Lua data library
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README.md

luadata

Luadata provides C and Lua APIs to handle binary data using Lua scripts. Here is a brief description of those:

1. Lua API

1.1 creation

data.new(table)

Returns a new data object initialized with the given byte array. For example:

d1 = data.new{0xFF, 0xFE, 0x00} --> returns a data object with 3 bytes.

data.new(number)

Returns a new data object with the size defined by the given argument in bytes. For example:

d2 = data.new(2) --> returns a data object with 2 bytes.

data.new(string)

Returns a new data object initialized with the given string. For example:

d2 = data.new'\a' --> returns a data object with 1 byte.

1.2 layout

data.layout(table)

Returns a new layout table based on table argument, which should have the following formats for its fields:

  1. field = {<offset>, <length> [,<type> [,<endian>]]} or
  2. field = {offset = <offset>, length = <length> [, endian = <endian>, type = <type>]}

Where, field is the name of the field, <offset> is the field offset, <length> is the field length, <type> is a string that indicates the field type ('number', 'string'), <endian> is ia string that indicates the field endianness ('host', 'net', 'little', 'big'). The default value for type is 'number'. The default value for endian is 'big'.

When <type> is not 'string', offset and length are in bits (MSB 0). Otherwise, offset and length are in bytes.

A field lying outside the bounds of the data object is always nil.

Here are a couple examples:

  • format 1:
l1 = data.layout{
  msb      = {0,  1},
  uint32   = {0, 32},
  uint64le = {0, 64, 'little'},
  str      = {0, 3, 'string'}
}
  • format 2:
l2 = data.layout{
  msb                  = {offset = 0, length = 1},
  net_unaligned_uint16 = {offset = 1, length = 16, endian = 'net'},
  str                  = {offset = 0, length = 3, endian = 'string'}
}

d:layout(layout | table)

Applies a layout table on a given data object. If a regular table is passed, it calls data.layout(table) first. For example:

d1:layout(l1) -- applies l1 layout into d1 data object
d2:layout{byte = {0, 8}} -- creates and applies a new layout into d2 data object

1.3 segment

d:segment([ offset [, length ])

Returns a new data object pointing for the same raw data (memory region) of a given data object, but limited by offset and length parameters. If length is ommited, it assumes that length is the original length minus the offset. If offset is ommited, it assumes the whole data. For example:

d1 = d:segment(0, 2) --> returns a data object with 2 bytes.
d2 = d:segment(2) --> returns a data object with 1 byte.
d3 = d:segment() --> returns a data object with 3 bytes.

Note, all the three data objects point to the same raw data of the d data object.

2. C API

2.1 creation

int ldata_newref(lua_State *L, void *ptr, size_t size);

Creates a new data object pointing to ptr (without copying it), leaves the data object on the top of the Lua stack and returns a reference for it. The data object will not be garbage-collected until it is unreferred.

2.2 deletion

void ldata_unref(lua_State *L, int ref);

Removes the ptr from the data object and releases the data-object reference, allowing it to be garbage-collected. After that, it is safe to free the ptr pointer.

2.3 conversion

void * ldata_topointer(lua_State *L, int index, size_t *size);

Returns a pointer for the raw data referenced by the data object at the given index. If the value at the given index is not a valid data object or the data object is empty (that is, it has no raw data), then it returns NULL and size will be set with zero.

Note, similarly to lua_tolstring, there is no guarantee that the pointer returned by ldata_topointer will be valid after the corresponding value is removed from the stack.

3. Examples

Lua

C