pappl-device(3)

NAME
pappl-device - pappl device functions

LIBRARY
Printer Application Framework (libpappl, "pkg-config --cflags --libs pappl")

SYNOPSIS
#include <pappl/pappl.h>

typedef struct _pappl_device_s pappl_device_t;

void
papplDeviceAddScheme(const char *scheme, pappl_dtype_t dtype, pappl_devlist_cb_t list_cb, pappl_devopen_cb_t open_cb, pappl_devclose_cb_t close_cb, pappl_devread_cb_t read_cb, pappl_devwrite_cb_t write_cb, pappl_devstatus_cb_t status_cb);

void
papplDeviceClose(pappl_device_t *device);

void
papplDeviceError(pappl_device_t *device, const char *message, ...);

void
papplDeviceFlush(pappl_device_t *device);

void *
papplDeviceGetData(pappl_device_t *device);

pappl_dmetrics_t *
papplDeviceGetMetrics(pappl_device_t *device, pappl_dmetrics_t *metrics);

pappl_preason_t
papplDeviceGetStatus(pappl_device_t *device);

bool
papplDeviceList(pappl_dtype_t types, pappl_device_cb_t cb, void *data, pappl_deverror_cb_t err_cb, void *err_data);

pappl_device_t *
papplDeviceOpen(const char *device_uri, const char *name, pappl_deverror_cb_t err_cb, void *err_data);

int
papplDeviceParse1284ID(const char *device_id, cups_option_t **pairs);

ssize_t
papplDevicePrintf(pappl_device_t *device, const char *format, ...);

ssize_t
papplDevicePuts(pappl_device_t *device, const char *s);

ssize_t
papplDeviceRead(pappl_device_t *device, void *buffer, size_t bytes);

void
papplDeviceSetData(pappl_device_t *device, void *data);

ssize_t
papplDeviceWrite(pappl_device_t *device, const void *buffer, size_t bytes);

DESCRIPTION
The PAPPL device functions provide access to output device connections and to list available output devices. Output devices are accessed using Uniform Resource Identifier (URI) strings such as "file:///path/to/file-or-directory", "socket://11.22.33.44", and "usb://make/model?serial=number".

The papplDeviceList function lists available output devices, providing each available output device to the supplied callback function. The list only contains devices whose URI scheme supports discovery, at present USB printers and network printers that advertise themselves using DNS-SD/mDNS and/or SNMPv1.

The papplDeviceOpen function opens a connection to an output device using its URI. The papplDeviceClose function closes the connection.

The papplDevicePrintf, papplDevicePuts, and papplDeviceWrite functions send data to the device, while the papplDeviceRead function reads data from the device.

The papplDeviceGetMetrics function gets statistical information about all communications with the device while it has been open, while the papplDeviceGetStatus function gets the hardware status of a device and maps it to the pappl_preason_t bitfield.

ENUMERATIONS

  pappl_devtype_e
Device type bit values

PAPPL_DEVTYPE_ALL
    All printers

PAPPL_DEVTYPE_CUSTOM_LOCAL
    Local printer using a custom interface or protocol

PAPPL_DEVTYPE_CUSTOM_NETWORK
    Network printer using a custom interface or protocol

PAPPL_DEVTYPE_DNS_SD
    Network printers discovered via DNS-SD/mDNS

PAPPL_DEVTYPE_FILE
    Local file/directory

PAPPL_DEVTYPE_LOCAL
    All local printers

PAPPL_DEVTYPE_NETWORK
    All network printers

PAPPL_DEVTYPE_SNMP
    Network printers discovered via SNMP

PAPPL_DEVTYPE_SOCKET
    Network printers using raw socket

PAPPL_DEVTYPE_USB
    USB printers

FUNCTIONS

  papplDeviceAddScheme
Add a device URI scheme.

void papplDeviceAddScheme (
    const char *scheme,
    pappl_devtype_t dtype,
    pappl_devlist_cb_t list_cb,
    pappl_devopen_cb_t open_cb,
    pappl_devclose_cb_t close_cb,
    pappl_devread_cb_t read_cb,
    pappl_devwrite_cb_t write_cb,
    pappl_devstatus_cb_t status_cb,
    pappl_devid_cb_t id_cb
);

This function registers a device URI scheme with PAPPL, so that devices using the named scheme can receive print data, report status information, and so forth. PAPPL includes support for the following URI schemes:

•   dnssd: Network printers discovered using DNS-SD.

