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
5package http2
6
7import "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.
15func 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.
28func 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.
37func 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.
48func asciiToLower(s string) (lower string, ok bool) {
49	if !isASCIIPrint(s) {
50		return "", false
51	}
52	return strings.ToLower(s), true
53}
54