FIDO_DEV_SET_IO_FUNCTIONS(3)

NAME
fido_dev_set_io_functions - 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;

int
fido_dev_set_io_functions(fido_dev_t *dev, const fido_dev_io_t *io);

DESCRIPTION
The fido_dev_set_io_functions interface defines the I/O handlers used to talk to dev. Its usage is optional. By default, libfido2 will use the operating system's native HID interface to talk to a FIDO device.

A fido_dev_io_open_t function is expected to return a non-NULL opaque pointer on success, and NULL on error. The returned opaque pointer is never dereferenced by libfido2.

A fido_dev_io_close_t function receives the opaque handle obtained from fido_dev_io_open_t. It is not expected to be idempotent.

A fido_dev_io_read_t function reads from dev. The first parameter taken is the opaque handle obtained from fido_dev_io_open_t. The read buffer is pointed to by the second parameter, and the third parameter holds its size. Finally, the last argument passed to fido_dev_io_read_t is the number of milliseconds the caller is willing to sleep, should the call need to block. If this value holds -1, fido_dev_io_read_t may block indefinitely. The number of bytes read is returned. On error, -1 is returned.

Conversely, a fido_dev_io_write_t function writes to dev. The first parameter taken is the opaque handle returned by fido_dev_io_open_t. The write buffer is pointed to by the second parameter, and the third parameter holds its size. A fido_dev_io_write_t function may block. The number of bytes written is returned. On error, -1 is returned.

No references to io are held by fido_dev_set_io_functions().

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