css - utils.go

     1  package css
     2  
     3  import (
     4  	"errors"
     5  	"io"
     6  	"strconv"
     7  	"strings"
     8  
     9  	"vimagination.zapto.org/parser"
    10  )
    11  
    12  // Unquote unquotes a CSS quoted string.
    13  func Unquote(str string) (string, error) {
    14  	if len(str) < 2 || str[0] != '\'' && str[0] != '"' || str[0] != str[len(str)-1] {
    15  		return "", ErrBadString
    16  	}
    17  
    18  	tk := parser.NewStringTokeniser(str[1 : len(str)-1])
    19  
    20  	var buf strings.Builder
    21  
    22  	for {
    23  		next := tk.ExceptRun("\"'\\")
    24  
    25  		buf.WriteString(tk.Get())
    26  
    27  		switch next {
    28  		case -1:
    29  			return buf.String(), nil
    30  		case rune(str[0]):
    31  			return "", ErrBadString
    32  		case '\\':
    33  			if err := unescape(&tk, &buf); err != nil {
    34  				return "", err
    35  			}
    36  		default:
    37  			tk.Next()
    38  		}
    39  	}
    40  }
    41  
    42  func unescape(tk *parser.Tokeniser, buf *strings.Builder) error {
    43  	tk.Next()
    44  	tk.Get()
    45  
    46  	if tk.Accept(hexDigits) {
    47  		for range 5 {
    48  			tk.Accept(hexDigits)
    49  		}
    50  
    51  		unicode, _ := strconv.ParseUint(tk.Get(), 16, 32)
    52  
    53  		buf.WriteRune(rune(unicode))
    54  
    55  		tk.Accept(whitespace)
    56  		tk.Get()
    57  	} else {
    58  		tk.Get()
    59  
    60  		if tk.Next() == -1 {
    61  			return io.ErrUnexpectedEOF
    62  		}
    63  	}
    64  
    65  	return nil
    66  }
    67  
    68  // UnURL retrieves the escaped URL from a 'url(...)' string value."
    69  func UnURL(str string) (string, error) {
    70  	if len(str) < 5 || strings.ToLower(str[:4]) != "url(" || str[len(str)-1] != ')' {
    71  		return "", ErrBadURL
    72  	}
    73  
    74  	tk := parser.NewStringTokeniser(str[4 : len(str)-1])
    75  
    76  	tk.AcceptRun(whitespace)
    77  	tk.Get()
    78  
    79  	var buf strings.Builder
    80  
    81  	for {
    82  		next := tk.ExceptRun("\"'\\()" + whitespace)
    83  
    84  		buf.WriteString(tk.Get())
    85  
    86  		switch next {
    87  		case ' ', '\t', '\r', '\n', '\f':
    88  			if tk.AcceptRun(whitespace) != -1 {
    89  				return "", ErrBadURL
    90  			}
    91  
    92  			fallthrough
    93  		case -1:
    94  			return buf.String(), nil
    95  		case '\\':
    96  			if err := unescape(&tk, &buf); err != nil {
    97  				return "", err
    98  			}
    99  		default:
   100  			return "", ErrBadURL
   101  		}
   102  	}
   103  }
   104  
   105  // Errors
   106  var (
   107  	ErrBadString = errors.New("bad string")
   108  	ErrBadURL    = errors.New("bad url")
   109  )
   110