15.10. Forwarding Jobs

Options:

bkBerkeley compatible control file
bq_format=format of filtered output
lpd_bouncefilter job and transfer output
control_filter=Control file filter
control_file_line_order=Control file line order
nline_after_fileN line after data file
send_data_firstsend data files first

If a spool queue is doing store and forward operations, then rather than printing a job the control files and data files are sent to the remote printer. In order to do this, the following items must be arranged.

If necessary, the job must be processed by filters on the local host.
The control file must be prepared and updated according to the requirements of the remote site.
A connection must be established to the remote site.
The data files and control files must be transferred to the remote site.

One of the more serious problems is when a print spooler (LPR) program does not generate print jobs in a manner compatible with a remote system. While LPRng performs checks for improper implementations of RFC1179, it will try to accept a job even under the most severe abuse of the protocol. However, other spoolers are not so forgiving. Some spoolers require that the contents of the control file be in exactly the order that the original 1988 BSD lpr software generated them. While some entries can be missing, all the entries present in the file must be in an explicit order.

The bk (Berkeley lpd compatible control file) option causes lpr and lpd to reformat the control file, removing objectionable entries. The control file of a job being sent to a remote printer will have its control file entries restricted to letters in (and the same order) as HPJCLIMWT1234. You can use the control_file_line_order option to specify an even more restricted set, and use the nline_after_file option to have the file information line (N value) come after the data file entry.

However, there are some very odd commercial implementations that require more information than is present. To assist with this, the control_filter option can be used. This specifies a program that will process the control file before it is sent to a remote destination. The control_filter program is run with the standard set of filter options. STDIN is attached to the control file and the STDOUT will be used as the control file value sent to the remote host.

The exit code of the control_filter is used to determine whether to proceed in processing. See Errorcodes for details.

Sequence of Operations:

A copy of the control file information is made and the copy will be modified during processing, rather than the original.
If the lpd_bounce option is specified then a temporary file is created and the job is printed using the procedures for printing to a device, but to the file. This includes all of the filter operations, banners, and so forth. The working copy of the control file is set to have the temporary file as the data file to be sent to the remote destination, and the data file format is set to the bq_format value.
The control file is rewritten according to the requirements of the routing information, if any. For each destination in the routing information and each copy, a new job identifier value will be generated.
The control file is rewritten according to the bk and control_file_line_order options. If a control filter is specified, the control filter program is run and the output of the program is used as the new control file.
A connection is made to the remote host, and the data and control files are transferred to the remote host using the RFC1179 protocol. If the send_data_first option is specified the data files are sent first.
If the job was sent successfully, the job status is updated in the same manner as for a printed job.