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lzlib: 'lzread!' never returns more than it was asked for.

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Fixes a bug whereby 'lzread!' could return more than COUNT.

* guix/lzlib.scm (lzread!): Rewrite in a semi-functional style.
This commit is contained in:
Ludovic Courtès 2019-05-24 15:20:46 +02:00
parent 2e5c71b2a2
commit c131bea276
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GPG key ID: 090B11993D9AEBB5
1 changed files with 19 additions and 20 deletions
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39
guix/lzlib.scm
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@ -494,29 +494,28 @@ (define lz-decompress-total-out-size
;; High level functions.
(define* (lzread! decoder file-port bv
(define* (lzread! decoder port bv
#:optional (start 0) (count (bytevector-length bv)))
"Read up to COUNT bytes from FILE-PORT into BV at offset START. Return the
"Read up to COUNT bytes from PORT into BV at offset START. Return the
number of uncompressed bytes actually read; it is zero if COUNT is zero or if
the end-of-stream has been reached."
;; WARNING: Because we don't alternate between lz-reads and lz-writes, we can't
;; process more than lz-decompress-write-size from the file-port.
(when (> count (lz-decompress-write-size decoder))
(set! count (lz-decompress-write-size decoder)))
(let ((file-bv (get-bytevector-n file-port count)))
(unless (eof-object? file-bv)
(lz-decompress-write decoder file-bv 0 (bytevector-length file-bv))))
(let ((read 0))
(let loop ((rd 0))
(if (< start (bytevector-length bv))
(begin
(set! rd (lz-decompress-read decoder bv start (- (bytevector-length bv) start)))
(set! start (+ start rd))
(set! read (+ read rd)))
(set! rd 0))
(unless (= rd 0)
(loop rd)))
read))
(define (feed-decoder! decoder)
;; Feed DECODER with data read from PORT.
(match (get-bytevector-n port (lz-decompress-write-size decoder))
((? eof-object? eof) eof)
(bv (lz-decompress-write decoder bv))))
(let loop ((read 0)
(start start))
(cond ((< read count)
(match (lz-decompress-read decoder bv start (- count read))
(0 (if (eof-object? (feed-decoder! decoder))
read
(loop read start)))
(n (loop (+ read n) (+ start n)))))
(else
read))))
(define (lzwrite! encoder source source-offset source-count
target target-offset target-count)