•   file: Character device files, plain files, and directories.

•   snmp: Network printers discovered using SNMPv1.

•   socket: Network printers using a hostname or numeric IP address.

•   usb: Class 1 (unidirectional) or 2 (bidirectional) USB printers.

The "scheme" parameter specifies the URI scheme and must consist of lowercase letters, digits, "-", "_", and/or ".", for example "x-foo" or "com.example.bar".

The "dtype" parameter specifies the device type and should be PAPPL_DTYPE_CUSTOM_LOCAL for locally connected printers and PAPPL_DTYPE_CUSTOM_NETWORK for network printers.

Each of the callbacks corresponds to one of the papplDevice functions:

•   "list_cb": Implements discovery of devices (optional)

•   "open_cb": Opens communication with a device and allocates any device-
      specific data as needed

•   "close_cb": Closes communication with a device and frees any device-
      specific data as needed

•   "read_cb": Reads data from a device

•   "write_cb": Write data to a device

•   "status_cb": Gets basic printer state information from a device (optional)

•   "id_cb": Gets the current IEEE-1284 device ID from a device (optional)

The "open_cb" callback typically calls papplDeviceSetData to store a pointer to contextual information for the connection while the "close_cb", "id_cb", "read_cb", "write_cb", and "status_cb" callbacks typically call papplDeviceGetData to retrieve it.

  papplDeviceAddScheme2
Add a device URI scheme with supply-level queries.

void papplDeviceAddScheme2 (
    const char *scheme,
    pappl_devtype_t dtype,
    pappl_devlist_cb_t list_cb,
    pappl_devopen_cb_t open_cb,
    pappl_devclose_cb_t close_cb,
    pappl_devread_cb_t read_cb,
    pappl_devwrite_cb_t write_cb,
    pappl_devstatus_cb_t status_cb,
    pappl_devsupplies_cb_t supplies_cb,
    pappl_devid_cb_t id_cb
);

This function registers a device URI scheme with PAPPL, so that devices using the named scheme can receive print data, report status information, and so forth. PAPPL includes support for the following URI schemes:

•   dnssd: Network printers discovered using DNS-SD.

•   file: Character device files, plain files, and directories.

•   snmp: Network printers discovered using SNMPv1.

•   socket: Network printers using a hostname or numeric IP address.

•   usb: Class 1 (unidirectional) or 2 (bidirectional) USB printers.

The "scheme" parameter specifies the URI scheme and must consist of lowercase letters, digits, "-", "_", and/or ".", for example "x-foo" or "com.example.bar".

The "dtype" parameter specifies the device type and should be PAPPL_DTYPE_CUSTOM_LOCAL for locally connected printers and PAPPL_DTYPE_CUSTOM_NETWORK for network printers.

Each of the callbacks corresponds to one of the papplDevice functions:

•   "list_cb": Implements discovery of devices (optional)

•   "open_cb": Opens communication with a device and allocates any device-
      specific data as needed

•   "close_cb": Closes communication with a device and frees any device-
      specific data as needed

•   "read_cb": Reads data from a device

•   "write_cb": Write data to a device

•   "status_cb": Gets basic printer state information from a device (optional)

•   "supplies_cb": Gets supply level information from a device (optional)

•   "id_cb": Gets the current IEEE-1284 device ID from a device (optional)

The "open_cb" callback typically calls papplDeviceSetData to store a pointer to contextual information for the connection while the "close_cb", "id_cb", "read_cb", "write_cb", "status_cb", and "supplies_cb" callbacks typically call papplDeviceGetData to retrieve it.

  papplDeviceClose
Close a device connection.

void papplDeviceClose (
    pappl_device_t *device
);

This function flushes any pending write data and closes the connection to a device.

  papplDeviceError
Report an error on a device.

void papplDeviceError (
    pappl_device_t *device,
    const char *message,
    ...
);

This function reports an error on a device using the client-supplied callback function. It is normally called from any custom device URI scheme callbacks you implement.

  papplDeviceFlush
Flush any buffered data to the device.

void papplDeviceFlush (
    pappl_device_t *device
);

This function flushes any pending write data sent using the papplDevicePrintf, papplDevicePuts, or papplDeviceWrite functions to the device.

  papplDeviceGetData
Get device-specific data.

void * papplDeviceGetData (
    pappl_device_t *device
);

This function returns any device-specific data that has been set by the device open callback. It is normally only called from any custom device URI scheme callbacks you implement.

  papplDeviceGetID
Get the IEEE-1284 device ID.

char * papplDeviceGetID (
    pappl_device_t *device,
    char *buffer,
    size_t bufsize
);

This function queries the IEEE-1284 device ID from the device and copies it to the provided buffer. The buffer must be at least 64 bytes and should be at least 1024 bytes in length.

