Thank you Stephen and Tony for your examples. I found the following
private function in db/private/mysql/connection.rkt:
(define (hex-string->bytes s)
(define (hex-digit->int c)
(let ([c (char->integer c)])
(cond [(<= (char->integer #\0) c (char->integer #\9))
(- c (char->integer #\0))]
[(<= (char->integer #\a) c (char->integer #\f))
(+ 10 (- c (char->integer #\a)))]
[(<= (char->integer #\A) c (char->integer #\F))
(+ 10 (- c (char->integer #\A)))])))
(unless (and (string? s) (even? (string-length s))
(regexp-match? #rx"[0-9a-zA-Z]*" s))
(raise-type-error 'hex-string->bytes
"string containing an even number of hexadecimal
digits" s))
(let* ([c (quotient (string-length s) 2)]
[b (make-bytes c)])
(for ([i (in-range c)])
(let ([high (hex-digit->int (string-ref s (+ i i)))]
[low (hex-digit->int (string-ref s (+ i i 1)))])
(bytes-set! b i (+ (arithmetic-shift high 4) low))))
b))
Can this function be exported? I'm willing to make a patch with docs
and tests - is file/sha1 the right place?
Thanks,
Dave
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