improve documentation of some functions and more readme work

src/config/loader.rs

@@ -0,0 +1,40 @@
+use std::ops::Deref;
+use anyhow::{bail, Context, Result};
+use toml::Value;
+use uefi::proto::device_path::LoadedImageDevicePath;
+use crate::config::{latest_version, RootConfiguration};
+use crate::utils;
+
+fn load_raw_config() -> Result<Vec<u8>> {
+    let current_image_device_path_protocol =
+        uefi::boot::open_protocol_exclusive::<LoadedImageDevicePath>(uefi::boot::image_handle())
+            .context("unable to get loaded image device path")?;
+    let path = current_image_device_path_protocol.deref().to_boxed();
+
+    let content = utils::read_file_contents(&path, "sprout.toml")
+        .context("unable to read sprout.toml file")?;
+    Ok(content)
+}
+
+pub fn load() -> Result<RootConfiguration> {
+    let content = load_raw_config()?;
+    let value: Value = toml::from_slice(&content).context("unable to parse sprout.toml file")?;
+
+    let version = value
+        .get("version")
+        .cloned()
+        .unwrap_or_else(|| Value::Integer(latest_version() as i64));
+
+    let version: u32 = version
+        .try_into()
+        .context("unable to get configuration version")?;
+
+    if version != latest_version() {
+        bail!("unsupported configuration version: {}", version);
+    }
+
+    let config: RootConfiguration = value
+        .try_into()
+        .context("unable to parse sprout.toml file")?;
+    Ok(config)
+}