DTLS_GET_DATA_MTU(3ossl)

✨ DTLS_get_data_mtu — get maximum data payload size ✨

okay bestie, so this is the DTLS_get_data_mtu page from the OpenSSL manuals (yes, the 3ossl girlies 💅) and she's short, she's sweet, and she knows exactly how big your payload can be. let's get into it 🦋

---

🌸 SYNOPSIS 🌸

#include <openssl/ssl.h>

size_t DTLS_get_data_mtu(const SSL *ssl);

like, that's it. one function, one arg, one size_t. iconic honestly.

---

💖 DESCRIPTION 💖

so the way this works is: DTLS_get_data_mtu() hands you back the maximum data payload size for the established DTLS connection ssl 🔥

and how does it figure that out? it does the math based on two things:

• the DTLS record MTU, and
• the overhead of the DTLS record header, encryption and authentication that's currently in use on that connection.

so it's not a guess, it's not vibes, it's literally the real overhead situation of your specific connection. no cap 💀

---

🎀 RETURN VALUES 🎀

• success — returns the maximum data payload size, slay 👑
• failure — returns 0. that's the fail state, bestie, don't ignore a 0 🚩

---

🦋 HISTORY 🦋

DTLS_get_data_mtu() was added in OpenSSL 1.1.1. so she's been around a minute, she's a legend at this point ⭐

---

💜 COPYRIGHT 💜

Copyright 2016 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>.

fr fr, read the license. it's giving legally binding and we respect her 💅

---

and that's the whole page, bestie!! this one shipped as part of OpenSSL 3.5.9, dated 2026-09-29, and it's the DTLS_GET_DATA_MTU(3ossl) manual 🫶 mwah, go check your payload sizes 🌈💖