printer_server QUEUE-DIRECTORY

    Act as a server for printer_client: see that program
    for user documentation.

    This program is intended to be invoked from an
    .ssh/authorized_keys file line of the form:

        command="printer_server QUEUE-DIRECTORY" ...

    The QUEUE-DIRECTORY name must be absolute.

    The QUEUE-DIRECTORY holds files to be printed.  When
    it is being written, such a file has the .out
    extension.  When it is ready for printing, the
    extension name is changed to .ps.  When it has been
    printed, the extension name is changed to .done.

    The printer_server reads commands from its standard
    input and executes them.  In these commands FILE
    refers to a file name that cannot contain a slash
    (/) or begin with a dot (.).  The commands are:

    get FILE
        Return the QUEUE-DIRECTORY/FILE file in the
	standard output.

    sum FILE
        Return the MD5 sum of QUEUE-DIRECTORY/FILE file
	in the standard output.

    done FILE
        Change the extension of QUEUE-DIRECTORY/FILE to
	.done.  The file must previously have had
	extension .ps or .done.

    ready FILE
        Ditto but change the extension to .ps instead
	of to .done.

    remove FILE
        Remove QUEUE-DIRECTORY/FILE.  File must have
	extension .out, .ps, or .done.

    listfiles
        List all the files in the QUEUE-DIRECTORY, one
	line per file name, in lexical order.

    listdir
        List QUEUE-DIRECTORY as per `ls -ltr'.  Error
	messages are treated as standard output

    After producing any required output, each of these
    commands outputs a line containing just:

    	%%-HPCM_DONE-%%

    Any errors terminate the command and output:

        %%-HPCM_ERROR-%%
	error messages
	%%-HPCM_DONE-%%

    It is assumed %%-HPCM_XXX-%% lines never appear in
    a postscript file or as a file name.