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-module(mb2_bencoding). -author("Tim Carey-Smith <dev@spork.in>"). -vsn("1.0"). -include_lib("logging.hrl"). -include_lib("eunit.hrl"). %% API -export([encode/1, decode/1, parse/1]). %%==================================================================== %% API %%==================================================================== %%-------------------------------------------------------------------- %% Function: encode/1 %% Description: Encode an erlang term into a String %%-------------------------------------------------------------------- encode({string, Str}) -> L = length(Str), {ok, lists:concat([L, ':', Str])}; encode({integer, Int}) -> {ok, lists:concat(['i', Int, 'e'])}; encode({list, Items}) -> {ok, EncodedItems} = encode_list(Items), Encoded = lists:concat(["l", lists:concat(EncodedItems), "e"]), {ok, Encoded}; encode({dict, Items}) -> {ok, EncodedItems} = encode_dict(Items), Encoded = lists:concat(["d", lists:concat(EncodedItems), "e"]), {ok, Encoded}; encode(Term) -> ?ERR("Not a bencoded structure: ~p~n", [Term]), {error, invalid_structure}. %%-------------------------------------------------------------------- %% Function: decode/1 %% Description: Decode a string to an erlang term. %%-------------------------------------------------------------------- decode(String) -> case decode_b(String) of {ok, Result, []} -> {ok, Result}; {ok, _Result, Rest} -> ?ERR("Unparsed data: ~p~n", [Rest]), {error, extra_data_given}; {error, Reason} -> {error, Reason} end. %%-------------------------------------------------------------------- %% Function: parse/1 %% Description: Parse a file into an erlang term. %%-------------------------------------------------------------------- parse(FileName) -> case file:read_file(FileName) of {ok, Data} -> String = binary_to_list(Data), decode(String); E -> E end. %%==================================================================== %% Internal functions %%==================================================================== %% encoding encode_list(Items) -> EncodedItems = lists:map(fun (I) -> {ok, Item} = encode(I), Item end, Items), {ok, EncodedItems}. encode_dict(Items) -> {ok, EncodedItems} = encode_dict_recurse(Items, []), {ok, lists:reverse(EncodedItems)}. encode_dict_recurse([], EncodedItems) -> {ok, EncodedItems}; encode_dict_recurse([{K1, V1} | Rest], Accum) -> {ok, K} = encode(K1), {ok, V} = encode(V1), encode_dict_recurse(Rest, [V, K | Accum]). %% decoding decode_b(String) -> First = hd(String), case First of $i -> decode_integer(String); $l -> decode_list(String); $d -> decode_dict(String); _S -> decode_string(String) end. decode_integer([$i | String]) -> case split_on($e, String) of {ok, IntegerString, Rest} -> case string:to_integer(IntegerString) of {error, Reason} -> {error, Reason}; {Integer, _} -> {ok, {integer, Integer}, Rest} end; E -> E end. decode_list([$l | String]) -> {ok, Items, Rest} = decode_list_recurse(String, []), {ok, {list, Items}, Rest}. decode_list_recurse([$e | Rest], Items) -> {ok, lists:reverse(Items), Rest}; decode_list_recurse(String, Items) -> {ok, Item, Rest} = decode_b(String), decode_list_recurse(Rest, [Item | Items]). decode_dict([$d | String]) -> {ok, Items, Rest} = decode_list_recurse(String, []), {ok, Dict} = items_to_dict(Items, []), {ok, {dict, Dict}, Rest}. items_to_dict([], Dict) -> {ok, lists:reverse(Dict)}; items_to_dict(Items, Dict) -> [K, V | Rest] = Items, items_to_dict(Rest, [{K, V} | Dict]). decode_string(String) -> {ok, LengthString, Data} = split_on($:, String), {Length, _} = string:to_integer(LengthString), {Content, Rest} = lists:split(Length, Data), {ok, {string, Content}, Rest}. split_on(Char, String) -> case lists:splitwith(char_pred(Char), String) of {Match, [Char | Rest]} -> {ok, Match, Rest}; _ -> ?ERR("Terminator ~c not found~n", [Char]), {error, terminator_not_found} end. char_pred(C) -> fun(E) -> E /= C end. -ifdef(EUNIT). encode_integer_test() -> {ok, "i100e"} = encode({integer, 100}). encode_string_empty_test() -> {ok, "0:"} = encode({string, ""}). encode_string_hello_test() -> {ok, "5:hello"} = encode({string, "hello"}). encode_list_empty_test() -> {ok, "le"} = encode({list, []}). encode_list_test() -> {ok, "l4:spam4:eggse"} = encode({list, [{string, "spam"}, {string, "eggs"}]}). encode_list_2_test() -> {ok, "l3:onei2ee"} = encode({list, [{string, "one"}, {integer, 2}]}). encode_dict_empty_test() -> {ok, "de"} = encode({dict, []}). encode_dict_test() -> {ok, "d3:cow3:moo4:spam4:eggse"} = encode({dict, [{{string, "cow"}, {string, "moo"}}, {{string, "spam"}, {string, "eggs"}}]}). encode_unknown_test() -> {error, invalid_structure} = encode({wont, work}). decode_raw_integer_test() -> {ok, {integer, 100}, []} = decode_integer("i100e"). decode_raw_integer_invalid_test() -> {error, terminator_not_found} = decode_integer("i100"). decode_integer_test() -> {ok, {integer, 100}} = decode("i100e"). decode_string_test() -> {ok, {string, "spam"}} = decode("4:spam"). decode_list_empty_test() -> {ok, {list, []}} = decode("le"). decode_list_test() -> {ok, {list, [{integer, 30}, {integer, 2}]}} = decode("li30ei2ee"). decode_dict_empty_test() -> {ok, {dict, []}} = decode("de"). decode_dict_test() -> {ok, {dict, [{{integer, 30}, {integer, 2}}, {{integer, 102}, {integer, 4}}]}} = decode("di30ei2ei102ei4ee"). encode_decode_dict_test() -> String = "di30ei2ei102ei4ee", {ok, Term} = decode(String), {ok, String} = encode(Term). encode_decode_crazy_dict_test() -> String = "d3:cow3:moo4:spam4:eggse", {ok, Term} = decode(String), {ok, String} = encode(Term). -endif.

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