Using a custom stream wrapper as test stub for PHP's http:// stream wrapper

I'm writing a custom stream wrapper to use as a stub in unit tests for an HTTP client class that uses the built-in http:// stream wrapper.

Specifically, I need control over the value returned in the 'wrapper_data' key by calls to stream_get_meta_data on streams created by the custom stream wrapper. Unfortunately, the documentation on custom stream wrappers is woeful and the API seems unintuitive.

What method in a custom wrapper controls the the meta wrapper_data response?

Using the class at the bottom I've only been able to get the following result when I var_dump(stream_get_meta_data($stream)); on streams created with the custom wrapper ...

array(10) {
  'wrapper_data' =>
  class CustomHttpStreamWrapper#5 (3) {
    public $context =>
    resource(13) of type (stream-context)
    public $position =>
    int(0)
    public $bodyData =>
    string(14) "test body data"
  }
  ...

But I need to coax the wrapper into yielding something like the following on meta data retrieval so I can test the client class's parsing of the data returned by the real http:// stream wrapper ...

array(10) {
  'wrapper_data' => Array(
       [0] => HTTP/1.1 200 OK
       [1] => Content-Length: 438
   )
   ...

Here's the code I have currently for the custom wrapper:

class CustomHttpStreamWrapper {

    public $context;
    public $position = 0;
    public $bodyData = 'test body data';

    public function stream_open($path, $mode, $options, &$opened_path) {
        return true;
    }

    public function stream_read($count) {
        $this->position += strlen($this->bodyData);
        if ($this->position > strlen($this->bodyData)) {
            return false;
        }
        return $this->bodyData;
    }

    public function stream_eof() {
        return $this->position >= strlen($this->bodyData);
    }

    public function stream_stat() {
        return array('wrapper_data' => array('test'));
    }

    public function stream_tell() {
        return $this->position;
    }
}

stream_get_meta_data is implemented in ext/standard/streamfunc.c. The relevant part is

if (stream->wrapperdata) {
    MAKE_STD_ZVAL(newval);
    MAKE_COPY_ZVAL(&stream->wrapperdata, newval);

    add_assoc_zval(return_value, "wrapper_data", newval);
}

i.e. whatever zval stream->wrapperdata holds is "copied" to/referenced by $retval["wrapper_data"].
Your custom wrapper code is "handled" by user_wrapper_opener in main/streams/userspace.c. And there you have

/* set wrapper data to be a reference to our object */
stream->wrapperdata = us->object;

us->object "is" the instance of your custom wrapper that has been instantiated for the stream. I haven't found a way to influence stream->wrapperdata from userspace scripts other than that.
But you could implement Iterator/IteratorAggregate and/or ArrayAccess if all you need is foreach($metadata['wrapper_data'] ...) and $metadata['wrapper_data'][$i].
E.g.

<?php
function test() {
    stream_wrapper_register("mock", "CustomHttpStreamWrapper") or die("Failed to register protocol");
    $fp = fopen("mock://myvar", "r+");
    $md = stream_get_meta_data($fp);

    echo "Iterator / IteratorAggregate\n";
    foreach($md['wrapper_data'] as $e) {
        echo $e, "\n";
    }

    echo "\nArrayAccess\n";
    echo $md['wrapper_data'][0], "\n";

    echo "\nvar_dump\n";
    echo var_dump($md['wrapper_data']);
}

class CustomHttpStreamWrapper implements IteratorAggregate, ArrayAccess  {
    public $context;
    public $position = 0;
    public $bodyData = 'test body data';

    protected $foo = array('HTTP/1.1 200 OK', 'Content-Length: 438', 'foo: bar', 'ham: eggs');
    /* IteratorAggregate */
    public function getIterator() {
        return new ArrayIterator($this->foo);
    }
    /* ArrayAccess */
    public function offsetExists($offset) { return array_key_exists($offset, $this->foo); }
    public function offsetGet($offset ) { return $this->foo[$offset]; }
    public function offsetSet($offset, $value) { $this->foo[$offset] = $value; }
    public function offsetUnset($offset) { unset($this->foo[$offset]); }

    /* StreamWrapper */
    public function stream_open($path, $mode, $options, &$opened_path) {
        return true;
    }

    public function stream_read($count) {
        $this->position += strlen($this->bodyData);
        if ($this->position > strlen($this->bodyData)) {
            return false;
        }
        return $this->bodyData;
    }

    public function stream_eof() {
        return $this->position >= strlen($this->bodyData);
    }

    public function stream_stat() {
        return array('wrapper_data' => array('test'));
    }

    public function stream_tell() {
        return $this->position;
    }
}

test();

prints

Iterator / IteratorAggregate
HTTP/1.1 200 OK
Content-Length: 438
foo: bar
ham: eggs

ArrayAccess
HTTP/1.1 200 OK

var_dump
object(CustomHttpStreamWrapper)#1 (4) {
  ["context"]=>
  resource(5) of type (stream-context)
  ["position"]=>
  int(0)
  ["bodyData"]=>
  string(14) "test body data"
  ["foo":protected]=>
  array(4) {
    [0]=>
    string(15) "HTTP/1.1 200 OK"
    [1]=>
    string(19) "Content-Length: 438"
    [2]=>
    string(8) "foo: bar"
    [3]=>
    string(9) "ham: eggs"
  }
}