Operations

## 4.3 Operations

### 4.3.1 sane_init

This function must be called before any other SANE function can be called. The behavior of a SANE backend is undefined if this function is not called first or if the status code returned by sane_init is different from SANE_STATUS_GOOD. The version code of the backend is returned in the value pointed to by version_code. If that pointer is NULL, no version code is returned. Argument authorize is either a pointer to a function that is invoked when the backend requires authentication for a specific resource or NULL if the frontend does not support authentication.

SANE_Status sane_init (SANE_Int * version_code,
SANE_Authorization_Callback authorize);


The authorization function may be called by a backend in response to any of the following calls:

sane_open, sane_control_option, sane_start
If a backend was initialized without authorization function, then authorization requests that cannot be handled by the backend itself will fail automatically and the user may be prevented from accessing protected resources. Backends are encouraged to implement means of authentication that do not require user assistance. E.g., on a multi-user system that authenticates users through a login process a backend could automatically lookup the apporpriate password based on resource- and user-name.

The authentication function type has the following declaration:

#define SANE_MAX_USERNAME_LEN   128

typedef void (*SANE_Authorization_Callback)
(SANE_String_Const resource,

Three arguments are passed to the authorization function: resource is a string specifying the name of the resource that requires authorization. A frontend should use this string to build a user-prompt requesting a username and a password. The username and password arguments are (pointers to) an array of SANE_MAX_USERNAME_LEN and SANE_MAX_PASSWORD_LEN characters, respectively. The authorization call should place the entered username and password in these arrays. The returned strings must be ASCII-NUL terminated.

### 4.3.2 sane_exit

This function must be called to terminate use of a backend. The function will first close all device handles that still might be open (it is recommended to close device handles explicitly through a call to sane_close(), but backends are required to release all resources upon a call to this function). After this function returns, no function other than sane_init() may be called (regardless of the status value returned by sane_exit(). Neglecting to call this function may result in some resources not being released properly.

void sane_exit (void);


### 4.3.3 sane_get_devices

This function can be used to query the list of devices that are available. If the function executes successfully, it stores a pointer to a NULL terminated array of pointers to SANE_Device structures in *device_list. The returned list is guaranteed to remain unchanged and valid until (a) another call to this function is performed or (b) a call to sane_exit() is performed. This function can be called repeatedly to detect when new devices become available. If argument local_only is true, only local devices are returned (devices directly attached to the machine that SANE is running on). If it is false, the device list includes all remote devices that are accessible to the SANE library.

SANE_Status sane_get_devices (const SANE_Device *** device_list,
SANE_Bool local_only);


This function may fail with SANE_STATUS_NO_MEM if an insufficient amount of memory is available.

Backend Implementation Note
SANE does not require that this function is called before a sane_open() call is performed. A device name may be specified explicitly by a user which would make it unnecessary and undesirable to call this function first.

### 4.3.4 sane_open

This function is used to establish a connection to a particular device. The name of the device to be opened is passed in argument name. If the call completes successfully, a handle for the device is returned in *h. As a special case, specifying a zero-length string as the device requests opening the first available device (if there is such a device).

SANE_Status sane_open (SANE_String_Const name, SANE_Handle * h);


This function may fail with one of the following status codes.

SANE_STATUS_DEVICE_BUSY:
The device is currently busy (in use by somebody else).
SANE_STATUS_INVAL:
The device name is not valid.
SANE_STATUS_IO_ERROR:
An error occured while communicating with the device.
SANE_STATUS_NO_MEM:
An insufficent amount of memory is available.
SANE_STATUS_ACCESS_DENIED:
Access to the device has been denied due to insufficient or invalid authentication.