5   Note: This function can block for up to several seconds depending on

5   the type of connection.

  papplDeviceGetMetrics
Get the device metrics.

pappl_devmetrics_t * papplDeviceGetMetrics (
    pappl_device_t *device,
    pappl_devmetrics_t *metrics
);

This function returns a copy of the device metrics data, which includes the number, length (in bytes), and duration (in milliseconds) of read, status, and write requests for the current session. This information is normally used for performance measurement and optimization during development of a printer application. It can also be useful diagnostic information.

  papplDeviceGetStatus
Get the printer status bits.

pappl_preason_t  papplDeviceGetStatus (
    pappl_device_t *device
);

This function returns the current printer status bits, as applicable to the current device.

The status bits for USB devices come from the original Centronics parallel printer "standard" which was later formally standardized in IEEE 1284-1984 and the USB Device Class Definition for Printing Devices. Some vendor extensions are also supported.

The status bits for network devices come from the hrPrinterDetectedErrorState property that is defined in the SNMP Printer MIB v2 (RFC 3805).

This function returns a pappl_preason_t bitfield which can be passed to the papplPrinterSetReasons function. Use the PAPPL_PREASON_DEVICE_STATUS value as the value of the "remove" argument.

5   Note: This function can block for several seconds while getting the status

5   information.

  papplDeviceGetSupplies
Get the current printer supplies.

int  papplDeviceGetSupplies (
    pappl_device_t *device,
    int max_supplies,
    pappl_supply_t *supplies
);

This function returns the number, type, and level of current printer supply levels, as applicable to the current device.

The supply levels for network devices come from the prtSupplyTable and prtMarkerColorantTable properties that are defined in the SNMP Printer MIB v2 (RFC 3805).

The supply levels for other devices are not standardized and must be queried using other methods.

5   Note: This function can block for several seconds while getting the supply

5   information.

  papplDeviceIsSupported
Determine whether a given URI is supported.

bool  papplDeviceIsSupported (
    const char *uri
);

This function determines whether a given URI or URI scheme is supported as a device.

  papplDeviceList
List available devices.

bool  papplDeviceList (
    pappl_devtype_t types,
    pappl_device_cb_t cb,
    void *data,
    pappl_deverror_cb_t err_cb,
    void *err_data
);

This function lists the available devices, calling the "cb" function once per device that is discovered/listed. The callback function receives the device URI, IEEE-1284 device ID (if any), and "data" pointer, and returns true to stop listing devices and false to continue.

The "types" argument determines which devices are listed, for example PAPPL_DEVTYPE_ALL will list all types of devices while PAPPL_DEVTYPE_USB only lists USB printers.

Any errors are reported using the supplied "err_cb" function. If you specify NULL for this argument, errors are sent to stderr.

5   Note: This function will block (not return) until each of the device URI

5   schemes has reported all of the devices or the supplied callback function

5   returns true.

  papplDeviceOpen
Open a connection to a device.

pappl_device_t * papplDeviceOpen (
    const char *device_uri,
    const char *name,
    pappl_deverror_cb_t err_cb,
    void *err_data
);

This function opens a connection to the specified device URI. The "name" argument provides textual context for the connection and is usually the name (title) of the print job.

Any errors are reported using the supplied "err_cb" function. If you specify NULL for this argument, errors are sent to stderr.

  papplDeviceParseID
Parse an IEEE-1284 device ID string.

int  papplDeviceParseID (
    const char *device_id,
    cups_option_t **pairs
);

This function parses an IEEE-1284 device ID string and returns an array of key/value pairs as a cups_option_t array. The returned array must be freed using the cupsFreeOptions function.

  papplDevicePrintf
Write a formatted string.

ssize_t  papplDevicePrintf (
    pappl_device_t *device,
    const char *format,
    ...
);

This function buffers a formatted string that will be sent to the device. The "format" argument accepts all printf format specifiers and behaves identically to that function.

