Re: LZO decompression utility method on Windows using ctypes for dummies

> From: Kim Hansen <[email protected]>

 
> There is also a header file lzo1x.h, which contains the call signature
for
> the lzo decompress function I should bind to:
> 
> /* safe decompression with overrun testing */
> LZO_EXTERN(int)
> lzo1x_decompress_safe   ( const lzo_byte *src, lzo_uint  src_len,
>                                 lzo_byte *dst, lzo_uintp dst_len,
>                                 lzo_voidp wrkmem /* NOT USED */ );


1) You'll have to look at the documentation for that API if you haven't
already. Often functions like this require some steps to be taken first,
and possibly after the real work is done. So for instance you might need
functions to initialize and finalize a lzo context. Not that you do, just
look into that.

2) "lzo_byte", etc are not real variable types in C. Those are "typedefs"
which frustratingly conceal the real types to those reading the function
declaration above. So you will need to find out what the real types are for
ctypes. This usually can be found in the same header. It is very likely
that they are:

lzo_byte : unsigned char
lzo_uint : unsigned int
lzo_uintp : unsigned int *
lzo_voidp : void *



>     in_len = len - 5;
>     out_len = (in[1] << 24) | (in[2] << 16) | (in[3] << 8) | in[4];
>     if ((int)out_len < 0 || in_len > out_len + out_len / 64 + 16 + 3)
>         goto header_error;
> 

Here they appear to be looking at the compressed input directly, using an
understanding of the file format, to figure out how big the decompressed
version will be so that the required space can be first allocated. Surely
there is a better way than that. Once that is done, an appropriately sized
buffer can be allocated from within ctypes via create_string_buffer().





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