HTTP Client Connection Adapters

Zend\Http\Client is based on a connection adapter design. The connection adapter is the object in charge of performing the actual connection to the server, as well as writing requests and reading responses. This connection adapter can be replaced, and you can create and extend the default connection adapters to suit your special needs, without the need to extend or replace the entire HTTP client class.

Currently, zend-http provides four built-in client connection adapters:

The client can accept an adapter via either its setAdapter() method, or during instantiation via its adapter configuration option. When using configuration, the value of the adapter option may be one of:

The Socket adapter

The default connection adapter used when none is specified is the Zend\Http\Client\Adapter\Socket adapter. The Socket adapter is based on PHP's built-in fsockopen() function, and does not require any special extensions or compilation flags.

The Socket adapter allows several extra configuration options that can be set via either the client's constructor or setOptions() method:

Parameter Description Expected Type Default Value
persistent Whether to use persistent TCP connections boolean FALSE
ssltransport SSL transport layer (eg. sslv2, tls) string ssl
sslcert Path to a PEM encoded SSL certificate string NULL
sslpassphrase Passphrase for the SSL certificate file string NULL
sslverifypeer Whether to verify the SSL peer string TRUE
sslcapath Path to SSL certificate directory string NULL
sslallowselfsigned Whether to allow self-signed certificates string FALSE
sslusecontext Enables proxied connections to use SSL even if the proxy connection itself does not. boolean FALSE

Persistent TCP connections

Using persistent TCP connections can potentially speed up HTTP requests, but in most use cases, will have little positive effect and might overload the HTTP server you are connecting to. It is recommended to use persistent TCP connections only if you connect to the same server very frequently, and are sure that the server is capable of handling a large number of concurrent connections. In any case you are encouraged to benchmark the effect of persistent connections on both the client speed and server load before using this option.

Additionally, when using persistent connections, we recommend enabling Keep-Alive HTTP requests as described in the client configuration section; otherwise persistent connections might have little or no effect.

HTTPS SSL stream parameters

ssltransport, sslcert and sslpassphrase are only relevant when connecting using HTTPS. While the default SSL/TLS settings should work for most applications, you might need to change them if the server you are connecting to requires special client setup. If so, please read the PHP manual chapter on SSL and TLS transport options.

Changing the HTTPS transport layer

use Zend\Http\Client;

// Set the configuration parameters
$config = [
    'adapter'      => Client\Adapter\Socket::class,
    'ssltransport' => 'tls',
];

// Instantiate a client object
$client = new Client('https://www.example.com', $config);

// The following request will be sent over a TLS secure connection.
$response = $client->send();

The result of the example above will be similar to opening a TCP connection using the following PHP command:

fsockopen('tls://www.example.com', 443);

Customizing and accessing the Socket adapter stream context

Zend\Http\Client\Adapter\Socket provides direct access to the underlying stream context used to connect to the remote server. This allows the user to pass specific options and parameters to the TCP stream, and to the SSL wrapper in case of HTTPS connections.

You can access the stream context using the following methods of Zend\Http\Client\Adapter\Socket:

Setting stream context options for the Socket adapter

use Zend\Http\Client;

// Array of options
$options = [
    'socket' => [
        // Bind local socket side to a specific interface
        'bindto' => '10.1.2.3:50505',
    ],
    'ssl'    => [
        // Verify server side certificate,
        // do not accept invalid or self-signed SSL certificates
        'verify_peer'       => true,
        'allow_self_signed' => false,

        // Capture the peer's certificate
        'capture_peer_cert' => true,
    ],
];

// Create an adapter object and attach it to the HTTP client:
$adapter = new Client\Adapter\Socket();
$client  = new Client();
$client->setAdapter($adapter);

// Method 1: pass the options array to setStreamContext():
$adapter->setStreamContext($options);

// Method 2: create a stream context and pass it to setStreamContext():
$context = stream_context_create($options);
$adapter->setStreamContext($context);

// Method 3: get the default stream context and set the options on it:
$context = $adapter->getStreamContext();
stream_context_set_option($context, $options);

// Now, perform the request:
$response = $client->send();

// If everything went well, you can now access the context again:
$opts = stream_context_get_options($adapter->getStreamContext());
echo $opts['ssl']['peer_certificate'];

Set stream context options prior to requests

Note that you must set any stream context options before using the adapter to perform actual requests. If no context is set before performing HTTP requests with the Socket adapter, a default stream context will be created. This context resource could be accessed after performing any requests using the getStreamContext() method.

The Proxy adapter

Zend\Http\Client\Adapter\Proxy is similar to the default Socket adapter; the primary difference is that the connection is made through an HTTP proxy server instead of a direct connection to the target server. This allows usage of Zend\Http\Client behind proxy servers, which is sometimes required for security or performance reasons.

