1 // Copyright 2021 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 package http2
6 7 import "strings"
8 9 // The HTTP protocols are defined in terms of ASCII, not Unicode. This file
10 // contains helper functions which may use Unicode-aware functions which would
11 // otherwise be unsafe and could introduce vulnerabilities if used improperly.
12 13 // asciiEqualFold is strings.EqualFold, ASCII only. It reports whether s and t
14 // are equal, ASCII-case-insensitively.
15 func asciiEqualFold(s, t string) bool {
16 if len(s) != len(t) {
17 return false
18 }
19 for i := 0; i < len(s); i++ {
20 if lower(s[i]) != lower(t[i]) {
21 return false
22 }
23 }
24 return true
25 }
26 27 // lower returns the ASCII lowercase version of b.
28 func lower(b byte) byte {
29 if 'A' <= b && b <= 'Z' {
30 return b + ('a' - 'A')
31 }
32 return b
33 }
34 35 // isASCIIPrint returns whether s is ASCII and printable according to
36 // https://tools.ietf.org/html/rfc20#section-4.2.
37 func isASCIIPrint(s string) bool {
38 for i := 0; i < len(s); i++ {
39 if s[i] < ' ' || s[i] > '~' {
40 return false
41 }
42 }
43 return true
44 }
45 46 // asciiToLower returns the lowercase version of s if s is ASCII and printable,
47 // and whether or not it was.
48 func asciiToLower(s string) (lower string, ok bool) {
49 if !isASCIIPrint(s) {
50 return "", false
51 }
52 return strings.ToLower(s), true
53 }
54