From 9e45ba103224554b757c77cc0b2dc93823ed62b7 Mon Sep 17 00:00:00 2001
From: Jiahao XU <Jiahao_XU@outlook.com>
Date: Fri, 22 Jul 2022 19:48:37 +1000
Subject: [PATCH] Impl new RAII type `helpers::flock::FileLock`

that locks a file exclusive or shared

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>
---
 src/helpers.rs       |  3 +++
 src/helpers/flock.rs | 45 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 src/helpers/flock.rs

diff --git a/src/helpers.rs b/src/helpers.rs
index a1ef3c5f..55593da3 100644
--- a/src/helpers.rs
+++ b/src/helpers.rs
@@ -42,6 +42,9 @@ pub use tls_version::TLSVersion;
 mod crate_name;
 pub use crate_name::CrateName;
 
+mod flock;
+pub use flock::FileLock;
+
 pub fn cargo_home() -> Result<&'static Path, io::Error> {
     static CARGO_HOME: OnceCell<PathBuf> = OnceCell::new();
 
diff --git a/src/helpers/flock.rs b/src/helpers/flock.rs
new file mode 100644
index 00000000..2c0707b5
--- /dev/null
+++ b/src/helpers/flock.rs
@@ -0,0 +1,45 @@
+use std::fs::File;
+use std::io;
+use std::ops;
+
+use fs4::FileExt;
+
+#[derive(Debug)]
+pub struct FileLock(File);
+
+impl FileLock {
+    /// NOTE that this function blocks, so it cannot
+    /// be called in async context.
+    pub fn new_exclusive(file: File) -> io::Result<Self> {
+        file.lock_exclusive()?;
+
+        Ok(Self(file))
+    }
+
+    /// NOTE that this function blocks, so it cannot
+    /// be called in async context.
+    pub fn new_shared(file: File) -> io::Result<Self> {
+        file.lock_shared()?;
+
+        Ok(Self(file))
+    }
+}
+
+impl Drop for FileLock {
+    fn drop(&mut self) {
+        let _ = self.unlock();
+    }
+}
+
+impl ops::Deref for FileLock {
+    type Target = File;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl ops::DerefMut for FileLock {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}