Using the Proxy adapter requires several additional client configuration parameters to be set, in addition to the default adapter option:

Parameter Description Expected Type Example Value
proxy_host Proxy server address string 'proxy.myhost.com'’ or '10.1.2.3'
proxy_port Proxy server TCP port integer 8080 (default) or 81
proxy_user Proxy user name, if required string 'shahar' or '' for none (default)
proxy_pass Proxy password, if required string 'secret' or '' for none (default)
proxy_auth Proxy HTTP authentication type string Zend\Http\Client::AUTH_BASIC (default)

proxy_host should always be set; if it is not set, the client will fall back to a direct connection using Zend\Http\Client\Adapter\Socket. proxy_port defaults to '8080'; if your proxy listens on a different port, you must set this one as well.

proxy_user and proxy_pass are only required if your proxy server requires you to authenticate. Providing these will add a 'Proxy-Authentication' header to the request. If your proxy does not require authentication, you can leave these two options out.

proxy_auth sets the proxy authentication type, if your proxy server requires authentication. Possible values are similar to the ones accepted by the Zend\Http\Client::setAuth() method. Currently, only basic authentication (Zend\Http\Client::AUTH_BASIC) is supported.

Using Zend\Http\Client behind a proxy server

use Zend\Http\Client;

// Set the configuration parameters
$config = [
    'adapter'    => Client\Adapter\Proxy::class,
    'proxy_host' => 'proxy.int.zend.com',
    'proxy_port' => 8000,
    'proxy_user' => 'shahar.e',
    'proxy_pass' => 'bananashaped',
];

// Instantiate a client object
$client = new Client('http://www.example.com', $config);

// Continue working...

As mentioned, if proxy_host is not set or is set to a blank string, the connection will fall back to a regular direct connection. This allows you to write your application in a way that allows a proxy to be used optionally, according to a configuration parameter.

Access to stream context

Since the proxy adapter inherits from Zend\Http\Client\Adapter\Socket, you can use the stream context access method (see above) to set stream context options on Proxy connections.

The cURL Adapter

cURL is a standard HTTP client library that is distributed with many operating systems and can be used in PHP via the cURL extension. It offers functionality for many special cases which can occur for a HTTP client and make it a perfect choice for a HTTP adapter. It supports secure connections, proxies, and multiple authentication mechanisms. In particular, it is very performant with regards to transfering large files.

Setting cURL options

use Zend\Http\Client;

$config = [
    'adapter'     => Client\Adapter\Curl::class,
    'curloptions' => [CURLOPT_FOLLOWLOCATION => true],
];
$client = new Client($uri, $config);

By default, the cURL adapter is configured to behave exactly like the Socket adapter, and it also accepts the same configuration parameters as the Socket and Proxy adapters. You can also change the cURL options by either specifying the 'curloptions' key in the constructor of the adapter, or by calling setCurlOption($name, $value); option names correspond to the CURL_* constants of the cURL extension. You can get access to the underling cURL handle by calling $adapter->getHandle();

The cURL configuration options that can be set via setCurlOption($name, $value) method are:

Parameter Description Expected Type Default Value
proxyuser Whether to use persistent TCP connections boolean FALSE
proxypass SSL transport layer (eg. sslv2, tls) string ssl
proxyhost Path to a PEM encoded SSL certificate string NULL
proxyport Passphrase for the SSL certificate file string NULL
sslverifypeer Whether to verify the SSL peer string TRUE

Transfering files by handle

You can use cURL to transfer very large files over HTTP by filehandle.

use Zend\Http\Client;

$putFileSize   = filesize('filepath');
$putFileHandle = fopen('filepath', 'r');

$adapter = new Client\Adapter\Curl();
$client = new Client();
$client->setAdapter($adapter);
$client->setMethod('PUT');
$adapter->setOptions([
    'curloptions' => [
        CURLOPT_INFILE     => $putFileHandle,
        CURLOPT_INFILESIZE => $putFileSize,
    ],
]);
$client->send();

The Test adapter

Testing code that relies on HTTP connections poses difficulties. For example, testing an application that pulls an RSS feed from a remote server will require a network connection, which is not always available.

Zend\Http\Client\Adapter\Test provides a solution for these situations and acts as a mock object for unit tests. You can write your application to use Zend\Http\Client, and, when testing (either in your unit test suite, or in non-production environments), replace the default adapter with the test adapter, allowing you to run tests without actually performing server connections.

Zend\Http\Client\Adapter\Test provides two additional methods, setResponse() and addResponse(). Each takes one parameter, which represents an HTTP response as either text or a Zend\Http\Response object. setResponse() sets an individual response to always return from any request; addResponse() allows aggregating a sequence of responses. In both cases, responses are returned without performing actual HTTP requests.

Testing against a single HTTP response stub

use Zend\Http\Client;

// Instantiate a new adapter and client
$adapter = new Client\Adapter\Test();
$client  = new Client(
    'http://www.example.com',
    ['adapter' => $adapter]
);

// Set the expected response
$adapter->setResponse(
    "HTTP/1.1 200 OK\r\n"
    . "Content-type: text/xml\r\n"
    . "\r\n"
    . '<?xml version="1.0" encoding="UTF-8"?>'
    . '<rss version="2.0" '
    . '     xmlns:content="http://purl.org/rss/1.0/modules/content/"'
    . '     xmlns:wfw="http://wellformedweb.org/CommentAPI/"'
    . '     xmlns:dc="http://purl.org/dc/elements/1.1/">'
    . '  <channel>'
    . '    <title>Premature Optimization</title>'
    // and so on...
    . '</rss>'
);

$response = $client->send();
// .. continue parsing $response..

