Url::parse removes host from Windows-style file URL

[msrd0]

When trying to parse a windows-style file: URL that contains a hostname, that hostname is removed from the resulting URL:

use url::Url; // 2.5.8

fn main() {
    println!("{}", Url::parse("file://irgendwo/I:/m/nirgendwo").unwrap());
    // prints file:///I:/m/nirgendwo
}

When we use a Unix-style URL (file://irgendwo/im/nirgendwo), it is returned unmodified (i.e. including the hostname).

We can, however, construct a Windows-style URL manually using .set_host():

use url::Url; // 2.5.8

fn main() {
    let mut url = Url::parse("file:///I:/m/nirgendwo").unwrap();
    url.set_host(Some("irgendwo"));
    println!("{url}");
    // prints file://irgendwo/I:/m/nirgendwo
}

[msrd0]

I think I found the culprit:

rust-url/url/src/parser.rs

Lines 544 to 551 in 55ff72d

	// For file URLs that have a host and whose path starts
	// with the windows drive letter we just remove the host.
	if !has_host {
	self.serialization
	.drain(host_start as usize..host_end as usize);
	host_end = host_start;
	host = HostInternal::None;
	}

This was apparently added in #537.

Removing that code results in three test "failures":

errors:

  name: <file://example.net/C:/>
  err:  unexpected success

  name: <file://1.2.3.4/C:/>
  err:  unexpected success

  name: <file://[1::8]/C:/>
  err:  unexpected success

I didn't find any mention in the spec that hosts should be trimmed for windows-style file urls at first glance. Is removing the host from the URL really the intended behaviour? If it is, I would appreciate an option to disable this host removal.

[msrd0]

WhatWG has three reference implementations. I tested all three and none of them remove the hostname of file URL's.

JavaScript: (via https://jsdom.github.io/whatwg-url/)

C++:

$ adaparse 'file://irgendwo/I:/m/nirgendwo'
{
        "buffer":"file://irgendwo/I:/m/nirgendwo",
        "protocol":"file:",
        "host":"irgendwo",
        "path":"/I:/m/nirgendwo",
        "opaque path":false,
        "protocol_end":5,
        "username_end":7,
        "host_start":7,
        "host_end":15,
        "port":null,
        "pathname_start":15,
        "search_start":null,
        "hash_start":null
}

Python:

Python 3.13.13 (main, Apr  7 2026, 20:49:46) [Clang 22.1.1 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from pywhatwgurl import URL
>>> url = URL("file://irgendwo/I:/m/nirgendwo")
>>> url
URL('file://irgendwo/I:/m/nirgendwo')
>>> url.hostname
'irgendwo'
>>> url.pathname
'/I:/m/nirgendwo'

[Scripter17]

I didn't find any mention in the spec that hosts should be trimmed for windows-style file urls at first glance. Is removing the host from the URL really the intended behaviour? If it is, I would appreciate an option to disable this host removal.

It's probably from an old version of the spec. In #1124 I removed some code that refers to a part of the spec that used to exist but now doesn't.

Agonizingly, the url spec is alive.