aoc-input-build

About

aoc-input-build is a Rust library to be used as build dependency from build.rs. It downloads input files for Advent of Code.

Installing

Add this library as build dependency.

cargo add --build aoc-input-build

Usage

// in build.rs
use aoc_input_build::download_inputs;

fn main() {
    let root_dir = env!("CARGO_MANIFEST_DIR"); // root of the project, should always be set to CARGO_MANIFEST_DIR env var
    let token = env!("AOC_TOKEN"); // session cookie from https://adventofcode.com/
    let year = 2025; // which year of Advent of Code to use

    download_inputs(root_dir, token, year);
}

To download input file for a day, a dayXX.rs file must be present in src/ (where XX stands for the day's number e.g. day01.rs, single digit numbers with a leading zero). The input files will be downloaded to input/ subdirectory and called dayXX.txt.

Downloading files with build script ensures that they will be available when the project is built. That means you can use include_str! macro to load input. Or you can use an aoc helper that doesn't support downloading input files and you don't have to manually get them.

Here is an example of a correct project structure:

.
├── build.rs
├── Cargo.lock
├── Cargo.toml
├── input - will download input files here
│   ├── day01.txt
│   └── day02.txt
└── src
    ├── day01.rs
    ├── day02.rs
    └── main.rs

The build script will re-run when any file inside src/ or input/ is changed. But once the input files are downloaded, subsequent execution of the build script won't download those days again. Change of year also won't trigger input file re-download.

To download an input file again, you need to delete it and rebuild the project.

Contributing

Feedback and pull requests are welcome.

AoC automation

This script does follow the automation guidelines on the /r/adventofcode community wiki.

Once inputs are downloaded, they are cached locally (see download_inputs()).

If you suspect your input is corrupted, you can delete the file and rebuild project with cargo build to re-run build script.

The User-Agent header in fetch_input() is set to me.