Re: Why does LoadString return NULL for zero-length strings?

[Luiz Henrique de Figueiredo <lhf@...>]

The attached patch fixes this glitch:

> assert(loadstring(('').dump(function()X''end):gsub('\2%z%z%zX','\0\0\0')))()
stdin:1: 1: bad string in precompiled chunk

Thanks for spotting it.
--lhf

--- lundump.c,orig	2008-04-04 16:51:41.000000000 -0300
+++ lundump.c	2008-09-02 08:10:19.000000000 -0300
@@ -73,12 +73,15 @@
  return x;
 }
 
-static TString* LoadString(LoadState* S)
+static TString* LoadString(LoadState* S, TString* p)
 {
  size_t size;
  LoadVar(S,size);
  if (size==0)
-  return NULL;
+ {
+  IF (p==NULL, "bad string");
+  return p;
+ }
  else
  {
   char* s=luaZ_openspace(S->L,S->b,size);
@@ -120,7 +123,7 @@
 	setnvalue(o,LoadNumber(S));
 	break;
    case LUA_TSTRING:
-	setsvalue2n(S->L,o,LoadString(S));
+	setsvalue2n(S->L,o,LoadString(S,NULL));
 	break;
    default:
 	error(S,"bad constant");
@@ -147,7 +150,7 @@
  for (i=0; i<n; i++) f->locvars[i].varname=NULL;
  for (i=0; i<n; i++)
  {
-  f->locvars[i].varname=LoadString(S);
+  f->locvars[i].varname=LoadString(S,NULL);
   f->locvars[i].startpc=LoadInt(S);
   f->locvars[i].endpc=LoadInt(S);
  }
@@ -155,7 +158,7 @@
  f->upvalues=luaM_newvector(S->L,n,TString*);
  f->sizeupvalues=n;
  for (i=0; i<n; i++) f->upvalues[i]=NULL;
- for (i=0; i<n; i++) f->upvalues[i]=LoadString(S);
+ for (i=0; i<n; i++) f->upvalues[i]=LoadString(S,NULL);
 }
 
 static Proto* LoadFunction(LoadState* S, TString* p)
@@ -164,7 +167,7 @@
  if (++S->L->nCcalls > LUAI_MAXCCALLS) error(S,"code too deep");
  f=luaF_newproto(S->L);
  setptvalue2s(S->L,S->L->top,f); incr_top(S->L);
- f->source=LoadString(S); if (f->source==NULL) f->source=p;
+ f->source=LoadString(S,p);
  f->linedefined=LoadInt(S);
  f->lastlinedefined=LoadInt(S);
  f->nups=LoadByte(S);