scsh-0.6/scsh/fileinfo.scm

186 lines
6.8 KiB
Scheme

;;; Copyright (c) 1993, 1994 by Olin Shivers.
;;; chase? true (the default) means if the file is a symlink, chase the link
;;; and report on the file it references. chase? = #f means check the actual
;;; file itself, even if it's a symlink.
;;; (file-not-accessible? perms fd/port/fname)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; PERMS is 3 bits, not 9.
;;; writeable means (1) file exists & is writeable OR (2) file doesn't exist
;;; and directory is writeable. That is, writeable means writeable or
;;; creatable.
;;;
;;; There's a Posix call, access(), that checks using the *real* uid, not
;;; the effective uid, so that setuid programs can figure out if the luser
;;; has perms. file-not-accessible? is defined in terms of the effective uid,
;;; so we can't use access().
;;;
;;; This is a kind of bogus function. The only way to do a real check is to
;;; try an open() and see if it flies. Otherwise, there's an obvious atomicity
;;; problem. Also, we special case root, saying root always has all perms. But
;;; not even root can write on a read-only filesystem, such as a CD ROM. In
;;; this case, we'd blithely say the file was writeable -- there's no way to
;;; check for a ROFS without doing an open(). We need a euid analog to
;;; access(). Ah, well.
;;;
;;; I also should define a family of real uid perm-checking calls.
;;;
;;; Return values:
;;; #f Accessible in at least one of the requested ways.
;;; search-denied Can't stat
;;; permission File exists but is protected
;;; (also for errno/rofs)
;;; no-directory Some directory doesn't exist
;;; nonexistent File itself doesn't exist
;;;
;;; Otherwise, signals an error.
(define (fd/port/fname-not-accessible? perms fd/port/fname)
(with-errno-handler ((err data)
((errno/acces) 'search-denied)
((errno/notdir) 'no-directory)
;; If the file doesn't exist, we usually return
;; 'nonexistent, but we special-case writability
;; for the directory check.
((errno/noent)
(and (or (zero? (bitwise-and perms 2))
;; This string? test *has* to return #t.
;; If fd/port/fname is an fd or a port,
;; we wouldn't get an errno/noent error!
;; Just being paranoid...
(not (string? fd/port/fname))
;; OK, check to see if we can create
;; files in the directory.
(fd/port/fname-not-accessible?
2
(directory-as-file-name
(file-name-directory fd/port/fname))))
'nonexistent)))
(file-info-not-accessible? perms
(file-info fd/port/fname))))
(define (file-info-not-accessible? perms info)
(let ((uid (user-effective-uid)))
(and (let ((acc (file-info:mode info)))
(cond ((zero? uid) #f) ; Root can do as he wishes.
((= (file-info:uid info) (user-effective-uid)) ; User
(zero? (bitwise-and acc (arithmetic-shift perms 6))))
((or (= (file-info:gid info) (user-effective-gid)) ; Group
(memv (file-info:gid info) (user-supplementary-gids)))
(zero? (bitwise-and acc (arithmetic-shift perms 3))))
(else ; Other
(zero? (bitwise-and acc perms)))))
'permission)))
;;;;;;
(define (file-not-readable? fd/port/fname)
(fd/port/fname-not-accessible? 4 fd/port/fname))
(define (file-not-writable? fd/port/fname)
(fd/port/fname-not-accessible? 2 fd/port/fname))
(define (file-not-executable? fd/port/fname)
(fd/port/fname-not-accessible? 1 fd/port/fname))
(define (file-readable? fd/port/fname)
(not (file-not-readable? fd/port/fname)))
(define (file-writable? fd/port/fname)
(not (file-not-writable? fd/port/fname)))
(define (file-executable? fd/port/fname)
(not (file-not-executable? fd/port/fname)))
(define (file-info-not-readable? info) (file-info-not-accessible? 4 info))
(define (file-info-not-writable? info) (file-info-not-accessible? 2 info))
(define (file-info-not-executable? info) (file-info-not-accessible? 1 info))
(define (file-info-readable? info) (not (file-info-not-readable? info)))
(define (file-info-writable? info) (not (file-info-not-writable? info)))
(define (file-info-executable? info) (not (file-info-not-executable? info)))
;;; Spelling corrected.
(define file-not-writeable?
(deprecated-proc file-not-writable? "file-not-writeable?"
"Use file-not-writable? instead"))
(define file-writeable?
(deprecated-proc file-writable? "file-writeable?"
"Use file-writable? instead"))
;;;;;;
;;; Returns
;;; #f exists
;;; #t doesn't exist
;;; 'search-denied can't stat
;;; ...or signals an error
(define (file-not-exists? fd/port/fname . maybe-chase?)
(with-errno-handler
((err data)
((errno/acces) 'search-denied)
((errno/noent errno/notdir) #t))
(apply file-info fd/port/fname maybe-chase?)
#f))
(define (file-exists? fd/port/fname . maybe-chase?)
(not (apply file-not-exists? fd/port/fname maybe-chase?)))
;;;;;;
;;; stat and derived file-{mode,size,owner,group,times,inode,...} ops.
(define-simple-syntax (define-stat-proc proc info-slot)
(define (proc fname/fd/port . maybe-chase?)
(info-slot (apply file-info fname/fd/port maybe-chase?))))
(define-stat-proc file-type file-info:type)
(define-stat-proc file-group file-info:gid)
(define-stat-proc file-inode file-info:inode)
(define-stat-proc file-last-access file-info:atime)
(define-stat-proc file-last-mod file-info:mtime)
(define-stat-proc file-last-status-change file-info:ctime)
(define-stat-proc file-mode file-info:mode)
(define-stat-proc file-nlinks file-info:nlinks)
(define-stat-proc file-owner file-info:uid)
(define-stat-proc file-size file-info:size)
(define (file-info-to-fname/fd/port predicate)
(lambda (fname/fd/port . maybe-chase?)
(predicate (apply file-info fname/fd/port maybe-chase?))))
(define (file-info-directory? file-info)
(eq? 'directory (file-info:type file-info)))
(define file-directory?
(file-info-to-fname/fd/port file-info-directory?))
(define (file-info-fifo? file-info)
(eq? 'fifo (file-info:type file-info)))
(define file-fifo? (file-info-to-fname/fd/port file-info-fifo?))
(define (file-info-regular? file-info)
(eq? 'regular (file-info:type file-info)))
(define file-regular? (file-info-to-fname/fd/port file-info-regular?))
(define (file-info-socket? file-info)
(eq? 'socket (file-info:type file-info)))
(define file-socket? (file-info-to-fname/fd/port file-info-socket?))
(define (file-info-special? file-info)
(let ((type (file-info:type file-info)))
(or (eq? 'block-special type) (eq? 'char-special type))))
(define file-special? (file-info-to-fname/fd/port file-info-special?))
(define (file-info-symlink? file-info)
(eq? 'symlink (file-info:type file-info)))
(define (file-symlink? fd/port/fname) ; No MAYBE-CHASE?, of course.
(file-info-symlink? (file-info fd/port/fname #f)))