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file/zip: clamp timestamps to supported range #4451

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file/zip: clamp timestamps to supported range #4451

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3 changes: 3 additions & 0 deletions pkgs/racket-doc/file/scribblings/zip.scrbl
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,9 @@ Timestamps in @exec{zip} archives are precise only to two seconds; by
default, the time is rounded toward the future (like WinZip or PKZIP),
but time is rounded toward the past (like Java) if
@racket[round-timestamps-down?] is true.
The @exec{zip} archive format only supports timestamps between January 1,
1980 and December 31, 2107. Timestamps outside of this range will be
clamped to the closest representable timestamp.

The @racket[sys-type] argument determines the system type recorded in
the archive.
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30 changes: 24 additions & 6 deletions racket/collects/file/zip.rkt
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Expand Up @@ -60,15 +60,33 @@

;; date->msdos-time : date -> msdos-time
(define (date->msdos-time date round-down?)
(bitwise-ior (arithmetic-shift (+ (if round-down? 0 1) (date-second date)) -1)
(arithmetic-shift (date-minute date) 5)
(arithmetic-shift (date-hour date) 11)))
(define-values (h m s)
;; Zip cannot represent timestamps before 1980-01-01T00:00:00
(cond
[(< (date-year date) 1980)
(values 0 0 0)]
[(> (date-year date) 2107)
(values 23 59 59)]
[else
(values (date-hour date) (date-minute date) (date-second date))]))
(bitwise-ior (arithmetic-shift (+ (if round-down? 0 1) s) -1)
(arithmetic-shift m 5)
(arithmetic-shift h 11)))

;; date->msdos-date : date -> msdos-date
(define (date->msdos-date date)
(bitwise-ior (date-day date)
(arithmetic-shift (date-month date) 5)
(arithmetic-shift (- (date-year date) 1980) 9)))
(define-values (y m d)
;; Zip cannot represent timestamps before 1980-01-01T00:00:00
(cond
[(< (date-year date) 1980)
(values 1980 1 1)]
[(> (date-year date) 2107)
(values 2107 12 31)]
[else
(values (date-year date) (date-month date) (date-day date))]))
(bitwise-ior d
(arithmetic-shift m 5)
(arithmetic-shift (- y 1980) 9)))

;; seekable-port? : port -> boolean
(define (seekable-port? port)
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