SSL_GET_SESSION(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

🎀 SSL_GET_SESSION(3ossl) 🎀

okay so bestie, this is the OpenSSL manual page for the session-getting girlies: SSL_get_session, SSL_get0_session, and SSL_get1_session. It's giving "where is my TLS/SSL session data?" and honestly, valid. 💅

✨ NAME ✨

SSL_get_session, SSL_get0_session, SSL_get1_session — retrieve TLS/SSL session data 🫶

🌸 SYNOPSIS 🌸

#include <openssl/ssl.h>

SSL_SESSION *SSL_get_session(const SSL *ssl);
SSL_SESSION *SSL_get0_session(const SSL *ssl);
SSL_SESSION *SSL_get1_session(SSL *ssl);

💖 DESCRIPTION 💖

SSL_get_session() returns a pointer to the SSL_SESSION actually used in ssl. Important: the reference count of the SSL_SESSION is not incremented, so that pointer can become invalid by other operations. Like, it's cute but it's fragile, okay? 😭

SSL_get0_session() is the same as SSL_get_session(). Same vibes, same pointer situation. ✨

SSL_get1_session() is the same as SSL_get_session(), but the reference count of the SSL_SESSION is incremented by one. So it's the "actually keep this around" version, bestie. 💖

🦋 NOTES 🦋

The ssl session contains all information required to re-establish the connection without a full handshake for SSL versions up to and including TLSv1.2. In TLSv1.3 the same is true, but sessions are established after the main handshake has occurred. The server will send the session information to the client at a time of its choosing, which may be some while after the initial connection is established (or never). Not me waiting for a session ticket that may simply never arrive 💀

Calling these functions on the client side in TLSv1.3 before the session has been established will still return an SSL_SESSION object, but that object cannot be used for resuming the session. See SSL_SESSION_is_resumable(3) for information on how to determine whether an SSL_SESSION object can be used for resumption or not. Vibe check your session before you try to resume, fr fr.

Additionally, in TLSv1.3, a server can send multiple messages that establish a session for a single connection. In that case, on the client side, the above functions will only return information on the last session that was received. On the server side they will only return information on the last session that was sent, or if no session tickets were sent then the session for the current connection. Last one wins, apparently. Main character session energy. 👑

The preferred way for applications to obtain a resumable SSL_SESSION object is to use a new session callback as described in SSL_CTX_sess_set_new_cb(3). The new session callback is only invoked when a session is actually established, so this avoids the problem described above where an application obtains an SSL_SESSION object that cannot be used for resumption in TLSv1.3. It also enables applications to obtain information about all sessions sent by the server. This is the way. Obsessed. 🌈

A session will be automatically removed from the session cache and marked as non-resumable if the connection is not closed down cleanly, e.g. if a fatal error occurs on the connection or SSL_shutdown(3) is not called prior to SSL_free(3). Messy shutdown = no resumable session for you, bestie. 😭

In TLSv1.3 it is recommended that each SSL_SESSION object is only used for resumption once. One resumption and done — it's giving limited edition. ✨

SSL_get0_session() returns a pointer to the actual session. As the reference counter is not incremented, the pointer is only valid while the connection is in use. If SSL_clear(3) or SSL_free(3) is called, the session may be removed completely (if considered bad), and the pointer obtained will become invalid. Even if the session is valid, it can be removed at any time due to timeout during SSL_CTX_flush_sessions(3). So don't get too attached to that raw pointer, okay? It's not giving forever. 💀

If the data is to be kept, SSL_get1_session() will increment the reference count, so that the session will not be implicitly removed by other operations but stays in memory. In order to remove the session SSL_SESSION_free(3) must be explicitly called once to decrement the reference count again. Keep it alive, then free it responsibly. We love an accountable icon. 🫶

SSL_SESSION objects keep internal link information about the session cache list, when being inserted into one SSL_CTX object's session cache. One SSL_SESSION object, regardless of its reference count, must therefore only be used with one SSL_CTX object (and the SSL objects created from this SSL_CTX object). No sharing your session object between SSL_CTX besties — that's not the move. 💅

👑 RETURN VALUES 👑

The following return values can occur:

  • NULL — There is no session available in ssl.
  • Pointer to an SSL_SESSION — The return value points to the data of an SSL session.

🌈 SEE ALSO 🌈

ssl(7), SSL_free(3), SSL_clear(3), SSL_SESSION_free(3) 🦋

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

okay bye bestie — this iconic page is from OpenSSL version 3.5.0, dated 2026-09-25, and it's SSL_GET_SESSION(3ossl); love that for us 💅✨🎀

📦 where this page comes from