.\" $OpenBSD: BIO_s_fd.3,v 1.13 2023/11/16 20:19:23 schwarze Exp $ .\" full merge up to: OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400 .\" .\" This file is a derived work. .\" The changes are covered by the following Copyright and license: .\" .\" Copyright (c) 2022 Ingo Schwarze .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: November 16 2023 $ .Dt BIO_S_FD 3 .Os .Sh NAME .Nm BIO_s_fd , .Nm BIO_set_fd , .Nm BIO_get_fd , .Nm BIO_new_fd , .Nm BIO_fd_non_fatal_error , .Nm BIO_fd_should_retry .Nd file descriptor BIO .Sh SYNOPSIS .In openssl/bio.h .Ft const BIO_METHOD * .Fo BIO_s_fd .Fa "void" .Fc .Ft long .Fo BIO_set_fd .Fa "BIO *b" .Fa "int fd" .Fa "long close_flag" .Fc .Ft long .Fo BIO_get_fd .Fa "BIO *b" .Fa "int *c" .Fc .Ft BIO * .Fo BIO_new_fd .Fa "int fd" .Fa "int close_flag" .Fc .Ft int .Fn BIO_fd_non_fatal_error "int errnum" .Ft int .Fn BIO_fd_should_retry "int retval" .Sh DESCRIPTION .Fn BIO_s_fd returns the file descriptor BIO method. This is a wrapper around the platform's file descriptor routines such as .Xr read 2 and .Xr write 2 . .Pp .Xr BIO_read 3 and .Xr BIO_write 3 read or write the underlying descriptor. .Xr BIO_puts 3 is supported but .Xr BIO_gets 3 is not. .Pp If the close flag is set, .Xr close 2 is called on the underlying file descriptor when the .Vt BIO is freed. .Pp .Xr BIO_reset 3 attempts to set the file pointer to the start of the file using .Fn lseek fd 0 0 . .Pp .Xr BIO_seek 3 sets the file pointer to position .Fa ofs from start of file using .Fn lseek fd ofs 0 . .Pp .Xr BIO_tell 3 returns the current file position by calling .Fn lseek fd 0 1 . .Pp .Fn BIO_set_fd sets the file descriptor of .Vt BIO .Fa b to .Fa fd and the close flag to .Fa close_flag . .Pp .Fn BIO_get_fd places the file descriptor in .Fa c if it is not .Dv NULL and also returns the file descriptor. .Pp .Fn BIO_new_fd returns a file descriptor BIO using .Fa fd and .Fa close_flag . .Pp .Fn BIO_fd_non_fatal_error determines whether the error status code .Fa errnum represents a recoverable error. .Fn BIO_fd_should_retry determines whether a recoverable error occurred by inspecting both .Xr errno 2 and .Fa retval , which is supposed to usually be the return value of a previously called function like .Xr BIO_read 3 or .Xr BIO_write 3 . These two functions are mostly used internally; in application code, it is usually easier and more robust to use .Xr BIO_should_retry 3 , which works for any BIO type. .Pp The behaviour of .Xr BIO_read 3 and .Xr BIO_write 3 depends on the behavior of the platform's .Xr read 2 and .Xr write 2 calls on the descriptor. If the underlying file descriptor is in a non-blocking mode, then the BIO will behave in the manner described in the .Xr BIO_read 3 and .Xr BIO_should_retry 3 manual pages. .Pp File descriptor BIOs should not be used for socket I/O. Use socket BIOs instead. .Pp .Xr BIO_ctrl 3 .Fa cmd arguments correspond to macros as follows: .Bl -column BIO_CTRL_GET_CLOSE BIO_get_close(3) -offset 3n .It Fa cmd No constant Ta corresponding macro .It Dv BIO_C_FILE_SEEK Ta Xr BIO_seek 3 .It Dv BIO_C_FILE_TELL Ta Xr BIO_tell 3 .It Dv BIO_C_GET_FD Ta Fn BIO_get_fd .It Dv BIO_C_SET_FD Ta Fn BIO_set_fd .It Dv BIO_CTRL_GET_CLOSE Ta Xr BIO_get_close 3 .It Dv BIO_CTRL_RESET Ta Xr BIO_reset 3 .It Dv BIO_CTRL_SET_CLOSE Ta Xr BIO_set_close 3 .El .Sh RETURN VALUES .Fn BIO_s_fd returns the file descriptor BIO method. .Pp When called on a file descriptor BIO object, .Xr BIO_method_type 3 returns the constant .Dv BIO_TYPE_FD and .Xr BIO_method_name 3 returns a pointer to the static string .Qq file descriptor . .Pp .Fn BIO_set_fd always returns 1. .Pp .Fn BIO_get_fd returns the file descriptor or -1 if the .Vt BIO has not been initialized. .Pp .Fn BIO_new_fd returns the newly allocated .Vt BIO or .Dv NULL if an error occurred. .Pp .Fn BIO_fd_non_fatal_error returns 1 if .Fa errnum is .Dv EAGAIN , .Dv EALREADY , .Dv EINPROGRESS , .Dv EINTR , or .Dv ENOTCONN and 0 otherwise, even if .Fa errnum is 0. .Pp .Fn BIO_fd_should_retry returns 1 if .Fn BIO_fd_non_fatal_error errno is 1 and .Fa retval is either 0 or \-1, or 0 otherwise. .Sh EXAMPLES This is a file descriptor BIO version of "Hello World": .Bd -literal -offset indent BIO *out; out = BIO_new_fd(fileno(stdout), BIO_NOCLOSE); BIO_printf(out, "Hello World\en"); BIO_free(out); .Ed .Sh SEE ALSO .Xr BIO_new 3 , .Xr BIO_read 3 , .Xr BIO_s_socket 3 , .Xr BIO_seek 3 , .Xr BIO_should_retry 3 .Sh HISTORY .Fn BIO_s_fd , .Fn BIO_set_fd , and .Fn BIO_get_fd first appeared in SSLeay 0.6.0, .Fn BIO_fd_should_retry in SSLeay 0.6.5, and .Fn BIO_new_fd and .Fn BIO_fd_non_fatal_error in SSLeay 0.8.0. All these functions have been available since .Ox 2.4 .