SSL_WANT(3SSL)

📦
version 4.0.3 · 14 versions
, in ubuntu stonking

💖 SSL_WANT — bestie, let's find out what this TLS/SSL I/O thing actually WANTS 💖

okay so this is the SSL_WANT(3SSL) page from OpenSSL, and it's literally the page that tells you why your SSL I/O operation just went "🥺 not right now". It's the friend who texts "wyd" and you need to decode the vibe. Let's go. 🦋

✨ NAME ✨

SSL_want, SSL_want_nothing, SSL_want_read, SSL_want_write, SSL_want_x509_lookup, SSL_want_retry_verify, SSL_want_async, SSL_want_async_job, SSL_want_client_hello_cb — these get you state information for a TLS/SSL I/O operation. That's the whole job. 💅

✨ SYNOPSIS ✨

#include <openssl/ssl.h>

int SSL_want(const SSL *ssl);
int SSL_want_nothing(const SSL *ssl);
int SSL_want_read(const SSL *ssl);
int SSL_want_write(const SSL *ssl);
int SSL_want_x509_lookup(const SSL *ssl);
int SSL_want_retry_verify(const SSL *ssl);
int SSL_want_async(const SSL *ssl);
int SSL_want_async_job(const SSL *ssl);
int SSL_want_client_hello_cb(const SSL *ssl);

ngl, that's a lot of nearly-identical function names, but they're all serving their own lil purpose and I respect it 🫶

✨ DESCRIPTION ✨

SSL_want() returns state information for the SSL object ssl. And listen — ssl MUST NOT be NULL. Not "shouldn't", not "preferably". MUST NOT. Don't be out here passing NULL, bestie, that's not the move. 😭

The other SSL_want_*() calls? They're just shortcuts for the possible states that SSL_want() could hand back. Same energy, less reading. ✨

✨ NOTES ✨

SSL_want() peeks at the internal state information of the SSL object. Its return values are similar to what SSL_get_error(3) gives you.

BUT — and this is the part where people get caught slipping 🙈 — unlike SSL_get_error(3), which also evaluates (indirectly) the error queue, this one gets its results by examining an internal state flag only.

So that means: the info from SSL_want() should only be used for normal operation under nonblocking I/O. 💀 Error conditions are not handled here, and they must be treated using SSL_get_error(3). Like, that's not this function's job, don't put that on her.

The result returned by SSL_want() should always be consistent with the result of SSL_get_error(3). periodt. ✨

✨ RETURN VALUES ✨

These are the values SSL_want() can currently hand you back, and what each one is giving:

SSL_NOTHING

There is no data to be written or to be read. She's chillin. Nothing to do here. 😌

SSL_WRITING

There are data in the SSL buffer that must be written to the underlying BIO layer in order to complete the actual SSL_*() operation. A call to SSL_get_error(3) should return SSL_ERROR_WANT_WRITE.

SSL_READING

More data must be read from the underlying BIO layer in order to complete the actual SSL_*() operation. A call to SSL_get_error(3) should return SSL_ERROR_WANT_READ.

SSL_X509_LOOKUP

The operation did not complete because an application callback set by SSL_CTX_set_client_cert_cb() has asked to be called again. A call to SSL_get_error(3) should return SSL_ERROR_WANT_X509_LOOKUP.

SSL_RETRY_VERIFY

The operation did not complete because a certificate verification callback has asked to be called again via SSL_set_retry_verify(3). A call to SSL_get_error(3) should return SSL_ERROR_WANT_RETRY_VERIFY.

SSL_ASYNC_PAUSED

An asynchronous operation partially completed and was then paused. See SSL_get_all_async_fds(3). A call to SSL_get_error(3) should return SSL_ERROR_WANT_ASYNC.

SSL_ASYNC_NO_JOBS

The asynchronous job could not be started because there were no async jobs available in the pool (see ASYNC_init_thread(3)). A call to SSL_get_error(3) should return SSL_ERROR_WANT_ASYNC_JOB.

SSL_CLIENT_HELLO_CB

The operation did not complete because an application callback set by SSL_CTX_set_client_hello_cb() has asked to be called again. A call to SSL_get_error(3) should return SSL_ERROR_WANT_CLIENT_HELLO_CB.

And for the shortcut girlies ✨ — SSL_want_nothing(), SSL_want_read(), SSL_want_write(), SSL_want_x509_lookup(), SSL_want_retry_verify(), SSL_want_async(), SSL_want_async_job(), and SSL_want_client_hello_cb() — they return 1 when the corresponding condition is true, or 0 otherwise. Simple. Binary. Iconic. 💅

🌈 QUIC-SPECIFIC CONSIDERATIONS 🌈

For QUIC, these functions relate only to the TLS handshake layer. That's it, that's the whole note. Keep it in mind 🧚

✨ SEE ALSO ✨

go read those too, bestie, they're all part of the same friend group 🫶

✨ HISTORY ✨

  • The SSL_want_client_hello_cb() function and the SSL_CLIENT_HELLO_CB return value were added in OpenSSL 1.1.1.
  • SSL_want_retry_verify() was added in OpenSSL 3.0.

glow-up timeline, honestly ✨📈

Copyright 2001-2026 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>.

and that's the whole page, bestie 💜 this was SSL_WANT(3SSL) from OpenSSL, version 4.0.3, dated 2026-09-29 — now go forth and check your state flags responsibly, no cap 🎀✨

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