backend(7)

Name

Synopsis

#include <cups/cups.h>

const char *cupsBackendDeviceURI(char **argv);

void cupsBackendReport(const char *device_scheme,
                       const char *device_uri,
                       const char *device_make_and_model,
                       const char *device_info,
                       const char *device_id,
                       const char *device_location);

ssize_t cupsBackChannelWrite(const char *buffer,
                             size_t bytes, double timeout);

int cupsSideChannelRead(cups_sc_command_t *command,
                        cups_sc_status_t *status, char *data,
                        int *datalen, double timeout);

int cupsSideChannelWrite(cups_sc_command_t command,
                         cups_sc_status_t status, const char *data,
                         int datalen, double timeout);

Description

Like filters, backends must be capable of reading from a filename on the command-line or from the standard input, copying the standard input to a temporary file as required by the physical interface.

The command name (argv[0]) is set to the device URI of the destination printer. Authentication information in argv[0] is removed, so backend developers are urged to use the DEVICE_URI environment variable whenever authentication information is required. The cupsBackendDeviceURI() function may be used to retrieve the correct device URI.

Back-channel data from the device should be relayed to the job filters using the cupsBackChannelWrite function.

Backends are responsible for reading side-channel requests using the cupsSideChannelRead() function and responding with the cupsSideChannelWrite() function. The CUPS_SC_FD constant defines the file descriptor that should be monitored for incoming requests.

Device Discovery

    device-class scheme "Unknown" "device-info"
    device-class device-uri "device-make-and-model" "device-info"
    device-class device-uri "device-make-and-model" "device-info" "device-id"
    device-class device-uri "device-make-and-model" "device-info" "device-id" "device-location"

The cupsBackendReport() function can be used to generate these lines and handle any necessary escaping of characters in the various strings.

The device-class field is one of the following values:

direct

The device-uri refers to a specific direct-access device with no options, such as a parallel, USB, or SCSI device.

file

The device-uri refers to a file on disk.

network

The device-uri refers to a networked device and conforms to the general form for network URIs.

serial

The device-uri refers to a serial device with configurable baud rate and other options. If the device-uri contains a baud value, it represents the maximum baud rate supported by the device.

The scheme field provides the URI scheme that is supported by the backend. Backends should use this form only when the backend supports any URI using that scheme. The device-uri field specifies the full URI to use when communicating with the device.

The device-make-and-model field specifies the make and model of the device, e.g. "Example Foojet 2000". If the make and model is not known, you must report "Unknown".

The device-info field specifies additional information about the device. Typically this includes the make and model along with the port number or network address, e.g. "Example Foojet 2000 USB #1".

The optional device-id field specifies the IEEE-1284 device ID string for the device, which is used to select a matching driver.

The optional device-location field specifies the physical location of the device, which is often used to pre-populate the printer-location attribute when adding a printer.

Permissions

Exit Status

CUPS_BACKEND_OK

The print file was successfully transmitted to the device or remote server.

CUPS_BACKEND_FAILED

The print file was not successfully transmitted to the device or remote server. The scheduler will respond to this by canceling the job, retrying the job, or stopping the queue depending on the state of the printer-error-policy attribute.

CUPS_BACKEND_AUTH_REQUIRED

The print file was not successfully transmitted because valid authentication information is required. The scheduler will respond to this by holding the job and adding the 'cups-held-for-authentication' keyword to the "job-reasons" Job Description attribute.

CUPS_BACKEND_HOLD

The print file was not successfully transmitted because it cannot be printed at this time. The scheduler will respond to this by holding the job.

CUPS_BACKEND_STOP

The print file was not successfully transmitted because it cannot be printed at this time. The scheduler will respond to this by stopping the queue.

CUPS_BACKEND_CANCEL

The print file was not successfully transmitted because one or more attributes are not supported or the job was canceled at the printer. The scheduler will respond to this by canceling the job.

CUPS_BACKEND_RETRY

The print file was not successfully transmitted because of a temporary issue. The scheduler will retry the job at a future time - other jobs may print before this one.

CUPS_BACKEND_RETRY_CURRENT

The print file was not successfully transmitted because of a temporary issue. The scheduler will retry the job immediately without allowing intervening jobs.

All other exit code values are reserved.

Environment

DEVICE_URI

The device URI associated with the printer.

Files

Notes

Unless you are a developer and know what you are doing, please do not run backends directly. Instead, use the lp(1) or lpr(1) programs to send print jobs or lpinfo(8) to query for available printers using the backend. The one exception is the SNMP backend - see cups-snmp(8) for more information.

Notes

See Also

Copyright