scsh-0.6/scsh/fileinfo.scm

;;; 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 (file-not-accessible? perms fd/port/fname)
  (let ((uid (user-effective-uid)))
    (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.
				   (file-not-accessible? 2
				     (directory-as-file-name
				       (file-name-directory fd/port/fname))))
			       'nonexistent)))

      (and (let* ((info (file-info fd/port/fname))
		  (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)  (file-not-accessible? 4 fd/port/fname))
(define (file-not-writable?   fd/port/fname)  (file-not-accessible? 2 fd/port/fname))
(define (file-not-executable? fd/port/fname)  (file-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)))

;;; 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-directory? fname/fd/port . maybe-chase?)
  (eq? 'directory (apply file-type fname/fd/port maybe-chase?)))

(define (file-fifo? fname/fd/port . maybe-chase?)
  (eq? 'fifo (apply file-type fname/fd/port maybe-chase?)))

(define (file-regular? fname/fd/port . maybe-chase?)
  (eq? 'regular (apply file-type fname/fd/port maybe-chase?)))

(define (file-socket? fname/fd/port . maybe-chase?)
  (eq? 'socket (apply file-type fname/fd/port maybe-chase?)))

(define (file-special? fname/fd/port . maybe-chase?)
  (let ((type (apply file-type fname/fd/port maybe-chase?)))
    (or (eq? 'block-special type) (eq? 'char-special type))))

(define (file-symlink? fname/fd/port)  ; No MAYBE-CHASE?, of course.
  (eq? 'symlink (file-type fname/fd/port #f)))