backend - cups backend transmission interfaces

Copyright © 2020-2024 by OpenPrinting. 2021-02-28 CUPS backend(7)

Backends are a special type of filter(7) which is used to send print data to and discover different devices on the system. 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. DEVICEDISCOVERY When run with no arguments, the backend should list the devices and schemes it supports or is advertising to the standard output. The output consists of zero or more lines consisting of any of the following forms: 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 Backends without world read and execute permissions are run as the root user. Otherwise, the backend is run using an unprivileged user account, typically "lp".

In addition to the environment variables listed in cups(1) and filter(7), CUPS backends can expect the following environment variable: DEVICE_URI The device URI associated with the printer.

The following exit codes are defined for backends: 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.

backend - cups backend transmission interfaces

CUPS printer drivers and backends are deprecated and will no longer be supported in a future feature release of CUPS. Printers that do not support IPP can be supported using applications such as ippeveprinter(1).

cups(1), cups-files.conf(5), cups-snmp(8), cupsd(8), filter(7), lp(1), lpinfo(8), lpr(1), CUPS Online Help (http://localhost:631/help)

backendbackendjobusertitlenum-copiesoptions [ filename ] #include<cups/cups.h>constchar*cupsBackendDeviceURI(char**argv); voidcupsBackendReport(constchar*device_scheme, constchar*device_uri, constchar*device_make_and_model, constchar*device_info, constchar*device_id, constchar*device_location); ssize_tcupsBackChannelWrite(constchar*buffer, size_tbytes, doubletimeout); intcupsSideChannelRead(cups_sc_command_t*command, cups_sc_status_t*status, char*data, int*datalen, doubletimeout); intcupsSideChannelWrite(cups_sc_command_tcommand, cups_sc_status_tstatus, constchar*data, intdatalen, doubletimeout);