src/Request.php
public function withUri(UriInterface $uri, $preserveHost = false)
    {
        $clone = clone $this;
        $clone->uri = $uri;
        $headerHost = $clone->getHeader('Host');

        if (!$preserveHost || empty($headerHost)) {
            if (!empty($clone->getUri()->getHost())) {
                $clone->headers['Host'] = [$clone->getUri()->getHost()];
            }
        }

        return $clone;
    }
public function withUri(UriInterface $uri, $preserveHost = false)
    {
        $clone = clone $this;
        $clone->uri = $uri;
        $headerHost = $clone->getHeader('Host');

        if (!$preserveHost || empty($headerHost)) {
            if (!empty($clone->getUri()->getHost())) {
                $clone->headers['Host'] = [$clone->getUri()->getHost()];
            }
        }

        return $clone;
    }
Returns an instance with the provided URI.

This method MUST update the Host header of the returned request by
default if the URI contains a host component. If the URI does not
contain a host component, any pre-existing Host header MUST be carried
over to the returned request.

You can opt-in to preserving the original state of the Host header by
setting `$preserveHost` to `true`. When `$preserveHost` is set to
`true`, this method interacts with the Host header in the following ways:

- If the Host header is missing or empty, and the new URI contains
a host component, this method MUST update the Host header in the returned
request.
- If the Host header is missing or empty, and the new URI does not contain a
host component, this method MUST NOT update the Host header in the returned
request.
- If a Host header is present and non-empty, this method MUST NOT update
the Host header in the returned request.

This method MUST be implemented in such a way as to retain the
immutability of the message, and MUST return an instance that has the
new UriInterface instance.

@link http://tools.ietf.org/html/rfc3986#section-4.3

@param UriInterface $uri          New request URI to use.
@param bool         $preserveHost Preserve the original state of the Host header.

@return static