.\" $OpenBSD: BIO_dup_chain.3,v 1.2 2023/04/09 06:27:52 jsg Exp $
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.\" Copyright (c) 2022 Ingo Schwarze <schwarze@openbsd.org>
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.Dd $Mdocdate: April 9 2023 $
.Dt BIO_DUP_CHAIN 3
.Os
.Sh NAME
.Nm BIO_dup_chain ,
.Nm BIO_dup_state
.Nd copy a BIO chain
.Sh SYNOPSIS
.In openssl/bio.h
.Ft BIO *
.Fn BIO_dup_chain "BIO *b"
.Ft long
.Fn BIO_dup_state "BIO *b" "BIO *new_bio"
.Sh DESCRIPTION
.Fn BIO_dup_chain
copies the chain starting at
.Fa b
by iteratively copying
.Fa b
and all the BIOs following it
and joining the copies in the same order as in the original chain.
The copying operation is neither a deep copy nor a shallow copy.
.Pp
Some parts of the state of each BIO are copied,
in particular with respect to the values returned by
.Xr BIO_get_init 3 ,
.Xr BIO_test_flags 3 ,
and
.Xr BIO_get_shutdown 3 .
.\" XXX new_bio->num = bio->num;
Other parts of the state of the BIOs are not copied
but instead initialized to 0,
in particular with respect to the values returned by
.Xr BIO_number_read 3 ,
.Xr BIO_number_written 3 ,
and
.Xr BIO_get_retry_reason 3 .
The custom data pointer that can be used by custom BIO types
and that can be retrieved with
.Xr BIO_get_data 3
is set to
.Dv NULL
in the copied BIO objects rather than copied.
The reference count of each BIO in the copied chain is set to 1.
.Pp
For each BIO in the chain, copying the data that was set with
.Xr BIO_set_ex_data 3
is attempted, which may involve calling application-defined
callback functions.
.Pp
The following pointers are copied
rather than creating deep copies of the objects pointed to:
.Bl -bullet
.It
The
.Fa type
pointer used for creating each BIO with
.Xr BIO_new 3 ,
implying that functions like
.Xr BIO_method_name 3
return pointers to the same strings for the BIOs in the copied chain,
and that these strings are not copied.
.It
All function pointers, in particular those installed with
.Xr BIO_set_callback_ex 3
and
.Xr BIO_get_callback_ex 3 .
.It
The pointer installed with
.Xr BIO_set_callback_arg 3 ,
which implies that for BIOs using
.Xr BIO_debug_callback 3 ,
those in the copied chain use the same BIOs for debugging output
as the corresponding ones in the original chain,
and none of the debugging output BIOs are copied.
.El
.Pp
.Fn BIO_dup_state
is a macro that calls
.Xr BIO_ctrl 3
with a
.Fa cmd
argument of
.Dv BIO_CTRL_DUP .
It is automatically called for each BIO during
.Fn BIO_dup_chain
after the copied BIO is initialized and data copied into it,
but before the data set with
.Xr BIO_set_ex_data 3
is copied into the new BIO and before it is linked into the new chain.
.Pp
This control operation may modify the operation of
.Fn BIO_dup_chain
for particular types of BIOs contained in the chain,
for example initializing or copying additional data.
For BIO types provided by the library, such additional effects
are documented in the respective manual pages, in particular in
.Xr BIO_f_buffer 3 ,
.Xr BIO_f_cipher 3 ,
.Xr BIO_f_md 3 ,
.Xr BIO_f_ssl 3 ,
.Xr BIO_s_bio 3 ,
and
.Xr BIO_s_connect 3 .
.Sh RETURN VALUES
.Fn BIO_dup_chain
returns a pointer to the newly allocated copy of the BIO
.Fa b
on success or
.Dv NULL
on failure .
.Pp
.Fn BIO_dup_state
returns 1 on success or a value less than or equal to zero on failure.
.Sh SEE ALSO
.Xr BIO_get_data 3 ,
.Xr BIO_new 3 ,
.Xr BIO_next 3 ,
.Xr BIO_push 3
.Sh HISTORY
.Fn BIO_dup_chain
and
.Fn BIO_dup_state
first appeared in SSLeay 0.8.0 and have been available since
.Ox 2.4 .