Hijacking Ruby Syntax in Ruby (RubyConf 2018)
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#rubyconf 2018 presentation in RubyKaigi track, discussing about how to use (or abuse) Ruby's meta programming features
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Hijacking Ruby Syntax in Ruby (RubyConf 2018)
- 1. HIJACKING RUBY SYNTAX IN RUBY RubyConf 2018 LA 2018/11/15 (Thu) @joker1007 & @tagomoris
- 2. Self-Intro Joker ▸ id: joker1007 ▸ Repro inc. CTO ▸ I’m familiar with Ruby/Rails/Fluentd/ECS/Presto. ▸ This talk is my first speech abroad!!
- 3. Satoshi Tagomori (@tagomoris) Fluentd, MessagePack-Ruby, Norikra, Woothee, ... Arm Ltd.
- 5. Agenda ▸ Ruby Features ▸ binding ▸ Tracepoint ▸ method hook ▸ Hacks ▸ finalist, overrider, abstriker ▸ with_resources, deferral
- 6. Ruby Features: Binding Binding ▸ Context object, includes: ▸ Kernel#binding receiver ▸ local variables ▸ For template engines (?) ▸ Methods: ▸ #receiver, #eval, #local_variables, #local_variable_get, #local_variable_defined?, #local_variable_set
- 7. Binding creates new object per call
- 8. Setting variables are ignored on binding
- 9. Overwriting existing variable is effective!
- 10. Ruby Features: Binding Binding#local_variable_set ▸ Method to ▸ add a variable only in a binding instance ▸ overwrite values of existing variables in original context
- 11. Ruby Features: TracePoint TracePoint ▸ Tracing events in VM ▸ and call hook block ▸ For various events: ▸ :line , :raise ▸ :class , :end ▸ :call , :return , :c_call , :c_return , :b_call , :b_return ▸ :thread_begin , :thread_end , :fiber_switch ▸ "We can use TracePoint to gather information specifically for exceptions:" (from Ruby doc) ▸ This is COMPLETELY WRONG statement...
- 13. TracePoint interrupted the argument (stringified) and return value (upcased)
- 15. Ruby Features: TracePoint TracePoint Methods ▸ Methods: ▸ Control: disable, enable, enabled? ▸ Event what/where: event, defined_class, path, lineno ▸ Method names: method_id, callee_id ▸ Event special: raised_exception, return_value ▸ And: binding ▸ So what? ▸ We can use TracePoint ▸ to gather information ▸ to overwrite everything
- 17. Ruby Features: Refinements ▸ Refinements provide a way to extend a class locally ▸ Useful use case. (Safety monkey patching) Ruby Features: Refinements
- 18. Another use case ▸ Super private method Ruby Features: Refinements
- 19. Ruby Features: Method Hooks ▸ Ruby has six method hooks ▸ Module#method_added ▸ Module#method_removed ▸ Module#method_undefined ▸ BasicObject#singleton_method_added ▸ BasicObject#singleton_method_removed ▸ BasicObject#singleton_method_undefined Ruby Features: method hooks
- 20. Sample: #method_added Ruby Features: method hooks
- 21. Method hook provides a way to implement method modifier.
- 22. Hacks: Method modifiers ▸ final (https://github.com/joker1007/finalist) ▸ forbid method override ▸ override (https://github.com/joker1007/overrider) ▸ enforce method has super method ▸ abstract (https://github.com/joker1007/abstriker) ▸ enforce method override These method modifiers work when Ruby defines class. It is runtime, but in most case, before main logic. Hacks: method modifiers
- 23. Sample code: finalist Hacks: method modifiers
- 25. Sample code: abstriker Hacks: method modifiers
- 26. How to implement method modifiers I use so many hook methods. #included, #extended, #method_added, and TracePoint. And I use Ripper. In other words, I use the power of many black magics !! Hacks: method modifiers
- 27. Use case of method_added in finalist Ruby Features: method hooks MyObject Finalist def method_added def verify_final_method ▸ #method_added checks violations call
- 28. Limitation of Method Hooks ▸ But it is not enough to implement “finalist” actually ▸ Ruby has so many cases of method definition ▸ def or #define_method ▸ #include module ▸ #extend, #prepend ▸ Each case has dedicated hooks Ruby Features: method hooks
- 29. #include changes only chain of method discovering Foo Object Bar Insert module to hierarchy It is different from method adding Class#ancestors displays class-module hierarchy Ruby Features: method hooks
- 30. Hooks in finalist gem hook method override event by method_added subclass singleton_method_added subclass class methods included included modules extended extended moduled
- 31. And I talk about TracePoint too
- 32. overrider and abstriker use TracePoint ▸ #inherited and #included to start TracePoint Tracepoint in overrider, abstriker MyObject Overrider/Abstriker def included(or inherited) TracePoint.trace(:end, :c_return, :raise) call
- 33. Tracepoint in overrider, abstriker TracePoint Hook Overrider self.override_methods = [ :method_a, :method_b, ] ▸ Use Method#super_method method to check method existence (ex. method(:method_a).super_method)
- 34. Why use TracePoint? ▸ In order to verify method existence at the end of class definition. ▸ Ruby interpreter needs to wait until the end of class definition to know a method absence. ▸ override and abstract cannot detect violation just when they are called. ▸ In ruby, The only way to detect the violation is TracePoint.
