s_client accepts host/port as positional argument.

This allows the user to provide the target host and optional port to
openssl s_client as an optional positional argument, rather than as the
argument to the -connect flag. This rationalises the user experience of
s_client: given that the only logical purpose of s_client is to connect
to a host, it is difficult to understand why there is an (effectively
mandatory) command option to pass to make that happen.

This patch forbids providing *both* -connect and the positional
argument, because it would likely be too difficult to reconcile.
Otherwise, using the positional argument behaves exactly the same as
using -connect does.
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1171)

apps/s_client.c

@@ -1421,8 +1421,22 @@ int s_client_main(int argc, char **argv)
         }
     }
     argc = opt_num_rest();
-    if (argc != 0)
+    if (argc == 1) {
+        /* If there's a positional argument, it's the equivalent of
+         * OPT_CONNECT.
+         * Don't allow -connect and a separate argument.
+         */
+        if (connectstr != NULL) {
+            BIO_printf(bio_err,
+                       "%s: must not provide both -connect option and target parameter\n",
+                       prog);
             goto opthelp;
+        }
+        connect_type = use_inet;
+        connectstr = *opt_rest();
+    } else if (argc != 0) {
+        goto opthelp;
+    }
 
 #ifndef OPENSSL_NO_NEXTPROTONEG
     if (min_version == TLS1_3_VERSION && next_proto_neg_in != NULL) {
@@ -1434,7 +1448,7 @@ int s_client_main(int argc, char **argv)
         int res;
         char *tmp_host = host, *tmp_port = port;
         if (connectstr == NULL) {
-            BIO_printf(bio_err, "%s: -proxy requires use of -connect\n", prog);
+            BIO_printf(bio_err, "%s: -proxy requires use of -connect or target parameter\n", prog);
             goto opthelp;
         }
         res = BIO_parse_hostserv(proxystr, &host, &port, BIO_PARSE_PRIO_HOST);
@@ -1459,7 +1473,7 @@ int s_client_main(int argc, char **argv)
             OPENSSL_free(tmp_port);
         if (!res) {
             BIO_printf(bio_err,
-                       "%s: -connect argument malformed or ambiguous\n",
+                       "%s: -connect argument or target parameter malformed or ambiguous\n",
                        prog);
             goto end;
         }

doc/man1/s_client.pod

@@ -113,6 +113,7 @@ B<openssl> B<s_client>
 [B<-ctlogfile>]
 [B<-keylogfile file>]
 [B<-early_data file>]
+[B<target>]
 
 =head1 DESCRIPTION
 
@@ -135,8 +136,10 @@ Print out a usage message.
 
 =item B<-connect host:port>
 
-This specifies the host and optional port to connect to. If not specified
-then an attempt is made to connect to the local host on port 4433.
+This specifies the host and optional port to connect to. It is possible to
+select the host and port using the optional target positional argument instead.
+If neither this nor the target positonal argument are specified then an attempt
+is made to connect to the local host on port 4433.
 
 =item B<-proxy host:port>
 
@@ -592,6 +595,13 @@ Reads the contents of the specified file and attempts to send it as early data
 to the server. This will only work with resumed sessions that support early
 data and when the server accepts the early data.
 
+=item B<[target]>
+
+Rather than providing B<-connect>, the target hostname and optional port may
+be provided as a single positional argument after all options. If neither this
+nor B<-connect> are provided, falls back to attempting to connect to localhost
+on port 4433.
+
 =back
 
 =head1 CONNECTED COMMANDS