PHP Best Practices and Living Standards Martin Kruli

PHP Best Practices and Living Standards Martin Kruliš by Martin Kruliš (v 1. 0) 29. 3. 2017 1

Coding Style only opening tag (no closing) <? php namespace VendorPackage; namespace on first row use Foo. Interface; use Bar. Class as Bar; class declaration class Foo extends Bar implements Foo. Interface on one row { final public function sample. Method($a, $b = null) { space between if ($a === $b) { operator and vars class/method bar($a); block on } elseif ($a > $b) { new block opening on the same line $foo->bar($a, $b); } } } 4 space indenting by Martin Kruliš (v 1. 0) 29. 3. 2017 2

Standardization PSR � PHP Standard Recommendations ◦ Standardization beyond language specifications ◦ Improves cooperation, library designs, … ◦ Accepted �PSR-1, PSR-2 Coding style guidelines �PSR-3 Logger interface �PSR-4 Autoloading (classes) �PSR-7 HTTP message interface �… ◦ Drafts, pending reviews �Container interface, PHPDoc standard, … by Martin Kruliš (v 1. 0) 29. 3. 2017 3

Autoloading � Automatic Loading of Classes ◦ Useful for libraries, reduces the number of includes ◦ __autoload(), spl_autoload_register() � PSR-4 Autoloading ◦ Defines naming conventions for the relation namespaces + classes vs directories + files ◦ Example �ExamplesFooBar class �<projectroot>/lib/Examples/Foo/Bar. php file by Martin Kruliš (v 1. 0) 29. 3. 2017 4

Components � Component-based Development ◦ Modern applications use components to promote encapsulation and separation of concerns �Component – a software module that provides some well defined functionality through a set of interfaces �In PHP, typically a class (small set of classes) that implements well-defined interface(s) ◦ Component construction and management �A centralized manager (application server, container, …) has to be present to create components �Especially to handle component dependencies by Martin Kruliš (v 1. 0) 29. 3. 2017 5

Components � Example ◦ Components and their dependencies Presenters Page Presenters Template Renderer Logger Mailer User Auth. Database (ORM, Not. ORM) by Martin Kruliš (v 1. 0) 29. 3. 2017 6

Containers � Component Management ◦ Creation and interlinking may be tedious �Who creates components? �When are the components created? �Where is the component configuration? �How do one component find other components it needs to use? �… ◦ Better to be managed centrally �Using application server, container, component registry, … by Martin Kruliš (v 1. 0) 29. 3. 2017 7

Dependency Injection � Dependency Injection ◦ Design pattern that implements inversion of control �Component is not responsible for seeking its own dependencies �Dependencies are injected externally (by container) ◦ Declaring dependencies �In configuration, by annotations, using reflection, … �Problem of cyclic dependencies �DB component requires log to log errors �Log may require DB component to save messages by Martin Kruliš (v 1. 0) 29. 3. 2017 8

Dependency Injection � Example Component naming convention /** * @component Welcome. Page */ class Welcome. Page. Controller implements IController { Annotations (inject by interface) /** @inject IDatabase */ public $db; /** @inject name="News. Service" */ public $news; Annotations (inject by name) function __construct(ILog $log) {. . . } } Constructor injection (by type hinting) by Martin Kruliš (v 1. 0) 29. 3. 2017 9

Front Controller Revision � Front Controller ◦ Software design pattern that provides centralized entry point for all request (commands) Class/Component Initializing the libraries, setting up components HTTP Front Controller (index. php) Method Action … Controller/Presenter … dispatching Routing and Action Controller/Presenter by Martin Kruliš (v 1. 0) 29. 3. 2017 10

HTTP Request Processing � Request Data Validation ◦ Repetitive, tedious, and error prone ◦ Can be done automatically in framework class Galery. Presneter extends Presenter { Get PK from $_GET["galery"] and use /** @GET(DBGallery) */ it to find and create DBGallery object public $galery; /** @GET(int) @optional */ Fills in (int)$_GET["offset"] if exists public $offset; /** @param(img) FILES(type="image/jpeg") */ public function Add. Photo. Action($img) {. . . } } $img holds metadata of uploaded file, which has image/jpeg MIME by Martin Kruliš (v 1. 0) 29. 3. 2017 11

HTTP Request Processing � PHP HTTP Wrapper ◦ Automatically loads data into global fields �$_GET, $_POST, $_FILES, $_SERVER (headers), … � Problems ◦ Tied strictly to URL query encoding �SEO applications may require different URL format ◦ Only one request may be processed by the script �Modern applications may be more complex ◦ Global variables go against dependency injection ◦ Tedious testing �It is more difficult to perform unit testing by Martin Kruliš (v 1. 0) 29. 3. 2017 12

PSR HTTP API � PSR-7 HTTP Message Interface ◦ Defines two interfaces �PsrHttpMessageRequest. Interface �PsrHttpMessageResponse. Interface �derived from PsrHttpMessage. Interface ◦ These interfaces encapsulate both headers and body of request/response �Provide easy access/manipulation with headers �Streaming interface for body �Better upload handling (Uploaded. File. Interface) by Martin Kruliš (v 1. 0) 29. 3. 2017 13

REST API � Representational State Transfer (REST) ◦ Server API which offers retrieval and manipulation with application resources in a HTTP-compliant way �Resources are identified by URIs �Operations are performed by HTTP requests ◦ REST formal constraints are �Client-server model �Stateless interface (no client context is cached at server) �Cacheable (response defines whether it can be cached) �Uniform interface �Layered system (proxies, servers may be replicated) by Martin Kruliš (v 1. 0) 29. 3. 2017 14

