How to stream binary data from file to POST body in PHP - php

Question

I'm not a PHP expert so please excuse the lack of correct terminology. Here is some background: There is a service running somewhere on the web and I have to communicate with it via REST API. The API requires me to send binary data (more specifically a ZIP) via POST request. The response will return other binary data that is to be saved in a file.
Since the request data and the response data may be arbitrarily large, I want to stream or buffer the data while reading it from and saving it in a file. The request has to be done in PHP.
Below is a code snippet I use to perform the POST request and handle the response (nevermind missing error handling). As you can see I have two files: "request-data" is a file containing the data I like to POST, "response-data" is the file where I write the response.
$binaryRequestFile = fopen('request-data', 'rb');
$binaryResponseFile = fopen('response-data', 'wb');
$url = "http://some/url";
$headerStr .= "Content-Type: application/zip\r\n";
$options = array(
'http' => array(
'header' => $headerStr,
'follow_location' => false,
'max_redirects' => 0,
'method' => 'POST',
'content' => stream_get_contents($binaryRequestFile),
'ignore_errors' => true
),
);
$context = stream_context_create($options);
$responseData = fopen($url, false, false, $context);
while (!feof($responseData)) {
if (fwrite($binaryResponseFile, fread($responseData, 4 * 1024)) === FALSE) {
return null;
}
}
fclose($responseData);
The code above works, but I'd rather not use stream_get_contents to read the whole request data into memory. Isn't there a way to stream the data directly into the request similar to what is done with the response? I prefer using built-in PHP functionality, no external modules or CURL.