Use uint32_t to index into xls string table; fixes #129

[jennybc]

libxls clearly anticipates that the string table size might require an unsigned 32 bit integer, e.g.:

readxl/src/libxls/xlsstruct.h

Lines 240 to 246 in 0587f00

	typedef struct SST
	{
	DWORD num;
	DWORD numofstr;
	BYTE strings;
	}
	SST;

readxl/src/libxls/xlsstruct.h

Lines 398 to 412 in 0587f00

	typedef struct st_sst
	{
	DWORD count;
	DWORD lastid;
	DWORD continued;
	DWORD lastln;
	DWORD lastrt;
	DWORD lastsz;
	struct str_sst_string
	{
	BYTE* str;
	}
	* string;
	}
	st_sst;

readxl/src/xls.c

Line 137 in 0587f00

void xls_addSST(xlsWorkBook* pWB,SST* sst,DWORD size)

readxl/src/xls.c

Line 152 in 0587f00

void xls_appendSST(xlsWorkBook* pWB,BYTE* buf,DWORD size)

(all these types are defined here)

But then it was indexing into the table with a 16 bit integer and therefore vulnerable to getting the wrong strings. It takes a large sheet to expose this, i.e. more than 65535 unique strings. Which is the case with the xls from #129.

Two questions:

• Should I add a test for this? It would require a very large xls, plus it doesn't really seem like something readxl should be responsible for.
• Should I try to push this change back into libxls? It's not trivial for me, because it's on sourceforge and uses svn, whereas I've only done this with Git/GitHub. Yet it's a tiny change and seems like a no-brainer.

[hadley]

I have no idea how you figured this out — impressive!

I don't think you need to worry about a test or pushing back to libxls. You could file an issue, pointing to this fix.

[jennybc]

I have no idea how you figured this out

Let's just say the cumulative edit of 6 characters does not reflect the cumulative effort 😅.

[jimhester]

FWIW I think you should absolutely send a patch upstream for future changes. To do so

1. svn checkout https://svn.code.sf.net/p/libxls/code/trunk libxls-code
2. Make your changes locally
3. Use svn diff > my.patch to create a patch, which you can send to them.

There is also a github mirror (https://github.com/svn2github/libxls) you can use, just make your changes and git diff > my.patch although you will have to edit the patch to apply cleanly with svn.

[jennybc]

Thanks @jimhester. This particular change has already been incorporated based just on a sourceforge exchange.

https://sourceforge.net/p/libxls/bugs/28/
https://sourceforge.net/p/libxls/code/175/

But I will do it properly in future.