All about Erubis (English)

Introduction to Erubis ‣ Pure Ruby implementation of eRuby ‣ Very fast • http://jp.rubyist.net/magazine/?0022-FasterThanC ‣ Highly functional • HTML escape in default • Changing embedded pattern • Support PHP, Java, JS, C, Perl, Scheme • and so on... copyright(c) 2009 kuwata-lab.com all rights reserved. 5

Basically Usage Ruby program: require 'rubygems' # if need require 'erubis' str = File.read('template.eruby') eruby = Erubis::Eruby.new(str) print eruby.result(binding()) command-line: $ erubis template.eruby # execute $ erubis -x template.eruby # convert into Ruby $ erubis -z template.eruby # syntax check copyright(c) 2009 kuwata-lab.com all rights reserved. 6

HTML Escape in Default str =<<END <%= %> ... WITH escaping, <%= var %> <%== %> ... WITHOUT escaping <%== var %> END eruby = Erubis::Eruby.new(str, :escape=>true) puts eruby.result(:var=>"<B&B>") output: <B&am;> User can choose escape or not <B&B> escape in default (choosability) copyright(c) 2009 kuwata-lab.com all rights reserved. 7

Changing Embedded Pattern ‣ ex : use '[% %]' instead of '<% %>' [% for x in @list %] <li>[%= x %]</li> You must escape regexp meta [% end %] characters by backslash! ## Ruby Erubis::Eruby.new(str, :pattern=>'[% %]') ## command-line $ erubis -p '[% %]' ﬁle.eruby copyright(c) 2009 kuwata-lab.com all rights reserved. 8

Use Hash or Object instead of Binding example of using Hash example of using Object hash = { @title = "Example" :title => "Example", @items = [1, 2, 3] :items => [1, 2, 3], } erubis = erubis = Erubis::Eruby.new(str) Erubis::Eruby.new(str) puts erubis.evaluate(self) puts erubis.result(hash) <h1><%= title%></h1> <h1><%= @title%></h1> <% for x in items %> <% for x in @items %> <% end %> <% end %> copyright(c) 2009 kuwata-lab.com all rights reserved. 9

Enhancer ‣ Ruby modules which enhances Erubis features ## do HTML escape <%= %> in default module EscapeEnhancer def add_expr(src, code, indicator) if indicator == '=' src << " _buf<<escapeXml(#{code})" elsif indicator == '==' src << " _buf<<(#{code}).to_s;" end end It is easy to override Erubis features because internal of Erubis is splitted into end many small methods. copyright(c) 2009 kuwata-lab.com all rights reserved. 10

Enhancer (cont') ### Enhance which prints into stdout ### (you can use print() in statements) module StdoutEnhancer use _buf=$stdout def add_preamble(src) instead of _buf="" src << "_buf = $stdout;" end def add_postamble(src) src << "n""n" end use "" (empty string) end instead of _buf.to_s copyright(c) 2009 kuwata-lab.com all rights reserved. 11

Usage of Enhancer All you have to do is to include ### Ruby or extend ehnacer modules class MyEruby < Erubis::Eruby include Erubis::EscapeEnhancer include Erubis::PercentLineEnhancer end puts MyEruby.new(str).result(:items=>[1,2,3]) Specify names with ',' ### command-line $ erubis -E Escape,Percent ﬁle.eruby copyright(c) 2009 kuwata-lab.com all rights reserved. 12

Standard Enhancers ‣ EscapeEnhancer : escape html in default ‣ PercentLineEnhancer : recognize lines starting with '%' as embedded statements ‣ InterporationEnhancer : use _buf<<"#{expr}" for speed ‣ DeleteIndentEnhancer : delete HTML indentation ‣ StdoutEnhancer : use _buf=$stdout instead of _buf="" ‣ ... and so on (you can show list of all by erubis -h) copyright(c) 2009 kuwata-lab.com all rights reserved. 13

Context Data ‣ You can specify data to pass into template ﬁle (context data) in command-line ### command-line $ erubis -c '{arr: [A, B, C]}' template.eruby # YAML $ erubis -c '@arr=%w[A B C]' template.eruby # Ruby <% for x in @arr %> <li>A</li> <li><%= x %></li> <li>B</li> <% end %> <li>C</li> copyright(c) 2009 kuwata-lab.com all rights reserved. 14

