GUID
[Class: Getting and setting entity values.]

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Detailed Description

Globally Unique ID's provide a way to uniquely identify some thing. A GUID is a unique, cryptographically random 128-bit value. The identifier is so random that it is safe to assume that there is no other such item on the planet Earth, and indeed, not even in the Galaxy or beyond.

QOF GUID's can be used independently of any other subsystem in QOF. In particular, they do not require the use of other parts of the object subsystem. New GUID's are usually created by initialising a new entity using qof_instance_init, rather than calling GUID functions directly.

Files
file	guid.h
	globally unique ID User API
Data Structures
union	_GUID
Defines
#define	GUID_DATA_SIZE   16
#define	GUID_ENCODING_LENGTH   32
Typedefs
typedef union _GUID	GUID
Functions
void	guid_init (void)
void	guid_init_with_salt (const void *salt, size_t salt_len)
void	guid_init_only_salt (const void *salt, size_t salt_len)
void	guid_shutdown (void)
void	guid_new (GUID *guid)
GUID	guid_new_return (void)
const GUID *	guid_null (void)
GUID *	guid_malloc (void)
void	guid_free (GUID *guid)
const gchar *	guid_to_string (const GUID *guid)
gchar *	guid_to_string_buff (const GUID *guid, gchar *buff)
gboolean	string_to_guid (const gchar *string, GUID *guid)
gboolean	guid_equal (const GUID *guid_1, const GUID *guid_2)
gint	guid_compare (const GUID *g1, const GUID *g2)
guint	guid_hash_to_guint (gconstpointer ptr)
GHashTable *	guid_hash_table_new (void)

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Define Documentation

#define GUID_DATA_SIZE   16

The type used to store guids

Definition at line 52 of file guid.h.

#define GUID_ENCODING_LENGTH   32

number of characters needed to encode a guid as a string not including the null terminator.

Definition at line 64 of file guid.h.

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Function Documentation

gboolean guid_equal	(	const GUID *	guid_1,
		const GUID *	guid_2
	)

Given two GUIDs, return TRUE if they are non-NULL and equal. Return FALSE, otherwise.

Definition at line 652 of file guid.c.

{
    if (guid_1 && guid_2)
        return (memcmp (guid_1, guid_2, GUID_DATA_SIZE) == 0);
    else
        return FALSE;
}

guint guid_hash_to_guint

(

gconstpointer

ptr

)

Given a GUID *, hash it to a guint

Definition at line 677 of file guid.c.

{
    const GUID *guid = ptr;

    if (!guid)
    {
        PERR ("received NULL guid pointer.");
        return 0;
    }

    if (sizeof (guint) <= sizeof (guid->data))
    {
        return (*((guint *) guid->data));
    }
    else
    {
        guint hash = 0;
        unsigned int i, j;

        for (i = 0, j = 0; i < sizeof (guint); i++, j++)
        {
            if (j == GUID_DATA_SIZE)
                j = 0;

            hash <<= 4;
            hash |= guid->data[j];
        }

        return hash;
    }
}

void guid_init

(

void

)

Initialize the id generator with a variety of random sources.

Note:

Only one of guid_init(), guid_init_with_salt() and guid_init_only_salt() should be called. Calling any initialization function a second time will reset the generator and erase the effect of the first call.

Definition at line 325 of file guid.c.

{
    size_t bytes = 0;

    /* Not needed; taken care of on first malloc.
     * guid_memchunk_init(); */

    md5_init_ctx (&guid_context);

    /* entropy pool */
    bytes += init_from_file ("/dev/urandom", 512);

    /* files */
    {
        const char *files[] = { "/etc/passwd",
            "/proc/loadavg",
            "/proc/meminfo",
            "/proc/net/dev",
            "/proc/rtc",
            "/proc/self/environ",
            "/proc/self/stat",
            "/proc/stat",
            "/proc/uptime",
            NULL
        };
        int i;

        for (i = 0; files[i] != NULL; i++)
            bytes += init_from_file (files[i], BLOCKSIZE);
    }

    /* directories */
    {
        const char *dirname;
        const char *dirs[] = {
            "/proc",
            P_tmpdir,
            "/var/lock",
            "/var/log",
            "/var/mail",
            "/var/spool/mail",
            "/var/run",
            NULL
        };
        int i;

        for (i = 0; dirs[i] != NULL; i++)
            bytes += init_from_dir (dirs[i], 32);

        dirname = g_get_home_dir ();
        if (dirname != NULL)
            bytes += init_from_dir (dirname, 32);
    }

