# 300

No, not the movie. I'm a nerd who's spent half their day so far configuring nginx, it should be obvious at this point.

---

Since I have my code 1) [on my Gitea (now Forgejo) instance](https://git.askiiart.net/askiiart/askiiart-net), and 2) [mirrored](https://github.com/askiiart/askiiart.github.io) on GitHub, I didn't just want to set up a simple [308 Permanent Redirect](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/308) from [/.git](/.git) to my code in one place. I wanted users to be able to see both options, both Gitea and GitHub, and apparently there's actually a thing for that already, I can just use that!

## ok but how?

300 seems great, but there's no standardized way to use it. The number, and the `Location` header as the preferred choice is all that's actually standardized. Straight from [RFC 9110](https://httpwg.org/specs/rfc9110.html#status.300):

> If the server has a preferred choice, the server *SHOULD* generate a Location header field containing a preferred choice's URI reference. The user agent MAY use the Location field value for automatic redirection.
>
> For request methods other than HEAD, the server *SHOULD* generate content in the 300 response containing a list of representation metadata and URI reference(s) from which the user or user agent can choose the one most preferred.

Does this mean to return some HTML? A JSON dict? YAML? An image of a pickle with that info overlaid on top of it!? *Nobody knows!* And from the Mozilla docs:

> As there is no standardized way of choosing one of the responses, this response code is very rarely used.

Very helpful.

## ok but actually how?

After a bit of Googling, I found [this Stack Overflow thread](https://stackoverflow.com/questions/8905545/what-is-the-exact-response-structure-for-http-status-code-300-multiple-choices), which just says this<sup>[<a href="#browser-specific-info">note</a>]</sup>:

> The "multiple choices" are done by sending the links in hypertext (HTML) content and let the *user* pick.

Well, that's boring. Guess I'll do that then.

```language-nginx
    location  /.git {
        add_header Location "https://git.askiiart.net/askiiart/askiiart-net";
        return 300 '<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"></head><body><a href="https://git.askiiart.net/askiiart/askiiart-net">Self-hosted</a><br><a href="https://github.com/askiiart/askiiart.github.io">GitHub</a></body></html>';
    }
```

## nginx is hard

That config looks fine, right? It just sets the `Location` header and returns this basic menu to pick from. But it won't open in any browsers, Firefox displays nothing, and has `NS_ERROR_WONT_HANDLE_CONTENT` in the developer tools, and Chrome shows a `ERR_INVALID_RESPONSE` error. Running `curl -I https://askiiart.net`, and...

```sh
HTTP/1.1 300 
Server: nginx/1.25.3
Date: Wed, 06 Dec 2023 16:36:01 GMT
Content-Type: application/octet-stream
Content-Length: 223
Connection: keep-alive
```

There's no Location header there! And the browsers are probably refusing to show it because of the wrong `Content-Type` – and no, adding a header with `add_header` doesn't work for that one, either.

Turns out in order to be able to use `add_header`, you first need to set `default_type` (which sets a default `Content-Type`). I could've set that in the `location /.git` block, but I just decided to make it global.

So here's the fixed config:

```language-nginx
    # actually much higher in file
    default_type "text/html";

    location  /.git {
        add_header Location "https://git.askiiart.net/askiiart/askiiart-net";
        return 300 '<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"></head><body><a href="https://git.askiiart.net/askiiart/askiiart-net">Self-hosted</a><br><a href="https://github.com/askiiart/askiiart-net">GitHub</a></body></html>';
    }
```

Yep, that works! I had set up my IP address pages the same way, so let's fix that:

```language-nginx
    location /ip {
        default_type text/plain;
        return 200 "$remote_addr";
    }

    location /ip/json {
        default_type application/json;
        return 200 '{"ip":"$remote_addr"}';
    }
```

These still don't work, they just return my reverse proxy container's gateway's address, but that's for another time.

## Open your eyes... wake up, *Link*

Turns out might be a standard way to do it! From [RFC 9110](https://httpwg.org/specs/rfc9110.html#status.300), again:

> It is possible to communicate the list using a set of Link header fields [RFC5988](https://httpwg.org/specs/rfc9110.html#RFC8288), each with a relationship of "alternate", though deployment is a chicken-and-egg problem.

I'll probably figure out the `Link` header some other time and will add this later, at which point I'll post an addendum. Until then, bye I guess!

## Footnotes and stuff

#### browser-specific info

Elsewhere in the Quora thread it says, in short, that Firefox and Chrome just displays the HTML, and Safari will follow the `Location` header. Edit: Apparently I forgot to link the Quora thread, so I've got no idea what I'm referencing here. Sorry! \[[Back](#ok-but-actually-how)\]