Ubuntu Manpage: bee - BitTorrent Serialization Format Encoder/Decoder

NAME

       bee - BitTorrent Serialization Format Encoder/Decoder

SYNOPSIS

       package require Tcl  8.4

       package require bee  ?0.1?

       ::bee::encodeString string

       ::bee::encodeNumber integer

       ::bee::encodeListArgs value...

       ::bee::encodeList list

       ::bee::encodeDictArgs key value...

       ::bee::encodeDict dict

       ::bee::decode string ?endvar? ?start?

       ::bee::decodeIndices string ?endvar? ?start?

       ::bee::decodeChannel chan -command cmdprefix ?-exact? ?-prefix data?

       cmdprefix eof token

       cmdprefix error token message

       cmdprefix value token value

       ::bee::decodeCancel token

       ::bee::decodePush token string

_________________________________________________________________

DESCRIPTION

       The bee package provides de- and encoder commands for data in bencoding (speak 'bee'), the
       serialization format for data and messages used by the BitTorrent application.

PUBLIC API

ENCODER
The package provides one encoder command for each of the basic forms, and two commands per
container, one taking a proper tcl data structure to encode in the container, the other
taking the same information as several arguments.

::bee::encodeString string
Returns the bee-encoding of the string.

::bee::encodeNumber integer
Returns the bee-encoding of the integer number.

::bee::encodeListArgs value...
Takes zero or more bee-encoded values and returns the bee-encoding of their list.

::bee::encodeList list
Takes a list of bee-encoded values and returns the bee-encoding of the list.

::bee::encodeDictArgs key value...
Takes zero or more pairs of keys and values and returns the bee-encoding of the
dictionary they form. The values are expected to be already bee-encoded, but the
keys must not be. Their encoding will be done by the command itself.

::bee::encodeDict dict
Takes a dictionary list of string keys and bee-encoded values and returns the bee-
encoding of the list. Note that the keys in the input must not be bee-encoded
already. This will be done by the command itself.

DECODER
The package provides two main decoder commands, one for decoding a string expected to
contain a complete data structure, the other for the incremental decoding of bee-values
arriving on a channel. The latter command is asynchronous and provides the completed
decoded values to the user through a command callback.

::bee::decode string ?endvar? ?start?
Takes the bee-encoding in the string and returns one decoded value. In the case of
this being a container all contained values are decoded recursively as well and the
result is a properly nested tcl list and/or dictionary.

If the optional endvar is set then it is the name of a variable to store the index
of the first character after the decoded value into. In other words, if the string
contains more than one value then endvar can be used to obtain the position of the
bee-value after the bee-value currently decoded. together with start, see below, it
is possible to iterate over the string to extract all contained values.

The optional start index defaults to 0, i.e. the beginning of the string. It is the
index of the first character of the bee-encoded value to extract.

::bee::decodeIndices string ?endvar? ?start?
Takes the same arguments as ::bee::decode and returns the same information in
endvar. The result however is different. Instead of the tcl value contained in the
string it returns a list describing the value with respect to type and location
(indices for the first and last character of the bee-value). In case of a container
the structure also contains the same information for all the embedded values.

Formally the results for the various types of bee-values are:

string A list containing three elements:

• The constant string string, denoting the type of the value.

• An integer number greater than or equal to zero. This is the index of
the first character of the bee-value in the input string.

• An integer number greater than or equal to zero. This is the index of
the last character of the bee-value in the input string.

Note that this information is present in the results for all four types of bee-
values, with only the first element changing according to the type of the value.

integer
The result is like for strings, except that the type element contains the
constant string integer.

list The result is like before, with two exceptions: One, the type element
contains the constant string list. And two, the result actually contains
four elements. The last element is new, and contains the index data as
described here for all elements of the bee-list.

dictionary
The result is like for strings, except that the type element contains the
constant string dict. A fourth element is present as well, with a slightly
different structure than for lists. The element is a dictionary mapping from
the strings keys of the bee-dictionary to a list containing two elements.
The first of them is the index information for the key, and the second
element is the index information for the value the key maps to. This
structure is the only which contains not only index data, but actual values
from the bee-string. While the index information of the keys is unique
enough, i.e. serviceable as keys, they are not easy to navigate when trying
to find particular element. Using the actual keys makes this much easier.