### 4.3.5 sane_close

This function terminates the association between the device handle passed in argument h and the device it represents. If the device is presently active, a call to sane_cancel() is performed first. After this function returns, handle h must not be used anymore.

void sane_close (SANE_Handle h);


### 4.3.6 sane_get_option_descriptor

This function is used to access option descriptors. The function returns the option descriptor for option number n of the device represented by handle h. Option number 0 is guaranteed to be a valid option. Its value is an integer that specifies the number of options that are available for device handle h (the count includes option 0). If n is not a valid option index, the function returns NULL. The returned option descriptor is guaranteed to remain valid (and at the returned address) until the device is closed.

const SANE_Option_Descriptor *
sane_get_option_descriptor (SANE_Handle h, SANE_Int n);


### 4.3.7 sane_control_option

This function is used to set or inquire the current value of option number n of the device represented by handle h. The manner in which the option is controlled is specified by parameter a. The possible values of this parameter are described in more detail below. The value of the option is passed through argument v. It is a pointer to the memory that holds the option value. The memory area pointed to by v must be big enough to hold the entire option value (determined by member size in the corresponding option descriptor). The only exception to this rule is that when setting the value of a string option, the string pointed to by argument v may be shorter since the backend will stop reading the option value upon encountering the first NUL terminator in the string. If argument i is not NULL, the value of *i will be set to provide details on how well the request has been met. The meaning of this argument is described in more detail below.

SANE_Status sane_control_option (SANE_Handle h, SANE_Int n,
SANE_Action a, void *v,
SANE_Int * i);


 Symbol Code Description SANE_ACTION_GET_VALUE 0 Get current option value. SANE_ACTION_SET_VALUE 1 Set option value. The option value passed through argument v may be modified by the backend if the value cannot be set exactly. SANE_ACTION_SET_AUTO 2 Turn on automatic mode. Backend or device will automatically select an appropriate value. This mode remains effective until overridden by an explicit set value request. The value of parameter v is completely ignored in this case and may be NULL.

Table 7: Action Values (SANE_Action)

After setting a value via an action value of SANE_ACTION_SET_VALUE, additional information on how well the request has been met is returned in *i (if i is non-NULL). The returned value is a bitset that may contain any combination of the values described in Table 8.

 Symbol Code Description SANE_INFO_INEXACT 1 This value is returned when setting an option value resulted in a value being selected that does not exactly match the requested value. For example, if a scanner can adjust the resolution in increments of 30dpi only, setting the resolution to 307dpi may result in an actual setting of 300dpi. When this happens, the bitset returned in *i has this member set. In addition, the option value is modified to reflect the actual (rounded) value that was used by the backend. Note that inexact values are admissible for strings as well. A backend may choose to round'' a string to the closest matching legal string for a constrained string value. SANE_INFO_RELOAD_OPTIONS 2 The setting of an option may affect the value or availability of one or more other options. When this happens, the SANE backend sets this member in *i to indicate that the application should reload all options. This member may be set if and only if at least one option changed. SANE_INFO_RELOAD_PARAMS 4 The setting of an option may affect the parameter values (see sane_get_parameters()). If setting an option affects the parameter values, this member will be set in *i. Note that this member may be set even if the parameters did not actually change. However, it is guaranteed that the parameters never change without this member being set.

Table 8: Additional Information Returned When Setting an Option

This function may fail with one of the following status codes.

SANE_STATUS_UNSUPPORTED:
The operation is not supported for the specified handle and option number.
SANE_STATUS_INVAL:
The option value is not valid.
SANE_STATUS_IO_ERROR:
An error occured while communicating with the device.
SANE_STATUS_NO_MEM:
An insufficent amount of memory is available.
SANE_STATUS_ACCESS_DENIED:
Access to the option has been denied due to insufficient or invalid authentication.

### 4.3.8 sane_get_parameters

This function is used to obtain the current scan parameters. The returned parameters are guaranteed to be accurate between the time a scan has been started (sane_start() has been called) and the completion of that request. Outside of that window, the returned values are best-effort estimates of what the parameters will be when sane_start() gets invoked. Calling this function before a scan has actually started allows, for example, to get an estimate of how big the scanned image will be. The parameters passed to this function are the handle h of the device for which the parameters should be obtained and a pointer p to a parameter structure. The parameter structure is described in more detail below.

