Re: BIO Filter for compression

[root]

"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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Re: BIO Filter for compression

[Edson E. Watanabe]

Great! Thanks for your help.
Edson E. Watanabe
7COMm
Sao Paulo
Brazil

- Original Message -
From: "root" [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Sunday, July 09, 2000 4:26 PM
Subject: Re: BIO Filter for compression




 "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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