solving cross-cutting concerns in php - dutchphp conference 2016

Solving Cross-Cutting Concerns in PHPAlexander Lisachenko

About me:

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lisachenkolisachenko

https://twitter.com/lisachenko

https://github.com/lisachenko

‣ Head of Software Architecture at Alpari (RU) Forex Broker

About me:

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http://go.aopphp.com




‣ Have worked with computers since 7 years old

About me:

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‣ Clean code advocate, guru in enterprise architecture

About me:

2







‣ Clean code advocate, guru in enterprise architecture

‣ Author of the aspect-oriented framework Go! AOP http://go.aopphp.com

About me:

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Agenda

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Agenda‣ Advantages of Object-Oriented Paradigm

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Agenda‣ Advantages of Object-Oriented Paradigm‣ Limitations of OOP and how they affect our

application

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application‣ Existing object-oriented ways of solving

cross-cutting concerns

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cross-cutting concerns‣ Pros and cons: the aspect-oriented

approach of solving cross-cutting concerns

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cross-cutting concerns‣ Pros and cons: the aspect-oriented

approach of solving cross-cutting concerns‣ Examples of using aspects in real life

applications3

Текст

Object-Oriented ParadigmSolution to the complexity

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ModularityWe connect classes, components, bundles, and frameworks.

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ReusabilityWe use existing code to create new code on the top.

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EncapsulationWe hide implementation details from the outside world.

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Is it a silver bullet?Object-Oriented Paradigm

Edsger W. Dijkstra

“Object-oriented programming is an exceptionally bad idea which could only have originated in California.”

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Joe Armstrong

“…You wanted a banana but what you got [with OOP] was a gorilla holding the banana

and the entire jungle”

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What are the problems?

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What are the problems?‣ Limitation of object-oriented

representation of real life processes

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representation of real life processes‣ Essential complexity results in strong

coupling between components

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representation of real life processes‣ Essential complexity results in strong

coupling between components‣ Essential complexity results in scattered

implementation of our concerns

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Текст

Cross-cutting concernsWhat they are and why we should think about them

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Cross-cutting concerns are aspects of a program that affect

other concerns.

Cross-cutting concerns - why they affect our code?

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Task: Implement an audit system that checks access permission for each public method over

all classes in our system and then logs this information into the security journal.

Clean model

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Authorization control…

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Logging and audit…

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Error handling…

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Code tangling

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Code scattering

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Текст

OOP waysWhat do we have in OOP to fight cross-cutting concerns?

DecoratorDesign pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.

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Decorator+ Respects LSP - We can pass an instance of a

decorator everywhere the original object is expected. + Keeps SRP for the original class because it doesn’t

contain secondary concerns now

- Too many decorator classes for each combination of concern+concrete interface

- Secondary concerns (authorization, caching, etc.) are scattered across all decorators

- Additional overhead for calling original methods

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MediatorDefines an object that incapsulates all logic of interactions between objects, giving them the ability to work without explicit references to each other

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Mediator+ All secondary concerns can be moved to separate

classes without duplication (SRP for secondary concerns)

+ Keeps SRP for the original class, because it doesn’t contain secondary concerns now

+ The most flexible way of extending a system- Requires specific changes in the original class to

perform notification of mediator - Hard to debug code with complex logic of interaction

because there are no explicit links between objects

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Текст

Take control of everythingWhat if we combine all the best features of the decorator and mediator into the one pattern?

Aspect-Oriented ParadigmA programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns

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Go! AOP Framework

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Go! AOP Framework

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‣ Inspired by famous AspectJ and Spring frameworks

Go! AOP Framework

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‣ Over 800 stargazers on Github - thank you!

Go! AOP Framework

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‣ Over 800 stargazers on Github - thank you!‣ Over 200k installations on Packagist

Go! AOP Framework

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‣ Over 800 stargazers on Github - thank you!‣ Over 200k installations on Packagist‣ PHP5.6, PHP7.0 and Opcache compatible

Go! AOP Framework

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‣ Over 800 stargazers on Github - thank you!‣ Over 200k installations on Packagist‣ PHP5.6, PHP7.0 and Opcache compatible‣ There are bridges for SF2, ZF2, Laravel…

Let’s take our clean code…

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Let’s take our clean code…

Method execution is an event

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…and subscribe to our event

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Pointcut - describes list of interesting events

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Joinpoint - defines an event object

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Joinpoint - defines an event object

Advice - event handler

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How it works

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All aspects (or advisors) are registered in the aspect kernel

How it works

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The special php://filter stream filter is registered via stream_filter_register()

php://filter

How it works

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The composer class loader is replaced with a weaving proxy

How it works

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Lexical analysis and parsing of AST is performed (nikic/PHP-Parser)

How it works

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Static reflection is created from the AST (goaop/parser-reflection)

How it works

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The original class is renamed and replaced with a new class with additional behavior; stored in the

cache

How it works

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cacheSimple inheritance

How it works

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cacheSimple inheritance

Overridden method

Текст

Go! AOP joinpointsWhat can be intercepted?

Method interceptors:

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Method interceptors:

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Can be a final class or a trait!

Property interceptors:

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Logic interceptors:

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AOP+ Keeps SRP for the original class because it doesn’t

contain secondary concerns now + All secondary concerns are stored in separate classes

without duplication (SRP for secondary concerns) + Very flexible way of extending our system (like mediator

does) + Does not require changes in original classes

- No tools to debug AOP code; no help from IDE - Overhead for AOP initialization and execution

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Go! AOP: Debugging with XDebug

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Go! AOP: Plugin for the PhpStorm

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Pointcut syntax highlighting, completion and analysis

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Navigate to advice/advised elements

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Текст

Circuit breaker Prevents one failure from reoccurring continuously

Logic of CircuitBreaker

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‣ For each public method execution we count the number of failures in APC/Memcache.

https://github.com/ejsmont-artur/php-circuit-breaker


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‣ If the number of failures is too high, then we break the circuit to prevent subsequent failures.



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‣ If the circuit is broken, then the original method body should not be executed for the configured amount of time.



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‣ If the circuit is broken, then the original method body should not be executed for the configured amount of time.

‣ https://github.com/ejsmont-artur/php-circuit-breaker can be used.


Step 1. Define an annotation

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Step 2. Define an aspect

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All methods with «Fuse» annotation

Step 3. Use it in your code

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More examples for AOP

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‣ Profiling methods with pinba extension and Intaro Pinboard


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‣ Feature toggle pattern


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‣ Feature toggle pattern‣ Authorization control


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‣ Feature toggle pattern‣ Authorization control‣ Traditional caching, logging, transaction

control, security audit


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control, security audit‣ Design by contract programming (Php-Deal

library)


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control, security audit‣ Design by contract programming (Php-Deal

library)‣ Aspect-oriented testing (AspectMock)

Conclusion

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Conclusion

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‣ OOP is a nice tool for solving accidental complexity but not for essential complexity.

Conclusion

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‣ Pay attention to code scattering and code tangling.

Conclusion

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‣ Try to extract secondary concerns into separate classes via OOP decomposition for small applications.

Conclusion

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‣ Try to extract secondary concerns into separate classes via OOP decomposition for small applications.

‣ Try to use AOP for complex enterprise applications.

Thank you for the attention!

https://github.com/goaop https://github.com/lisachenko https://twitter.com/lisachenko

https://github.com/goaop



solving cross-cutting concerns in php - dutchphp conference 2016

Presentations & Public Speaking