SANE_Status sane_get_parameters (SANE_Handle h,
SANE_Parameters * p);

typedef struct
{
SANE_Frame format;
SANE_Bool last_frame;
SANE_Int bytes_per_line;
SANE_Int pixels_per_line;
SANE_Int lines;
SANE_Int depth;
}
SANE_Parameters;


Member format specifies the format of the next frame to be returned. The possible values for type SANE_Frame are described in Table 9. The meaning of these values is described in more detail in Section 3.2.

 Symbol Code Description SANE_FRAME_GRAY 0 Band covering human visual range. SANE_FRAME_RGB 1 Pixel-interleaved red/green/blue bands. SANE_FRAME_RED 2 Red band of a red/green/blue image. SANE_FRAME_GREEN 3 Green band of a red/green/blue image. SANE_FRAME_BLUE 4 Blue band of a red/green/blue image.

Table 9: Frame Format (SANE_Frame)

Member last_frame is set to SANE_TRUE if and only if the frame that is currently being acquired (or the frame that will be acquired next if there is no current frame) is the last frame of a multi frame image (e.g., the current frame is the blue component of a red, green, blue image).

Member lines specifies how many scan lines the frame is comprised of. If this value is -1, the number of lines is not known a priori and the frontend should call sane_read() until it returns a status of SANE_STATUS_EOF.

Member bytes_per_line specifies the number of bytes that comprise one scan line.

Member depth specifies the number of bits per sample.

Member pixels_per_line specifies the number of pixels that comprise one scan line.

Assume B is the number of channels in the frame, then the bit depth d (as given by member depth) and the number of pixels per line n (as given by this member pixels_per_line) are related to c, the number of bytes per line (as given by member bytes_per_line) as follows:

c >= \left{ ll B*\lfloor (n + 7) / 8\rfloor if d=1 (1) B*n *d / 8 if d>1 \right.

Note that the number of bytes per line can be larger than the minimum value imposed by the right side of this equation. A frontend must be able to properly cope with such padded'' image formats.

### 4.3.9 sane_start

This function initiates aquisition of an image from the device represented by handle h.

SANE_Status sane_start (SANE_Handle h);

This function may fail with one of the following status codes.
SANE_STATUS_CANCELLED:
The operation was cancelled through a call to sane_cancel.
SANE_STATUS_DEVICE_BUSY:
The device is busy. The operation should be retried later.
SANE_STATUS_JAMMED:
The document feeder is jammed.
SANE_STATUS_NO_DOCS:
The document feeder is out of documents.
SANE_STATUS_COVER_OPEN:
The scanner cover is open.
SANE_STATUS_IO_ERROR:
An error occurred while communicating with the device.
SANE_STATUS_NO_MEM:
An insufficent amount of memory is available.
SANE_STATUS_INVAL:
The scan cannot be started with the current set of options. The frontend should reload the option descriptors, as if SANE_INFO_RELOAD_OPTIONS had been returned from a call to sane_control_option(), since the device's capabilities may have changed.

This function is used to read image data from the device represented by handle h. Argument buf is a pointer to a memory area that is at least maxlen bytes long. The number of bytes returned is stored in *len. A backend must set this to zero when a status other than SANE_STATUS_GOOD is returned. When the call succeeds, the number of bytes returned can be anywhere in the range from 0 to maxlen bytes.

SANE_Status sane_read (SANE_Handle h, SANE_Byte * buf,
SANE_Int maxlen, SANE_Int * len);

If this function is called when no data is available, one of two things may happen, depending on the I/O mode that is in effect for handle h.
1. If the device is in blocking I/O mode (the default mode), the call blocks until at least one data byte is available (or until some error occurs).

2. If the device is in non-blocking I/O mode, the call returns immediately with status SANE_STATUS_GOOD and with *len set to zero.
The I/O mode of handle h can be set via a call to sane_set_io_mode().

This function may fail with one of the following status codes.