Context Data File ‣ Load '*.yaml' or '*.rb' as context data ﬁle $ erubis -f data.yaml template.eruby # YAML $ erubis -f data.rb template.eruby # Ruby data.yaml data.rb title: Example @title = "Example" items: @items = - name: Foo [ {"name"=>"Foo"}, - name: Bar {"name"=>"Bar"}, ] copyright(c) 2009 kuwata-lab.com all rights reserved. 15

Debug Print ‣ <%=== expr %> represents debug print <%=== @var %> No need to write the same expression twice ### Ruby code $stderr.puts("*** debug: @var=#{@var.inspect}") ### Result *** debug: @var=["A", "B", "C"] copyright(c) 2009 kuwata-lab.com all rights reserved. 16

Support Other Programming Langs ‣ PHP, Java, JS, C, Perl,Scheme (only for convertion) <% for (i=0; i<n; i++) { %> (example of C) <li><%= "%d", i %> <% } %> same format as printf() #line 1 "ﬁle.ec" (output of erubis -xl c ﬁle.ec) for (i=0; i<n; i++) { fputs("<li>", stdout); fprintf(stdout, "%d", i); fputs("n", stdout); } copyright(c) 2009 kuwata-lab.com all rights reserved. 17

Conslution ‣ Erubis is very functional and extensible • HTML escape in default • Changing embedded pattern • Enhancer • Context data and ﬁle • Debug print • Support PHP, Java, JS, C, Perl, and Scheme copyright(c) 2009 kuwata-lab.com all rights reserved. 18

Issue : local variables can be changed ‣ When using binding(), local variables can be non-local • Difficult to find if exists i=0 ### file.erb str = File.read('file.erb') <% for i in 1..3 %> ERB.new(str).result(binding) <li><%= i %></li> p i #=> 3 <% end %> Changed insidiously! copyright(c) 2009 kuwata-lab.com all rights reserved. 20

Cause of the issue ‣ binding() passes all local variables into template ﬁle • It is impossible to pass only variables which you truly want to pass • It is hard to recognize what variables are passed b = Bingind.new This is ideal b[:title] = "Example" but impossible... b[:items] = [1, 2, 3] copyright(c) 2009 kuwata-lab.com all rights reserved. 21

Solution by ERB ‣ Nothing, but the author of ERB introduced a solution to deﬁne custom Struct • http://d.hatena.ne.jp/m_seki/20080528/1211909590 Foo = Struct.new(:title, :items) class Foo def env; binding(); end end ctx = Foo.new("Example", [1,2,3]) ERB.new(str).result(ctx.env) copyright(c) 2009 kuwata-lab.com all rights reserved. 22

Solution by Erubis ‣ Use Hash instead of Binding It is very clear what erubis.result(:items=>[1, 2, 3]) data are passed! def result(b=TOPLEVEL_BINDING) if b.is_a?(Hash) s = b.collect{|k,v| "#{k}=b[#{k.inspect}];"}.join b = binding() eval s, b Set hash values as local vars end with creating new Binding return eval(@src, b) end copyright(c) 2009 kuwata-lab.com all rights reserved. 23

Solution by Erubis (cont') ‣ Use Object instead of Binding @items = [1, 2, 3]; <% for x in @items %> erubis.evaluate(self) <% end %> def evaluate(ctx) Convert Hash values into if ctx.is_a?(Hash) instance variables hash = ctx; ctx = Object.new hash.each {|k,v| ctx.instance_variable_set("@#{k}", v) } end return ctx.instance_eval(@src) end copyright(c) 2009 kuwata-lab.com all rights reserved. 24

Issue : cost of convertion and parsing ERB 1. 8.6 Erubis::Eruby ERB 1. 8.7 Erubis::Eruby ERB 1.9.1 Erubis::Eruby 0 10 20 30 (sec) Costs of parsing and Execution convertion are higher Parsing(by eval) than of execution Convertion(eRuby to Ruby) copyright(c) 2009 kuwata-lab.com all rights reserved. 25

Solution by ERB ‣ Convertion cost : nothing ‣ Parsing cost : helper to deﬁne method • Usage is much different from normal usage class Foo extend ERB::DefMethod def_erb_method('render', 'template.erb') end print Foo.new.render copyright(c) 2009 kuwata-lab.com all rights reserved. 26