REST API � Representational State Transfer (REST) ◦ HTTP request methods reflect desired operations �GET – retrieve the resource (nullipotent) �POST – append new sub-entity in the resource �PUT – insert/replace the resource (idempotent) �DELETE – remove the resource (idempotent) ◦ Example �API for photo gallery �/gallery – collection of all galleries �/gallery/kittens - photos in gallery with ID=kittens �/gallery/kittens/kitten 01 – photo kitten 01 by Martin Kruliš (v 1. 0) 29. 3. 2017 15

REST API � REST Example /gallery (collection of galleries) /gallery/kittens (photos in gallery) …/kitten 01 (single photo) Get the list of all galleries (JSON) Get the list of photos in the gallery (JSON) Get the image (jpeg) POST Create a new gallery Create a new photo in a gallery Not generally used. Perhaps for adding image metadata… PUT Replace list of galleries (atypical) Replace entire list of photos in gallery Replace/insert an image (of given ID) DELETE Empty the whole application Remove all photos of a gallery Remove the given image GET by Martin Kruliš (v 1. 0) 29. 3. 2017 16

PHP Micro Frameworks � PHP Slim Framework Example $app = new SlimApp; $app->get('/hello/{name}', function (Request $request, Response $response) { $name = $request->get. Attribute('name'); $response->get. Body()->write("Hello, $name"); return $response; }); $app->run(); by Martin Kruliš (v 1. 0) 29. 3. 2017 17

Error Handling � Application Errors Who is General Failure and why is he reading my disk? ◦ User errors (e. g. , filling a wrong value to form) �Ideally, they should be part of normal operations (application explains problem/offers remedy) ◦ Temporary errors/soft errors (e. g. , DBMS is offline) �“Try it later” message + notify administrator by e-mail ◦ Hard errors (bugs) �Generic message for the user “error occurred …” �Log the error and notify administrator �Position in the code, stack trace, variable dumps, … �URL, POST body, logged user, session data, … �In some cases it might help to allow user add comments by Martin Kruliš (v 1. 0) 29. 3. 2017 18

Errors in PHP � Error Levels ◦ Define the severity of the error �E_ERROR – fatal errors, terminate the script �E_WARNING – severe errors, but recoverable �E_NOTICE – unusual situations (possible error) �E_USER_xxx – user level error, warning, or notice �E_STRICT – suggestion for improvement ◦ The log can filter selected error levels �Controlled in php. ini or by error_reporting() ◦ User errors can be triggered manually �trigger_error() by Martin Kruliš (v 1. 0) 29. 3. 2017 19

Error Handling in PHP � Error Control Operator ◦ Symbol @ prepended to an expression ◦ All error messages from the expression are ignored ◦ For specific local solutions only (use with caution) $data = @file('data_file. txt') or die('Error…'); � Information about Errors ◦ The handling callback gets error level and position ◦ debug_backtrace() – retrieves current call stack ◦ debug_print_backtrace() – prints call stack by Martin Kruliš (v 1. 0) 29. 3. 2017 20

Exceptions � Concept of Exceptions ◦ Similar to other object languages �Exceptions are thrown and caught (throw, catch) �Exception is an object of class Exception or derived class ◦ Used for reporting errors �Especially from deeply nested code ◦ Note that … �Uncaught exception causes Fatal Error �Destructors should not throw exceptions �Throwing-catching process is somewhat slow by Martin Kruliš (v 1. 0) 29. 3. 2017 21

Exceptions � Try-catch Blocks ◦ Exception-safe code is wrapped in try block ◦ First matching catch block handles the exception �Exception is matched by its class try { . . . throw new Exception('Error …'); . . . } catch (My. Exception $e) { . . . My exception handler. . . } catch (Exception $e) { . . . Generic exception handler. . . } by Martin Kruliš (v 1. 0) 29. 3. 2017 22

Exceptions � Creating Custom Exceptions ◦ Exception class is derived from Exception ◦ Derived classes need not to override any methods �If the constructor is overridden, parent constructor must be invoked �It is recommended to redefine __to. String() ◦ When to customize… �To distinguish a new error type �To additional data to the exception object by Martin Kruliš (v 1. 0) 29. 3. 2017 23

Logging � Logger ◦ Component that ensures logging ◦ Works as a sink for all messages �Single write interface, configurable output �Saves messages in files/database, sends e-mails ◦ Distinguish several levels of severity �errors, warnings, notices, … ◦ Many ways to implement �PSR-3 Logger Interface Example by Martin Kruliš (v 1. 0) 29. 3. 2017 24

Configuration � Application Configuration ◦ Essential for larger projects ◦ Structured format �Easy to write, easy to access from code ◦ API that provides read-only access to the values �In a structured way (nested arrays/objects) ◦ Typical formats �Native PHP (e. g. , array declaration) �INI, XML, JSON, SQLite, … �Haml, Yaml, Neon, … Example by Martin Kruliš (v 1. 0) 29. 3. 2017 25

Caching � Caching ◦ Universal concept for reducing I/O or computations �Database selects, file operations, … �Generating previews, summaries, … ◦ May be an important part of data management APIs �E. g. , inside ORM framework ◦ PSR-6 Caching interface �Generalized interface for caching libraries �Both for in-memory and persistent caches �Items are identified by string keys �Items have TTL/expiration �Support for deferred updates by Martin Kruliš (v 1. 0) 29. 3. 2017 26

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