visio: Handle '\0' and '\xFF'.

- maple/visio.c:
   - `ochar()`: Handle `'\xFF'` by sending `IAC` `IAC` instead.
   - `iac_count()`: Add comments about `IAC` `IAC` represents `'\xFF'`.
- maple/bbslua.c: `bl_k2s()`: Handle `'\0'`.
- maple/pfterm.c:
   - Add configuration macro `PFTERM_SUPPORT_IAC`
   - macro `FTDBCS_ISBADLEAD()`: Accept `'\xFF'` if `PFTERM_SUPPORT_IAC` is defined
   - `outc()`: Do not ignore `'\xFF'` if `PFTERM_SUPPORT_IAC` is defined.

maple/bbslua.c

@@ -1041,7 +1041,7 @@ bl_k2s(lua_State* L, int v)
 #endif
 
 #if IS_NORMAL_KEY(-1)  /* Negative key values are ignored */
-    if (v <= 0)
+    if (v < 0)
         lua_pushnil(L);
     else
 #endif

maple/pfterm.c

@@ -35,6 +35,7 @@
  #define USE_PFTERM
  #undef PFTERM_HAVE_VKEY
  #define PFTERM_EXPOSED_VISIO_VI
+ #define PFTERM_SUPPORT_IAC   /* `ochar()` handles `'\xFF'` correctly */
 #endif //M3_USE_PFTERM
 
 #ifndef PFTERM_HAVE_VKEY
@@ -374,9 +375,13 @@ static FlatTerm ft;
 #define FTDBCS_ISLEAD(x) (((unsigned char)(x))>=(0x80))
 #define FTDBCS_ISTAIL(x) (((unsigned char)(x))>=(0x40))
 
-//  - 0xFF is used as telnet IAC, don't use it!
+#ifdef PFTERM_SUPPORT_IAC
 //  - 0x80 is invalid for Big5.
+#define FTDBCS_ISBADLEAD(x) (((unsigned char)(x)) == 0x80)
+#else
+//  - 0xFF is used as telnet IAC, don't use it!
 #define FTDBCS_ISBADLEAD(x) ((((unsigned char)(x)) == 0x80) || (((unsigned char)(x)) == 0xFF))
+#endif
 
 // even faster:
 // #define FTDBCS_ISLEAD(x) (((unsigned char)(x)) & 0x80)
@@ -1327,8 +1332,12 @@ outstr(const char *str)
 void
 outc(unsigned char c)
 {
+#ifndef PFTERM_SUPPORT_IAC
     // 0xFF is invalid for most cases (even DBCS),
-    if (c == 0xFF || c == 0x00)
+    if (c == 0xFF)
+        return;
+#endif
+    if (c == 0x00)
         return;
 
     fterm_markdirty();

maple/visio.c

@@ -91,7 +91,7 @@ output(
 
     size = vo_size;
     data = vo_pool;
-    if (size + len > VO_MAX - 8)
+    if (size + len >= VO_MAX - 8)
     {
         telnet_flush(data, size);
         size = len;
@@ -129,12 +129,16 @@ ochar(
 
     data = vo_pool;
     size = vo_size;
-    if (size > VO_MAX - 2)
+    if (size >= VO_MAX - 2)
     {
         telnet_flush(data, size);
         size = 0;
     }
     data[size++] = ch;
+    if (ch == IAC)  /* `'\xff'` => `IAC` `IAC` */
+    {
+        data[size++] = ch;
+    }
     vo_size = size;
 }
 
@@ -1586,6 +1590,8 @@ iac_count(
                 }
             }
         }
+    case IAC:  /* `IAC` `IAC` => `'\xff'` */
+    default:;
     }
     return 1;
 }