Use Rust for formatting

The fprintf implementation included in crt0 is too rudimental

native/src/init/lib.rs

@@ -1,13 +1,26 @@
+#![feature(format_args_nl)]
+
 use logging::setup_klog;
+use rootdir::inject_magisk_rc;
 // Has to be pub so all symbols in that crate is included
 pub use magiskpolicy;
 
 mod logging;
+mod rootdir;
 
 #[cxx::bridge]
 pub mod ffi {
     #[namespace = "rust"]
     extern "Rust" {
         fn setup_klog();
+        fn inject_magisk_rc(fd: i32, tmp_dir: Utf8CStrRef);
+    }
+
+    unsafe extern "C++" {
+        include!("../base/include/base.hpp");
+
+        #[namespace = "rust"]
+        #[cxx_name = "Utf8CStr"]
+        type Utf8CStrRef<'a> = base::ffi::Utf8CStrRef<'a>;
     }
 }

native/src/init/rootdir.cpp

@@ -77,24 +77,7 @@ static void patch_rc_scripts(const char *src_path, const char *tmp_path, bool wr
         rc_list.clear();
 
         // Inject Magisk rc scripts
-        LOGD("Inject magisk rc\n");
-        fprintf(dest.get(), R"EOF(
-on post-fs-data
-    start logd
-    exec %2$s 0 0 -- %1$s/magisk --post-fs-data
-
-on property:vold.decrypt=trigger_restart_framework
-    exec %2$s 0 0 -- %1$s/magisk --service
-
-on nonencrypted
-    exec %2$s 0 0 -- %1$s/magisk --service
-
-on property:sys.boot_completed=1
-    exec %2$s 0 0 -- %1$s/magisk --boot-complete
-
-on property:init.svc.zygote=stopped
-    exec %2$s 0 0 -- %1$s/magisk --zygote-restart
-)EOF", tmp_path, MAGISK_PROC_CON);
+        rust::inject_magisk_rc(fileno(dest.get()), tmp_path);
 
         fclone_attr(fileno(src.get()), fileno(dest.get()));
     }

native/src/init/rootdir.rs

@@ -0,0 +1,37 @@
+use std::fs::File;
+use std::io::Write;
+use std::mem;
+use std::os::fd::{FromRawFd, RawFd};
+
+use base::{debug, Utf8CStr};
+
+pub fn inject_magisk_rc(fd: RawFd, tmp_dir: &Utf8CStr) {
+    debug!("Injecting magisk rc");
+
+    let mut file = unsafe { File::from_raw_fd(fd) };
+
+    write!(
+        file,
+        r#"
+on post-fs-data
+    start logd
+    exec {1} 0 0 -- {0}/magisk --post-fs-data
+
+on property:vold.decrypt=trigger_restart_framework
+    exec {1} 0 0 -- {0}/magisk --service
+
+on nonencrypted
+    exec {1} 0 0 -- {0}/magisk --service
+
+on property:sys.boot_completed=1
+    exec {1} 0 0 -- {0}/magisk --boot-complete
+
+on property:init.svc.zygote=stopped
+    exec {1} 0 0 -- {0}/magisk --zygote-restart
+"#,
+        tmp_dir, "u:r:magisk:s0"
+    )
+    .ok();
+
+    mem::forget(file)
+}