---
name: "gnutls_handshake_set_hook_function"
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_handshake_set_hook_function"
---

# gnutls\_handshake\_set\_hook\_function(3)

API function

## NAME

gnutls\_handshake\_set\_hook\_function - API function

## SYNOPSIS

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

**void gnutls\_handshake\_set\_hook\_function(gnutls\_session\_t** *session***, unsigned int** *htype***, int** *when***, gnutls\_handshake\_hook\_func** *func***);**

## ARGUMENTS

- gnutls\_session\_t session

  is a **gnutls\_session\_t** type

- unsigned int htype

  the **gnutls\_handshake\_description\_t** of the message to hook at

- int when

  **GNUTLS\_HOOK\_**\* depending on when the hook function should be called

- gnutls\_handshake\_hook\_func func

  is the function to be called

## DESCRIPTION

This function will set a callback to be called after or before the specified handshake message has been received or generated. This is a generalization of **gnutls\_handshake\_set\_post\_client\_hello\_function()**.

To call the hook function prior to the message being generated or processed use **GNUTLS\_HOOK\_PRE** as  *when* parameter, **GNUTLS\_HOOK\_POST** to call after, and **GNUTLS\_HOOK\_BOTH** for both cases.

This callback must return 0 on success or a gnutls error code to terminate the handshake.

To hook at all handshake messages use an  *htype* of **GNUTLS\_HANDSHAKE\_ANY**.

## WARNING

You should not use this function to terminate the handshake based on client input unless you know what you are doing. Before the handshake is finished there is no way to know if there is a man-in-the-middle attack being performed.

## 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/