php parse_url reverse — parsed url

These are the two functions I use for decomposing and rebuilding URLs:

function http_parse_query($query) {
    $parameters = array();
    $queryParts = explode('&', $query);
    foreach ($queryParts as $queryPart) {
        $keyValue = explode('=', $queryPart, 2);
        $parameters[$keyValue[0]] = $keyValue[1];
    }
    return $parameters;
}

function build_url(array $parts) {
    return (isset($parts['scheme']) ? "{$parts['scheme']}:" : '') . 
        ((isset($parts['user']) || isset($parts['host'])) ? '//' : '') . 
        (isset($parts['user']) ? "{$parts['user']}" : '') . 
        (isset($parts['pass']) ? ":{$parts['pass']}" : '') . 
        (isset($parts['user']) ? '@' : '') . 
        (isset($parts['host']) ? "{$parts['host']}" : '') . 
        (isset($parts['port']) ? ":{$parts['port']}" : '') . 
        (isset($parts['path']) ? "{$parts['path']}" : '') . 
        (isset($parts['query']) ? "?{$parts['query']}" : '') . 
        (isset($parts['fragment']) ? "#{$parts['fragment']}" : '');
}

// Example
$parts = parse_url($url);

if (isset($parts['query'])) {
    $parameters = http_parse_query($parts['query']);
    foreach ($parameters as $key => $value) {
        $parameters[$key] = $value; // do stuff with $value
    }
    $parts['query'] = http_build_query($parameters);
}

$url = build_url($parts);