lib/etorrent-1.0/src/etorrent_bcoding.erl

   1 %%%-------------------------------------------------------------------
   2 %%% File    : bcoding.erl
   3 %%% Author  : Jesper Louis Andersen <jlouis@succubus>
   4 %%% License : See COPYING
   5 %%% Description : Functions for handling bcoded values
   6 %%%
   7 %%% Created : 24 Jan 2007 by Jesper Louis Andersen <jlouis@succubus>
   8 %%%-------------------------------------------------------------------
   9 -module(etorrent_bcoding).
  10 -author("Jesper Louis Andersen <jesper.louis.andersen@gmail.com>").
  11 -vsn("1.0").
  12
  13 %% API
  14 -export([encode/1, decode/1, search_dict/2, search_dict_default/3,
  15         parse/1]).
  16
  17 %%====================================================================
  18 %% API
  19 %%====================================================================
  20 %%--------------------------------------------------------------------
  21 %% Function: encode/1
  22 %% Description: Encode an erlang term into a String
  23 %%--------------------------------------------------------------------
  24 encode(BString) ->
  25     case BString of
  26         {string, String} -> encode_string(String);
  27         {integer, Integer} -> encode_integer(Integer);
  28         {list, Items} -> encode_list([encode(I) || I <- Items]);
  29         {dict, Items} -> encode_dict(encode_dict_items(Items))
  30     end.
  31
  32 %%--------------------------------------------------------------------
  33 %% Function: decode/1
  34 %% Description: Decode a string to an erlang term.
  35 %%--------------------------------------------------------------------
  36 decode(String) ->
  37     {Res, []} = decode_b(String),
  38     Res.
  39
  40 %%--------------------------------------------------------------------
  41 %% Function: search_dict/1
  42 %% Description: Search the dict for a key. Returns the value or crashes.
  43 %%--------------------------------------------------------------------
  44 search_dict(Key, {dict, Elems}) ->
  45     case lists:keysearch(Key, 1, Elems) of
  46         {value, {_, V}} ->
  47             V;
  48         false ->
  49             false
  50     end.
  51
  52 search_dict_default(Key, Dict, Default) ->
  53     case search_dict(Key, Dict) of
  54         false ->
  55             Default;
  56         X ->
  57             X
  58     end.
  59
  60 %%--------------------------------------------------------------------
  61 %% Function: parse/1
  62 %% Description: Parse a file into a Torrent structure.
  63 %%--------------------------------------------------------------------
  64 parse(File) ->
  65     {ok, IODev} = file:open(File, [read]),
  66     Data = read_data(IODev),
  67     ok = file:close(IODev),
  68     decode(Data).
  69
  70 %%====================================================================
  71 %% Internal functions
  72 %%====================================================================
  73
  74 %% Encode a string.
  75 encode_string(Str) ->
  76     L = length(Str),
  77     lists:concat([L, ':', Str]).
  78
  79 encode_integer(Int) ->
  80     lists:concat(['i', Int, 'e']).
  81
  82 encode_list(Items) ->
  83     lists:concat(["l", lists:concat(Items), "e"]).
  84
  85 encode_dict(Items) ->
  86     lists:concat(["d", lists:concat(Items), "e"]).
  87
  88 encode_dict_items([]) ->
  89     [];
  90 encode_dict_items([{I1, I2} | Rest]) ->
  91     I = encode(I1),
  92     J = encode(I2),
  93     [I, J | encode_dict_items(Rest)].
  94
  95 decode_b([]) ->
  96     empty_string;
  97 decode_b([H | Rest]) ->
  98     case H of
  99         $i ->
 100             decode_integer(Rest);
 101         $l ->
 102             decode_list(Rest);
 103         $d ->
 104             decode_dict(Rest);
 105         $e ->
 106             {end_of_data, Rest};
 107         S ->
 108             %% This might fail, and so what ;)
 109             attempt_string_decode([S|Rest])
 110     end.
 111
 112 charPred(C) ->
 113     fun(E) ->
 114             E /= C end.
 115
 116 attempt_string_decode(String) ->
 117     {Number, Data} = lists:splitwith(charPred($:), String),
 118     {ParsedNumber, _} = string:to_integer(Number),
 119     Rest1 = tl(Data),
 120     {StrData, Rest} = lists:split(ParsedNumber, Rest1),
 121     {{string, StrData}, Rest}.
 122
 123 decode_integer(String) ->
 124     {IntegerPart, RestPart} = lists:splitwith(charPred($e), String),
 125     {Int, _} = string:to_integer(IntegerPart),
 126     {{integer, Int}, tl(RestPart)}.
 127
 128 decode_list(String) ->
 129     {ItemTree, Rest} = decode_list_items(String, []),
 130     {{list, ItemTree}, Rest}.
 131
 132 decode_list_items([], Accum) -> {lists:reverse(Accum), []};
 133 decode_list_items(Items, Accum) ->
 134     case decode_b(Items) of
 135         {end_of_data, Rest} ->
 136             {lists:reverse(Accum), Rest};
 137         {I, Rest} -> decode_list_items(Rest, [I | Accum])
 138     end.
 139
 140 decode_dict(String) ->
 141     {Items, Rest} = decode_dict_items(String, []),
 142     {{dict, lists:reverse(Items)}, Rest}.
 143
 144 decode_dict_items([], Accum) ->
 145     {Accum, []};
 146 decode_dict_items(String, Accum) ->
 147     case decode_b(String) of
 148         {end_of_data, Rest} ->
 149             {Accum, Rest};
 150         {Key, Rest1} -> {Value, Rest2} = decode_b(Rest1),
 151                         decode_dict_items(Rest2, [{Key, Value} | Accum])
 152     end.
 153
 154 read_data(IODev) ->
 155     eat_lines(IODev, []).
 156
 157 eat_lines(IODev, Accum) ->
 158     case io:get_chars(IODev, ">", 8192) of
 159         eof ->
 160             lists:concat(lists:reverse(Accum));
 161         String ->
 162             eat_lines(IODev, [String | Accum])
 163     end.