- 35. Advanced TracePoint: Detect particular class end Advanced Tracepoint :end event cannot trace definition by `Class.new`. Use :c_return and return_value to detect particular class end
- 36. Advanced TracePoint: Ripper combination Advanced Tracepoint ▸ Ripper: ▸ a standard library, a parser for Ruby code ▸ outputs token list and S-expression ▸ S-expression is similar to AST ▸ has token string and token position ▸ Future option: RubyVM::AbstractSyntaxTree (2.6.0 or later)
- 38. Advanced TracePoint: Ripper combination Advanced Tracepoint Detect target Sexp node by TracePoint#lineno Sexp node type expresses the style of method cal
- 39. Ripper empowers TracePoint ▸ Conclusion: ▸ TracePoint detects events and where it occurs ▸ Ripper.sexp provides how methods were called ▸ Other use case ▸ power_assert gem also uses this combination Advanced Tracepoint
- 40. Black Magic is dangerous actually, but it is very fun, and it extends Ruby potential These gems are proof of concepts, But these are decent practical.
- 41. Ruby Quiz Break (25-30min) What the difference between: - #undef_method - #remove_method
- 42. RUBY QUIZ class Foo def foo class Foo def foo class Bar < Foo def foo class Bar < Foo def foo Bar.new.foo()
- 43. RUBY QUIZ class Foo def foo class Foo def foo class Bar < Foo class Bar < Foo Bar.new.foo() remove_method(:foo) def foo NoMethodError undef_method(:foo)
- 44. Hack: with_resources Add "with" Statement to Ruby ▸ Safe resource allocate/release ▸ Ensure to release resources ▸ at the end of a lexical scope ▸ in reverse order of allocation ▸ Idioms used very frequently ▸ Other languages: ▸ Java: try-with-resources ▸ Python: with ▸ C#: using
- 45. Hack: with_resources Safe Resource Allocation/Release Statement in Ruby ▸ Open method with blocks ▸ File.open(path){|f| ... } ▸ Ruby way (?) ▸ More indentation ▸ Not implemented sometimes (e.g., TCPSocket)
- 46. Hack: with_resources with_resources.gem ▸ Safe resource allocation ▸ Top level #with ▸ by Kernel refinement ▸ Resource allocation as lambda ▸ Multi statements to allocate resources ▸ to release first resource if second resource allocation raises exception ▸ Block to define scope for resources https://github.com/tagomoris/with_resources
- 47. Hack: with_resources Implementing #with in Ruby ▸ TracePoint ▸ "b_return": pass allocated resources to block arguments ▸ "line": identify allocated resources in lambda ▸ Binding ▸ detect newly defined local variables in allocation lambda ▸ Refinements ▸ introduce #with in top-level without side effects https://github.com/tagomoris/with_resources
- 48. Hack: deferral Alternative: defer? ▸ Multi-step resource allocation in a method ▸ Nesting! w/ #with ▸ not so bad ▸ many nesting looks a bit messy :( ▸ Alternative? ▸ defer in golang
- 49. Hack: deferral Adding #defer to Ruby ▸ Block based #defer ▸ Should work ▸ Requires 1-level nesting *always* ▸ Defer.start, end (+ nesting) look too much (than golang) ▸ Abnormal case: reassigning variables
- 50. Hack: deferral deferral.gem ▸ Safe resource release ▸ Top level #defer ▸ by Kernel refinements ▸ Deferred processing to release resources ▸ at the end of scope (method, block) ▸ or exception raised
- 51. Hack: deferral Implementing "defer" in Ruby ▸ #defer ▸ Enable TracePoint if not yet ▸ Initialize internal stack frame ▸ TracePoint ▸ Monitor method call stack ▸ Get the snapshot of local variables in defer block ▸ Call release blocks at the end of scope ▸ Binding ▸ save/restore local variables of release block ▸ Refinements ▸ introduce #defer in top-level without side effects stack level 0 stack level 1
- 52. The Hard Thing in Magical World: Debugging!
- 53. "Give yourself to the dark side. It is the only way you can save your (Ruby)friends." - Darth vader Thank You! @joker1007 & @tagomoris