FIDO_DEV_SET_IO_FUNCTIONS(3)

NAME
fido_dev_set_io_functions, fido_dev_set_sigmask, fido_dev_set_timeout - FIDO 2 device I/O interface

SYNOPSIS
#include <fido.h>

    typedef void *fido_dev_io_open_t(const char *);
    typedef void  fido_dev_io_close_t(void *);
    typedef int   fido_dev_io_read_t(void *, unsigned char *, size_t, int);
    typedef int   fido_dev_io_write_t(void *, const unsigned char *, size_t);
    typedef struct fido_dev_io {
    	fido_dev_io_open_t  *open;
    	fido_dev_io_close_t *close;
    	fido_dev_io_read_t  *read;
    	fido_dev_io_write_t *write;
    } fido_dev_io_t;
    #ifdef _WIN32
    typedef int fido_sigset_t;
    #else
    typedef sigset_t fido_sigset_t;
    #endif

int
fido_dev_set_io_functions(fido_dev_t *dev, const fido_dev_io_t *io);
int
fido_dev_set_sigmask(fido_dev_t *dev, const fido_sigset_t *sigmask);
int
fido_dev_set_timeout(fido_dev_t *dev, int ms);

DESCRIPTION
The fido_dev_set_io_functions() function sets the I/O handlers used by libfido2 to talk to dev. By default, these handlers are set to the operating system's native HID or NFC interfaces. They are defined as follows:

fido_dev_open_t
    Receives a const char * holding a path and opens the corresponding device, returning a non-NULL opaque pointer on success and NULL on error.

fido_dev_close_t
    Receives the opaque pointer returned by fido_dev_open_t and closes the device.

fido_dev_read_t
    Reads a single transmission unit (HID report, APDU) from a device. The first parameter is the opaque pointer returned by fido_dev_open_t. The second parameter is the read buffer, and the third parameter is the read buffer size. The fourth parameter is the number of milliseconds the caller is willing to sleep, should the call need to block. If this value holds -1, fido_dev_read_t may block indefinitely. On success, the number of bytes read is returned. On error, -1 is returned.

fido_dev_write_t
    Writes a single transmission unit (HID report, APDU) to dev. The first parameter is the opaque pointer returned by fido_dev_open_t. The second parameter is the write buffer, and the third parameter is the number of bytes to be written. A fido_dev_write_t may block. On success, the number of bytes written is returned. On error, -1 is returned.

When calling fido_dev_set_io_functions(), the open, close, read, and write fields of io may not be NULL.

No references to io are held by fido_dev_set_io_functions().

The fido_dev_set_sigmask() function may be used to specify a non-NULL signal mask sigmask to be used while libfido2's default I/O handlers wait on dev. On UNIX-like operating systems, fido_sigset_t is defined as sigset_t. On Windows, fido_sigset_t is defined as int and fido_dev_set_sigmask() is a no-op.

No references to sigmask are held by fido_dev_set_sigmask().

The fido_dev_set_timeout() function informs libfido2 not to block for more than ms milliseconds while communicating with dev. If a timeout occurs, the corresponding fido_dev_* function will fail with FIDO_ERR_RX. If ms is -1, then libfido2 may block indefinitely. This is the default behaviour. When using the Windows Hello backend, ms is used as a guidance and may be overwritten by the platform.

RETURN VALUES
On success, fido_dev_set_io_functions(), fido_dev_set_sigmask(), and fido_dev_set_timeout() return FIDO_OK. On error, a different error code defined in <fido/err.h> is returned.