    /* process and parent ids */
    {
        pid_t pid;

        pid = getpid ();
        md5_process_bytes (&pid, sizeof (pid), &guid_context);
        bytes += sizeof (pid);

#ifdef HAVE_GETPPID
        pid = getppid ();
        md5_process_bytes (&pid, sizeof (pid), &guid_context);
        bytes += sizeof (pid);
#endif
    }

    /* user info */
    {
#ifdef HAVE_GETUID
        uid_t uid;
        gid_t gid;
        char *s;

        s = getlogin ();
        if (s != NULL)
        {
            md5_process_bytes (s, strlen (s), &guid_context);
            bytes += strlen (s);
        }

        uid = getuid ();
        md5_process_bytes (&uid, sizeof (uid), &guid_context);
        bytes += sizeof (uid);

        gid = getgid ();
        md5_process_bytes (&gid, sizeof (gid), &guid_context);
        bytes += sizeof (gid);
#endif
    }

    /* host info */
    {
#ifdef HAVE_GETHOSTNAME
        char string[1024];

        memset (string, 0, sizeof (string));
        gethostname (string, sizeof (string));
        md5_process_bytes (string, sizeof (string), &guid_context);
        bytes += sizeof (string);
#endif
    }

    /* plain old random */
    {
        int n, i;

        srand ((unsigned int) time (NULL));

        for (i = 0; i < 32; i++)
        {
            n = rand ();

            md5_process_bytes (&n, sizeof (n), &guid_context);
            bytes += sizeof (n);
        }
    }

    /* time in secs and clock ticks */
    bytes += init_from_time ();

    PINFO ("got %llu bytes", (unsigned long long int) bytes);

    if (bytes < THRESHOLD)
        PWARN ("only got %llu bytes.\n"
            "The identifiers might not be very random.\n",
            (unsigned long long int) bytes);

    guid_initialized = TRUE;
}

void guid_init_only_salt	(	const void *	salt,
		size_t	salt_len
	)

Initialize the id generator with the data given in the salt argument, but not with any other source. Calling this function with a specific argument will reliably produce a specific sequence of ids.

Parameters:

	salt	The additional random values to add to the generator.
	salt_len	The length of the additional random values.

Note:

Only one of guid_init(), guid_init_with_salt() and guid_init_only_salt() should be called. Calling any initialization function a second time will reset the generator and erase the effect of the first call.

Definition at line 467 of file guid.c.

{
    md5_init_ctx (&guid_context);

    md5_process_bytes (salt, salt_len, &guid_context);

    guid_initialized = TRUE;
}

void guid_init_with_salt	(	const void *	salt,
		size_t	salt_len
	)

Initialize the id generator with a variety of random sources. and with the data given in the salt argument. This argument can be used to add additional randomness to the generated ids.

Parameters:

	salt	The additional random values to add to the generator.
	salt_len	The length of the additional random values.

Note:

Only one of guid_init(), guid_init_with_salt() and guid_init_only_salt() should be called. Calling any initialization function a second time will reset the generator and erase the effect of the first call.

Definition at line 459 of file guid.c.

{
    guid_init ();

    md5_process_bytes (salt, salt_len, &guid_context);
}

GUID* guid_malloc

(

void

)

Efficiently allocate & free memory for GUIDs

Definition at line 100 of file guid.c.

{
    if (!guid_memchunk)
        guid_memchunk_init ();
    return g_chunk_new (GUID, guid_memchunk);
}

void guid_new

(

GUID *

guid

)

Generate a new id. If no initialization function has been called, guid_init() will be called before the id is created.

Parameters:

guid

A pointer to an existing guid data structure. The existing value will be replaced with a new value.

This routine uses the md5 algorithm to build strong random guids. Note that while guid's are generated randomly, the odds of this routine returning a non-unique id are astronomically small. (Literally astronomically: If you had Cray's on every solar system in the universe running for the entire age of the universe, you'd still have less than a one-in-a-million chance of coming up with a duplicate id. 2^128 == 10^38 is a really really big number.)

Definition at line 487 of file guid.c.

