sunet/netrc.scm

394 lines
15 KiB
Scheme

;;; netrc.scm -- parse authentication information contained in ~/.netrc
;;
;; $Id: netrc.scm,v 1.7 2002/04/04 23:22:28 interp Exp $
;;
;; Please send suggestions and bug reports to <emarsden@mail.dotcom.fr>
;;; Overview =====================================================
;;
;; On Unix systems the ~/.netrc file (in the user's home directory)
;; may contain information allowing automatic login to remote hosts.
;; The format of the file is defined in the ftp(1) manual page.
;; Example lines are
;;
;; machine ondine.cict.fr login marsden password secret
;; default login anonymous password user@site
;;
;; The ~/.netrc file should be protected by appropriate permissions,
;; and (like /usr/bin/ftp) this library will refuse to read the file if
;; it is badly protected. (unlike /usr/bin/ftp this library will always
;; refuse to read the file -- /usr/bin/ftp refuses it only if the password
;; is given for a non-default account). Appropriate permissions are set
;; if only the user has permissions on the file.
;;
;; Note following restrictions / differences:
;; * The macdef statement (defining macros) is not supported.
;; * The settings for one machine must be on a single line.
;; * The is no error proof while reading the file.
;; * default need not be the last line of the netrc-file
;;; Entry points =======================================================
;;
;; What you probably want, is to read out the default netrc-file. Do the
;; following:
;;
;; (let ((netrc-record (netrc:parse)))
;; (netrc:lookup netrc-record "name of the machine"))
;;
;; and you will receive three values: login-name, password and account-name.
;; If you only want the login-name or the password, use netrc:lookup-login
;; or netrc:lookup-password resp.
;;
;; You will get either the login / password for the specified machine,
;; or a default login / password if the machine is unknown.
;;
;;
;; (user-mail-address) -> string
;; Calculate the user's email address, as per the Emacs function of
;; the same name. Will take into account the environment variable
;; REPLYTO, if set. Otherwise the mail-address will look like
;; user@hostname.
;;
;; (netrc:parse [filename [fallback-password [fallback-login]]])
;; -> netrc-record
;; * parses the netrc file and returns a netrc-record, containing all
;; necessary information for the following procedures.
;; * FILENAME defaults to "~/.netrc"
;; FALLBACK-PASSWORD defaults to the result of (user-mail-address)
;; FALLBACK-LOGIN defaults to "anonymous"
;; * if the netrc file does not provide a default password or a default
;; login (stated by the "default" statement), FALLBACK-PASSWORD and
;; FALLBACK-LOGIN will be used as default password or login, respectively.
;; (thus, user-mail-address is only called if the netrc file does not
;; contain a default specification)
;; * if the netrc file does not exist, a netrc-record filled with
;; default values is returned.
;; * if the netrc file does not have the correct permissions, a message is
;; printed to current error port and a netrc-record filled with default
;; values is returned.
;;
;; (netrc:try-parse filename fallback-password fallback-login) -> netrc-record
;; parses the netrc file and returns a netrc-record, containing all
;; necessary information for the following procedures.
;; if there is no file called FILENAME, the according error will be raised
;; if the specified file does not have the correct permissions set,
;; a netrc-refuse-warning will be signalled.
;; so if you don't like the error handling of netrc:parse, use
;; netrc:try-parse and catch the signalled conditions.
;;
;; (netrc:lookup netrc-record machine [default?]) -> string x string x string
;; Return the login,password,account information for MACHINE
;; specified by the netrc file.
;; If DEFAULT? is #t, default values are returned if no such
;; MACHINE is specified in the netrc file. Otherwise, #f,#f,#f
;; is returned
;;
;; (netrc:lookup-password netrc-record machine [default?]) -> string
;; Return the password information for MACHINE specified by the
;; netrc file.
;; If DEFAULT? is #t, the default password is returned if no such
;; MACHINE is specified. Otherwise, #f is returned.
;;
;; (netrc:lookup-login netrc-record machine [default?]) -> string
;; Return the login information for MACHINE specified by the
;; netrc file.
;; If DEFAULT? is #t, the default login is returned if no such
;; MACHINE is specified. Otherwise, #f is returned.
