PHP: How to get the Content-Length from stream request for chunk download

Question

I'm attempting to download archives from an external site in chunks. However, I'm encountering an issue where the Content-Length header, which I'm trying to retrieve using get_headers(), is not present.

Has anyone else experienced this issue when saving chunked responses and trying to retrieve the Content-Length?

$options = array(
    'http' => array(
        'header' => "Authorization: Bearer $accessToken\r\n"
    )
);
$context = stream_context_create($options);

// I'm trying to get the Content-Length to limit the file download to files larger than 1GB.
// $file_headers = get_headers($sourceFile, 1, $context);
// if($file_headers["Content-Type"])

$sourceFileStream = fopen($sourceFile, 'rb', false, $context);

How can I retrieve the Content-Type or the size of the response stream?

Answer 1

I assume the response is sent with Transfer-Encoding: chunked

Therefore, there is no Content-Length header field (RFC 7320): A sender MUST NOT send a Content-Length header field in any message that contains a Transfer-Encoding header field.

But you're lucky – the RFC also provides an algorithm to decode a chunked transfer and get its length.