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add `file-truncate'

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original commit: 48e0509381ece9a356a4f4d225767f5cdd079b88
This commit is contained in:
Matthew Flatt 2013-01-17 21:44:20 -06:00
parent eef5d7b712
commit 5c93f3a38b
1 changed files with 8 additions and 62 deletions
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70
collects/mzlib/os.rkt
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@ -68,48 +68,6 @@
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; truncate-file
;; From fcntl.h
(define O_RDONLY #x0000)
(define O_WRONLY #x0001)
(define O_RDWR #x0002)
(define O_APPEND #x0008)
(define O_CREAT #x0100)
(define O_TRUNC #x0200)
(define O_EXCL #x0400)
;; winize : string -> string
(define (winize fn-name)
(if (eq? 'windows (system-type)) (string-append "_" fn-name) fn-name))
;; open : string int -> int
(define open
(delay-ffi-obj (winize "open") #f (_fun #:save-errno 'posix _string _int -> _int)))
;; close : int -> int
(define close
(delay-ffi-obj (winize "close") #f (_fun #:save-errno 'posix _int -> _int)))
;; ftruncate : int int -> int
(define ftruncate
(if (eq? 'windows (system-type))
(delay-ffi-obj "_chsize" #f (_fun #:save-errno 'posix _int _llong -> _int))
(delay-ffi-obj "ftruncate" #f (_fun #:save-errno 'posix _int _llong -> _int))))
;; on-c-fail : int (-> X) int or X
(define (on-c-fail thunk fail-k)
(let ([val (thunk)])
(cond
[(> val -1) val]
[(= (saved-errno) (lookup-errno 'EINTR))
;; interrupted by a signal; retry
(on-c-fail thunk fail-k)]
[else (fail-k)])))
(define scheme_security_check_file
(delay-ffi-obj "scheme_security_check_file" #f
(_fun _string _string _int -> _void)))
(define SCHEME_GUARD_FILE_WRITE #x2)
;; truncate-file : path int -> void
(define truncate-file
(opt-lambda (file [size 0])
@ -119,25 +77,13 @@
(when (not (integer? size))
(error 'truncate-file
"expects argument of type <integer>; given ~s" size))
((force scheme_security_check_file)
"truncate-file"
(if (path? file) (path->string file) file)
SCHEME_GUARD_FILE_WRITE)
(let ([fd (on-c-fail
(lambda ()
((force open) file O_WRONLY))
(lambda ()
(error 'truncate-file "could not open file")))])
(on-c-fail
(lambda ()
((force ftruncate) fd size))
(lambda ()
((force close) fd)
(error 'truncate-file "could not truncate file")))
(on-c-fail
(lambda ()
((force close) fd))
void)
(void))))
(let ([c (make-custodian)]) ; avoid leaks on errors
(dynamic-wind
void
(lambda ()
(define out (open-output-file file 'update))
(file-truncate out size))
(lambda ()
(custodian-shutdown-all c))))))
(provide truncate-file)