# Boxcars

![ci](https://github.com/nickbabcock/boxcars/workflows/ci/badge.svg) [![](https://docs.rs/boxcars/badge.svg)](https://docs.rs/boxcars) [![Version](https://img.shields.io/crates/v/boxcars.svg?style=flat-square)](https://crates.io/crates/boxcars)

Boxcars is a [Rocket League](http://www.rocketleaguegame.com/) replay parser library written in
Rust.

## Features

- ✔ Safe: Stable Rust with no unsafe
- ✔ Fast: Parse over a hundred replays per second per CPU core
- ✔ Fuzzed: Extensively fuzzed against potential malicious input
- ✔ Ergonomic: Serialization support is provided through [serde](https://github.com/serde-rs/serde)

See where Boxcars in used:

- Inside the [rrrocket CLI app](https://github.com/nickbabcock/rrrocket) to turn Rocket League Replays into JSON
- Compiled to [WebAssembly and embedded in a web page](https://rl.nickb.dev/)
- Underpins the python analyzer of the [popular calculated.gg site](https://calculated.gg/)
- Powers the [`subtr-actor`](https://github.com/rlrml/subtr-actor) library that offers an ergonomic interface to processing replay data

## Quick Start

Below is an example to output the replay structure to json:

```rust
use boxcars::{ParseError, Replay};
use std::error;
use std::fs;
use std::io::{self, Read};

fn parse_rl(data: &[u8]) -> Result<Replay, ParseError> {
    boxcars::ParserBuilder::new(data)
        .must_parse_network_data()
        .parse()
}

fn run(filename: &str) -> Result<(), Box<dyn error::Error>> {
    let filename = "assets/replays/good/rumble.replay";
    let buffer = fs::read(filename)?;
    let replay = parse_rl(&buffer)?;
    serde_json::to_writer(&mut io::stdout(), &replay)?;
    Ok(())
}
```

The above example will parse both the header and network data of a replay file, and return an
error if there is an issue either header or network data.  Since the network data will often
change with each Rocket League patch, the default behavior is to ignore any errors from the
network data and still be able to return header information.

## Variations

If you're only interested the header (where tidbits like goals and scores are stored) then you
can achieve an 1000x speedup by directing boxcars to only parse the header.

- By skipping network data one can parse and aggregate thousands of replays in
under a second to provide an immediate response to the user. Then a full
parsing of the replay data can provide additional insights when given time.
- By ignoring network data errors, boxcars can still provide details about
newly patched replays based on the header.

Boxcars will also check for replay corruption on error, but this can be configured to always
check for corruption or never check.

## Benchmarks

To run the boxcar benchmarks:

```
cargo bench

# Or if you want to see if compiling for the
# given cpu eeks out tangible improvements:
# RUSTFLAGS="-C target-cpu=native" cargo bench
```

Since Boxcars allows you to pick and choose what to parse, below is a table
with the following options and the estimated elapsed time.

| Header | Corruption Check | Body | Output JSON | Elapsed | Throughput |
| -      | -                | -    | -           | -       | -          |
| ✔      |                  |      |             | 68.0 µs |            |
| ✔      | ✔                | ✔    |             | 6.6 ms | 223 MiB/s  |
| ✔      |                  | ✔    |             | 6.3 ms | 232 MiB/s  |
| ✔      | ✔                | ✔    | ✔           | 35 ms |  531 MiB/s ^1  |

^1: JSON serialization throughput includes the amount of JSON produced

## Special Thanks

Special thanks needs to be given to everyone in the Rocket League community who figured out the replay format and all its intricacies. Boxcars wouldn't exist if it weren't for them. I heavily leaned on implementations in [rattletrap](https://github.com/tfausak/rattletrap), [RocketLeagueReplayParser](https://github.com/jjbott/RocketLeagueReplayParser), and [Bakkes' replay parser](https://github.com/Bakkes/CPPRP). One of those should be your go to Rocket League Replay tool, unless you need speed, as those implementations are more mature than boxcars.

## Difference between rattletrap and boxcars

- Rattletrap is a binary that ingests rocket league replays and outputs JSON, while boxcars is a lower level parsing library. Boxcars underpins Rrrocket, a cli binary that outputs JSON similar to Rattletrap
- Rattletrap can roundtrip replays (convert them into JSON and then write them out back to a replay losslessly). Boxcars is focussed on parsing replays.
- In part due to allowing roundtrip parsing, rattletrap JSON output is 2x larger than boxcars (rrrocket) even when accounting for output minification.

Below are some differences in the model:

rattletrap:

```json
"properties": {
  "value": {
    "BuildID": {
      "kind": "IntProperty",
      "size": "4",
      "value": {
        "int": 1401925076
      }
    },
  }
}
```

boxcars:

```json
"properties": {
  "BuildID": 1401925076
}
```

---

rattletrap:

```json
"actor_id": {
  "limit": 2047,
  "value": 1
},
```

boxcars:

```json
"actor_id": 1
```

---

rattletrap:

```json
"value": {
  "spawned": {
    "class_name": "TAGame.GameEvent_Soccar_TA",
    "flag": true,
    "initialization": {
      "location": {
        "bias": 2,
        "size": {
          "limit": 21,
          "value": 0
        },
        "x": 0,
        "y": 0,
        "z": 0
      }
    },
    "name": "GRI_TA_1",
    "name_index": 0,
    "object_id": 85,
    "object_name": "Archetypes.GameEvent.GameEvent_Soccar"
  }
}
```

boxcars:

```json
"actor_id": 1,
"name_id": 1,
"object_id": 85,
"initial_trajectory": {
  "location": {
    "x": 0,
    "y": 0,
    "z": 0
  },
  "rotation": null
}
```

While rattletrap provides convenience conversions, boxcars omit them in favor of a more raw view of the replay:

- to derive `object_name`: `replay.objects[x.object_id]`
- to derive `name`: `replay.names[x.name_id]`

---

Attribute updates:

rattletrap:

```json
{
  "actor_id": {
    "limit": 2047,
    "value": 7
  },
  "value": {
    "updated": [
      {
        "id": {
          "limit": 98,
          "value": 34
        },
        "name": "Engine.PlayerReplicationInfo:PlayerName",
        "value": {
          "string": "Nadir"
        }
      }
    ]
  }
}
```

boxcars:

```json
{
  "actor_id": 7,
  "stream_id": 34,
  "object_id": 161,
  "attribute": {
    "String": "Nadir"
  }
}
```

To derive rattletrap's `name` for the attribute use `replay.objects[attribute.object_id]`

## Fuzzing

Boxcars contains a fuzzing suite. If you'd like to run it, first install [cargo-fuzz](https://github.com/rust-fuzz/cargo-fuzz)

```
cargo install cargo-fuzz
```

There are several scenarios to fuzz (`cargo fuzz list`), and the best one to run is `no-crc-body`, due to all aspects of the replay being fuzzed without a crc check:

```
cargo +nightly fuzz run no-crc-body
```