AFAIK URL encoding the cookie value is still kind of a defacto standard, it’s an ancient relict based on the old, ugly Netscape cookie specs, that basically says that semicolons, commas and whitespaces are disallowed, and should be encoded, for example using URL encoding. Neither does it does it require enocding, nor does it force the use or URL encoding, but that’s how it was implemented.
So when passing a string to the constructor, WP_Http_Cookie assumes that the data is from a cookie, and therefore the cookie value is encoded and needs to be decoded. Personally i think it should not do that, and leave it up to the developer to handle values as needed, as mentioned in Ticket 19922.
However, when dispatching a request, WP_Http_Cookie::getHeaderValue is invoked, and this is where a filter is available, wp_http_cookie_value. Assuming that the cookie value you are receiving is URL encoded, you could re-encode it using this filter.
function wp_http_cookie_value_filter($value, $name)
{
return urlencode($value);
}
add_filter('wp_http_cookie_value', 'wp_http_cookie_value_filter', 10, 2);
However this would ofcourse apply to all requests, so as long as you can’t tell for sure that you are the only one using this filter and/or making requests that contain cookies, it’s probably a pretty bad idea.
Maybe if your cookie has a very unique name you could use that to filter only your specific cookie values:
function wp_http_cookie_value_filter($value, $name)
{
if($name === 'my_very_special_cookie')
{
return urlencode($value);
}
return $value;
}
add_filter('wp_http_cookie_value', 'wp_http_cookie_value_filter', 10, 2);
Other than that you are probably better off using your workaround, ie manipulate the cookie value only for your specific requests.