Fix cache-control header clearing comment text when editing issue (#2…

…2604)

The `no-store` cache control added in #20432 is causing form input to be
cleared unnecessarily on page reload. Instead use
`max-age=0,private,must-revalidate` which avoids this.

This was particularly a problem when typing a long comment for an issue
and then for example changing the label. The page would be reloaded and
lose the unsubmitted comment.

Fixes #22603

modules/httpcache/httpcache.go

@@ -21,12 +21,12 @@ func AddCacheControlToHeader(h http.Header, maxAge time.Duration, additionalDire
 
  if setting.IsProd {
  if maxAge == 0 {
- directives = append(directives, "no-store")
+ directives = append(directives, "max-age=0", "private", "must-revalidate")
  } else {
  directives = append(directives, "private", "max-age="+strconv.Itoa(int(maxAge.Seconds())))
  }
  } else {
- directives = append(directives, "no-store")
+ directives = append(directives, "max-age=0", "private", "must-revalidate")
 
  // to remind users they are using non-prod setting.
  h.Add("X-Gitea-Debug", "RUN_MODE="+setting.RunMode)