parsing version data

also added a binary for testing and an example file for now

Cargo.toml

@@ -3,6 +3,12 @@ name = "factorio_types"
 version = "0.1.0"
 edition = "2021"
 
+[[bin]]
+name = "testing"
+path = "src/bin/testing.rs"
+doc = false
+
+
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]

src/bin/testing.rs

@@ -0,0 +1,14 @@
+use std::{fs::File, io::BufReader};
+
+use factorio_types::ModSettings;
+
+fn main() -> anyhow::Result<()> {
+    let file = File::open("./mod-settings.dat")?;
+    let buf_reader = BufReader::new(file);
+
+    let settings = ModSettings::from_reader(buf_reader)?;
+
+    println!("{settings:?}");
+
+    Ok(())
+}

src/lib.rs

@@ -1,5 +1,11 @@
-use std::collections::HashMap;
+#![feature(array_chunks)]
+#![feature(iter_collect_into)]
 
+use std::{collections::HashMap, io::Read};
+
+use anyhow::{anyhow, Context};
+
+#[derive(Debug)]
 pub enum PropertyTree {
     None,
     Bool(bool),
@@ -8,3 +14,49 @@ pub enum PropertyTree {
     List(Vec<PropertyTree>),
     Dictionary(HashMap<String, PropertyTree>),
 }
+
+#[derive(Debug)]
+pub struct ModSettings {
+    pub version: [u16; 4],
+    pub data: PropertyTree,
+}
+
+impl ModSettings {
+    /// This reads from a reader based on this file specification
+    /// https://wiki.factorio.com/Mod_settings_file_format
+    pub fn from_reader<R>(mut reader: R) -> anyhow::Result<ModSettings>
+    where
+        R: Read,
+    {
+        // Fetching first 8 little endian bytes representing version
+        // https://wiki.factorio.com/Version_string_format
+        let mut version_bytes = [0u8; 8];
+        reader
+            .read_exact(&mut version_bytes)
+            .context("Failed trying to get first 8 bytes representing version number")?;
+
+        // Grab the null byte that follows the version number
+        let _padding_byte = reader
+            .by_ref()
+            .bytes()
+            .next()
+            .ok_or(anyhow!("Unexpected EOF"))
+            .context("Failed trying to grab null byte that follows version number");
+
+        // Mapping pairs of 2 u8s into single le u16s
+        let mut version_map = version_bytes.array_chunks().map(|b| u16::from_le_bytes(*b));
+
+        // Load u16s into an array
+        let version = [
+            version_map.next().unwrap(),
+            version_map.next().unwrap(),
+            version_map.next().unwrap(),
+            version_map.next().unwrap(),
+        ];
+
+        Ok(ModSettings {
+            version,
+            data: PropertyTree::None,
+        })
+    }
+}