Descriptor

The descriptor describes the type and content of the bencoded token the bview points to and where the data can be found in the bencoded buffer. This information allows bview to navigate through the bencoded buffer and provide access to the values.

A descriptor_table holds a contiguous sequence of descriptors and a pointer to a bencoded string. it is the result of parsing data with descriptor_parser.

Details

A descriptor is a 16 byte structure that describes the structural elements of a bencoded value. Integers and string have one descriptor. Lists and dicts have one descriptor at the start and one descriptor descriptor at the end of the datastructure.

A descriptor stores the type of the bencode data type and the position relative to the start of the buffer in a descriptor_type value. The data stored depends on the type of the bencode value:

type: the bencode data type

position: the position in the bencoded data buffer relative to the start.

• integer:

  value: the integer value.

• string:

  offset: the position in the string where the actual string data starts.

  size: the size of the string data.

• list:

  offset: the number of descriptors until the list end descriptor.

  size: the size of the list

• dict:

  offset: the number of descriptors until the dict end descriptor.

  size: the size of the dict

Following examples shows how descriptors describe the bencoded data:

bencoded data:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
| | | | | | | | | |  |  |  |  |  |  |  |
l i e 1 l 3 : f o o  3  :  b  a  r  e  e

json formatted : [ 1, ["foo", "bar"] ]

+-----+--------------------------------------------------------------------+
| idx |  descriptor                                                        |
+-----+--------------------------------------------------------------------+
| 0   |   (type: list,                 position: 0,  offset: 3, size: 2)   |
| 1   |   (type: integer | list_value  position: 1,  value:1           )   |
| 2   |   (type: list    | list_value  position: 4,  offset: 3, size: 2)   |
| 3   |   (type: string  | list_value  position: 5,  offset: 2, size: 3)   |
| 4   |   (type: string  | list_value  position: 10, offset: 2, size: 3)   |
| 5   |   (type: list    | end         position: 15, offset: 3, size: 2)   |
| 6   |   (type: list    | end         position: 16, offset: 6, size: 2)   |
| 7   |   (type: stop,                 position: 17, offset: 0, size: 0)   |
+-----+--------------------------------------------------------------------+

bencoded data:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
| | | | | | | | | |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
d 4 : s p a m i 1 e  3  :  b  a  r  l  i  1  e  i  2  e  e  e

json formatted : { "spam": 1, "bar": [1, 2] }

+-----+--------------------------------------------------------------------+
| idx |  descriptor                                                        |
+-----+--------------------------------------------------------------------+
| 0   |   (type: dict,                 position: 0,  offset: 8, size: 2)   |
| 1   |   (type: string  | dict_key,   position: 1,  offset: 2, size: 4)   |
| 2   |   (type: integer | dict_value, position: 7,  value: 1          )   |
| 3   |   (type: string  | dict_key,   position: 10, offset: 2, size: 3)   |
| 4   |   (type: list    | dict_value, position: 15, offset: 3, size: 2)   |
| 5   |   (type: integer | list_value, position: 16, value: 1          )   |
| 6   |   (type: integer | list_value, position: 19, value: 2          )   |
| 7   |   (type: list    | end,        position: 22, offset: 3, size: 2)   |
| 8   |   (type: dict    | end,        position: 23, offset: 8, size: 2)   |
| 9   |   (type: stop,                 position: 24)                       |
+-----+--------------------------------------------------------------------+