chore: remove once_cell dependency

Now that MSRV is 1.65, we can replace the once_cell dependency by using
a standard mutex.

Author: vthib

Cargo.lock

@@ -74,9 +74,5 @@ glob = "0.3.1"
 tempfile = "3.8"
 yara = { version = "0.21", features = ["vendored"] }
 
-# Only needed in tests because Mutex::new is not const
-# in 1.62 MSRV. Can be removed once MSRV is bumped above it.
-once_cell = "1.18"
-
 [package.metadata.docs.rs]
 features = ["authenticode", "memmap"]

boreal/Cargo.toml

@@ -79,8 +79,6 @@ use base64 as _;
 #[cfg(test)]
 use glob as _;
 #[cfg(test)]
-use once_cell as _;
-#[cfg(test)]
 use tempfile as _;
 #[cfg(test)]
 use yara as _;

boreal/src/lib.rs

@@ -185,21 +185,25 @@ impl Compiler {
 #[cfg(all(feature = "object", feature = "authenticode"))]
 fn build_compiler() -> boreal::Compiler {
     use boreal::module::Pe;
-    use once_cell::sync::Lazy;
-
-    // Can be replaced with a std Mutex once MSRV is bumped to 1.63.
-    static PE_MODULE: Lazy<Pe> = Lazy::new(|| {
-        // Safety:
-        // - This is in a critical section that ensures a single thread can call this function
-        // - The only openssl code in this codebase is in the authenticode parsing, called when
-        //   scanning. Since to scan rules must first be compiled, and this is called on the very
-        //   first build of a compiler, there can be no other threads calling into OpenSSL while
-        //   this is called.
-        unsafe { Pe::new_with_signatures() }
-    });
+    use std::sync::Mutex;
+
+    static PE_MODULE: Mutex<Option<Pe>> = Mutex::new(None);
 
     let mut compiler = boreal::Compiler::new_without_pe_module();
-    compiler.add_module(*PE_MODULE);
+    {
+        let mut mutex = PE_MODULE.lock().unwrap();
+        let pe_module = mutex.get_or_insert_with(|| {
+            // Safety:
+            // - This is in a critical section that ensures a single thread can call this function
+            // - The only openssl code in this codebase is in the authenticode parsing, called when
+            //   scanning. Since to scan rules must first be compiled, and this is called on the very
+            //   first build of a compiler, there can be no other threads calling into OpenSSL while
+            //   this is called.
+            unsafe { Pe::new_with_signatures() }
+        });
+        compiler.add_module(*pe_module);
+    }
+
     compiler
 }