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From: krishnan@sunybcs.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: 4.2BSD LPR Spooler Protocol
Message-ID: <2830@sunybcs.UUCP>
Date: Fri, 3-Apr-87 12:53:37 EST
Article-I.D.: sunybcs.2830
Posted: Fri Apr  3 12:53:37 1987
Date-Received: Sun, 5-Apr-87 07:20:31 EST
References: <328@hqda-ai.UUCP>
Organization: SUNY/Buffalo Computer Science
Lines: 99
Keywords: bsd spooler protocol



These are the comments I extracted from the program I wrote for printing
from a Lisp Machine ( Symbolics or TI's ) to a printer on a Unix machine.
The top level interface was designed by Bill Baxter.



;;; The 4.3 BSD line printer protocol is described below. This is implemented
;;; by the function lpd
;;;
;;; The lisp machine is a client which talks with the Unix machine through 
;;; the lpd port # 515 and a local port 515. The  local port number should 
;;; less than 1023 for "lpd" on the Unix machine to acknowledge the request.
;;;
;;; The following protocol is followed for each of the necessary operations
;;; while sending a job to be queued.
;;;
;;; Printing a file "lpr" ::
;;;
;;;            1) Send the string "^Bprinter\n"
;;;            2) Check for a response of 0 from the Unix machine
;;;            3) Send the data file over using the sub-protocol described below.
;;;               3.1) Send the string "^C<no-of-bytes> <file-name>\n"
;;;               3.2) Send the data file
;;;               3.3) Check for a response of 0 from the Unix machine
;;;            4) Send the control file using the same sub-protocol
;;;
;;;
;;; Checking the queue "lpq" ::
;;;
;;;            1) Send the string "^Cprinter\n"
;;;
;;; Checking the queue more thoroughly "lpq -l" ::
;;;
;;;            1) Send the string "^Dprinter\n"
;;;
;;; Removing jobs from a queue "lprm"
;;;
;;;            1) Send the string "^Eprinter person job-number\n"
;;;
;;; Note that you cannot remove a remote job unless the request comes from the
;;; machine where the print request was originally made
;;;
;;; This program does not incorporate a local queue and relies on the
;;; queue of the Unix machine.
;;;
;;; Examples:
;;;
;;;    Lpr file-name qms ellie :landscape ( t/nil )
;;;
;;; The program keeps track of the default file name, the default-host, and the
;;; default-printer. Once a command has been issued with the the necessary keyword
;;; parameters, the default parameters are updated suitably. 
;;;
;;; Now the user can simply type
;;;
;;; Lpr 
;;;
;;; to print the file again.
;;;
;;; To display the queue, the user can simply type
;;;
;;; Lpq
;;;
;;; The default host name, and the default printer are "ellie" and "qms" 
;;; "qms" respectively until they are explicitly changed by invoking the
;;; function with a keyword parameter
;;;
;;; To remove this job from the queue, the user can type
;;;
;;; Lprm
;;;
;;; The job number is understood to be the last job spooled
;;;
;;;
;;; Job numbers can be explicitly specified by typing
;;;
;;; Lprm :job <job-number>
;;;


There is a security problem if you want to control access to printers.
This arises because, the Unix host has to make the symbolics a trusted
host for printing by including it in the "hosts.lpd" file. We are
currently working on a solution to that problem.

			G. Krishnan




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