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.\" ========================================================================
.\"
.IX Title "nbd_opt_extended_headers 3"
.TH nbd_opt_extended_headers 3 2024-05-08 libnbd-1.20.1 LIBNBD
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH NAME
nbd_opt_extended_headers \- request the server to enable extended
headers
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <libnbd.h>
\&
\& int nbd_opt_extended_headers (
\&       struct nbd_handle *h
\&     );
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Request that the server use extended headers, by sending
\&\f(CW\*(C`NBD_OPT_EXTENDED_HEADERS\*(C'\fR.  This can only be used if
\&\fBnbd_set_opt_mode\fR\|(3) enabled option mode; furthermore, libnbd
defaults to automatically requesting this unless you use
\&\fBnbd_set_request_extended_headers\fR\|(3) or
\&\fBnbd_set_request_structured_replies\fR\|(3) prior to connecting.
This function is mainly useful for integration testing of corner
cases in server handling.
.PP
This function returns true if the server replies with success,
false if the server replies with an error, and fails only if
the server does not reply (such as for a loss of connection).
Note that some servers fail a second request as redundant;
libnbd assumes that once one request has succeeded, then
extended headers are supported (as visible by
\&\fBnbd_get_extended_headers_negotiated\fR\|(3)) regardless if
later calls to this function return false.  If this function
returns true, the use of structured replies is implied.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
This call returns a boolean value.
.SH ERRORS
.IX Header "ERRORS"
On error \f(CW\-1\fR is returned.
.PP
Refer to "ERROR HANDLING" in \fBlibnbd\fR\|(3)
for how to get further details of the error.
.PP
The following parameters must not be NULL: \f(CW\*(C`h\*(C'\fR.
For more information see "Non-NULL parameters" in \fBlibnbd\fR\|(3).
.SH "HANDLE STATE"
.IX Header "HANDLE STATE"
nbd_opt_extended_headers
can be called when the handle is in the following state:
.PP
.Vb 8
\& ┌─────────────────────────────────────┬─────────────────────────┐
\& │ Handle created, before connecting   │ ❌ error                │
\& │ Connecting                          │ ❌ error                │
\& │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
\& │ Connected to the server             │ ❌ error                │
\& │ Connection shut down                │ ❌ error                │
\& │ Handle dead                         │ ❌ error                │
\& └─────────────────────────────────────┴─────────────────────────┘
.Ve
.SH VERSION
.IX Header "VERSION"
This function first appeared in libnbd 1.18.
.PP
If you need to test if this function is available at compile time
check if the following macro is defined:
.PP
.Vb 1
\& #define LIBNBD_HAVE_NBD_OPT_EXTENDED_HEADERS 1
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbd_aio_opt_extended_headers\fR\|(3),
\&\fBnbd_create\fR\|(3),
\&\fBnbd_get_extended_headers_negotiated\fR\|(3),
\&\fBnbd_opt_go\fR\|(3),
\&\fBnbd_set_opt_mode\fR\|(3),
\&\fBnbd_set_request_extended_headers\fR\|(3),
\&\fBnbd_set_request_structured_replies\fR\|(3),
\&\fBlibnbd\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Eric Blake
.PP
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
.PP
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.
.PP
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110\-1301 USA