NAME

     funopen, fropen, fwopen — open a stream

LIBRARY

     library “libbsd”

SYNOPSIS

     #include <bsd/stdio.h>

     FILE *
     funopen(const void *cookie, int (*readfn)(void *, char *, int), int (*writefn)(void *, const char *, int),
         off_t (*seekfn)(void *, off_t, int), int (*closefn)(void *));

     FILE *
     fropen(void *cookie, int (*readfn)(void *, char *, int));

     FILE *
     fwopen(void *cookie, int (*writefn)(void *, const char *, int));

DESCRIPTION

     The funopen() function associates a stream with up to four “I/O functions”.  Either readfn or writefn must
     be specified; the others can be given as an appropriately-typed NULL pointer.  These I/O functions will be
     used to read, write, seek and close the new stream.

     In general, omitting a function means that any attempt to perform the associated operation on the resulting
     stream will fail.  If the close function is omitted, closing the stream will flush any buffered output and
     then succeed.

     The calling conventions of readfn, writefn, seekfn and closefn must match those, respectively, of read(2),
     write(2), lseek(2), and close(2) with the single exception that they are passed the cookie argument
     specified to funopen() in place of the traditional file descriptor argument.

     Read and write I/O functions are allowed to change the underlying buffer on fully buffered or line buffered
     streams by calling setvbuf(3).  They are also not required to completely fill or empty the buffer.  They
     are not, however, allowed to change streams from unbuffered to buffered or to change the state of the line
     buffering flag.  They must also be prepared to have read or write calls occur on buffers other than the one
     most recently specified.

     All user I/O functions can report an error by returning -1.  Additionally, all of the functions should set
     the external variable errno appropriately if an error occurs.

     An error on closefn() does not keep the stream open.

     As a convenience, the include file <stdio.h> defines the macros fropen() and fwopen() as calls to funopen()
     with only a read or write function specified.

RETURN VALUES

     Upon successful completion, funopen() returns a FILE pointer.  Otherwise, NULL is returned and the global
     variable errno is set to indicate the error.

ERRORS

     [EINVAL]           The funopen() function was called without either a read or write function.  The
                        funopen() function may also fail and set errno for any of the errors specified for the
                        routine malloc(3).

SEE ALSO

     fcntl(2), open(2), fclose(3), fopen(3), fseek(3), setbuf(3)

HISTORY

     The funopen() functions first appeared in 4.4BSD.

BUGS

     The funopen() function may not be portable to systems other than BSD.

     On FreeBSD, OpenBSD and DragonFly the funopen() interface erroneously assumes that fpos_t is an integral
     type, and uses it in the seekfn hook; but because code using a seekfn hook will fail to build on systems
     where fpos_t is a struct, and it will need to be slightly fixed anyway, the implementation provided by
     libbsd (in the same way as NetBSD) uses the correct off_t types.