{
    static int counter = 0;
    struct md5_ctx ctx;

    if (guid == NULL)
        return;

    if (!guid_initialized)
        guid_init ();

    /* make the id */
    ctx = guid_context;
    md5_finish_ctx (&ctx, guid->data);

    /* update the global context */
    init_from_time ();

    /* Make it a little extra salty.  I think init_from_time was buggy,
     * or something, since duplicate id's actually happened. Or something
     * like that.  I think this is because init_from_time kept returning
     * the same values too many times in a row.  So we'll do some 'block
     * chaining', and feed in the old guid as new random data.
     *
     * Anyway, I think the whole fact that I saw a bunch of duplicate 
     * id's at one point, but can't reproduce the bug is rather alarming.
     * Something must be broken somewhere, and merely adding more salt
     * is just hiding the problem, not fixing it.
     */
    init_from_int (433781 * counter);
    init_from_buff (guid->data, GUID_DATA_SIZE);

    if (counter == 0)
    {
        FILE *fp;

        fp = fopen ("/dev/urandom", "r");
        if (fp == NULL)
            return;

        init_from_stream (fp, 32);

        fclose (fp);

        counter = GUID_PERIOD;
    }

    counter--;
}

GUID guid_new_return

(

void

)

Generate a new id. If no initialization function has been called, guid_init() will be called before the id is created.

Returns:

guid A data structure containing a newly allocated GUID. Caller is responsible for calling guid_free().

Definition at line 538 of file guid.c.

{
    GUID guid;

    guid_new (&guid);

    return guid;
}

const GUID* guid_null

(

void

)

Returns a GUID which is guaranteed to never reference any entity.

Definition at line 119 of file guid.c.

{
    static int null_inited = 0;
    static GUID null_guid;

    if (!null_inited)
    {
        int i;
        char *tmp = "NULLGUID.EMPTY.";

        /* 16th space for '\O' */
        for (i = 0; i < GUID_DATA_SIZE; i++)
            null_guid.data[i] = tmp[i];

        null_inited = 1;
    }

    return &null_guid;
}

void guid_shutdown

(

void

)

Release the memory chunk associated with gui storage. Use this only when shutting down the program, as it invalidates *all* GUIDs at once.

Definition at line 477 of file guid.c.

{
#ifndef HAVE_GLIB29
    guid_memchunk_shutdown ();
#endif
}

const gchar* guid_to_string

(

const GUID *

guid

)

The guid_to_string() routine returns a null-terminated string encoding of the id. String encodings of identifiers are hex numbers printed only with the characters '0' through '9' and 'a' through 'f'. The encoding will always be GUID_ENCODING_LENGTH characters long.

XXX This routine is not thread safe and is deprecated. Please use the routine guid_to_string_buff() instead.

Parameters:

guid

The guid to print.

Returns:

A pointer to the starting character of the string. The returned memory is owned by this routine and may not be freed by the caller.

Definition at line 611 of file guid.c.

{
#ifdef G_THREADS_ENABLED
    static GStaticPrivate guid_buffer_key = G_STATIC_PRIVATE_INIT;
    gchar *string;

    string = g_static_private_get (&guid_buffer_key);
    if (string == NULL)
    {
        string = malloc (GUID_ENCODING_LENGTH + 1);
        g_static_private_set (&guid_buffer_key, string, g_free);
    }
#else
    static char string[64];
#endif

    encode_md5_data (guid->data, string);
    string[GUID_ENCODING_LENGTH] = '\0';

    return string;
}

gchar* guid_to_string_buff	(	const GUID *	guid,
		gchar *	buff
	)

The guid_to_string_buff() routine puts a null-terminated string encoding of the id into the memory pointed at by buff. The buffer must be at least GUID_ENCODING_LENGTH+1 characters long. This routine is handy for avoiding a malloc/free cycle. It returns a pointer to the >>end<< of what was written. (i.e. it can be used like 'stpcpy' during string concatenation)

Parameters:

	guid	The guid to print.
	buff	The buffer to print it into.

Returns:

A pointer to the terminating null character of the string.

gboolean string_to_guid	(	const gchar *	string,
		GUID *	guid
	)

Given a string, decode the id into the guid if guid is non-NULL. The function returns TRUE if the string was a valid 32 character hexadecimal number. This function accepts both upper and lower case hex digits. If the return value is FALSE, the effect on guid is undefined.

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