---
name: "gnutls_session_ext_register"
section: "3"
platform: "linux"
package: "gnutls"
version: "3.8.13-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/gnutls_session_ext_register"
---

# gnutls\_session\_ext\_register(3)

API function

## NAME

gnutls\_session\_ext\_register - API function

## SYNOPSIS

**#include \<gnutls/gnutls.h\>**

**int gnutls\_session\_ext\_register(gnutls\_session\_t** *session***, const char \*** *name***, int** *id***, gnutls\_ext\_parse\_type\_t** *parse\_point***, gnutls\_ext\_recv\_func** *recv\_func***, gnutls\_ext\_send\_func** *send\_func***, gnutls\_ext\_deinit\_data\_func** *deinit\_func***, gnutls\_ext\_pack\_func** *pack\_func***, gnutls\_ext\_unpack\_func** *unpack\_func***, unsigned** *flags***);**

## ARGUMENTS

- gnutls\_session\_t session

  the session for which this extension will be set

- const char \* name

  the name of the extension to register

- int id

  the numeric id of the extension

- gnutls\_ext\_parse\_type\_t parse\_point

  the parse type of the extension (see gnutls\_ext\_parse\_type\_t)

- gnutls\_ext\_recv\_func recv\_func

  a function to receive the data

- gnutls\_ext\_send\_func send\_func

  a function to send the data

- gnutls\_ext\_deinit\_data\_func deinit\_func

  a function deinitialize any private data

- gnutls\_ext\_pack\_func pack\_func

  a function which serializes the extension's private data (used on session packing for resumption)

- gnutls\_ext\_unpack\_func unpack\_func

  a function which will deserialize the extension's private data

- unsigned flags

  must be zero or flags from **gnutls\_ext\_flags\_t**

## DESCRIPTION

This function will register a new extension type. The extension will be only usable within the registered session. If the extension type is already registered then **GNUTLS\_E\_ALREADY\_REGISTERED** will be returned, unless the flag **GNUTLS\_EXT\_FLAG\_OVERRIDE\_INTERNAL** is specified. The latter flag when specified can be used to override certain extensions introduced after 3.6.0. It is expected to be used by applications which handle custom extensions that are not currently supported in GnuTLS, but direct support for them may be added in the future.

Each registered extension can store temporary data into the gnutls\_session\_t structure using **gnutls\_ext\_set\_data()**, and they can be retrieved using **gnutls\_ext\_get\_data()**.

The validity of the extension registered can be given by the appropriate flags of **gnutls\_ext\_flags\_t**. If no validity is given, then the registered extension will be valid for client and TLS1.2 server hello (or encrypted extensions for TLS1.3).

## RETURNS

**GNUTLS\_E\_SUCCESS** on success, otherwise a negative error code.

## SINCE

3\.5.5

## REPORTING BUGS

Report bugs to \<bugs@gnutls.org\>.\
 Home page: https://www.gnutls.org

## COPYRIGHT

Copyright © 2001-2023 Free Software Foundation, Inc., and others.\
 Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.

## SEE ALSO

The full documentation for **gnutls** is maintained as a Texinfo manual. If the /usr/share/doc/gnutls/ directory does not contain the HTML form visit

- https://www.gnutls.org/manual/