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HTTP transport for Elastic PHP clients

This is a HTTP transport PHP library for communicate with Elastic products, like Elasticsearch.

It implements PSR-7 standard for managing HTTP messages and PSR-18 for sending HTTP requests. Moreover, it uses the PSR-17 for building PSR-7 objects like HTTP requests, HTTP responses, URI, etc.

It uses the HTTPlug library to automatic discovery a PSR-18 client, a PSR-17 factory and the HttpAsyncClient interface with Promise for asyncronous HTTP requestes.

The architecture of the Transport is flexible and customizable, you can configure it using a PSR-18 client, a PSR-3 logger and a custom NodePoolInterface, to manage a cluster of nodes.

Quick start

The main component of this library is the Transport class.

This class uses 3 components:

• a PSR-18 client, using ClientInterface;
• a Node pool, using NodePoolInterface;
• a PSR-3 logger, using LoggerInterface.

While the PSR-3 and PSR-18 are well known standard in the PHP community, the NodePoolInterface is a new interface proposed in this library. The idea of this interface is to provide a class that is able to select a node for a list of hosts. For instance, using Elasticsearch, that is a distributed search engine, you need to manage a cluster of nodes. Each node exposes a common HTTP API and you can send the HTTP requests to one or more nodes. The NodePoolInterface is a component that can be used to manage the routing of the HTTP requests to the cluster node topology.

In order to buid a Transport instance, you can use the TransportBuilder as follows:

use Elastic\Transport\TransportBuilder;

$transport = TransportBuilder::create()
    ->setHosts(['localhost:9200'])
    ->build();

This example shows how to set the transport to communicate with one node located at localhost:9200 (e.g. Elasticsearch default port).

By default, TransportBuilder will use the autodiscovery feature of HTTPlug for the PSR-18 client, the SimpleNodePool as NodePoolInterface and the NullLogger as LoggerInterface.

The Tranport class itself implements the PSR-18 and the HttpAsyncClient interfaces, that means you can use it to send any HTTP request using the Tranport::sendRequest() function as follows:

use Http\Discovery\Psr17FactoryDiscovery;

$factory = Psr17FactoryDiscovery::findRequestFactory();
$request = $factory->createRequest('GET', '/info'); // PSR-7 request
$response = $transport->sendRequest($request);
var_dump($response); // PSR-7 response

The sendRequest function will use $request to send the HTTP request to the localhost:9200 node specified in the previous example code. This behaviour can be used to specify only the URL path in the HTTP request, the host is selected at runtime using the NodePool implementation.

NOTE: if you send a $request that contains already a host the Transport will use it without using the NodePool to select a node specified in TransportBuilder::setHosts() settings.

For instance, the following example will send the /info request to domain and not localhost.

use Elastic\Transport\TransportBuilder;

$transport = TransportBuilder::create()
    ->setHosts(['localhost:9200'])
    ->build();

$request = new Request('GET', 'https://domain.com/info');
$response = $transport->sendRequest($request); // the HTTP request will be sent to domain.com

echo $transport->lastRequest()->getUri()->getHost(); // domain.com

Asyncronous requests

You can send an asyncronous HTTP request using the Transport::sendAsyncRequest() as follows:

use Http\Discovery\Psr17FactoryDiscovery;

$factory = Psr17FactoryDiscovery::findRequestFactory();
$request = $factory->createRequest('GET', '/info'); // PSR-7 request
$promise= $transport->sendAsyncRequest($request);
var_dump($promise); // Promise
var_dump($promise->wait()); // PSR-7 response

The $promise contains a Promise object. A promise is an object that does not block the execution of PHP. This means the promise does not contain the HTTP response. In order to read the HTTP response you need to use the wait() function.

Another approach to use a promise is to specify the functions to be called on success and on faliure of the HTTP request. This can achieved using the then() function as follows:

$promise->then(function (ResponseInterface $response) {
    // onFulfilled callback, $reponse is PSR-7
    echo 'The response is available';

    return $response;
}, function (Exception $e) {
    // onRejected callback
    echo 'An error happens';

    throw $e;
});

For more information about the usage of Promise objetcs you can read the documentation from HTTPlug.

Set the number of retries

You can specify the number of retries for any HTTP requests. This means if the HTTP request will fail the client will automatically try to perform another request (or more).

