## Digests

Digests — Content digests.

## Synopsis

    typedef             librdf_digest;
    typedef             librdf_digest_factory;
    librdf_digest *     librdf_new_digest                   (librdf_world *world,
                                                             const char *name);
    void                librdf_free_digest                  (librdf_digest *digest);
    void                librdf_digest_init                  (librdf_digest *digest);
    void                librdf_digest_update                (librdf_digest *digest,
                                                             const unsigned char *buf,
                                                             size_t length);
    void                librdf_digest_update_string         (librdf_digest *digest,
                                                             const unsigned char *string);
    void                librdf_digest_final                 (librdf_digest *digest);
    void *              librdf_digest_get_digest            (librdf_digest *digest);
    size_t              librdf_digest_get_digest_length     (librdf_digest *digest);
    char *              librdf_digest_to_string             (librdf_digest *digest);
    void                librdf_digest_print                 (librdf_digest *digest,
                                                             FILE *fh);

## Description

Create a message digest over a block of data. Includes implementations of MD5, RMD160 and SHA1.

## Details

### librdf_digest

    typedef struct librdf_digest_s librdf_digest;

Redland content digest class.

### librdf_digest_factory

    typedef struct librdf_digest_factory_s librdf_digest_factory;

Redland digest factory class.

### librdf_new_digest ()

    librdf_digest *     librdf_new_digest                   (librdf_world *world,
                                                             const char *name);

Constructor - create a new librdf_digest object.

After construction, data should be added to the digest using librdf_digest_update or librdf_digest_update_string with librdf_digest_final to signify finishing. Then the digest value can be returned directly with librdf_digest_get_digest of librdf_digest_get_digest_length bytes or as a hex encoded string with librdf_digest_to_string. The digest can be re-initialised for new data with librdf_digest_init.

`world` : | redland world object
`name` : | the digest name to use to create this digest
Returns : | new librdf_digest object or NULL

### librdf_free_digest ()

    void                librdf_free_digest                  (librdf_digest *digest);

Destructor - destroy a librdf_digest object.

`digest` : | the digest

### librdf_digest_init ()

    void                librdf_digest_init                  (librdf_digest *digest);

(Re)initialise the librdf_digest object.

This is automatically called on construction but can be used to re-initialise the digest to the initial state for digesting new data.

`digest` : | the digest

### librdf_digest_update ()

    void                librdf_digest_update                (librdf_digest *digest,
                                                             const unsigned char *buf,
                                                             size_t length);

Add more data to the librdf_digest object.

`digest` : | the digest
`buf` : | the data buffer
`length` : | the length of the data

### librdf_digest_update_string ()

    void                librdf_digest_update_string         (librdf_digest *digest,
                                                             const unsigned char *string);

Add a string to the librdf_digest object.

`digest` : | the digest
`string` : | string to add

### librdf_digest_final ()

    void                librdf_digest_final                 (librdf_digest *digest);

Finish the digesting of data.

The digest can now be returned via `librdf_digest_get_digest()`.

`digest` : | the digest

### librdf_digest_get_digest ()

    void *              librdf_digest_get_digest            (librdf_digest *digest);

Get the calculated digested value.

`digest` : | the digest
Returns : | pointer to the memory containing the digest. It will be librdf_digest_get_digest_length bytes in length.

### librdf_digest_get_digest_length ()

    size_t              librdf_digest_get_digest_length     (librdf_digest *digest);

Get length of the calculated digested.

`digest` : | the digest
Returns : | size of the digest in bytes

### librdf_digest_to_string ()

    char *              librdf_digest_to_string             (librdf_digest *digest);

Get a string representation of the digest object.

`digest` : | the digest
Returns : | a newly allocated string that represents the digest. This must be released by the caller using `librdf_free_memory()`.

### librdf_digest_print ()

    void                librdf_digest_print                 (librdf_digest *digest,
                                                             FILE *fh);

Print the digest to a FILE handle.

`digest` : | the digest
`fh` : | file handle