zdigest(3)
==========

NAME
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zdigest - provides hashing functions (SHA-1 at present)

SYNOPSIS
--------
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//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
//  Constructor - creates new digest object, which you use to build up a
//  digest by repeatedly calling zdigest_update() on chunks of data.    
CZMQ_EXPORT zdigest_t *
    zdigest_new (void);

//  Destroy a digest object
CZMQ_EXPORT void
    zdigest_destroy (zdigest_t **self_p);

//  Add buffer into digest calculation
CZMQ_EXPORT void
    zdigest_update (zdigest_t *self, const byte *buffer, size_t length);

//  Return final digest hash data. If built without crypto support,
//  returns NULL.                                                  
CZMQ_EXPORT const byte *
    zdigest_data (zdigest_t *self);

//  Return final digest hash size
CZMQ_EXPORT size_t
    zdigest_size (zdigest_t *self);

//  Return digest as printable hex string; caller should not modify nor   
//  free this string. After calling this, you may not use zdigest_update()
//  on the same digest. If built without crypto support, returns NULL.    
CZMQ_EXPORT char *
    zdigest_string (zdigest_t *self);

//  Self test of this class.
CZMQ_EXPORT void
    zdigest_test (bool verbose);

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DESCRIPTION
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The zdigest class generates a hash from zchunks of data. The current
algorithm is SHA-1, chosen for speed. We are aiming to generate a
unique digest for a file, and there are no security issues in this
use case.

The current code depends on OpenSSL, which might be replaced by hard
coded SHA-1 implementation to reduce build dependencies.

EXAMPLE
-------
.From zdigest_test method
----
byte *buffer = (byte *) zmalloc (1024);
memset (buffer, 0xAA, 1024);

zdigest_t *digest = zdigest_new ();
assert (digest);
zdigest_update (digest, buffer, 1024);
const byte *data = zdigest_data (digest);
assert (data [0] == 0xDE);
assert (data [1] == 0xB2);
assert (data [2] == 0x38);
assert (data [3] == 0x07);
assert (streq (zdigest_string (digest),
               "DEB23807D4FE025E900FE9A9C7D8410C3DDE9671"));
zdigest_destroy (&digest);
free (buffer);
----
