Developing web apps using the Erlang-Web MVC framework.

1. Server-side web development Using ErlangWeb Stefan Comanescu

3. Named after the Danish mathematician Agner Krarup Erlang

4. First versions were running on a Prolog interpreter, a C emulator and a compiler were later written, for reasons concerning performance

5. In 1997 bit syntax and binaries were added (for protocol programming) and in the same year work started on OTP

6. Released as open source in 1998

7. SMP support was added in 2006

11. Templates – XHTML files and templating engine

12. Controller – Erlang functions called on dispatching rules

13. Dispatcher – Request routing based on regexp

15. Caching system

16. Annotations

18. config –dispatch.conf, errors.conf, projects.conf, server specific .conf

19. docroot –static files and folders (except html templates), e.g : js, css, img

20. lib –framework applications and applications created by the user

21. log –logs created while running in embedded mode and server specific log

22. pipes –OS pipes for cummunicating with the shell while in embeded mode

23. priv –project specific data (usually static html)

24. release –separated subdirectories for each release version

27. General format: ./bin/generate.erl TYPE -argument_name -argument_value

30. Generates basic CRUD functionality for the given header

33. Dynamic entries are matched with their URLs

34. Static routes are matched

35. If no patterns are matched, a 404 error page is displayed

37. Provides an easy to use API for setting and getting values from the dictionary

38. Used for retrieving GET/POST request data from the query string and also used by the expanding templates

40. wpart:fget(“get:page_number”).

41. wpart:fset(“user”,[[{“name”,”bogdan”},{age,21}],[{“name”,”marian”},{age,18}]]).

42. Request dictionary Sample browser request {<0.3110.0>,[ {&quot;get&quot;,[]}, {&quot;post&quot;,[ {&quot;action_type&quot;,&quot;add&quot;},{&quot;id&quot;,[]},{&quot;type&quot;,&quot;user&quot;},{&quot;user_password&quot;,&quot;nuitizic&quot;}, {&quot;user_phone&quot;,&quot;07273447823&quot;},{&quot;user_cnp&quot;,&quot;1901231231723&quot;}, {&quot;user_lastname&quot;,&quot;alex&quot;},{&quot;user_firstname&quot;,&quot;popescu&quot;} ] }, {&quot;__https&quot;,false}, {&quot;__cookies&quot;,[{&quot;eptic_cookie&quot;,&quot;nonode@nohost-7985065742948673537&quot;}]}, {&quot;session&quot;,[{&quot;user_id&quot;,&quot;1111111111111&quot;}, {&quot;groups&quot;,[&quot;admin&quot;]}]}, {&quot;__path&quot;,&quot;admin/add&quot;}, {&quot;__cookie_key&quot;,&quot;nonode@nohost-7985065742948673537&quot;},{&quot;__ip&quot;,{127,0,0,1}}, {&quot;__controller&quot;,controller} ] }

44. Has the arity 1, getting a proplist (list of key-value pairs)

45. Handles user input, model manipulation, etc.

47. Retval is one of the previous touples

49. The most commonly used namespace, wpart, is always expanded by the framework . When the parser meets <wpart:lookup … /> for example, it will call the function wpart_lookup:handle_call/1, with the whole xmerl parsed tag as an argument.

51. <wpart:otherwise> Something else </wpart:otherwise>

54. head – renders only the first element

55. tail – renders the last element of the list

56. filter – has an attribute named “pred” for filtering the list

57. find – the first element of the list where “pred” is evaled to true

60. pred, predicate used for some of the select tags, it's optional

61. e.g. : <wpart:list select=”map” list=”students” as=”student”> <span class=”name”><wpart:lookup value=”student:name”/></span> <span class=”group”><wpart:lookup value=”student:group”/></span> </wpart:list>

63. format, optional formatters

64. type, can have the values “text” (default) or “html”, setting “html” turns off html-escaping and can be dangerous

65. e.g : <wpart:lookup key=”name”/> <wpart:lookup key=”student:name”/>

67. Allows building of websites from small chunks of html

69. Not writing the same thing multiple times

70. Updating the common part of the pages only one time

72. <wtpl:parent path=Path /> - specifies which template will be filled with the content provided by the wtpl:content content

73. <wtpl:content name=Name/> - content that will fill the wtpl:include tag which has the same name as the tag 'name' attribute, in the file specified by wtpl:parent

75. wpart_gen:load_tpl(Namespace, Name, Path) – loads the html snippet specified by Path, and saves it in the memory under the key {Namespace,Name}

76. Tpl = wpart_gen:tpl_get(Namespace,Name) – gets the snippet from memory

77. wpart_gen:build_html(Tpl,Values) – builds the template file with the values from the list Values

78. Templating Engine wpart_gen – Template Format Anonymous slots: <!-- HTMLCode --> <% slot %> <!-- HTMLCode --> Named slots: <!-- HTMLCode --> <% name_of_the_slot %> <!-- HTMLCode -->

79. Templating Engine wpart_gen – Passed Values Anonymous slots: [Value | … ] All fields must be filled. Named slots: [{ “slot_name”, Value} | … ] The unfilled slots will remain empty.

81. timeout – every T minutes the cache is traversed and expired content is removed, each URL can have a different timeout.

82. no_cache

84. {static, “^/faq$”,”doc/faq.html”,[{cache,normal}]}.

85. {dynamic, “^/posts/?$”,[{cache,{timeout,30}}]}.

86. {dynamic, “^/the_time/?$”,[{cache,no_cache}]}.

88. Before processing any request, the function my_mod:is_cachable() will be called

90. {true,NewId} , if the request should be cached under NewId

91. false , if we don't want to check the cache

93. Allows separation of the target function from different types of functions, non-domain specific wrappers.

94. e.g.: before making a post to a blog you should be logged in and your message should be checked for “bad words” maybe; after posting the message the cache should be invalidated and your post-count could be modified.

95. Usual dataflow mechanisms can be used but it could make the code harder to read and repetitive.

96. Annotations Controller Syntax % keeps the stored macros -include_lib(“blog/include/utils_annotations.hrl”). % before posting ?AUTHENTICATE([“administrator”]). ?CHECK(blog_post). % after posting ?INVALIDATE(posts). ?UPDATE(user). post(_Args) -> ...

97. Annotations Annotation Module Syntax ?BEFORE. %% ?AFTER. annotation_name(AnnotationArg, TargetModule, TargetFunction, TargetFunctionArgs | TargetFunctionResult) -> Result Result :: {proceed, NewFunctionArgs | NewResult} | {skip, NewResult} | {error, {ErrorMod, ErrorFun, ErrorArgs}}

98. Annotations Annotation Module Example ?AFTER. check (blog_post, _Mod, _Fun, _Args) -> case is_bad(wpart:fget(“post:msg”)) of true-> {skip, {redirect, “http://correctiveschool.org”}}; _-> {proceed, _Args} end.

100. Erlang-Web comes with e_components for authentication, mnesia backup and for generating rss feeds

101. To search for an e_component we can run ./bin/e_component search component_name, command that will list all available components matching the name and their description

102. To install an e_component we run ./bin/e_component install component_name, the e_component is now copied in the lib folder of our application. ./bin/compile is now required, in order to compile the component's source files.

105. Erlang-Web comes with e_components for authentication, mnesia backup and for generating rss feeds

106. To search for an e_component we can run ./bin/e_component search component_name, command that will list all available components matching the name and their description

107. To install an e_component we run ./bin/e_component install component_name, the e_component is now copied in the lib folder of our application. ./bin/compile is now required, in order to compile the component's source files.