


bee(n)                      BitTorrent                     bee(n)


______________________________________________________________________________

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                            0.1                              1





bee(n)                      BitTorrent                     bee(n)


       ::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-encod-
              ing 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 val-
              ues 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                            0.1                              2





bee(n)                      BitTorrent                     bee(n)


       ::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:

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

                      o      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.

                      o      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 ele-
                     ment 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 ele-
                     ment 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 ele-
                     ment 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 contain-
                     ing two elements. The first of them is the index informa-
                     tion  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 infor-
                     mation  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                            0.1                              3





bee(n)                      BitTorrent                     bee(n)


       ::bee::decodeChannel chan -command cmdprefix ?-exact? ?-prefix data?
              The command creates a decoder for a series of bee-values  arriv-
              ing  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  mes-
                             sage   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 process-
                     ing after removal of the decoder.




bee                            0.1                              4





bee(n)                      BitTorrent                     bee(n)


              -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:





bee                            0.1                              5





bee(n)                      BitTorrent                     bee(n)


       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

CATEGORY
       Networking

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





























bee                            0.1                              6


