PSR-18

Abstracting HTTP Clients in PHP

PHP Benelux, Antwerp - January 26th, 2019

© David Buchmann

What is the difference between

guzzle/guzzle

and

guzzlehttp/guzzle?

Depending on an implementation

Once upon a time

FOSHttpCache needs to send HTTP requests to varnish for cache invalidation

HTTPlug

=> Márk Sági-Kazár

HTTP client interfaces
FOSHttpCache 2.0 depends on HTTPlug instead of Guzzle 6

PHP Framework Interoperability Group (PHP-FIG)

Initiative from framework and library projects
Defines PHP Standard Recommendations (PSR)

HTTP Request and Response: PSR-7

Interface for request
Extended interface for server side request
Interface for response
For server side applications, this is all you need
When building a client, you need more!

How to create an object without knowing the class?

1interface RequestFactoryInterface
2{
3    function createRequest(string $method, $uri)
4               : RequestInterface;
5}

HTTP Message Factories: PSR-17

=> Woody Gilk

Request factory
Stream factory
URI factory
(Server Request factory, Uploaded File factory, Response factory)

How to send that request?

1interface ClientInterface
2{
3  function sendRequest(RequestInterface $request)
4           : ResponseInterface;
5}

What is PSR-18?

HTTP Client: PSR-18

=> Tobias Nyholm

Psr\Http\Client\ClientInterface
And a bunch of exceptions...
- ClientExceptionInterface: base exception
- RequestExceptionInterface: request invalid
- NetworkExceptionInterface: DNS issue with target host, connection error

Interchangeable: Defined behaviour

Consumers of the client must know what to expect
No exceptions for HTTP reponses with error status codes, those are valid responses on HTTP level
Instead, throw application exceptions in your adapter

What about configuration?

Timeout settings, TLS, follow redirects, ...
Not for the caller to decide
Configure on the implementation
(e.g. constructor arguments)

But...

`1`	`sendRequest(RequestInterface` `$request,` `$config)`

Would make the PSR define configuration options
- What about unknown options?
- Or limit to a known set?
Instead, if you need different behaviours, inject multiple clients for specific purposes.

What about the cute elephant?

Httplug is still useful

Httplug Client interface extends PSR-18 interface, allowing a smooth upgrade path
Libraries should require ^1.0 || ^2.0
PSR-18 adapters for existing clients like Guzzle
Decorators for PSR-18 HTTP clients
Convenience clients on top of PSR-18

Httplug PluginClient

1public function handleRequest(
2    RequestInterface $request,
3    callable $next,
4    callable $first
5): Promise;

AddHost, AddPath, QueryDefaults
Header manipulation
Authentication, Cookie, Redirect, Retry
ContentLenght, ContentType, Decoder

Cache Plugin

Cache responses with a PSR-6 cache
Respect Cache-Control response header
Are we a proxy or a single client?

`1`	`CachePlugin::clientCache - max-age, no-cache`

`2`	`CachePlugin::serverCache - additionally: private`

Httplug Authentication

AuthPlugin
Authentication interface
- Basic (username:password), Bearer, Wsse
- Chain, Matching, RequestConditional
Alter request to add auth credentials
If you need a token, inject another client to the auth to send the requests to get the token

Other decorators

HttpClientPool: Round robin or least recently used over PSR-18 instances
HttpClientRouter: Use request matcher to chose which client to use for each request

BatchClient

1/**
2 * @param RequestInterface[] The requests to send
3 *
4 * @throws BatchException If any request threw
5 */
6public function sendRequests(
7    array $requests
8): BatchResult

HttpMethodsClient

1public function get($uri, array $headers = []): Re
2 
3public function post($uri, array $headers = [], $b
4 
5public function put($uri, array $headers = [], $bo
6 
7public function send(string $method, $uri, array $

Httplug discovery

Prefer dependency injection if possible!
Static methods to instantiate
- PSR-17 factories
- PSR-18 client
- or Httplug clients / factories

Symfony HttplugBundle

Configure PSR-18 Http clients
Configure plugins
Symfony toolbar integration
Flex: composer require http

HttplugBundle configuration

01httplug:
02  clients:
03    app:
04      http_methods_client: true
05      plugins:
06        - header_defaults:
07            headers:
08              "X-Conference": "Benelux"
09        - header_set:
10            headers:
11              "User-Agent": "PHP/Symfony"

HTTP request in Symfony

01/** @var HttpMethodsClient */
02private $httpClient;
03 
04public function status(): Response {
05try {
06  $r = $this->httpClient->get('http://php.net/');
07} catch (Exception $e) {
08  return new Response('Failed', 502);
09}
10return new Response(200 === $r->getStatusCode()
11    ? 'Success'
12    : 'Error');

Outlook

Who can promise a Promise?

`1`	`sendAsync(RequestInterface` `$request): Promise;`

`2`	`Promise::wait(): ResponseInterface;`

PSR for asynchronous clients would be nice, but first needs a standard for Promises
The PSR for HTTP clients is not the right place to define Promises

Meanwhile: Use Httplug

01interface Promise
02{
03    const PENDING = 'pending';
04    const FULFILLED = 'fulfilled';
05    const REJECTED = 'rejected';
06 
07    public function then(?callable $onFulfilled,
08    public function getState();
09    public function wait($unwrap = true);
10}

Fire off requests

01try {
02  $promises = [];
03  foreach ($uris as $u) {
04    $promises[$u] = $httpClient->sendAsyncRequest(
05      $requestFactory->createRequest('GET', $u)
06    );
07  }
08} catch (\Exception $e) {
09  return new Response('Configuration error', 500);
10}

Wait for it

01foreach ($promises as $uri => $promise) {
02   $s .= $uri.':';
03   try {
04      $r = $promise->wait();
05      if (200 === $r->getStatusCode()) {
06         $s .= 'Up and running';
07      } else {
08         $s .= 'Error: '.$r->getStatusCode();
09      }
10   } catch (\Exception $e) {
11      $s .= 'Network Error: '.$e->getMessage();
12   }
13}

then()

01$results = [];
02$promises = [];
03foreach ($uris as $u) {
04  $promise = $httpClient->sendAsyncRequest(
05    $requestFactory->createRequest('GET', $u));
06  $onFulfilled = function (ResponseInterface $r)
07    use ($u, $results) {
08    if (200 === $r->getStatusCode()) {
09     $results[$u] = 'Up and running';
10    } else {
11     $results[$u] = 'Error: '.$r->getStatusCode();
12    }
13  };
14}

then() callbacks

01...
02    $onRejected = function (Exception $r)
03      use ($u, $results) {
04      $results[$u] = 'Error: '.$e->getMessage();
05    };
06    $promise->then($onFulfilled, $onRejected);
07    $promises[] = $promise;
08  }
09} catch (Exception $e) {
10  return new Response('Configuration error', 500);
11}

Wait and build result page

1foreach ($promises as $promise) {
2   $promise->wait(false);
3}
4foreach ($results as $u => $text) {
5   $s .= $uri.':'.text;
6}