# Pack

## Name

Pack -- Byte packing and unpacking functions

## Synopsis

    gint        gnet_pack                       (const gchar *format,
                                                 gchar *buffer,
                                                 const gint length,
                                                 ...);
    gint        gnet_pack_strdup                (const gchar *format,
                                                 gchar **bufferp,
                                                 ...);
    gint        gnet_vpack                      (const gchar *format,
                                                 gchar *buffer,
                                                 const gint length,
                                                 va_list args);
    gint        gnet_calcsize                   (const gchar *format,
                                                 ...);
    gint        gnet_vcalcsize                  (const gchar *format,
                                                 va_list args);
    gint        gnet_unpack                     (const gchar *format,
                                                 gchar *buffer,
                                                 gint length,
                                                 ...);
    gint        gnet_vunpack                    (const gchar *format,
                                                 gchar *buffer,
                                                 gint length,
                                                 va_list args);

## Description

The pack module provides functions for converting data into bytes ("packing") and converting bytes to data ("unpacking"). For example, two integers and a string may be packed into a buffer to be transfered over the network. These functions are similar to the ones in Python and Perl.

## Details

### >gnet_pack ()

    gint        gnet_pack                       (const gchar *format,
                                                 gchar *buffer,
                                                 const gint length,
                                                 ...);

Writes Varargs to buffer. format is a string that describes the Varargs and how they are to be packed. This string is a list of characters, each describing the type of an argument in Varargs.

An example:

     char buf[5];
     int myint = 42;
     int mybyte = 23;

     gnet_pack("!ib", buf, sizeof(buf), myint, mybyte);
     /* Now buf is { 42, 0, 0, 0, 23 }; */

As a shortcut, most types can be prefixed by an integer to specify how many times the type is repeated. For example, "4i2b" is equivalent to "iiiibb". This repeat argument is refered below to as REPEAT.

Native byte order and sizes are used by default. If the first character of format is < then little endian order and standard sizes are used. If the first character is > or !, then big endian (or network) order and standard size are used. Standard sizes are 1 byte for chars, 2 bytes for shorts, and 4 bytes for ints and longs.

The types:

x is a NULL character. It can be used for padding. It does not correspond to an argument in Varargs.

b/B is a signed/unsigned char.

h/H is a signed/unsigned short.

i/I is a signed/unsigned int.

l/L is a signed/unsigned long.

f/D is a float/double (always native order/size). v is a void pointer (always native size).

s is a zero-terminated string.

S is a zero-padded string of maximum length REPEAT. We write up-to a NULL character or REPEAT characters, whichever comes first. We then write NULL characters up to a total of REPEAT characters. Special case: if REPEAT is not specified, we write the string as a non-NULL-terminated string (note that it can't be unpacked easily then).

r is a byte array of NEXT bytes. NEXT is the next argument passed to gnet_pack() and is a gint.

R is a byte array of REPEAT bytes. REPEAT must be specified.

p is a Pascal string. The string passed is a NULL-termiated string of less than 256 character. The string writen is a non-NULL-terminated string with a byte before the string storing the string length. REPEAT is repeat.

Mnemonics: (B)yte, s(H)ort, (I)nteger, (F)loat, (D)ouble, (V)oid pointer, (S)tring, (R)aw

Pack was inspired by Python's and Perl's pack. It is more like Python's than Perl's. Note that in GNet, a repeat of 0 does not align the data (as in Python).

format : | pack data format
buffer : | buffer to pack to
length : | length of buffer
... : | variables to pack from
Returns : | number of bytes packed; -1 on error.

### >gnet_pack_strdup ()

    gint        gnet_pack_strdup                (const gchar *format,
                                                 gchar **bufferp,
                                                 ...);

Writes Varargs into a buffer pointed to by bufferp. The buffer is allocated by the function and is caller owned. See gnet_pack() for more information.

format : | pack data format
bufferp : | pointer to a buffer (buffer is caller owned)
... : | variables to pack from
Returns : | bytes packed; -1 on error.

### >gnet_vpack ()

    gint        gnet_vpack                      (const gchar *format,
                                                 gchar *buffer,
                                                 const gint length,
                                                 va_list args);

Var arg interface to gnet_pack(). See gnet_pack() for more information.

format : | pack data format
buffer : | buffer to pack to
length : | length of buffer
args : | var args
Returns : | bytes packed; -1 on error.

### >gnet_calcsize ()

    gint        gnet_calcsize                   (const gchar *format,
                                                 ...);

Calculates the size of the buffer needed to pack Varargs by the given format. See gnet_pack() for more information.

format : | pack data format
... : | variables
Returns : | number of bytes required to pack; -1 on error.

### >gnet_vcalcsize ()

    gint        gnet_vcalcsize                  (const gchar *format,
                                                 va_list args);

Var arg interface to gnet_calcsize(). See gnet_calcsize() for additional information.

format : | pack data format
args : | var args
Returns : | number of bytes required to pack; -1 on error.

### >gnet_unpack ()

    gint        gnet_unpack                     (const gchar *format,
                                                 gchar *buffer,
                                                 gint length,
                                                 ...);

Reads the data in buffer into Varargs. format is a string that describes the Varargs and how they are to be packed. This string is a list of characters, each describing the type of an argument in Varargs.

An example:

     char buf[5] = { 42, 0, 0, 0, 23 };
     int myint;
     int mybyte;

     gnet_unpack("!ib", buf, sizeof(buf), &myint, &mybyte);
     /* Now myint is 42 and mybyte is 23 */

In unpack, the arguments must be pointers to the appropriate type. Strings and byte arrays are allocated dynamicly (by g_new()). The caller is responsible for g_free()-ing it.

As a shortcut, most types can be prefixed by an integer to specify how many times the type is repeated. For example, "4i2b" is equivalent to "iiiibb". This repeat argument is refered below to as REPEAT.

The types:

x is a pad byte. The byte is skipped and not stored. We do not check its value.

b/B is a signed/unsigned char.

h/H is a signed/unsigned short.

i/I is a signed/unsigned int.

l/L is a signed/unsigned long.

f/D is a float/double (always native order/size). v is a void pointer (always native size).

s is a zero-terminated string.

S is a zero-padded string of length REPEAT. We read REPEAT characters or until a NULL character. Any remaining characters are filled in with 0's. REPEAT must be specified.

r is a byte array of NEXT bytes. NEXT is the next argument and is a gint. REPEAT is repeat.

R is a byte array of REPEAT bytes. REPEAT must be specified.

p is a Pascal string. The first byte read is the length of the string and the string follows. The unpacked string will be a normal, NULL-terminated string. REPEAT is repeat.

format : | unpack data format
buffer : | buffer to unpack from
length : | length of buffer
... : | addresses of variables to unpack to
Returns : | number of bytes unpacked; -1 on error. The bytes are unpacked to the variables pointed to by the Varargs.

### >gnet_vunpack ()

    gint        gnet_vunpack                    (const gchar *format,
                                                 gchar *buffer,
                                                 gint length,
                                                 va_list args);

Var arg interface to gnet_unpack(). See gnet_unpack() for more information.

format : | unpack data format
buffer : | buffer to unpack from
length : | length of buffer
args : | var args
Returns : | number of bytes packed; -1 on error.