By default, the number of retries is zero (0). If you want you can change it using the Transport::setRetries() function, as follows:

use Elastic\Transport\TransportBuilder;

$transport = TransportBuilder::create()
    ->setHosts([
        '10.0.0.10:9200',
        '10.0.0.20:9200',
        '10.0.0.30:9200'
    ])
    ->build();

$transport->setRetries(1);
$factory = Psr17FactoryDiscovery::findRequestFactory();
$request = $factory->createRequest('GET', '/info'); 
// If a node is down, the transports retry automatically using another one 
$response = $transport->sendRequest($request); 

This feature can be interesting as retry mechanism especially useful if you have a cluster of nodes. You can read the following section about Node Pool to understand how to configure the selection of nodes in a cluster environment.

Node Pool

The SimpleNodePool is the default node pool algorithm used by Tranposrt. It uses the following default values: RoundRobin as SelectorInterface and NoResurrect as ResurrectInterface.

The Round-robin algorithm select the nodes in order, from the first node in the array to the latest. When arrived to the latest nodes, it will start again from the first.

* NOTE: the order of the nodes is randomized at runtime to maximize the usage of all the hosts.

The NoResurrect option does not try to resurrect the node that has been marked as dead. For instance, using Elasticsearch you can try to resurrect a dead node using the HEAD / API. If you want to use this behaviour you can use the ElasticsearchResurrect class.

Use a custom Selector

You can specify a SelectorInterface implementation when you create a NodePoolInterface instance. For instance, imagine you implemented a CustomSelector and a custom CustomResurrect you can use it as follows:

use Elastic\Transport\NodePool\SimpleNodePool;
use Elastic\Transport\TransportBuilder;

$nodePool = new SimpleNodePool(
    new CustomSelector(),
    new CustomResurrect()
);

$transport = TransportBuilder::create()
    ->setHosts(['localhost:9200'])
    ->setNodePool($nodePool)
    ->build();

Use a custom PSR-3 loggers

You can specify a PSR-3 LoggerInterface implementation using the TransportBuilder. For instance, if you want to use monolog library you can use the following configuration:

use Elastic\Transport\TransportBuilder;
use Monolog\Logger;
use Monolog\Handler\StreamHandler;

$logger = new Logger('name');
$logger->pushHandler(new StreamHandler('debug.log', Logger::DEBUG));

$transport = TransportBuilder::create()
    ->setHosts(['localhost:9200'])
    ->setLogger($logger)
    ->build();

Use a custom PSR-18 clients

You can specify a PSR-18 client using the TransportBuilder::setClient() function. For instance, if you want to use Symfony HTTP Client you can use the following configuration:

use Elastic\Transport\TransportBuilder;
use Symfony\Component\HttpClient\Psr18Client;

$transport = TransportBuilder::create()
    ->setHosts(['localhost:9200'])
    ->setClient(new Psr18Client)
    ->build();

As mentioned in the introduction, we use the HTTPlug library to automatic discovery a PSR-18 client.

You can use the TransportBuilder::setClient() to specify the client manually, for instance if you have multiple HTTP client library installed.

By default, if the PSR-18 client implements the HttpAsyncClient it will use it when using Transport::sendAsyncRequest(). If you want you can override this setting using the Transport::setAsyncClient() function. That means you can use a PSR-18 client for the syncronous requests and a different HttpAsyncClient client for the asyncronous requests.

OpenTelemetry

Starting from v8.9.0 we introduced the support of OpenTelemetry for the HTTP send request. Right now the support is only for syncronous HTTP call.

In order to enable the OpenTelemetry you need to set the ENV variable OTEL_PHP_INSTRUMENTATION_ELASTICSEARCH_ENABLED to true.

We added the support of OpenTelemetry natively in the Transport:sendRequest() function. By default, the Transport create a span from a Tracer provider (e.g. Global) with the following attributes:

http.request.method
url.full
server.address
server.port

We also added a $opts array as second optional parameter for the Transport:sendRequest() to pass additional attributes for OTel instrumentation.

We created an OpenTelemetry class to provide all the configuration.

Copyright and License

Copyright (c) Elasticsearch B.V.

This software is licensed under the MIT License. Read the LICENSE file for more information.