[#SSL_CTX_add_client_custom_ext]
= SSL_CTX_add_client_custom_ext
:mrdocs:

Register older‐style custom extension handlers for TLS/DTLS clients.

== Synopsis

Declared in `<openssl/ssl.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
SSL_CTX_add_client_custom_ext(
    xref:SSL_CTX.adoc[SSL_CTX]* ctx,
    unsigned int ext_type,
    xref:custom_ext_add_cb.adoc[custom_ext_add_cb] add_cb,
    xref:custom_ext_free_cb.adoc[custom_ext_free_cb] free_cb,
    void* add_arg,
    xref:custom_ext_parse_cb.adoc[custom_ext_parse_cb] parse_cb,
    void* parse_arg);
----

== Return Value

1 on success, or 0 on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| SSL context used by clients.
| *ext_type*
| Extension type (not a NID); must not be handled internally by OpenSSL.
| *add_cb*
| Callback that supplies extension data to send, or NULL for a zero‐length ClientHello extension.
| *free_cb*
| Optional callback to free data produced by `add_cb.`
| *add_arg*
| Application argument passed to `add_cb` and `free_cb.`
| *parse_cb*
| Callback that validates extension data received from the peer.
| *parse_arg*
| Application argument passed to `parse_cb.`
|===


[.small]#Created with https://www.mrdocs.com[MrDocs]#