path: root/lib/libcrypto/man/BIO_s_file.3

.\" $OpenBSD: BIO_s_file.3,v 1.17 2023/11/16 20:19:23 schwarze Exp $
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.Dd $Mdocdate: November 16 2023 $
.Dt BIO_S_FILE 3
.Os
.Sh NAME
.Nm BIO_s_file ,
.Nm BIO_new_file ,
.Nm BIO_new_fp ,
.Nm BIO_set_fp ,
.Nm BIO_get_fp ,
.Nm BIO_read_filename ,
.Nm BIO_write_filename ,
.Nm BIO_append_filename ,
.Nm BIO_rw_filename
.\" Nm BIO_CTRL_SET_FILENAME is unused and intentionally undocumented.
.Nd FILE BIO
.Sh SYNOPSIS
.In openssl/bio.h
.Ft const BIO_METHOD *
.Fo BIO_s_file
.Fa void
.Fc
.Ft BIO *
.Fo BIO_new_file
.Fa "const char *filename"
.Fa "const char *mode"
.Fc
.Ft BIO *
.Fo BIO_new_fp
.Fa "FILE *stream"
.Fa "int flags"
.Fc
.Ft long
.Fo BIO_set_fp
.Fa "BIO *b"
.Fa "FILE *fp"
.Fa "int flags"
.Fc
.Ft long
.Fo BIO_get_fp
.Fa "BIO *b"
.Fa "FILE **fpp"
.Fc
.Ft long
.Fo BIO_read_filename
.Fa "BIO *b"
.Fa "char *name"
.Fc
.Ft long
.Fo BIO_write_filename
.Fa "BIO *b"
.Fa "char *name"
.Fc
.Ft long
.Fo BIO_append_filename
.Fa "BIO *b"
.Fa "char *name"
.Fc
.Ft long
.Fo BIO_rw_filename
.Fa "BIO *b"
.Fa "char *name"
.Fc
.Sh DESCRIPTION
.Fn BIO_s_file
returns the BIO file method.
As its name implies, it is a wrapper around the stdio
.Vt FILE
structure and it is a source/sink BIO.
.Pp
Calls to
.Xr BIO_read 3
and
.Xr BIO_write 3
read and write data to the underlying stream.
.Xr BIO_gets 3
and
.Xr BIO_puts 3
are supported on file BIOs.
.Pp
.Xr BIO_flush 3
on a file BIO calls the
.Xr fflush 3
function on the wrapped stream.
.Pp
.Xr BIO_reset 3
attempts to change the file pointer to the start of file using
.Fn fseek stream 0 0 .
.Pp
.Xr BIO_seek 3
sets the file pointer to position
.Fa ofs
from the start of the file using
.Fn fseek stream ofs 0 .
.Pp
.Xr BIO_eof 3
calls
.Xr feof 3 .
.Pp
Setting the
.Dv BIO_CLOSE
flag calls
.Xr fclose 3
on the stream when the BIO is freed.
.Pp
.Fn BIO_new_file
creates a new file BIO with mode
.Fa mode .
The meaning of
.Fa mode
is the same as for the stdio function
.Xr fopen 3 .
The
.Dv BIO_CLOSE
flag is set on the returned BIO.
.Pp
.Fn BIO_new_fp
creates a file BIO wrapping
.Fa stream .
Flags can be:
.Dv BIO_CLOSE , BIO_NOCLOSE Pq the close flag ,
.Dv BIO_FP_TEXT
(sets the underlying stream to text mode, default is binary:
this only has any effect under Win32).
.Pp
.Fn BIO_set_fp
sets the file pointer of a file BIO to
.Fa fp .
.Fa flags
has the same meaning as in
.Fn BIO_new_fp .
.Pp
.Fn BIO_get_fp
retrieves the file pointer of a file BIO.
.Pp
.Xr BIO_seek 3
sets the position pointer to
.Fa offset
bytes from the start of file.
.Pp
.Xr BIO_tell 3
returns the value of the position pointer.
.Pp
.Fn BIO_read_filename ,
.Fn BIO_write_filename ,
.Fn BIO_append_filename ,
and
.Fn BIO_rw_filename
set the file BIO
.Fa b
to use file
.Fa name
for reading, writing, append or read write respectively.
.Pp
When wrapping stdout, stdin, or stderr, the underlying stream
should not normally be closed, so the
.Dv BIO_NOCLOSE
flag should be set.
.Pp
Because the file BIO calls the underlying stdio functions, any quirks
in stdio behaviour will be mirrored by the corresponding BIO.
.Pp
On Windows,
.Fn BIO_new_files
reserves for the filename argument to be UTF-8 encoded.
In other words, if you have to make it work in a multi-lingual
environment, encode file names in UTF-8.
