RushLink

A URL shortener and (maybe) a pastebin server for our #ru community.

Building

• go get -u github.com/go-bindata/go-bindata/...
• go generate ./...
• go build ./cmd/rushlink

Deploying

We recommend running rushlink behind a reverse proxy suitable for processing HTTP requests, such as nginx, or haproxy.

Sample nginx config

server {
    location / {
        root    /var/www/rushlink;
        proxy_pass http://127.0.0.1:8000;
        proxy_set_header Host rushlink.local;
        proxy_set_header X-Forwarded-For $remote_addr;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_http_version 1.1;
    }
}

rushlink automatically detects whether http or https is used when X-Forwarded-Proto is correctly set. Otherwise, pass -root_url https://rushlink.local to the binary (e.g. in the systemd unit file).

Sample systemd unit file

[Install]
WantedBy=nginx.service

[Service]
Type=simple
User=rushlink
Group=nogroup
ExecStart=/var/lib/rushlink/rushlink -database /var/lib/rushlink/db -file-store /var/lib/rushlink/filestore -root_url https://rushlink.local

---

Background

Libraries

Use standard-Go-libraries if the job can be done with those. As of now, these are the exceptions:

• github.com/gorilla/mux provides useful stuff for routing requests.
• github.com/gorilla/sessions for session management.
• go.etcd.io/bbolt is our database driver.
• github.com/pkg/errors provides a Wrap function.
• github.com/prometheus/client_golang/prometheus/... has easy Prometheus functionality.

Database

We use go.etcd.io/bbolt. This file should be the only file apart from our monolithic binary. All settings and keys should go in here. Any read-only data resides in the binary file (possibly compressed).

Namespacing

All shortened URLs exist as a key on the root of the webserver, i.e. /xd42. That means that we have to separate every other page with some kind of namespace. Ideas:

• /z/ reserved for flat pages.
• /z/static/ reserved for "static files".

Paste types

Previous, I was planning to put pastes (not redirects) in a separate bucket and below a url namespace. Then when one was created, we would immediately generate a redirect link.

Turns out it's easier though to just save a unit (we call it a "paste") which can be of different types. For example:

• Redirect
• Paste
• File
• Image
• Hypothetical other stuff:
  • Dead-drop
  • [...]?

Shorten keys and collisions

First of all: A sextet is a value of 6 bits.

For generating keys, we will initially generate a random value of 4 sextets, where the first bit is set to 0. If this collides with an existing key, we will generate a new one made out of 5 sextets, and set the prefix bits to 0b10. We will keep doing this until we don't have any collisions anymore.

To get proper-looking keys, we format the key to characters using the base64url alphabet described in (RFC4648, par. 5). The encoded value will be saved in the database.

UI design

As is tradition in a lot of URL-shortener/pastebin-like services, we will put everything in a single <pre> tag, and if possible, just serve text/plain. A good example is https://0x0.st.

The reason we would use text/html instead of text/plain is basically form submissions and JavaScript. Our main API should be cURL, but it would be useful if users could also use the website and/or drag-and-drop files and URLs.

On the other hand, using text/plain saves us so much effort, because we don't have to do any HTML/CSS/JavaScript. We have native terminal support, etc.

The best thing would probably to do both, and correctly listen to the Accept header that the client sends. We can still wrap the plain-text page in a single <pre> to keep it easy for ourselves.

Retention

• If we can, we don't want to have user accounts. We store the sessions forever, and store a user's data in there, without having to collect personal data in any way.
• URL-shortening links will be retained for always, unless the submitter revokes it, in which case it will be replaced by a 410 Gone page[*].
• The probles of pastes are not solved. This is an unsolved problem[*].

[*] In any case, we going to comply with all European laws and reasonable requests for deletion.

Privacy

We will try as hard as possible to not store any data about our users, and will only provide any data when we have the legal obligation to do so.