Solution by Erubis ‣ Convertion cost : cache Ruby code into file • 1st time : save converted Ruby code into *.cache file • 2nd time : read ruby code from *.cache file eruby = Erubis::Eruby.load_file("file.eruby") print eruby.result() Available even in CGI copyright(c) 2009 kuwata-lab.com all rights reserved. 27

Solution by Erubis (cont') ‣ Parsing cost : keep ruby code as Proc object • The same way to use • Almost the same speed as deﬁning method instance_eval can take a def evaluate(ctx) Proc object as argument @proc ||= eval(@src) instead of string (ruby code) ctx.instance_eval(@proc) end copyright(c) 2009 kuwata-lab.com all rights reserved. 28

Issue: extra line breaks ‣ eRuby outpus extra line breaks • Big problem for non-HTML text Extra line break <ul> <ul> <% for x in @list %> <li>AAA</li> <li><%= x %></li> <% end %> <li>BBB</li> </ul> Extra line break </ul> copyright(c) 2009 kuwata-lab.com all rights reserved. 29

Solution by ERB ‣ Provides various trim mode • ">" : removes LF at the end of line • "<>" : removes LF if "<%" is at the beginning of line and "%>" is at the end of line • "-" : removes extra spaces and LF around "<%-" and "-%>" • "%" : regard lines starting with "%" as embedded statements • "%>", "%<>", "-" : combination of "%" and ">"/"<>"/"-" ERB.new(str, nil, "%<>") copyright(c) 2009 kuwata-lab.com all rights reserved. 30

Solution by Erubis ‣ Change operation between embedded statement and expression • <% stmt %> : remove spaces around it • <%= expr %> : do nothing (leave as it is) <ul> Remove! <ul> <% for x in @list %> AAA <%= x %> BBB <% end %> CCC </ul> Leave as it is </ul> copyright(c) 2009 kuwata-lab.com all rights reserved. 31

Comparison of solutions ERB Erubis eRuby spec compatible × spec) (compatible) (extends Spec simplicity × opts) (only one rule) (too much Easy to implement × (very easy) (complicated) copyright(c) 2009 kuwata-lab.com all rights reserved. 32

Hint to think ‣ "Extra line breaks" problem has been recognized since early times • [ruby-list:18894] extra LF in output of eRuby ‣ Nobody hit on the idea of changing operations between stmts and exprs • Everybody looks <% %> and <%= %> as same • It is important to recoginize two things which looks to be the same things as different things copyright(c) 2009 kuwata-lab.com all rights reserved. 33

Issue : Escape HTML in default ‣ <%= expr %> should be HTML escaped in default! • But eRuby is not only for HTML but also for all of text ﬁle • However security is the most important thing ‣ How to do when not to escape? copyright(c) 2009 kuwata-lab.com all rights reserved. 34

Solution by ERB ‣ Nothing for officially ‣ Unofficial solution • Define a certain class which represents HTML string (not to escape) separately from String class • http://www2a.biglobe.ne.jp/~seki/ruby/erbquote.html copyright(c) 2009 kuwata-lab.com all rights reserved. 35

Solution by Erubis ‣ Enhance embedded pattern and Erubis class • Fast, and easy to implement eruby = Erubis::Eruby.new(str, :escape=>true) # or eruby = Erubis::EscapedEruby.new(str) puts eruby.evaluate(ctx) Hi <%= @name %>! # with escape Hi <%== @name %>! # without escape copyright(c) 2009 kuwata-lab.com all rights reserved. 36

Issue : hard to ﬁnd syntax error <% unless @items.blank? %> <table> <tbody> <% @items.each do |item| %> <tr class="item" id="item-<%=item.id%>"> <td class="item-id"><%= item.id %></td> <td class="item-name"> <% if item.url && !item.url.empty? %> <a href="<%= item.url %>"><%=item.name%></a> <% else %> <span><%=item.name%></span> <% end %> </td> </tr> • HTML and Ruby code are mixed <% end %> • It is hard to recognize corresponding </tbody> </table> 'end' (because 'do' and 'end' can be <% end %> separated 100 lines for example) copyright(c) 2009 kuwata-lab.com all rights reserved. 37