.Pp
The following
.Xr BIO_ctrl 3
.Fa cmd
constants correspond to macros:
.Bl -column BIO_C_GET_FILE_PTR "corresponding macro" -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_FILE_PTR Ta Fn BIO_get_fp
.It Dv BIO_C_SET_FILE_PTR Ta Fn BIO_set_fp
.It Dv BIO_C_SET_FILENAME Ta various, see below
.It Dv BIO_CTRL_EOF       Ta Xr BIO_eof 3
.It Dv BIO_CTRL_FLUSH     Ta Xr BIO_flush 3
.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
.Pp
The meaning of
.Dv BIO_C_SET_FILENAME
depends on the flags passed in the
.Xr BIO_ctrl 3
.Fa larg
argument:
.Bl -column "BIO_CLOSE | BIO_FP_READ | BIO_FP_WRITE" "BIO_append_filename()"\
 -offset 3n
.It Fa larg No argument                        Ta corresponding macro
.It Dv BIO_CLOSE | BIO_FP_READ                 Ta Fn BIO_read_filename
.It Dv BIO_CLOSE | BIO_FP_WRITE                Ta Fn BIO_write_filename
.It Dv BIO_CLOSE | BIO_FP_APPEND               Ta Fn BIO_append_filename
.It Dv BIO_CLOSE | BIO_FP_READ  | BIO_FP_WRITE Ta Fn BIO_rw_filename
.El
.Sh RETURN VALUES
.Fn BIO_s_file
returns the file BIO method.
.Pp
.Fn BIO_new_file
and
.Fn BIO_new_fp
return a file BIO or
.Dv NULL
if an error occurred.
.Pp
When called on a file BIO object,
.Xr BIO_method_type 3
returns the constant
.Dv BIO_TYPE_FILE
and
.Xr BIO_method_name 3
returns a pointer to the static string
.Qq FILE pointer .
.Pp
.Fn BIO_set_fp
and
.Fn BIO_get_fp
return 1 for success or 0 for failure (although the current
implementation never returns 0).
.Pp
.Xr BIO_seek 3
returns the same value as the underlying
.Xr fseek 3
function: 0 for success or -1 for failure.
.Pp
.Xr BIO_tell 3
returns the current file position.
.Pp
.Fn BIO_read_filename ,
.Fn BIO_write_filename ,
.Fn BIO_append_filename ,
and
.Fn BIO_rw_filename
return 1 for success or 0 for failure.
.Sh EXAMPLES
File BIO "hello world":
.Bd -literal -offset indent
BIO *bio_out;
bio_out = BIO_new_fp(stdout, BIO_NOCLOSE);
BIO_printf(bio_out, "Hello World\en");
.Ed
.Pp
Alternative technique:
.Bd -literal -offset indent
BIO *bio_out;
bio_out = BIO_new(BIO_s_file());
if(bio_out == NULL) /* Error ... */
if(!BIO_set_fp(bio_out, stdout, BIO_NOCLOSE)) /* Error ... */
BIO_printf(bio_out, "Hello World\en");
.Ed
.Pp
Write to a file:
.Bd -literal -offset indent
BIO *out;
out = BIO_new_file("filename.txt", "w");
if(!out) /* Error occurred */
BIO_printf(out, "Hello World\en");
BIO_free(out);
.Ed
.Pp
Alternative technique:
.Bd -literal -offset indent
BIO *out;
out = BIO_new(BIO_s_file());
if(out == NULL) /* Error ... */
if(!BIO_write_filename(out, "filename.txt")) /* Error ... */
BIO_printf(out, "Hello World\en");
BIO_free(out);
.Ed
.Sh SEE ALSO
.Xr BIO_new 3 ,
.Xr BIO_read 3 ,
.Xr BIO_seek 3
.Sh HISTORY
.Fn BIO_s_file ,
.Fn BIO_set_fp ,
.Fn BIO_get_fp ,
.Fn BIO_read_filename ,
.Fn BIO_write_filename ,
and
.Fn BIO_append_filename
first appeared in SSLeay 0.6.0.
.Fn BIO_new_file
and
.Fn BIO_new_fp
first appeared in SSLeay 0.8.0.
All these functions have been available since
.Ox 2.4 .
.Pp
.Fn BIO_rw_filename
first appeared in SSLeay 0.9.1 and has been available since
.Ox 2.6 .
.Sh BUGS
.Xr BIO_reset 3
and
.Xr BIO_seek 3
are implemented using
.Xr fseek 3
on the underlying stream.
The return value for
.Xr fseek 3
is 0 for success or -1 if an error occurred.
This differs from other types of BIO which will typically return
1 for success and a non-positive value if an error occurred.