bee(n)                            BitTorrent                            bee(n)



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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:

                     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
                     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

CATEGORY
       Networking

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




bee                                   0.1                               bee(n)
