Since base64 regroups the original 8-bits based binary into groups of 6 bits
for encoding, using padding as needed. So each original 8 bits is shared by two
6 bits, it is like a chain. To make your code work, you have to find out the
exact point, where a 8 bit is not shared. For example, change your buffer size
to "480", since 480 can be divided by both 8 and 6.
Good luck!
________________________________________
From: owner-openssl-us...@openssl.org [owner-openssl-us...@openssl.org] On
Behalf Of Frank B. Brokken [f.b.brok...@rug.nl]
Sent: Tuesday, December 30, 2008 3:11 AM
To: openssl-users@openssl.org
Subject: base64 decoding using an s_mem chain
Hi List-members,
The following problem has (in some form) popped up on this list repeatedly,
but after having browsed the archives until the beginning of this century I
didn't encounter (or simply missed?) a solution for my current problem, hence
the posting.
For some time now I'm trying to decode a base64 encoded file which is filtered
through a BIO_s_mem method. My intention is to write a function in which the
actual decoding is decoupled from the source of the encoded information as
well as from the destination of the decoded info, and so I thought of using a
BIO_s_mem method as an intermediate storage medium chained to a BIO_f_base64
method: obtain info the the source, put it into s_mem, base64 decode it, write
the decoded info to the destination.
As an initial attempt the following program does the trick, but a problem
occurs when I uncomment the section marked `Doesn't work'. In that case only
the first block of bytes that's read is decoded after which BIO_read
consistently returns 0.
The program as-is properly decodes base64 encoded information but requires me
to read all the encoded information into the s_mem buffer first, which is
unacceptable as it would require me to have all information available in
memory before base64 can start decoding.
So my questions are: What's the flaw in my reasoning (c.q. program)? And: what
must be done to decode information in a series of read-decode cycles rather
than using a `read-all, decode-all' procedure?
Here's the little program I used:
--------------------------------------------------------------------------
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <stdio.h>
int main()
{
BIO *bio, *b64;
char inbuf[500];
int inlen;
b64 = BIO_new(BIO_f_base64()); // define BIOs
BIO *mem = BIO_new(BIO_s_mem());
bio = BIO_push(b64, mem); // set up the chain
BIO_set_mem_eof_return(mem, 0); // define s_mem eof
// read info from some source
while ((inlen = fread(inbuf, 1, 500, stdin)) != 0)
{
BIO_write(mem, inbuf, inlen); // put it in the s_mem buffer
BIO_flush(mem);
// Doesn't work:
// while (1)
// { // read what's already available
// inlen = BIO_read(bio, inbuf, inlen);
// if (inlen <= 0) // no more, then done
// break;
// // write decoded info to a dest.
// fwrite(inbuf, 1, inlen, stdout);
// }
}
// same procedure, but now write to the destination after first
// reading all info into s_mem
while (1)
{
inlen = BIO_read(bio, inbuf, 200);
if (inlen <= 0)
break;
fwrite(inbuf, 1, inlen, stdout);
}
BIO_free_all(bio);
}
--------------------------------------------------------------------------
Any suggestion I receive will of course greatly be appreciated.
Cheers,
--
Frank B. Brokken
Center for Information Technology, University of Groningen
(+31) 50 363 9281
Public PGP key: http://pgp.surfnet.nl
Key Fingerprint: 8E36 9FC4 1DAA FCDF 1A0D B19F DAC4 BE50 38C6 6170
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______________________________________________________________________
OpenSSL Project http://www.openssl.org
User Support Mailing List openssl-users@openssl.org
Automated List Manager majord...@openssl.org