;;
;; (netrc:default-login netrc-record) -> string
;; Return the default login specified by the netrc file or "anonymous"
;;
;; (netrc:default-password netrc-record) -> string
;; Return the default password specified by the netrc file or
;; the mail-addres (result of (user-mail-address))
;;; Related work ========================================================
;;
;; * Graham Barr has written a similar library for Perl, called
;; Netrc.pm
;;
;; * ange-ftp.el (transparent remote file access for Emacs) parses the
;; user's netrc file
;;; Portability ==================================================
;;
;; getenv, scsh file primitives, regexp code, format
;; define-record, ecm-utilities
;;; Desirable things =============================================
;;
;; * Remove restrictions (as stated in 'Overview') and behave like
;; /usr/bin/ftp behaves
;; * perhaps: adding case-insensitivity (for host names)
;; * perhaps: better record-disclosers for netrc-entry- and netrc-records
; return the user's mail address, either specified by the environment
; variable REPLYTO or "user@hostname".
(define (user-mail-address)
(or (getenv "REPLYTO")
(string-append (user-login-name) "@" (system-fqdn))))
; looks up the desired machine in a netrc-record
; if the machine is found in the entries-section
; following three values are returned: login, password and account
; if the machine is not found in the entries-section
; the behavior depends on lookup-default? which defaults to #t:
; if lookup-default? is #t
; following three values are returned: default-login default-password #f
; otherwise #f #f #f is returned.
(define (netrc:lookup netrc-record machine . lookup-default?)
(let-optionals lookup-default?
((lookup-default? #t))
(let ((record (find-record netrc-record machine)))
(if record
(values (netrc-entry:login record)
(netrc-entry:password record)
(netrc-entry:account record))
(if lookup-default?
(values (netrc:default-login netrc-record)
(netrc:default-password netrc-record)
#f)
(values #f #f #f))))))
; does the same as netrc:lookup, but returns only the password (or #f)
(define (netrc:lookup-password netrc-record machine . lookup-default?)
(let-optionals lookup-default?
((lookup-default? #t))
(let ((record (find-record netrc-record machine)))
(if record
(netrc-entry:password record)
(and lookup-default?
(netrc:default-password netrc-record))))))
; does the same as netrc:lookup, but returns only the login (or #f)
(define (netrc:lookup-login netrc-record machine . lookup-default?)
(let-optionals lookup-default?
((lookup-default? #t))
(let ((record (find-record netrc-record machine)))
(if record
(netrc-entry:login record)
(and lookup-default?
(netrc:default-login netrc-record))))))
; does the work for netrc:parse
; file-name has to be resolved
(define (netrc:try-parse file-name default-password default-login)
(netrc:check-permissions file-name)
(let ((fd (open-input-file file-name))
(netrc-record (make-netrc '() default-password default-login file-name)))
(for-each-line (parse-line netrc-record) fd)))
; parses the netrc-file
; expected arguments: filename default-password default-login
; filename: filename of the .netrc-file (defaults to ~/.netrc)
; default-password: default password for any not specified machine
; defaults to (user-mail-address)
; default password in netrc-file overwrites this setting
; default-login: default login name for any not specified machine
; defaults to "anonymous"
; default login in netrc-file overwrites this setting
; * (default-login is expected after default-password as users usually want
; to change the default-password (to something else than their mail-address)
; rather than the login-name)(define (netrc:parse . args)
; * if the given file does not exist or it has the wrong permissions,
; than a default netrc-record is returned
; * if you don't want expected errors to be captured, use netrc:try-parse;
; note that you have to resolve the file-name on your own
(define-condition-type 'netrc-refuse '(warning))
(define netrc-refuse? (condition-predicate 'netrc-refuse))
(define (netrc:parse . args)
(let-optionals
args ((file-name "~/.netrc")
(default-password #f) ; both ...
(default-login #f)) ; ... are set if netrc-file does
; not provide default-values
(let* ((file-name (resolve-file-name file-name))
(local-default-login (lambda () "anonymous"))
(local-default-password (lambda () (user-mail-address)))
(local-default-netrc-record
(lambda ()
(make-netrc '()
(or default-login (local-default-login))
(or default-password (local-default-password))
#f))))
; i know, this double-handler sucks; has anyone a better idea?
(call-with-current-continuation
(lambda (exit)
(with-handler
(lambda (error more)
(if (netrc-refuse? error)
(format (current-error-port)
"netrc: Warning: ~a~%"
(car (condition-stuff error)))
(format (current-error-port)
"netrc: Warning: Unexpected error encountered: ~s~%"
error))
(exit (local-default-netrc-record)))
(lambda ()
(with-errno-handler*
(lambda (errno packet)
(if (= errno errno/noent)
(format (current-error-port)
"netrc: Warning: no such file or directory: ~a~%"
file-name)
(format (current-error-port)
"netrc: Warning: Error accessing file ~s~%"
file-name))
(exit (local-default-netrc-record)))
(lambda ()
(let ((netrc-record
(netrc:try-parse file-name default-password default-login)))
; If we get a netrc-record, we return it after
; checking default login and default password settings.