The above example shows how you can preset your HTTP client to return the response you need. Then, you can continue testing your own code, without being dependent on a network connection, the server's response, etc. In this case, the test would continue to check how the application parses the XML in the response body.

Sometimes, a single method call to an object can result in that object performing multiple HTTP transactions. In this case, it's not possible to use setResponse() alone because there's no opportunity to set the next response(s) your program might need before returning to the caller.

Testing Against Multiple HTTP Response Stubs

use Zend\Http\Client;

// Instantiate a new adapter and client
$adapter = new Client\Adapter\Test();
$client = new Client(
    'http://www.example.com',
    ['adapter' => $adapter]
);

// Set the first expected response
$adapter->setResponse(
    "HTTP/1.1 302 Found\r\n"
    . "Location: /\r\n"
    . "Content-Type: text/html\r\n"
    . "\r\n"
    . '<html>'
    . '  <head><title>Moved</title></head>'
    . '  <body><p>This page has moved.</p></body>'
    . '</html>'
);

// Set the next successive response
$adapter->addResponse(
    "HTTP/1.1 200 OK\r\n"
    . "Content-Type: text/html\r\n"
    . "\r\n"
    . '<html>'
    . '  <head><title>My Pet Store Home Page</title></head>'
    . '  <body><p>...</p></body>'
    . '</html>'
);

// inject the http client object ($client) into your object
// being tested and then test your object's behavior below

The setResponse() method clears any responses in the adapter's buffer and sets the first response that will be returned. The addResponse() method will add successive responses.

The responses will be replayed in the order that they were added. If more requests are made than the number of responses stored, the responses will cycle again in order.

In the example above, the adapter is configured to test your object's behavior when it encounters a 302 redirect. Depending on your application, following a redirect may or may not be desired behavior. In our example, we expect that the redirect will be followed and we configure the test adapter to help us test this. The initial 302 response is set up with the setResponse() method and the 200 response to be returned next is added with the addResponse() method. After configuring the test adapter, inject the HTTP client containing the adapter into your object under test and test its behavior.

Forcing the adapter to fail

If you need the adapter to fail on demand you can use setNextRequestWillFail($flag). The method will cause the next call to connect() to throw an Zend\Http\Client\Adapter\Exception\RuntimeException. This can be useful when our application caches content from an external site (in case the site goes down) and you want to test this feature.

use Zend\Http\Client;

// Instantiate a new adapter and client
$adapter = new Client\Adapter\Test();
$client  = new Client(
    'http://www.example.com',
    ['adapter' => $adapter]
);

// Force the next request to fail with an exception
$adapter->setNextRequestWillFail(true);

try {
    // This call will result in an exception.
    $client->send();
} catch (Client\Adapter\Exception\RuntimeException $e) {
    // ...
}

// Further requests will work as expected until
// you call setNextRequestWillFail(true) again

Creating your own connection adapters

Zend\Http\Client has been designed so that you can create and use your own connection adapters. You could, for example, create a connection adapter that uses persistent sockets, or a connection adapter with caching abilities, and use them as needed in your application.

In order to do so, you must create your own adapter class that implements Zend\Http\Client\Adapter\AdapterInterface. The following example shows the skeleton of a user-implemented adapter class. All the public functions defined in this example must be defined in your adapter as well.

namespace MyApp\Http\Client\Adapter;

use Zend\Http\Client\Adapter\AdapterInterface;

class BananaProtocol implements AdapterInterface
{
    /**
     * Set Adapter Options
     *
     * @param array $config
     */
    public function setOptions($config = [])
    {
        // This rarely changes - you should usually copy the
        // implementation in Zend\Http\Client\Adapter\Socket.
    }

    /**
     * Connect to the remote server
     *
     * @param string  $host
     * @param int     $port
     * @param boolean $secure
     */
    public function connect($host, $port = 80, $secure = false)
    {
        // Set up the connection to the remote server
    }

    /**
     * Send request to the remote server
     *
     * @param string        $method
     * @param Zend\Uri\Http $url
     * @param string        $http_ver
     * @param array         $headers
     * @param string        $body
     * @return string Request as text
     */
    public function write(
        $method,
        $url,
        $http_ver = '1.1',
        $headers = [],
        $body = ''
    ) {
        // Send request to the remote server.
        // This function is expected to return the full request
        // (headers and body) as a string
    }

    /**
     * Read response from server
     *
     * @return string
     */
    public function read()
    {
        // Read response from remote server and return it as a string
    }

    /**
     * Close the connection to the server
     *
     */
    public function close()
    {
        // Close the connection to the remote server - called last.
    }
}

Use the adapter as you would any other:

use MyApp\Http\Client\Adapter\BananaProtocol;
use Zend\Http\Client;

$client = new Client([
    'adapter' => BananaProtocol::class,
]);