golang.org/x/net@v0.25.1-0.20240516223405-c87a5b62e243/http2/ascii.go (about)

     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  }