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

.\"	$OpenBSD: BIO_f_buffer.3,v 1.11 2022/03/31 17:27:16 naddy Exp $
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.Dd $Mdocdate: March 31 2022 $
.Dt BIO_F_BUFFER 3
.Os
.Sh NAME
.Nm BIO_f_buffer ,
.Nm BIO_get_buffer_num_lines ,
.Nm BIO_set_read_buffer_size ,
.Nm BIO_set_write_buffer_size ,
.Nm BIO_set_buffer_size ,
.Nm BIO_set_buffer_read_data
.Nd buffering BIO
.Sh SYNOPSIS
.In openssl/bio.h
.Ft const BIO_METHOD *
.Fo BIO_f_buffer
.Fa void
.Fc
.Ft long
.Fo BIO_get_buffer_num_lines
.Fa "BIO *b"
.Fc
.Ft long
.Fo BIO_set_read_buffer_size
.Fa "BIO *b"
.Fa "long size"
.Fc
.Ft long
.Fo BIO_set_write_buffer_size
.Fa "BIO *b"
.Fa "long size"
.Fc
.Ft long
.Fo BIO_set_buffer_size
.Fa "BIO *b"
.Fa "long size"
.Fc
.Fo BIO_set_buffer_read_data
.Fa "BIO *b"
.Fa "void *buf"
.Fa "long num"
.Fc
.Sh DESCRIPTION
.Fn BIO_f_buffer
returns the buffering BIO method.
.Pp
Data written to a buffering BIO is buffered and periodically written
to the next BIO in the chain.
Data read from a buffering BIO comes from an internal buffer
which is filled from the next BIO in the chain.
Both
.Xr BIO_gets 3
and
.Xr BIO_puts 3
are supported.
.Pp
Calling
.Xr BIO_reset 3
on a buffering BIO clears any buffered data.
.Pp
.Fn BIO_get_buffer_num_lines
returns the number of lines currently buffered.
.Pp
.Fn BIO_set_read_buffer_size ,
.Fn BIO_set_write_buffer_size ,
and
.Fn BIO_set_buffer_size
set the read, write or both read and write buffer sizes to
.Fa size .
The initial buffer size is
.Dv DEFAULT_BUFFER_SIZE ,
currently 4096.
Any attempt to reduce the buffer size below
.Dv DEFAULT_BUFFER_SIZE
is ignored.
Any buffered data is cleared when the buffer is resized.
.Pp
.Fn BIO_set_buffer_read_data
clears the read buffer and fills it with
.Fa num
bytes of
.Fa buf .
If
.Fa num
is larger than the current buffer size, the buffer is expanded.
.Pp
Except
.Fn BIO_f_buffer ,
these functions are implemented as macros.
.Pp
Buffering BIOs implement
.Xr BIO_gets 3
by using
.Xr BIO_read 3
operations on the next BIO in the chain.
By prepending a buffering BIO to a chain
it is therefore possible to provide the functionality of
.Xr BIO_gets 3
if the following BIOs do not support it (for example SSL BIOs).
.Pp
Data is only written to the next BIO in the chain
when the write buffer fills or when
.Xr BIO_flush 3
is called.
It is therefore important to call
.Xr BIO_flush 3
whenever any pending data should be written
such as when removing a buffering BIO using
.Xr BIO_pop 3 .
.Xr BIO_flush 3
may need to be retried if the ultimate source/sink BIO is non-blocking.
.Sh RETURN VALUES
.Fn BIO_f_buffer
returns the buffering BIO method.
.Pp
.Fn BIO_get_buffer_num_lines
returns the number of lines buffered (may be 0).
.Pp
.Fn BIO_set_read_buffer_size ,
.Fn BIO_set_write_buffer_size ,
and
.Fn BIO_set_buffer_size
return 1 if the buffer was successfully resized or 0 for failure.
.Pp
.Fn BIO_set_buffer_read_data
returns 1 if the data was set correctly or 0 if there was an error.
.Sh SEE ALSO
.Xr BIO_ctrl 3 ,
.Xr BIO_flush 3 ,
.Xr BIO_new 3 ,
.Xr BIO_pop 3 ,
.Xr BIO_reset 3
.Sh HISTORY
.Fn BIO_f_buffer
first appeared in SSLeay 0.6.0.
.Fn BIO_get_buffer_num_lines
and
.Fn BIO_set_buffer_size
first appeared in SSLeay 0.6.5.
.Fn BIO_set_read_buffer_size
and
.Fn BIO_set_write_buffer_size
first appeared in SSLeay 0.8.0.
.Fn BIO_set_buffer_read_data
first appeared in SSLeay 0.9.0.
All these functions have been available since
.Ox 2.4 .