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(define-module (ldp etag))
(define alphabet
(string-join
'("abcdefghijklmnopqrstuvwxyz"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"0123456789"
"-_")
""))
(define (generate-etag-letter)
(string-ref alphabet (random (string-length alphabet))))
(define (generate-etag-letters n)
(if (<= n 0)
'()
(cons (generate-etag-letter)
(generate-etag-letters (- n 1)))))
(define-public (generate-etag)
(list->string (generate-etag-letters 16)))
(define-public (etag? x)
(define (aux i)
(or (>= i (string-length x))
(and (let ((c (string-ref x i)))
(or (and (char>=? c #\a) (char<=? c #\z))
(and (char>=? c #\A) (char<=? c #\Z))
(and (char>=? c #\0) (char<=? c #\9))
(char=? c #\-)
(char=? c #\_)))
(aux (+ i 1)))))
(and (string? x)
(aux 0)))
(define-public (the-etag x)
(unless (etag? x)
(scm-error 'wrong-type-arg
"the-etag"
"Expected a string satisfying etag? from (ldp etag)."
'()
(list x)))
x)
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