[feat] SSL RTT in both client and server statem. SSL_get_handshake_rtt makes it available

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/20248)

4 files changed, 27 insertions, 0 deletions

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index 6848dbad7a..bad54e0955 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -4747,6 +4747,21 @@ const char *SSL_get_version(const SSL *s)
     return ssl_protocol_to_string(sc->version);
 }
 
+__owur int SSL_get_handshake_rtt(const SSL *s, uint64_t *rtt)
+{
+    const SSL_CONNECTION *sc = SSL_CONNECTION_FROM_CONST_SSL(s);
+
+    if (sc == NULL)
+        return -1;
+    if (sc->ts_msg_write.t <= 0 || sc->ts_msg_read.t <= 0)
+        return 0; /* data not (yet) available */
+    if (sc->ts_msg_read.t < sc->ts_msg_write.t)
+        return -1;
+
+    *rtt = ossl_time2us(ossl_time_subtract(sc->ts_msg_read, sc->ts_msg_write));
+    return 1;
+}
+
 static int dup_ca_names(STACK_OF(X509_NAME) **dst, STACK_OF(X509_NAME) *src)
 {
     STACK_OF(X509_NAME) *sk;
diff --git a/ssl/ssl_local.h b/ssl/ssl_local.h
index 69a578dc5c..7ab84acc80 100644
--- a/ssl/ssl_local.h
+++ b/ssl/ssl_local.h
@@ -1249,6 +1249,9 @@ struct ssl_connection_st {
     int quiet_shutdown;
     /* we have shut things down, 0x01 sent, 0x02 for received */
     int shutdown;
+    /* Timestamps used to calculate the handshake RTT */
+    OSSL_TIME ts_msg_write;
+    OSSL_TIME ts_msg_read;
     /* where we are */
     OSSL_STATEM statem;
     SSL_EARLY_DATA_STATE early_data_state;
diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index e7a0d8ccfd..655b6ac17a 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -484,6 +484,8 @@ static WRITE_TRAN ossl_statem_client13_write_transition(SSL_CONNECTION *s)
             st->hand_state = TLS_ST_CW_COMP_CERT;
         else
             st->hand_state = TLS_ST_CW_CERT;
+
+        s->ts_msg_read = ossl_time_now();
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_PENDING_EARLY_DATA_END:
@@ -584,6 +586,7 @@ WRITE_TRAN ossl_statem_client_write_transition(SSL_CONNECTION *s)
          * No transition at the end of writing because we don't know what
          * we will be sent
          */
+        s->ts_msg_write = ossl_time_now();
         return WRITE_TRAN_FINISHED;
 
     case TLS_ST_CR_SRVR_HELLO:
@@ -600,6 +603,7 @@ WRITE_TRAN ossl_statem_client_write_transition(SSL_CONNECTION *s)
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_EARLY_DATA:
+        s->ts_msg_write = ossl_time_now();
         return WRITE_TRAN_FINISHED;
 
     case DTLS_ST_CR_HELLO_VERIFY_REQUEST:
@@ -607,6 +611,7 @@ WRITE_TRAN ossl_statem_client_write_transition(SSL_CONNECTION *s)
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_CR_SRVR_DONE:
+        s->ts_msg_read = ossl_time_now();
         if (s->s3.tmp.cert_req)
             st->hand_state = TLS_ST_CW_CERT;
         else
diff --git a/ssl/statem/statem_srvr.c b/ssl/statem/statem_srvr.c
index c33e8f64e9..6eb98040e8 100644
--- a/ssl/statem/statem_srvr.c
+++ b/ssl/statem/statem_srvr.c
@@ -547,12 +547,14 @@ static WRITE_TRAN ossl_statem_server13_write_transition(SSL_CONNECTION *s)
 
     case TLS_ST_SW_FINISHED:
         st->hand_state = TLS_ST_EARLY_DATA;
+        s->ts_msg_write = ossl_time_now();
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_EARLY_DATA:
         return WRITE_TRAN_FINISHED;
 
     case TLS_ST_SR_FINISHED:
+        s->ts_msg_read = ossl_time_now();
         /*
          * Technically we have finished the handshake at this point, but we're
          * going to remain "in_init" for now and write out any session tickets
@@ -702,9 +704,11 @@ WRITE_TRAN ossl_statem_server_write_transition(SSL_CONNECTION *s)
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_SW_SRVR_DONE:
+        s->ts_msg_write = ossl_time_now();
         return WRITE_TRAN_FINISHED;
 
     case TLS_ST_SR_FINISHED:
+        s->ts_msg_read = ossl_time_now();
         if (s->hit) {
             st->hand_state = TLS_ST_OK;
             return WRITE_TRAN_CONTINUE;