From Ruby to Erlang: An Experience Report

Chicago Erlang Factory Lite 2013

Transcript

1. From Ruby to Erlang:
   An Unexpected Journey
   Christopher Meiklejohn
   Friday, October 4, 13
   

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2. From Ruby to Erlang:
   An Experience Report
   Christopher Meiklejohn
   Friday, October 4, 13
   

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3. Friday, October 4, 13
   

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4. cmeiklejohn / @cmeik
   My Name is My Name
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5. What do you do?
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6. Friday, October 4, 13
   

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7. Friday, October 4, 13
   

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8. Friday, October 4, 13
   

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9. What did you do?
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10. Friday, October 4, 13
    

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11. Friday, October 4, 13
    

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12. The Story
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13. Friday, October 4, 13
    

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14. The Motivation
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15. The Application Story
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16. Application structure.
    The Application Story
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17. S
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18. S R
    R
    R
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19. S R
    R
    R
    T
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20. Building The Application
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21. {erl_opts, [debug_info,
    warnings_as_errors,
    {parse_transform, lager_transform}]}.
    {edoc_opts, [{preprocess, true}]}.
    {deps, [
    {erlydtl, "0.7.0",
    {git, "git://github.com/evanmiller/erlydtl.git", {tag,
    "6a9845f"}}},
    {node_package, "1.3.4",
    {git, "git://github.com/basho/node_package", {tag, "1.3.4"}}},
    {lager, ".*",
    {git, "git://github.com/basho/lager", {tag, "1.2.2"}}},
    {webmachine, ".*",
    {git, "git://github.com/basho/webmachine.git", {tag,
    "1.10.0"}}},
    {erlcloud, ".*",
    {git, "git://github.com/basho/erlcloud.git", {tag, "0.4.1p1"}}}
    ]}.
    riak_cs_control/rebar.con!g
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22. gen_server: State Coordination
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23. init([]) ->
    riak_cs_control_configuration:configure_s3_connection(),
    {ok, #state{}}.
    get_users() ->
    gen_server:call(?MODULE, get_users, infinity).
    get_user(KeyId) ->
    gen_server:call(?MODULE, {get_user, KeyId}, infinity).
    handle_call(get_users, _From, State) ->
    case handle_request({multipart_get, "users"}) of
    {ok, Response} ->
    Users = riak_cs_control_formatting:format_users(Response),
    {reply, {ok, Users}, State};
    Error ->
    {reply, Error, State}
    end;
    handle_call({get_user, KeyId}, _From, State) ->
    case handle_request({get, "user/" ++ KeyId}) of
    {ok, Response} ->
    User = riak_cs_control_formatting:format_user(Response),
    {reply, {ok, User}, State};
    Error ->
    {reply, Error, State}
    end; riak_cs_control/src/riak_cs_control_session.erl
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24. %% @doc Format a user, by ensuring that all keys are atomized.
    format_user({struct, _} = Attributes) ->
    {struct, AttributeList} = atomize(Attributes),
    {struct, append_admin_status(AttributeList)};
    format_user(Attributes) ->
    Attributes.
    %% @doc Given a proplist of attributes, add admin status.
    append_admin_status(Attributes) ->
    RiakCsAdminKey = riak_cs_control_configuration:cs_configuration(
    cs_admin_key),
    BinaryAdminKey = list_to_binary(RiakCsAdminKey),
    KeyId = proplists:get_value(key_id, Attributes),
    lists:append(Attributes, [{admin, KeyId =:= BinaryAdminKey}]).
    %% @doc Format an entire list of users.
    format_users(Users) -> [format_user(User) || User <- Users].
    riak_cs_control/src/riak_cs_control_formatting.erl
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25. Webmachine: REST API
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26. %% @doc Initialize the resource.
    init([]) ->
    {ok, #context{users=undefined,user=undefined}}.
    %% @doc Provide respones in JSON only.
    content_types_provided(ReqData, Context) ->
    {[{"application/json", to_json}], ReqData, Context}.
    %% @doc Validate CSRF token.
    forbidden(ReqData, Context) ->
    {riak_cs_control_security:is_protected(ReqData, Context),
    ReqData, Context}.
    %% @doc Support retrieval and creation of users.
    allowed_methods(ReqData, Context) ->
    {['HEAD', 'GET', 'POST'], ReqData, Context}.
    %% @doc Return true if we were able to retrieve the user.
    resource_exists(ReqData, Context) ->
    case maybe_retrieve_users(Context) of
    {true, NewContext} ->
    {true, ReqData, NewContext};
    {false, Context} ->
    {false, ReqData, Context}
    end.
    riak_cs_control/src/riak_cs_control_wm_users.erl
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27. %% @doc Attempt to retrieve the users and store in the context if
    %% possible.
    maybe_retrieve_users(Context) ->
    case Context#context.users of
    undefined ->
    case riak_cs_control_session:get_users() of
    {ok, Response} ->
    {true, Context#context{users=Response}};
    _ ->
    {false, Context}
    end;
    _Users ->
    {true, Context}
    end.
    %% @doc Return serialized users.
    to_json(ReqData, Context) ->
    case maybe_retrieve_users(Context) of
    {true, NewContext} ->
    Users = NewContext#context.users,
    Response = mochijson2:encode({struct, [{users, Users}]}),
    {Response, ReqData, NewContext};
    {false, Context} ->
    Response = mochijson2:encode({struct, [{users, []}]}),
    {Response, ReqData, Context}
    end.
    riak_cs_control/src/riak_cs_control_wm_users.erl
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28. Webmachine: Visual Debugger
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29. Friday, October 4, 13
    

