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.