; Otherwise, we return the default record with
; file-name stored.
; This is sub-optimal, as we may throw away badly
; structured .netrc-files silently. We need an error
; checking mechanism.
(if (netrc? netrc-record)
(begin
(if (eq? (netrc:default-login netrc-record) #f)
(set-netrc:default-login (local-default-login)))
(if (eq? (netrc:default-password netrc-record) #f)
(set-netrc:default-password (local-default-password)))
netrc-record)
(let ((default-netrc-record (local-default-netrc-record)))
(set-netrc:file-name default-netrc-record file-name)
default-netrc-record))))))))))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; nothing exported below
;; except
;; netrc:default-password
;; netrc:default-login
(define-record netrc-entry
machine
login
password
account)
(define-record netrc
entries ; list of netrc-entrys
default-login ; default-values (either library-default or netrc-file-default)
default-password
file-name) ; debug-purpose
(define-record-discloser type/netrc-entry
(lambda (netrc-entry)
(list 'netrc-entry))) ; perhaps something else later on
(define-record-discloser type/netrc
(lambda (netrc)
(list 'netrc))) ; perhaps something else later on
; finds a record in the entries-list of a netrc-record
; matching the given machine
; returns the netrc-entry-record if found, otherwise #f
(define (find-record netrc-record machine)
(find-first (lambda (rec)
(and (equal? (netrc-entry:machine rec) machine)
rec))
(netrc:entries netrc-record)))
;; raise error if any permissions are set for group or others.
(define (netrc:check-permissions file-name)
(let ((perms (- (file-mode file-name) 32768)))
(if (positive? (bitwise-and #b000111111 perms))
(signal 'netrc-refuse
(format #f
"Not parsing ~s (netrc file); dangerous permissions."
file-name)))))
; tries to match target on line and returns the first group,
; or #f if there is no match
(define (try-match target line)
(let ((match (string-match target line)))
(and match
(match:substring match 1))))
; parses the default line of the netrc-file
(define (parse-default netrc-record line)
(let ((login (try-match "login[ \t]+([^ \t]+)" line))
(password (try-match "password[ \t]+([^ \t]+)" line)))
(if login
(set-netrc:default-login netrc-record login))
(if password
(set-netrc:default-password netrc-record password))
netrc-record))
; parses a line of the netrc-file
(define (parse-line netrc-record)
(lambda (line)
(cond ((string-match "default" line)
(parse-default netrc-record line))
(else
(let ((machine (try-match "machine[ \t]+([^ \t]+)" line))
(login (try-match "login[ \t]+([^ \t]+)" line))
(password (try-match "password[ \t]+([^ \t]+)" line))
(account (try-match "account[ \t]+([^ \t]+)" line)))
(if (or machine login password account)
(add netrc-record machine login password account)
netrc-record)))))) ; return record on empty / wrong lines
; (This is a workaround. we should give a warning on malicious .netrc
; files. As we do not have an error checking system installed yet, we
; skip these lines silently.)
; adds machine login password account stored in a netrc-entry-record
; to the entries-list of a netrc-record
(define (add netrc-record machine login password account)
(set-netrc:entries netrc-record
(cons (make-netrc-entry machine login password account)
(netrc:entries netrc-record)))
netrc-record)
;; for testing
(define (netrc:dump netrc-record)
(format #t "~%--- Dumping ~s contents ---" (netrc:file-name netrc-record))
(for-each (lambda (rec)
(format #t "~% machine ~a login ~a password ~a account ~a"
(netrc-entry:machine rec)
(netrc-entry:login rec)
(netrc-entry:password rec)
(netrc-entry:account rec)))
(netrc:entries netrc-record))
(format #t "~% default login: ~s" (netrc:default-login netrc-record))
(format #t "~% default password: ~s" (netrc:default-password netrc-record))
(format #t "~%--- End of ~s contents ---~%" (netrc:file-name netrc-record)))
; runs proc for each line of fd (line is argument to proc)
; returns either nothing, if the fd had no line
; or the value returned by proc called on the last line
(define (for-each-line proc fd)
(let ((line (read-line fd)))
(if (not (eof-object? line))
(let loop ((last-result (proc line)))
(let ((line (read-line fd)))
(if (not (eof-object? line))
(loop (proc line))
last-result))))))
; finds first element in l for which pred doesn't return #f
; returns either #f (no such element found)
; or the result of the last call to pred
(define (find-first pred l)
(if (null? l) #f
(or (pred (car l))
(find-first pred (cdr l)))))
;; EOF