"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;

And this is the method

#define BIO_TYPE_COMP  (12|0x0200)  /* filter */

static BIO_METHOD methods_z=
 zbio_write, /* this is gzwrite() */
 zbio_read,  /*gzread() */
 zbio_ctrl, /* ctrl could set the compress level */

This is how I've called my bio:

BIO_METHOD *BIO_f_comp(void)

I use this BIO at the botton of a B64 bio and a encryption BIO, without
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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