::bee::decodeChannel chan -command cmdprefix ?-exact? ?-prefix data?
The command creates a decoder for a series of bee-values arriving on the channel
chan and returns its handle. This handle can be used to remove the decoder again.
Setting up another bee decoder on chan while a bee decoder is still active will
fail with an error message.

-command
The command prefix cmdprefix specified by the required option -command is
used to report extracted values and exceptional situations (error, and EOF
on the channel). The callback will be executed at the global level of the
interpreter, with two or three arguments. The exact call signatures are

cmdprefix eof token
The decoder has reached eof on the channel chan. No further
invocations of the callback will be made after this. The channel has
already been closed at the time of the call, and the token is not
valid anymore as well.

cmdprefix error token message
The decoder encountered an error, which is not eof. For example a
malformed bee-value. The message provides details about the error.
The decoder token is in the same state as for eof, i.e. invalid. The
channel however is kept open.

cmdprefix value token value
The decoder received and successfully decoded a bee-value. The
format of the equivalent tcl value is the same as returned by
::bee::decode. The channel is still open and the decoder token is
valid. This means that the callback is able to remove the decoder.

-exact By default the decoder assumes that the remainder of the data in the channel
consists only of bee-values, and reads as much as possible per event,
without regard for boundaries between bee-values. This means that if the the
input contains non-bee data after a series of bee-value the beginning of
that data may be lost because it was already read by the decoder, but not
processed.

The -exact was made for this situation. When specified the decoder will take
care to not read any characters behind the currently processed bee-value, so
that any non-bee data is kept in the channel for further processing after
removal of the decoder.

-prefix
If this option is specified its value is assumed to be the beginning of the
bee-value and used to initialize the internal decoder buffer. This feature
is required if the creator of the decoder used data from the channel to
determine if it should create the decoder or not. Without the option this
data would be lost to the decoding.

::bee::decodeCancel token
This command cancels the decoder set up by ::bee::decodeChannel and represented by
the handle token.

::bee::decodePush token string
This command appends the string to the internal decoder buffer. It is the runtime
equivalent of the option -prefix of ::bee::decodeChannel. Use it to push data back
into the decoder when the value callback used data from the channel to determine if
it should decode another bee-value or not.

FORMAT DEFINITION

Data in the bee serialization format is constructed from two basic forms, and two
container forms. The basic forms are strings and integer numbers, and the containers are
lists and dictionaries.

String S
A string S of length L is encoded by the string "L:S", where the length is written
out in textual form.

Integer N
An integer number N is encoded by the string "iNe".

List v1 ... vn
A list of the values v1 to vn is encoded by the string "lBV1...BVne" where "BVi" is
the bee-encoding of the value "vi".

Dict k1 -> v1 ...
A dictionary mapping the string key ki to the value vi, for i in 1 ... n is encoded
by the string "dBKiBVi...e" for i in 1 ... n, where "BKi" is the bee-encoding of
the key string "ki". and "BVi" is the bee-encoding of the value "vi".

Note: The bee-encoding does not retain the order of the keys in the input, but
stores in a sorted order. The sorting is done for the "raw strings".

Note that the type of each encoded item can be determined immediately from the first
character of its representation:

i Integer.

l List.

d Dictionary.

[0-9] String.

By wrapping an integer number into i...e the format makes sure that they are different
from strings, which all begin with a digit.

EXAMPLES

BUGS, IDEAS, FEEDBACK

       This document, and the package it describes,  will  undoubtedly  contain  bugs  and  other
       problems.    Please   report   such  in  the  category  bee  of  the  Tcllib  SF  Trackers
       [http://sourceforge.net/tracker/?group_id=12883].   Please  also  report  any  ideas   for
       enhancements you may have for either package and/or documentation.

KEYWORDS

       BitTorrent, bee, bittorrent, serialization, torrent

COPYRIGHT

       Copyright (c) 2004 Andreas Kupries <andreas_kupries@users.sourceforge.net>