endlessh: Error-out when specifying a port and listening on stdin

endlessh.c

@@ -289,6 +289,7 @@ struct config {
     .bind_family     = DEFAULT_BIND_FAMILY, \
 }
 
+static bool port_set = false;
 static void
 config_set_port(struct config *c, const char *s, int hardfail)
 {
@@ -302,6 +303,7 @@ config_set_port(struct config *c, const char *s, int hardfail)
     } else {
         c->port = tmp;
     }
+    port_set = true;
 }
 
 static void
@@ -676,6 +678,12 @@ main(int argc, char **argv)
         exit(EXIT_FAILURE);
     }
 
+    if (listen_on_stdin && port_set) {
+        fprintf(stderr,
+                "endlessh: Cannot specify a port when listening on stdin (-i)");
+        exit(EXIT_FAILURE);
+    }
+
     /* Set output (log) to line buffered */
     setvbuf(stdout, 0, _IOLBF, 0);