.Header), xmlMetadata...)
 
 	latest := pds[len(pds)-1]
-	ctx.Resp.Header().Set("Last-Modified", latest.Version.CreatedUnix.Format(http.TimeFormat))
+	// http.TimeFormat required a UTC time, refer to https://pkg.go.dev/net/http#TimeFormat
+	lastModifed := latest.Version.CreatedUnix.AsTime().UTC().Format(http.TimeFormat)
+	ctx.Resp.Header().Set("Last-Modified", lastModifed)
 
 	ext := strings.ToLower(filepath.Ext(params.Filename))
 	if isChecksumExtension(ext) {

routers/web/repo/githttp.go

@@ -395,7 +395,8 @@ func (h *serviceHandler) sendFile(ctx *context.Context, contentType, file string
 
 	ctx.Resp.Header().Set("Content-Type", contentType)
 	ctx.Resp.Header().Set("Content-Length", fmt.Sprintf("%d", fi.Size()))
-	ctx.Resp.Header().Set("Last-Modified", fi.ModTime().Format(http.TimeFormat))
+	// http.TimeFormat required a UTC time, refer to https://pkg.go.dev/net/http#TimeFormat
+	ctx.Resp.Header().Set("Last-Modified", fi.ModTime().UTC().Format(http.TimeFormat))
 	http.ServeFile(ctx.Resp, ctx.Req, reqFile)
 }