feat: add patcher

Cargo.toml

@@ -4,4 +4,12 @@ version = "0.0.0"
 edition = "2021"
 publish = false
 
+[profile.release]
+strip = true
+opt-level = "z"
+lto = true
+codegen-units = 1
+
 [dependencies]
+clap = { version = "4.4", features = ["derive"] }
+winreg = "0.51"

src/main.rs

@@ -1,3 +1,57 @@
+use std::fs;
+use std::path::PathBuf;
+use std::time::Instant;
+
+use clap::Parser;
+use winreg::{enums::HKEY_CLASSES_ROOT, RegKey};
+
+const SIGNATURE: &[u8] = &[
+    0x41, 0x80, 0xbe, 0x50, 0x01, 0x00, 0x00, 0x00, 0x74, 0x05, 0xe8,
+];
+
+const PATCH: &[u8] = &[
+    0x41, 0x80, 0xbe, 0x50, 0x01, 0x00, 0x00, 0x00, 0x90, 0x90, 0xe8,
+];
+
+#[derive(Parser)]
+#[command(author, version, about, long_about = None)]
+struct Cli {
+    input: Option<PathBuf>,
+    output: Option<PathBuf>,
+}
+
+fn patch(input: &PathBuf, output: &PathBuf) {
+    let mut binary = fs::read(input).expect("Could not read input file.");
+
+    let offset = binary
+        .windows(SIGNATURE.len())
+        .position(|window| window == SIGNATURE)
+        .expect("Could not find signature.");
+
+    binary[offset..offset + PATCH.len()].copy_from_slice(PATCH);
+    fs::write(output, binary).expect("Could not write output file.");
+}
+
 fn main() {
-    println!("Hello, world!");
+    let Cli { input, output } = Cli::parse();
+
+    #[rustfmt::skip]
+    let input = input.unwrap_or_else(|| {
+        let path: String = RegKey::predef(HKEY_CLASSES_ROOT)
+            .open_subkey("roblox-studio").unwrap()
+            .open_subkey("DefaultIcon").unwrap()
+            .get_value("").unwrap();
+
+        PathBuf::from(path)
+    });
+
+    let output = if cfg!(debug_assertions) {
+        output.unwrap_or_else(|| input.with_file_name("RobloxStudioBeta_INTERNAL.exe"))
+    } else {
+        output.unwrap_or_else(|| input.clone()) // TODO: Is convenience really worth it?
+    };
+
+    let now = Instant::now();
+    patch(&input, &output);
+    println!("Patched in {:?}.", now.elapsed());
 }