feat: add static filename and info served by fileserver to context vars

Signed-off-by: Arthur <git@arthur.pro>

modules/caddyhttp/fileserver/staticfiles.go

@@ -42,6 +42,9 @@ func init() {
 	caddy.RegisterModule(FileServer{})
 }
 
+const FileServerFilenameVarKey = "fileserver_filename"
+const FileServerFileinfoVarKey = "fileserver_fileinfo"
+
 // FileServer implements a handler that serves static files.
 //
 // The path of the file to serve is constructed by joining the site root
@@ -559,6 +562,14 @@ func (fsrv *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request, next c
 		w = statusOverrideResponseWriter{ResponseWriter: w, code: statusCodeOverride}
 	}
 
+	// add filename and file info to the request context vars so that other middlewares
+	// can find out what static file has been served by the fileserver.
+	// middlewares can access the vars as follows:
+	// caddyhttp.GetVar(r.Context(), fileserver.FileServerFilenameVarKey).(string)
+	// caddyhttp.GetVar(r.Context(), fileserver.FileServerFileinfoVarKey).(fs.FileInfo)
+	caddyhttp.SetVar(r.Context(), FileServerFilenameVarKey, filename)
+	caddyhttp.SetVar(r.Context(), FileServerFileinfoVarKey, info)
+
 	// let the standard library do what it does best; note, however,
 	// that errors generated by ServeContent are written immediately
 	// to the response, so we cannot handle them (but errors there