Bug: deno serve --host localhost prints invalid URL

[marvinhagemeister]

When passing --host localhost to deno serve, the CLI will print an invalid URL: http://::1:8000/

Steps to reproduce

// main.ts
export default {
  fetch(_req) {
    return new Response("it works");
  },
};

Then run deno serve --host localhost main.ts

CLI output

$ deno serve --host localhost main.ts 
deno serve: Listening on http://::1:8000/

Version: Deno 1.43.1

[mmastrac]

@marvinhagemeister is this Linux or Mac? It looks like the socket address is being resolved here which is a bit strange.

[marvinhagemeister]

@mmastrac I'm on macOS

[marvinhagemeister]

Turns out that the issue can be reproduced with Deno.serve alone:

Deno.serve({ hostname: "localhost" }, () => new Response("foo"));

Output:

$ deno run -A foo.ts
Listening on http://::1:8000/

[mmastrac]

@marvinhagemeister What do you have in /etc/hosts (cat /etc/hosts | grep "localhost")? Also, do you have IPv6 configured under your network settings?

I wonder if this is a weird IPv6 resolution thing.

[marvinhagemeister]

The default host file on macOS looks like this:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1       localhost
255.255.255.255	broadcasthost
::1             localhost

[dsherret]

Just ran into this on Windows. In v1.42.3 it prints localhost and in 1.43.1 it prints "::1"

Deno.serve({
  hostname: "localhost",
  onListen(details) {
    console.log(details);
  },
}, (request) => {
  return new Response(null);
})

[dsherret]

It also occurs on Linux and Mac: https://github.com/dsherret/dax/actions/runs/8951547585/job/24587971522

[AverageHelper]

Seems to also occur with Deno.serve in macOS and Deno 1.43.1:

// index.ts
Deno.serve({ hostname: "localhost" }, /* handler */);

Then deno run --allow-net index.ts prints http://::1:8000/

As an aside, pasting the given URL into Firefox results in a web search, rather than an attempt to connect to the local webserver as expected. According to RFC2732, the URL should instead be rendered as http://[::1]:8000/. Adding these brackets around the IPv6 address causes browsers to behave as expected.