Solution by ERB ‣ Nothing but '-x' option $ erb -x foo.eruby _erbout = ''; unless @items.blank? ; _erbout.concat "n" _erbout.concat "<table>n" _erbout.concat " <tr class="record">n" $ erb -x foo.eruby | ruby -wc Syntax OK copyright(c) 2009 kuwata-lab.com all rights reserved. 38

Solution by Erubis ‣ Provides a lot of command-line options • -x : show Ruby script • -X : suppress to print HTML • -N : print line numbers • -U : unify consecutive empty lines into a line • -C : remove consecutive empty lines (compact) • -z : check template syntax copyright(c) 2009 kuwata-lab.com all rights reserved. 39

$ cat foo.eruby <% unless @items.blank? %> <table> <% @items.each_with_index do|x, i| %> <tr class="record"> <td><%= i +1 %></td> <td><%=h x %></td> </tr> <% end %> </table> <% end %> copyright(c) 2009 kuwata-lab.com all rights reserved. 40

-x : show Ruby script $ erubis -x foo.eruby _buf = ''; unless @items.blank? _buf << '<table> '; @items.each_with_index do|x, i| _buf << ' <tr class="record"> <td>'; _buf << ( i +1 ).to_s; _buf << '</td> <td>'; _buf << (h x ).to_s; _buf << '</td> </tr> '; end _buf << '</table> '; end _buf.to_s copyright(c) 2009 kuwata-lab.com all rights reserved. 41

-X : suppress to print HTML $ erubis -X foo.eruby _buf = ''; unless @items.blank? @items.each_with_index do|x, i| _buf << ( i +1 ).to_s; _buf << (h x ).to_s; end end _buf.to_s copyright(c) 2009 kuwata-lab.com all rights reserved. 42

-N : print line numbers $ erubis -XN foo.eruby 1: _buf = ''; unless @items.blank? 2: 3: @items.each_with_index do|x, i| 4: 5: _buf << ( i +1 ).to_s; 6: _buf << (h x ).to_s; 7: 8: end 9: 10: end 11: _buf.to_s copyright(c) 2009 kuwata-lab.com all rights reserved. 43

-U : uniﬁy consecutive empty lines into a line $ erubis -XNU foo.eruby 1: _buf = ''; unless @items.blank? 3: @items.each_with_index do|x, i| 5: _buf << ( i +1 ).to_s; 6: _buf << (h x ).to_s; 8: end 10: end 11: _buf.to_s copyright(c) 2009 kuwata-lab.com all rights reserved. 44

-C : remove empty lines (compact) $ erubis -XNC foo.eruby 1: _buf = ''; unless @items.blank? 3: @items.each_with_index do|x, i| 5: _buf << ( i +1 ).to_s; 6: _buf << (h x ).to_s; 8: end 10: end 11: _buf.to_s copyright(c) 2009 kuwata-lab.com all rights reserved. 45

Issue : expr can contain statements embed return value of helper method by <%= %> block contains statements <%= form_for :user do %> <div> <%= text_ﬁeld :name %> </div> <% end %> beyond of eRuby spec! copyright(c) 2009 kuwata-lab.com all rights reserved. 46

Cause of Issue <%= 10.times do %> Hello <%= expr %> is expected <% end %> to be completed by itself Convert Syntax error! _buf = ""; _buf << ( 10.times do ).to_s; _buf << " Hellon"; end copyright(c) 2009 kuwata-lab.com all rights reserved. 47

Solution by ERB+Rails ‣ Change local variable (_erbout) on caller- size from callee-side agic!! b lack m Append to '_erbout' from Not use <%= %> internal of form_for() <% form_for do %> _erbout = "" Hello form_for do <% end %> _erbout.concat("Hello") end copyright(c) 2009 kuwata-lab.com all rights reserved. 48

Solution by Erubis+Merb ‣ Extend parser of Erubis Recognize blok in embedded expr <%= form_for do %> @_buf << (form_for do; Hello @_buf << "Hellon" <% end =%> end); Introduce end-of- Change _buf into block notation instance variable copyright(c) 2009 kuwata-lab.com all rights reserved. 49

