Data organization

A/B Street includes lots of large binary files to represent converted maps, scenarios, and prebaked simulation results. The files are too large to store in git, but the files are still logically tied to a version of the code, since the format sometimes changes. Additionally, all of the files are too large to include in the .zip release that most people use, but it should still be possible for players to download the optional content. Also, there are different versions of the game floating around, on native and web, that have to be associated with the proper version of these files.

It's all slightly confusing, so this page describes how it all works.

The data itself

If you peek into the data/ directory, it's mainly split into 3 subdirectories. system/ is used when running the game and is the subject of this page. input/ is used to store input and intermediate files for importing maps, and only developers running the importer should care about it. player/ contains local settings, map edits, and other data created in-game.

data/MANIFEST.json is a listing of all files in data/system/, along with their size and md5sum. Different tools compare this manifest to the local filesystem to figure out what to do.

There are also some other scripts and files in data/, but they should probably be moved.

Where the data is stored

data/system/ and data/input/ are stored in Amazon S3, at This S3 bucket is organized into versions: dev, 0.2.17, 0.2.18, etc. dev represents the latest version of all data files. The numbered versions correspond to releases and only contain data/system/, not data/input/. Depending how large these directories grow over time, I'll commit to keeping around at least 3 of the previous numbered versions, but I might delete older ones after that. is wired up to Cloudfront, via Google Domains. The CDN is faster than accessing the S3 bucket (in one region) directly.

Native, running from source

For people building the game from source, the process to keep data files fresh is to cargo run --bin updater -- download. This tool calculates md5sums of all local files, then compares it with the checked-in data/MANIFEST.json. Any difference results in a local file being deleted or a new file from S3 being downloaded. By editing data/player/data.json manually or using the UI in the game (found by loading a map, then choosing to download more maps), somebody can opt into downloading "extra/optional" cities.

Native, running from a release .zip

When the weekly .zip binary release for Mac, Linux, and Windows is produced, the game crate is built with --features release_s3. When the downloader UI is opened in-game, this causes downloads to occur from a versioned S3 directory, like 0.2.17, depending on the version string compiled into the game at that time. So somebody can run off the weekly release, opt into more cities, and get the correct version of the files, even if the format has changed in /dev/ since then.

Web, running locally

The strategy for managing files gets more interested when the game is compiled to WebAssembly, since browsers can't read from the local filesystem. game/src/ contains some crazy tricks to instead make asynchronous HTTP requests through the browser. When using game/, the files are served through a local HTTP server and symlinked to the local copy of data/system/.

Not all files are loaded through HTTP; some are actually statically compiled into the .wasm file itself! abstutil/src/ does this magic using the include_dir crate. Only a few critical large files, needed at startup, are included. There's an IO layer for listing and reading files that, on web, merges results from the bundled-in files and the remote files that're declared to exist in the bundled-in copy of data/MANIFEST.json.

Web, from S3

Everything's the same, except that since the URL isn't localhost, the game makes HTTP requests to the S3 bucket (or wherever the game is hosted). Additionally, the files are expected to be gzipped. The web version always pins to /dev, never a release version of the data, since the web client is always updated along with the data, for now.