graplsub-rs

Generate A Random Album Playlist for Subsonic-compatible servers.

Introduction

I was lamenting the general state of music player support for proper random album playlists, i.e. a large playlist featuring one complete album at a time.

I was previously using MPD and had resorted to writing a shell script to maintain a playlist with mpc for any of my clients to pick up. I've now switched to using Navidrome, the Subsonic-compatible server, and threatened to write a similar program to do the same using its API.

Well, here it is.

Installation

This is a Rust application, so after cloning this repo you can build it from source with cargo like:

$ cargo build --release

The binary should then be found in the target/release/ directory. Put it on your path or run it from anywhere.

Prerequisites

• A Subsonic-compatible server with an open API endpoint that supports at least API version 1.14.0. I have only tested against Navidrome which is currently on API version 1.16.1.
• More than one album 😀

Basic theory of operation

This thing quite simply uses the Subsonic API to poke songs into a playlist.

graplsub requests a large number of albums at random and then pushes the songs in, in order from each album. It does 100 albums by default (if you have that many), but can do up to 500 (API limitation). For me, 500 albums is usually around 5 days of music if left constantly playing.

Every time you run graplsub, it will delete the playlist and create it again with a new random order. This should not be a problem as Subsonic clients usually load a playlist into a play queue, and play that. If you have modified your library or just want to shuffle things again you can clear your play queue and load the playlist in again.

Personally I have graplsub run regularly so new music I add gets found.

Usage

All configuration is currently by environment variables.

Required environment variables

GRAPLSUB_USER

Your user name in the Subsonic server. The playlist will be owned by this user.

GRAPLSUB_PASS

Your password for accessing your Subsonic server. The user name and password are the same as what you would have put in any Subsonic client you use and have the same security implications.

Optional environment variables

GRAPLSUB_BASE_URL

Default: http://localhost:4533

This should be the same as the host and port that you have put into any Subsonic client that you use.

Don't put a trailing / — that will result in graplsub getting a HTML page from the Subsonic server instead of the JSON API, and it will complain about that.

I have not tested TLS (https) connections but I think they should work. Let me know!

GRAPLSUB_NUM_ALBUMS

Default: 100

How many albums full of songs to put in to the playlist each time.

Each time graplsub runs it will delete the playlist and create it again with this many albums worth of songs. Obviously albums have different numbers of tracks so it's hard to predict how big the playlist will be.

All tracks from each album will be added, in disc and track order.

The Subsonic API has a limit of 500 albums per request. It wouldn't be hard to paginate through the entire library to get all albums, but I didn't feel like there was much need — for me, 500 albums is usually more than 5 days of continuous music.

GRAPLSUB_PLAYLIST_NAME

Default: graplsub_random_albums

The name of the playlist to generate. This is going to be deleted each time you run graplsub so you wouldn't want to use one that is curated in any other way.

Limitations

graplsub works well enough for my needs now but there are a few things I can think of to improve either as a matter of pride or if nerd-sniped into it. These include:

• Batching of song submissions. At the moment each song is pushed into the playlist with an individual HTTP GET request. Since an album will often have tens of tracks on it this obviously means that for 500 albums that's thousands of HTTP requests each time to make a playlist. The Subsonic API does allow multiple songs to be added each time, though this is done by adding query parameters onto a GET request (don't blame me, I didn't design this…), so there is a limit to how far you could go with that. Even so, on my network it takes about 12 seconds to add approximately 2,000 tracks.
• It might be nice to accept command-line arguments or a config file instead of just environment variables.
• Public playlist option? By default new Subsonic playlists are private, meaning only visible to clients logged in using your own credentials. You can make them public and then all other users on your server can see them (only useful if they can also see your library, of course). You can set the playlist public after it's created, but at the moment that setting will be lost when graplsub deletes and re-creates the playlist. It wouldn't be hard to add a "public playlist" option, but no one in my house wants to listen to my library by random albums except me! 😀
• Maybe there would be some use in limiting the playlist length by track count or total playtime instead of just album count.
• It could be good to have an option to exclude "various artists" albums.
• I can see how one might want to only take albums from a particular library or set of libraries. Personally my default user account only sees my own library and I have to log in as a different user to see the shared libraries of others. In a more permissive setup though you'd get random albums from every library. Not all Subsonic servers even support multiple libraries (Navidrome does).
• Navidrome's Smart Playlists feature has some good ideas. It's a pity it couldn't solve my random album needs, but I'm told they're working on it. Anyway, it could be interesting to add some other playlist-building rules in addition to "random albums", like say "bias towards albums that haven't been listened to recently", or "choose albums from this set of genres". The full set of album and song metadata is available through the API so that's interesting.
• Running graplsub repeatedly is a waste of resources if you aren't actually going to look at the playlist again, but there is no way to change the order or pick up new music without doing so. It looks like there may be a way to extract from Navidrome some sort of "last update" time for the entire library so it could be possible to have graplsub optionally run in a mode that doesn't make a new playlist unless the library has changed.
• I could probably provide some binaries if anyone actually cares.

Security considerations

Subsonic security posture is fairly weak and I just have to work with that. All clients are using the same API as graplsub uses, so these same issues face them as well.

The API is all GET requests each of which carry the credentials as query parameters, so there's concerns about exposure in transit and in log files etc.

The password is salted and MD5 hashed but you probably don't need telling how weak MD5 is, and there is no protection against replaying credentials, i.e., if an attacker sees the MD5 token and the salt that are in each GET request they can just use them again at any time.

Hopefully then it's clear that you would never want to reuse credentials here.