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Add an assertion to check the format of encoded parameters

Whenever the midend calls encode_params, it also checks that the
result is a printable ASCII string that doesn't contain '#' or ':'.

Parameter strings are embedded in save files, so they have to fit within
ASCII.  They can't contain '#' or ':' because those delimit the
parameter section of a game ID.  Nothing explicitly says they can't
contain control characters, but those would be a particularly egregious
violation of the recommendation that parameter strings be easy to type
into a shell.

--- a/midend.c

+++ b/midend.c

@@ -383,6 +383,18 @@

     return me->ourgame->dup_params(me->params);

 }

+static char *encode_params(midend *me, const game_params *params, bool full)

+{

+    char *encoded = me->ourgame->encode_params(params, full);

+

+    /* Assert that the params consist of printable ASCII containing

+     * neither '#' nor ':'. */

+    for (int i = 0; encoded[i]; i++)

+        assert(encoded[i] >= 32 && encoded[i] < 127 &&

+	       encoded[i] != '#' && encoded[i] != ':');

+    return encoded;

+}

+

 static void midend_set_timer(midend *me)

 {

     me->timing = (me->ourgame->is_timed &&

@@ -618,8 +630,8 @@

      * We check both params and cparams, to be as safe as possible.

      */

-    old = me->ourgame->encode_params(me->params, true);

-    new = me->ourgame->encode_params(data->params, true);

+    old = encode_params(me, me->params, true);

+    new = encode_params(me, data->params, true);

     if (strcmp(old, new)) {

         /* Set a flag to distinguish this deserialise failure

          * from one due to faulty decoding */

@@ -627,8 +639,8 @@

         return "Undoing this new-game operation would change params";

     }

-    old = me->ourgame->encode_params(me->curparams, true);

-    new = me->ourgame->encode_params(data->cparams, true);

+    old = encode_params(me, me->curparams, true);

+    new = encode_params(me, data->cparams, true);

     if (strcmp(old, new)) {

         ctx->refused = true;

         return "Undoing this new-game operation would change params";

@@ -1390,7 +1402,7 @@

     for (i = 0; i < menu->n_entries; i++) {

         if (menu->entries[i].params) {

             me->encoded_presets[menu->entries[i].id] =

-                me->ourgame->encode_params(menu->entries[i].params, true);

+	        encode_params(me, menu->entries[i].params, true);

         } else {

             preset_menu_encode_params(me, menu->entries[i].submenu);

         }

@@ -1469,7 +1481,7 @@

 int midend_which_preset(midend *me)

 {

-    char *encoding = me->ourgame->encode_params(me->params, true);

+    char *encoding = encode_params(me, me->params, true);

     int i, ret;

     ret = -1;

@@ -1576,7 +1588,7 @@

          * the former is likely to persist across many code

          * changes).

          */

-        parstr = me->ourgame->encode_params(me->curparams, which == CFG_SEED);

+        parstr = encode_params(me, me->curparams, which == CFG_SEED);

         assert(parstr);

         if (which == CFG_DESC) {

             rest = me->desc ? me->desc : "";

@@ -1720,7 +1732,7 @@

             newparams = me->ourgame->dup_params(me->params);

-            tmpstr = me->ourgame->encode_params(newcurparams, false);

+            tmpstr = encode_params(me, newcurparams, false);

             me->ourgame->decode_params(newparams, tmpstr);

             sfree(tmpstr);

@@ -1792,7 +1804,7 @@

 {

     char *parstr, *ret;

-    parstr = me->ourgame->encode_params(me->curparams, false);

+    parstr = encode_params(me, me->curparams, false);

     assert(parstr);

     assert(me->desc);

     ret = snewn(strlen(parstr) + strlen(me->desc) + 2, char);

@@ -1808,7 +1820,7 @@

     if (!me->seedstr)

         return NULL;

-    parstr = me->ourgame->encode_params(me->curparams, true);

+    parstr = encode_params(me, me->curparams, true);

     assert(parstr);

     ret = snewn(strlen(parstr) + strlen(me->seedstr) + 2, char);

     sprintf(ret, "%s#%s", parstr, me->seedstr);

@@ -2017,7 +2029,7 @@

      * The current long-term parameters structure, in full.

      */

     if (me->params) {

-        char *s = me->ourgame->encode_params(me->params, true);

+        char *s = encode_params(me, me->params, true);

         wr("PARAMS", s);

         sfree(s);

     }

@@ -2026,7 +2038,7 @@

      * The current short-term parameters structure, in full.

      */

     if (me->curparams) {

-        char *s = me->ourgame->encode_params(me->curparams, true);

+        char *s = encode_params(me, me->curparams, true);

         wr("CPARAMS", s);

         sfree(s);

     }