1 files changed, 56 insertions, 0 deletions
diff --git a/util/src/fs.rs b/util/src/fs.rs
new file mode 100644
index 0000000..6a7a5b4
--- /dev/null
+++ b/util/src/fs.rs
@@ -0,0 +1,56 @@
+use std::io::{self, Result};
+use std::path::{Path, PathBuf};
+use rand::{Rng, distributions::Alphanumeric};
+use tokio::fs;
+
+/// Create a temporary file named `temp.[a-zA-Z0-9]{length}` in
+/// the given location and immediately open it. Returns the
+/// filename and the corresponding file handle. It is the caller's
+/// responsibility to clean up the temporary file when it is no
+/// longer needed.
+///
+/// Uses [`OpenOptions::create_new`][fs::OpenOptions::create_new]
+/// to detect filename collisions, in which case it will
+/// automatically retry until the operation succeeds.
+///
+/// # Errors
+///
+/// Returns the underlying [`io::Error`] if the operation fails
+/// due to reasons other than filename collision.
+pub async fn mktemp<T, B>(dir: T, basename: B, length: usize) -> Result<(PathBuf, fs::File)>
+where
+    T: AsRef<Path>,
+    B: Into<Option<&'static str>>
+{
+    let dir = dir.as_ref();
+    let basename = basename.into().unwrap_or("");
+    fs::create_dir_all(dir).await?;
+
+    loop {
+        let filename = dir.join(format!(
+            "{}{}{}",
+            basename,
+            if basename.is_empty() { "" } else { "." },
+            {
+                let string = rand::thread_rng()
+                .sample_iter(&Alphanumeric)
+                .take(length)
+                .collect::<Vec<u8>>();
+                String::from_utf8(string).unwrap()
+            }
+        ));
+
+        match fs::OpenOptions::new()
+            .create_new(true)
+            .write(true)
+            .open(&filename)
+            .await
+        {
+            Ok(file) => return Ok((filename, file)),
+            Err(err) => match err.kind() {
+                io::ErrorKind::AlreadyExists => continue,
+                _ => return Err(err)
+            }
+        }
+    }
+}