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30. Asset Management
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31. Serving assets.
    Asset Management
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32. %% @doc Return a context which determines if we serve
    %% up the application template or a file resource.
    identify_resource(ReqData, #context{resource=undefined}=Context) ->
    case wrq:disp_path(ReqData) of
    "" ->
    {true, Context#context{resource=template,
    filename=undefined}};
    _ ->
    Tokens = wrq:path_tokens(ReqData),
    Filename = normalize_filepath(Tokens),
    {true, Context#context{resource=filename,
    filename=Filename}}
    end;
    identify_resource(_ReqData, Context) ->
    {true, Context}.
    riak_cs_control/src/riak_cs_control_wm_asset.erl
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33. %% @doc If the file exists, allow it through, otherwise assume true if
    %% they are asking for the application template.
    resource_exists(ReqData, Context) ->
    case identify_resource(ReqData, Context) of
    {true, NewContext=#context{resource=template}} ->
    {true, ReqData, NewContext};
    {true, NewContext=#context{resource=filename,
    filename=Filename}} ->
    case filelib:is_regular(Filename) of
    true ->
    {true, ReqData, NewContext};
    _ ->
    {false, ReqData, NewContext}
    end
    end.
    riak_cs_control/src/riak_cs_control_wm_asset.erl
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34. %% @doc Return the proper content type of the file, or default to
    %% text/html.
    content_types_provided(ReqData, Context) ->
    case identify_resource(ReqData, Context) of
    {true, NewContext=#context{resource=filename,
    filename=Filename}} ->
    MimeType = webmachine_util:guess_mime(Filename),
    {[{MimeType, to_resource}], ReqData, NewContext};
    {true, NewContext} ->
    {[{"text/html", to_resource}], ReqData, NewContext}
    end.
    riak_cs_control/src/riak_cs_control_wm_asset.erl
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35. %% @doc Return the application template, or the contents of a file
    %% resource.
    to_resource(ReqData, Context) ->
    case identify_resource(ReqData, Context) of
    {true, NewContext=#context{resource=template}} ->
    Token = riak_cs_control_security:csrf_token(
    ReqData, Context),
    {ok, Content} = application_dtl:render(
    [{csrf_token, Token}]),
    {Content,
    wrq:set_resp_header("Set-Cookie",
    "csrf_token="++Token++
    "; httponly", ReqData),
    NewContext};
    {true, NewContext=#context{resource=filename,
    filename=Filename}} ->
    {ok, Source} = file:read_file(Filename),
    {Source, ReqData, NewContext}
    end.
    riak_cs_control/src/riak_cs_control_wm_asset.erl
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36. Generating assets.
    Asset Management
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37. {plugins, [rebar_js_handlebars_plugin, rebar_js_concatenator_plugin]}.
    riak_cs_control/rebar.con!g
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38. {js_handlebars, [
    {doc_root, "priv/www/js/templates"},
    {out_dir, "priv/www/js"},
    {target, "Ember.TEMPLATES"},
    {compiler, "Ember.Handlebars.compile"},
    {templates, [{"generated/templates.js", [
    "application.hbs",
    "users.hbs",
    "users/button.hbs",
    "users/new.hbs",
    "users/item.hbs",
    "users/index.hbs"]}]}
    ]}.
    riak_cs_control/rebar.con!g
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39. {js_concatenator, [
    {doc_root, "priv/www/js/vendor"},
    {out_dir, "priv/www/js"},
    {concatenations, [{"generated/vendor.js", [
    "jquery-1.7.2.js",
    "jquery-ui-1.8.16.custom.min.js",
    "spin-1.2.7.min.js",
    "handlebars.js",
    "ember-latest.js",
    "ember-data-latest.js",
    "minispade.js"], []}]}
    ]}.
    riak_cs_control/rebar.con!g
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40. ➜ riak_cs_control git:(master) rebar compile skip_deps=true
    ==> rel (compile)
    ==> riak_cs_control (compile)
    Compiled handlebars asset priv/www/js/generated/templates.js
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41. CSRF Protection
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42. %% @doc Validate CSRF token.
    forbidden(ReqData, Context) ->
    {riak_cs_control_security:is_protected(ReqData, Context),
    ReqData, Context}.
    riak_cs_control/src/riak_cs_control_wm_user.erl
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43. %% @doc Get the CSRF token from the cookie.
    -spec get_csrf_token(reqdata(), context()) -> csrf_token().
    get_csrf_token(ReqData, _Context) ->
    wrq:get_cookie_value("csrf_token", ReqData).
    %% @doc Ensure this request contains a valid csrf protection token.
    -spec is_valid_csrf_token(reqdata(), context()) -> boolean().
    is_valid_csrf_token(ReqData, Context) ->
    HeaderToken = wrq:get_req_header("X-CSRF-Token", ReqData),
    CookieToken = get_csrf_token(ReqData, Context),
    HeaderToken /= undefined andalso HeaderToken == CookieToken.
    %% @doc Is this a protected method?
    -spec is_protected_method(reqdata()) -> boolean().
    is_protected_method(ReqData) ->
    Method = wrq:method(ReqData),
    Method == 'POST' orelse Method == 'PUT'.
    %% @doc Is this a protected?
    -spec is_protected(reqdata(), context()) -> boolean().
