feat: lay the ground for login

src/utils.rs

@@ -83,3 +83,57 @@ pub mod shasum {
         }
     }
 }
+
+pub mod fs {
+    use std::{io, os::unix::fs::MetadataExt as _, path::Path};
+
+    use tokio::{fs::File, io::AsyncReadExt};
+
+    /// # Errors
+    ///
+    /// On any underlaying file i/o error.
+    ///
+    /// # Panics
+    ///
+    /// If a file's [`u64`] doesn't fit in memory.
+    pub async fn read_limited_path<const MAXSIZE: u64>(path: &Path) -> io::Result<Vec<u8>> {
+        let f = File::open(path).await?;
+        let size = f.metadata().await?.size();
+
+        if size > MAXSIZE {
+            return Err(io::Error::new(
+                io::ErrorKind::FileTooLarge,
+                "filesize is bigger than MAXSIZE",
+            ));
+        }
+        let mut buf = Vec::with_capacity(size.try_into().expect("u64 to fit in usize"));
+        // `.take()` just in case an open fd happens to grow, `.metadata()` SHOULD take
+        // properties from the fd and lock the read fd until its closed but still
+        f.take(MAXSIZE).read_to_end(&mut buf).await?;
+        Ok(buf)
+    }
+
+    /// # Errors
+    ///
+    /// On any underlaying file i/o error.
+    ///
+    /// # Panics
+    ///
+    /// If a file's [`u64`] doesn't fit in memory.
+    pub async fn read_limited_path_str<const MAXSIZE: u64>(path: &Path) -> io::Result<String> {
+        let f = File::open(path).await?;
+        let size = f.metadata().await?.size();
+
+        if size > MAXSIZE {
+            return Err(io::Error::new(
+                io::ErrorKind::FileTooLarge,
+                "filesize is bigger than MAXSIZE",
+            ));
+        }
+        let mut buf = String::with_capacity(size.try_into().expect("u64 to fit in usize"));
+        // `.take()` just in case an open fd happens to grow, `.metadata()` SHOULD take
+        // properties from the fd and lock the read fd until its closed but still
+        f.take(MAXSIZE).read_to_string(&mut buf).await?;
+        Ok(buf)
+    }
+}