scsh-0.5/scsh/pty.scm

105 lines
3.7 KiB
Scheme

;;; Pseudo terminals
;;; Copyright (c) 1995 by Olin Shivers.
;;; (fork-job/pty thunk)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Fork the process with stdio (fd's 0, 1, & 2 and also the current i/o ports)
;;; bound to a tty device. In the parent process, returns four values:
;;; [process pty-inport pty-outport ttyname]
;;; - PROCESS is a process object for the child.
;;; - PTY-{IN,OUT}PORT are input and output ports open on the controlling pty
;;; device. PTY-OUTPORT is unbuffered.
;;; - TTYNAME is the name of the child's tty, e.g. "/dev/ttyk4".
;;;
;;; The subprocess is placed in its own session, and the tty device
;;; becomes the control tty for the new session/process-group/process.
;;; The child runs with stio hooked up to the tty; the (error-output-port)
;;; port is unbuffered.
(define (fork-job/pty thunk)
(receive (pty-in ttyname) (open-pty)
(let* ((process (fork (lambda ()
(become-session-leader)
(let ((tty (open-control-tty ttyname
open/read+write)))
(move->fdes tty 0)
(dup->outport tty 1)
(set-port-buffering (dup->outport tty 2)
bufpol/none))
;; No good -- leaves old ones around:
(stdio->stdports thunk))))
(pty-out (dup->outport pty-in)))
(set-port-buffering pty-out bufpol/none)
(values process pty-in pty-out ttyname))))
;;; (open-pty)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Returns two values: [pty-inport ttyname]
;;; PTY-PORT is a port open on the pty.
;;; TTYNAME is the name of the tty, e.g., "/dev/ttyk4"
;;;
;;; Scheme doesn't allow bidirectional ports, so the returned port
;;; is an input port -- however, the underlying file descriptor is
;;; opened read+write, and you can use DUP->OUTPORT to map it to
;;; corresponding output ports.
(define (open-pty)
(let ((next-pty (make-pty-generator)))
(let loop ()
(cond ((next-pty) =>
(lambda (pty-name)
(cond ((with-errno-handler ((errno packet) (else #f))
(open-file pty-name open/read+write)) =>
(lambda (pty) ; Score!
(values pty (pty-name->tty-name pty-name))))
(else (loop))))) ; Open failed; try another pty.
(else (error "open-pty: could not open new pty"))))))
;;; The following code may in fact be system dependent.
;;; If so, we'll move it out to the architecture specific directories.
;;; Map between corresponding pty and tty filenames.
(define (pty/tty-name-mapper char)
(lambda (name)
(let ((ans (string-copy name)))
(string-set! ans 5 char) ; Change X in "/dev/Xtyzz" to CHAR.
ans)))
(define pty-name->tty-name (pty/tty-name-mapper #\t)) ;/dev/ttyk3 -> /dev/ptyk3
(define tty-name->pty-name (pty/tty-name-mapper #\p)) ;/dev/ptyk3 -> /dev/ttyk3
;;; Generator for the set of possible pty names.
(define (make-pty-generator)
(let* ((pattern (string-copy"/dev/ptyLN")) ; L=letter N=number
(l-pos 8)
(n-pos 9)
; (letters "pqrstuvwxyzPQRST") ; From telnetd source in BSD4.4.
; (numbers "0123456789abcdef")
(letters "pq") ; From telnetd source in BSD4.4.
(numbers "0123456789abcdef")
(num-letters (string-length letters))
(num-numbers (string-length numbers))
(l num-letters) ; Generator's state vars. The value
(n 0)) ; of the last elt that was generated.
; (We count backwards to (0,0); n fastest.)
(lambda ()
(call-with-current-continuation
(lambda (abort)
(if (zero? n)
(if (zero? l) (abort #f) ; No more.
(begin (set! l (- l 1))
(set! n (- num-numbers 1))
(string-set! pattern l-pos (string-ref letters l))))
(set! n (- n 1)))
(string-set! pattern n-pos (string-ref numbers n))
(string-copy pattern))))))