"Edson E. Watanabe" wrote:
> Did someone write a BIO filter for gzip/zlib compression/decompression?
> Is it easy to write?
> I think I could use crypto/evp/bio_b64.c as a starting point (writing a
> BIO_f_gzip filter for compressing and a BIO_f_gunzip for expanding), but I
> want to know if are there any pitfalls in implementing or installing new
> BIOs.
Yes,its very easy. I wrote one "ZBIO" from gzio.c code in GNU ZLIB for my
secure transfer of file server.You have to create a new BIO method and a
function to return a pointer to that method when its requested.Then you have
to fill its pointer to function members with the gzread/gzwrite code in ZLIB.
In fact, its just an exercise because there are few things to add/modify.
This is the new method context: (name of variables could be re-written like
in cipher bio or b64 bio...)
typedef struct z_struct
{
z_stream stream; /* This is original ZLIB context */
char mode;
int z_err;
int z_eof;
uLong crc;
int transparent;
int first;
int level;
char *buf;
} BIO_COMP_CTX;
And this is the method
#define BIO_TYPE_COMP (12|0x0200) /* filter */
static BIO_METHOD methods_z=
{
BIO_TYPE_COMP,"comp",
zbio_write, /* this is gzwrite() */
zbio_read, /*gzread() */
NULL,
NULL,
zbio_ctrl, /* ctrl could set the compress level */
zbio_new,
zbio_free,
};
This is how I've called my bio:
BIO_METHOD *BIO_f_comp(void)
{
return(&methods_z);
}
I use this BIO at the botton of a B64 bio and a encryption BIO, without
problems...
I use the same BIO for compress and uncompress: if I call BIO_read it
uncompresses and if I call BIO_wrie it compresses.
Hope this helps
Pablo J. Royo
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