Discussion ‣ Extend spec of eRuby ‣ Not use black magic (kool!) ‣ Available only for helper method, in fact • It is required to manipulate @_buf from internal of helper method ‣ Difﬁcult to provide general solution copyright(c) 2009 kuwata-lab.com all rights reserved. 50

Conslusion ‣ A lot of issues around eRuby! • Extra line breaks • Local variables are not local • Difficult to specify context variable • Large cost for convertion and parsing • HTML escape in default • Difficult to find syntax error • Can't embed return value of method with block copyright(c) 2009 kuwata-lab.com all rights reserved. 51

Template and Programming ‣ Template is also program code <ul> print "<ul>n" <% for x in @a %> for x in @a <li><%=x%></li> Equiv. print "<li>#{x}</li>n" <% end %> end </ul> print "</u>n" Possible to apply programming techniques or concepts to template system copyright(c) 2009 kuwata-lab.com all rights reserved. 53

Template and Method Template is a kind of method deﬁnition <ul> s = File.read('foo.eruby') <li><%=x%></li> e = Erubis::Eruby.new(s) </ul> puts e.evaluate(:x=>1) Context data is actual Rendering template is a argument for method kind of method invokation copyright(c) 2009 kuwata-lab.com all rights reserved. 54

Template and formal argument ‣ Formal arguments may be necessary for template <%#ARGS: items, name='guest' %> Hello <%= name %>! <% for x in items %> <li><%=x%></li> • Clear context variables <% end %> • Available default value copyright(c) 2009 kuwata-lab.com all rights reserved. 55

Template and modularity ‣ Also HTML should be Small & Many, not Single & Large • Same as principle of method deﬁnition <html> <html> Be beneﬁt for <body> designer! <body> </body> <h1><%=@title%></h1> </html> <ul id="menulist"> split <% for x in @items %> <h1><%=@title%></h1> <li><%=x%></li> <ul id="menulist"> </ul> <% end %> </ul> <% for x in @items %> </body> <li><%= x %></li> </html> <% end %> copyright(c) 2009 kuwata-lab.com all rights reserved. 56

Template and Object-Oriented ‣ Template inheritance in Django Parent template .... Available to overwrite {% block pagetitle %} or add contents <h1>{{title}}</h1> before/after {% endblock %} (method override) .... copyright(c) 2009 kuwata-lab.com all rights reserved. 57

Template and Aspect-Oriented ‣ Weave some code into other program • Similar to layer of Photoshop <table> "for x in @a" •Enable to split HTML <tr> and presentation <td> "print x" logics •Available to insert a </tr> logic into several "end" points (DRY) </table> copyright(c) 2009 kuwata-lab.com all rights reserved. 58

Template and Data Type ‣ End is coming to escape HTML in view layer • forget to escape, helper method argument, ... ‣ HTML should be different data type from String (http://www.oiwa.jp/~yutaka/tdiary/20051229.html) • No need to take care to escape or not • Prior art : str and unicode in Python • "HTML + String" should be String? or HTML? • Other escaping also should be considered (ex. SQL) copyright(c) 2009 kuwata-lab.com all rights reserved. 59

Conslusion ‣ Template is also programming code ‣ Available to apply programming techniques and concepts into template system • Formal argument, Inheritance, AOP, and so on ‣ Template system is still on developing stage copyright(c) 2009 kuwata-lab.com all rights reserved. 60

Bibliography ‣ Introduction to Template System (in Japanese) • http://jp.rubyist.net/magazine/?0024-TemplateSystem • http://jp.rubyist.net/magazine/?0024-TemplateSystem2 ‣ Erubis • http://www.kuwata-lab.com/erubis/ ‣ Benchmarks of many template systems • http://www.kuwata-lab.com/tenjin/ copyright(c) 2009 kuwata-lab.com all rights reserved. 61

Tenjin - template engine replacing eRuby ‣ Both ERB and Erubis are out of date • They are merely text-processor • Less features as template engine ‣ Tenjin : replacer of ERB/Erubis • Designed and implemented as template engine from the beginning • Provides a lot of features required for template engines - layout template, partial template, and so on • http://www.kuwata-lab.com/tenjin/ copyright(c) 2009 kuwata-lab.com all rights reserved. 63

All about Erubis (English)

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