| // Copyright 2013 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| //go:build go1.16 |
| // +build go1.16 |
| |
| package web |
| |
| import ( |
| "io/fs" |
| "path" |
| "strings" |
| "unicode/utf8" |
| ) |
| |
| // isText reports whether a significant prefix of s looks like correct UTF-8; |
| // that is, if it is likely that s is human-readable text. |
| func isText(s []byte) bool { |
| const max = 1024 // at least utf8.UTFMax |
| if len(s) > max { |
| s = s[0:max] |
| } |
| for i, c := range string(s) { |
| if i+utf8.UTFMax > len(s) { |
| // last char may be incomplete - ignore |
| break |
| } |
| if c == 0xFFFD || c < ' ' && c != '\n' && c != '\t' && c != '\f' { |
| // decoding error or control character - not a text file |
| return false |
| } |
| } |
| return true |
| } |
| |
| // isTextFile reports whether the file has a known extension indicating |
| // a text file, or if a significant chunk of the specified file looks like |
| // correct UTF-8; that is, if it is likely that the file contains human- |
| // readable text. |
| func isTextFile(fsys fs.FS, filename string) bool { |
| // Various special cases must be served raw, not converted to nice HTML. |
| if filename == "robots.txt" || strings.HasPrefix(filename, "doc/play/") { |
| return false |
| } |
| switch path.Ext(filename) { |
| case ".css", ".js", ".svg": |
| return false |
| } |
| |
| // the extension is not known; read an initial chunk |
| // of the file and check if it looks like text |
| f, err := fsys.Open(filename) |
| if err != nil { |
| return false |
| } |
| defer f.Close() |
| |
| var buf [1024]byte |
| n, err := f.Read(buf[0:]) |
| if err != nil { |
| return false |
| } |
| |
| return isText(buf[0:n]) |
| } |