Call the papplDeviceFlush function to ensure that the formatted string is immediately sent to the device.

  papplDevicePuts
Write a literal string.

ssize_t  papplDevicePuts (
    pappl_device_t *device,
    const char *s
);

This function buffers a literal string that will be sent to the device. Call the papplDeviceFlush function to ensure that the literal string is immediately sent to the device.

  papplDeviceRead
Read from a device.

ssize_t  papplDeviceRead (
    pappl_device_t *device,
    void *buffer,
    size_t bytes
);

This function reads data from the device. Depending on the device, this function may block indefinitely.

  papplDeviceRemoveScheme
Remove the named device URI scheme.

void papplDeviceRemoveScheme (
    const char *scheme
);

This function removes support for the named device URI scheme. Use only when you want to disable a URI scheme for security or functional reasons, for example to disable the "file" URI scheme.

  papplDeviceRemoveTypes
Remove device URI schemes of the specified types.

void papplDeviceRemoveTypes (
    pappl_devtype_t types
);

This function removes device URI schemes of the specified types. Use only when you want to disable URI schemes for security or functional reasons, for example to disable all network URI schemes.

  papplDeviceSetData
Set device-specific data.

void papplDeviceSetData (
    pappl_device_t *device,
    void *data
);

This function sets any device-specific data needed to communicate with the device. It is normally only called from the open callback that was registered for the device URI scheme.

  papplDeviceWrite
Write to a device.

ssize_t  papplDeviceWrite (
    pappl_device_t *device,
    const void *buffer,
    size_t bytes
);

This function buffers data that will be sent to the device. Call the papplDeviceFlush function to ensure that the data is immediately sent to the device.

STRUCTURES

  pappl_devmetrics_s
Device metrics

struct pappl_devmetrics_s
{
  size_t read_bytes;
  size_t read_msecs;
  size_t read_requests;
  size_t status_msecs;
  size_t status_requests;
  size_t write_bytes;
  size_t write_msecs;
  size_t write_requests;
};

TYPES

  pappl_devclose_cb_t
Device close callback

typedef void (*pappl_devclose_cb_t)(pappl_device_t *device);

  pappl_deverror_cb_t
Device error callback

typedef void (*pappl_deverror_cb_t)(const char *message, void *err_data);

  pappl_device_cb_t
Device callback - return true to stop, false to continue

typedef bool (*pappl_device_cb_t)(const char *device_info, const char *device_uri, const char *device_id, void *data);

  pappl_devid_cb_t
Device ID callback

typedef char * (*pappl_devid_cb_t)(pappl_device_t *device, char *buffer, size_t bufsize);

  pappl_devlist_cb_t
Device list callback

typedef bool (*pappl_devlist_cb_t)(pappl_device_cb_t cb, void *data, pappl_deverror_cb_t err_cb, void *err_data);

  pappl_devmetrics_t
Device metrics

typedef struct pappl_devmetrics_s pappl_devmetrics_t;

  pappl_devopen_cb_t
Device open callback

typedef bool (*pappl_devopen_cb_t)(pappl_device_t *device, const char *device_uri, const char *name);

  pappl_devread_cb_t
Device read callback

typedef ssize_t (*pappl_devread_cb_t)(pappl_device_t *device, void *buffer, size_t bytes);

  pappl_devstatus_cb_t
Device status callback

typedef pappl_preason_t (*pappl_devstatus_cb_t)(pappl_device_t *device);

  pappl_devsupplies_cb_t
Device supplies callback

typedef int (*pappl_devsupplies_cb_t)(pappl_device_t *device, int max_supplies, pappl_supply_t *supplies);

  pappl_devtype_t
Device type bitfield

typedef unsigned pappl_devtype_t;

  pappl_devwrite_cb_t
Device write callback

typedef ssize_t (*pappl_devwrite_cb_t)(pappl_device_t *device, const void *buffer, size_t bytes);

SEE ALSO
pappl(1), pappl-client(3), pappl-device(3), pappl-job(3), pappl-log(3), pappl-mainline(3), pappl-makeresheader(1), pappl-printer(3), pappl-resource(3), pappl-system(3), https://www.msweet.org/pappl

COPYRIGHT
Copyright © 2019-2022 by Michael R Sweet.

PAPPL is licensed under the Apache License Version 2.0 with an (optional) exception to allow linking against GPL2/LGPL2 software (like older versions of CUPS), so it can be used freely in any project you'd like. See the files "LICENSE" and "NOTICE" in the source distribution for more information.