Add DTLS_get_data_mtu() function

We add ssl_cipher_get_overhead() as an internal function, to avoid
having too much ciphersuite-specific knowledge in DTLS_get_data_mtu()
itself. It's going to need adjustment for TLSv1.3... but then again, so
is fairly much *all* of the SSL_CIPHER handling. This bit is in the noise.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index d5a6fe236e..1cf27b95aa 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -1817,6 +1817,9 @@ __owur int ssl_cipher_get_evp(const SSL_SESSION *s, const EVP_CIPHER **enc,
                               const EVP_MD **md, int *mac_pkey_type,
                               int *mac_secret_size, SSL_COMP **comp,
                               int use_etm);
+__owur int ssl_cipher_get_overhead(const SSL_CIPHER *c, size_t *mac_overhead,
+                                   size_t *int_overhead, size_t *blocksize,
+                                   size_t *ext_overhead);
 __owur int ssl_cipher_get_cert_index(const SSL_CIPHER *c);
 __owur const SSL_CIPHER *ssl_get_cipher_by_char(SSL *ssl,
                                                 const unsigned char *ptr);