SANE_STATUS_CANCELLED:
The operation was cancelled through a call to sane_cancel.
SANE_STATUS_EOF:
No more data is available for the current frame.
SANE_STATUS_JAMMED:
The document feeder is jammed.
SANE_STATUS_NO_DOCS:
The document feeder is out of documents.
SANE_STATUS_COVER_OPEN:
The scanner cover is open.
SANE_STATUS_IO_ERROR:
An error occurred while communicating with the device.
SANE_STATUS_NO_MEM:
An insufficent amount of memory is available.
SANE_STATUS_ACCESS_DENIED:
Access to the device has been denied due to insufficient or invalid authentication.

### 4.3.11 sane_cancel

This function is used to immediately or as quickly as possible cancel the currently pending operation of the device represented by handle h.

void sane_cancel (SANE_Handle h);

This function can be called at any time (as long as handle h is a valid handle) but usually affects long-running operations only (such as image is acquisition). It is safe to call this function asynchronously (e.g., from within a signal handler). It is important to note that completion of this operaton does not imply that the currently pending operation has been cancelled. It only guarantees that cancellation has been initiated. Cancellation completes only when the cancelled call returns (typically with a status value of SANE_STATUS_CANCELLED). Since the SANE API does not require any other operations to be re-entrant, this implies that a frontend must not call any other operation until the cancelled operation has returned.

### 4.3.12 sane_set_io_mode

This function is used to set the I/O mode of handle h. The I/O mode can be either blocking or non-blocking. If argument m is SANE_TRUE, the mode is set to non-blocking mode, otherwise it's set to blocking mode. This function can be called only after a call to sane_start() has been performed.

SANE_Status sane_set_io_mode (SANE_Handle h, SANE_Bool m);

By default, newly opened handles operate in blocking mode. A backend may elect not to support non-blocking I/O mode. In such a case the status value SANE_STATUS_UNSUPPORTED is returned. Blocking I/O must be supported by all backends, so calling this function with argument m set to SANE_FALSE is guaranteed to complete successfully.

This function may fail with one of the following status codes:

SANE_STATUS_INVAL:
No image acquisition is pending.
SANE_STATUS_UNSUPPORTED:
The backend does not support the requested I/O mode.

### 4.3.13 sane_get_select_fd

This function is used to obtain a (platform-specific) file-descriptor for handle h that is readable if and only if image data is available (i.e., when a call to sane_read() will return at least one byte of data). If the call completes successfully, the select file-descriptor is returned in *fd.

SANE_Status sane_get_select_fd (SANE_Handle h, SANE_Int *fd);

This function can be called only after a call to sane_start() has been performed and the returned file-descriptor is guaranteed to remain valid for the duration of the current image acquisition (i.e., until sane_cancel() or sane_start() get called again or until sane_read() returns with status SANE_STATUS_EOF). Indeed, a backend must guarantee to close the returned select file descriptor at the point when the next sane_read() call would return SANE_STATUS_EOF. This is necessary to ensure the application can detect when this condition occurs without actually having to call sane_read().

A backend may elect not to support this operation. In such a case, the function returns with status code SANE_STATUS_UNSUPPORTED.

Note that the only operation supported by the returned file-descriptor is a host operating-system dependent test whether the file-descriptor is readable (e.g., this test can be implemented using select() or poll() under UNIX). If any other operation is performed on the file descriptor, the behavior of the backend becomes unpredictable. Once the file-descriptor signals readable'' status, it will remain in that state until a call to sane_read() is performed. Since many input devices are very slow, support for this operation is strongly encouraged as it permits an application to do other work while image acquisition is in progress.

This function may fail with one of the following status codes:

SANE_STATUS_INVAL:
No image acquisition is pending.
SANE_STATUS_UNSUPPORTED:
The backend does not support this operation.

### 4.3.14 sane_strstatus

This function can be used to translate a SANE status code into a printable string. The returned string is a single line of text that forms a complete sentence, but without the trailing period (full-stop). The function is guaranteed to never return NULL. The returned pointer is valid at least until the next call to this function is performed.

const SANE_String_Const sane_strstatus (SANE_Status status);