Stream Contexts and POST Requests

Another concept introduced by streams is the context, which is basically a set of configuration options used in a streams operation. A context is created by passing an associative array of context options and their corresponding values to the stream_context_create function. One use of contexts with regard to the HTTP streams wrapper is making POST requests, as the wrapper uses the GET method by default.

<?php
$context = stream_context_create(array(
'http' => array(
'method' => 'POST',
'header' => implode("\r\n", array(
'Content-Type: application/x-www-form-urlencoded',
'Referer: http://localhost.example'
)),
'content' => http_build_query(array(
'paraml' => 'value1',
'param2' => 'value2'
))
)
));
$response = file_get_contents(
'http://localhost.example/process', false,
$context
);
?>

Here is a walk-through of this example.

• 'http’ is the streams wrapper being used.
• 'POST’ is the HTTP method of the request.
• The 'header’ stream context setting is populated with a string containing HTTP header key-value pairs, in this case for the Content-Type and Referer HTTP headers. The Content-Type header is used to indicate that the request body data is URL-encoded. When multiple custom headers are needed, they must be separated by a carriage return-line feed (“\r\n" also known as CRLF) sequence. The implode function is useful for this if key-value pairs for headers are stored in an enumerated array.
• The http_build_query function is being used to construct the body of the request. This function can also be used to construct query strings of URLs for GET requests.
• http://localhost.example/process is the URL of the resource being requested.
• file_get_contents is called to execute the request, the options for which are passed via the context $context created using stream_context_create.
• The body of the response is returned and stored in the variable $response.