    is_protected(ReqData, Context) ->
    (is_null_origin(ReqData) or
    not is_valid_csrf_token(ReqData, Context)) and
    is_protected_method(ReqData).
    riak_cs_control/src/riak_cs_control_security.erl
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44. The Testing Story
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45. EUnit: Unit Testing
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46. Similar to MiniTest; Test::Unit
    EUnit: Unit Testing
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47. length_test() -> ?assert(length([1,2,3]) =:= 3).
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48. -module(fib).
    -export([fib/1]).
    -include_lib("eunit/include/eunit.hrl").
    fib(0) -> 1;
    fib(1) -> 1;
    fib(N) when N > 1 -> fib(N-1) + fib(N-2).
    fib_test_() ->
    [?_assert(fib(0) =:= 1),
    ?_assert(fib(1) =:= 1),
    ?_assert(fib(2) =:= 2),
    ?_assert(fib(3) =:= 3),
    ?_assert(fib(4) =:= 5),
    ?_assert(fib(5) =:= 8),
    ?_assertException(error, function_clause, fib(-1)),
    ?_assert(fib(31) =:= 2178309)].
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49. The Dialyzer
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50. Discrepancy Analyzer for Erlang programs
    The Dialyzer
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51. Based on success typings
    The Dialyzer
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52. -module(test).
    -compile([export_all]).
    is_ok(Symbol) ->
    case Symbol of
    {ok, _} ->
    true;
    {error, _} ->
    false
    end.
    check() ->
    is_ok(ok).
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53. Checking whether the PLT /Users/cmeiklejohn/.dialyzer_plt is up-to-
    date... yes
    Proceeding with analysis...
    test.erl:13: Function check/0 has no local return
    test.erl:14: The call test:is_ok('ok') will never return since it
    differs in the 1st argument from the success typing arguments:
    ({'error',_} | {'ok',_})
    done in 0m0.60s
    -module(test).
    -compile([export_all]).
    is_ok(Symbol) ->
    case Symbol of
    {ok, _} ->
    true;
    {error, _} ->
    false
    end.
    check() ->
    is_ok(ok).
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54. QuickCheck / PropEr
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55. Property-based testing utilities
    QuickCheck / PropEr
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56. prop_reverse() ->
    ?FORALL(X, %% Binding
    list(int()), %% Generator
    %% Property
    lists:reverse(lists:reverse(X)) == X
    ).
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57. 3> eqc:quickcheck(eqc1:prop_reverse()).
    ......................................................................
    ..............................
    OK, passed 100 tests
    true
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58. prop_delete() ->
    ?FORALL(Ls, non_empty(list(int())),
    ?FORALL(X, elements(Ls),
    not lists:member(X, lists:delete(X, Ls)))).
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59. 10> eqc:quickcheck(eqc1:prop_delete()).
    ....................................................Failed! After 53
    tests.
    [-15,-12,1,1,9,17]
    1
    false
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60. 10> eqc:quickcheck(eqc1:prop_delete()).
    ....................................................Failed! After 53
    tests.
    [-15,-12,1,1,9,17]
    1
    Shrinking...(3 times)
    [1,1]
    1
    false
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61. prop_delete() ->
    ?FORALL(Ls, non_empty(list(int())),
    ?FORALL(X, elements(Ls),
    not lists:member(X, lists:delete(X, Ls)))).
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62. The Deployment Story
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63. The reltool Utility
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64. Standalone Erlang release; bundled runtime
    The reltool Utility
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65. The node_package Utility
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66. Fedora, Debian, BSD, OS X, SmartOS, Solaris
    The node_package Utility
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67. The HiPE Application
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68. Native code compilation
    The HiPE Application
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69. The Heroku Buildpack
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70. Git-based; dependencies through rebar
    The Heroku Buildpack
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71. The DSU Story
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72. Hot-code loading; control upgrade point.
    The DSU Story
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73. The Conclusion
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74. Easy to reason about; very small application.
    The Conclusion
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75. Lack of tooling; trivial solution to solve.
    The Conclusion
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76. Try Erlang for your next project!
    The Conclusion
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77. https://github.com/basho/riak_cs_control
    https://github.com/cmeiklejohn/webmachine-tutorial
    Thanks! Questions?
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