GNU bug report logs - #79619
repl versus compiler discrepancy in handling of bytevectors

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Jakob L. Kreuze" <zerodaysfordays <at> sdf.org>
To: bug-guile <at> gnu.org
Subject: repl versus compiler discrepancy in handling of bytevectors
Date: Sun, 12 Oct 2025 17:01:23 -0400

Hello,

I have program which works fine when compiled, but when pasted into a
REPL gives the following error message:

While compiling expression:
In procedure bytevector-copy!: Wrong type argument in position 3
(expecting mutable bytevector): #vu8()

I'm having a hard time narrowing down the source of the error,
though I do know that it occurs when the second call to
`parse-netstring' is evaluated, and I am assuming this is a bug because
my expectation would be that the REPL would behave exactly the same as
the Guile compiler.

Test case:

----------------------------- snip -----------------------------

(use-modules (rnrs bytevectors)
             (rnrs bytevectors gnu))

(define (bytevector-index haystack needle)
  (define len (bytevector-length haystack))
  (let loop ((i 0))
    (cond [(>= i len) #f]
          [(= needle (bytevector-u8-ref haystack i)) i]
          [else (loop (+ 1 i))])))

(define (parse-netstring bv)
  (define split-index (bytevector-index bv (char->integer #\:)))
  (unless split-index
    (throw 'scgi-parse-error "netstring contains no delimiter character"))
  (let* [(length-encoded (bytevector-slice bv 0 split-index))
         (length-parsed (string->number (utf8->string length-encoded)))]
    (unless length-parsed
      (throw 'scgi-parse-error (format #f "illegal netstring length '~a'" length-encoded)))
    (let* ([payload-start (+ 1 split-index)]
           [payload-end (+ 1 payload-start length-parsed)]
           [remaining (- (bytevector-length bv) payload-end)])
      (values (bytevector-slice bv payload-start length-parsed)
              (bytevector-slice bv payload-end remaining)))))

(parse-netstring (string->utf8 "13:Hello, world!,"))
(parse-netstring (string->utf8 "5:hello,"))

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