Code Examples

OpenHandle Erlang Code Examples

This page shows an Erlang example. This makes use of the 'json.erl' module available here: ejson-1.tgz.

Here's how Erlang (using the 'openhandle' module contained in file "openhandle.erl") can grab a handle data record:

% erl openhandle.erl

opens and compiles the Erlang module, and one can then enter "openhandle:get_handle("10100/nature")" at the prompt as

1> openhandle:get_handle("10100/nature").

which gives us:

If the Erlang interpreter is opened without the module one will need to compile it first as "c(openhandle)." That should compile and load both of the required modules (if not, you'll need to "c(json)." first). Then one can call "openhandle:get_handle("10100/nature")." as before.

Here's the code for the OpenHandle module:

% cat openhandle.erl
%%% Example OpenHandle client
%%
%%  This program is in the Public Domain.

-module(openhandle).
-export([get_handle/1]).
-import(json, [obj_find/2, decode_string/1]).
-vsn("1").

get_handle(Handle) ->
    inets:start(),
    format_handle(get_handle_json(http:request(get_url(Handle)))).

get_url(Handle) ->
    string:concat(string:concat(string:concat(get_base_url(), "?id="), Handle), "&format=json").

get_base_url() ->
    "http://nascent.nature.com/openhandle/handle".

get_handle_json({ok, {_, _, Body}}) ->
    json:decode_string(Body).

format_handle({ok, Json}) ->
    {ok, Handle_name} = json:obj_find("handle", Json),
    {ok, Values} = json:obj_find("handleValues", Json),
    Value_count = tuple_size(Values),
    io:format("The handle <~s> has ~B values:~n", [Handle_name, Value_count]),
    tuple_foldl(fun(V, N) -> format_value(V, N) end, 1, Values),
    ok.

tuple_foldl(Fun, Acc0, Tuple) ->
    lists:foldl(Fun, Acc0, tuple_to_list(Tuple)).

format_value({json_object, _} = Obj, N) ->
    io:format("~nvalue #~B:~n", [N]),
    lists:foreach(fun(F) -> find_and_format(F, Obj) end,  ["index", "type", "data", "permission", "ttl", "timestamp", "reference"]),
    1 + N.

find_and_format(Field, {json_object, _} = Obj) ->
    format_prop(1, Field, json:obj_find(Field, Obj)).

format_prop(Level, Name, {ok, {}}) ->
    io:format("~s~s = []~n", [get_prefix_str(Level), Name]);

format_prop(Level, Name, {ok, {json_object, L}}) ->
    io:format("~s~s = {~n", [get_prefix_str(Level), Name]),
    lists:foreach(fun(V) -> format_item(Level + 1, V) end, L),
    io:format("~s}~n", [get_prefix_str(Level)]);

format_prop(Level, Name, {ok, Value}) ->
    io:format("~s~s = ~s~n", [get_prefix_str(Level), Name, Value]).

format_item(Level, {Name, Value}) ->
    io:format("~s~s = ~s~n", [get_prefix_str(Level), Name, Value]).

get_prefix_str(Level) ->
    string:chars(32, 2 * Level).