Split cursor capabilities

storage_engine/src/cursor_capabilities/primitive.rs

@@ -0,0 +1,62 @@
+use tokio::io::{AsyncReadExt, AsyncWriteExt, AsyncSeekExt, SeekFrom};
+use tokio::fs::File;
+use async_trait::async_trait;
+
+use crate::storage_engine::{FilePosition, Result};
+
+#[async_trait]
+pub(crate) trait CursorCanRead<T> {
+    fn file(&mut self) -> &mut File;
+    fn eof_file_position(&self) -> FilePosition;
+
+    async fn read_bytes(&mut self, bytes: &mut [u8]) -> Result<()> {
+        self.file().read_exact(bytes).await?;
+        Ok(())
+    }
+
+    async fn get_bytes(&mut self, count: usize) -> Result<Vec<u8>> {
+        let mut result: Vec<u8> = Vec::with_capacity(count);
+        self.read_bytes(&mut result).await?;
+        Ok(result)
+    }
+
+    async fn seek_to(&mut self, file_position: FilePosition) -> Result<FilePosition> {
+        let file_position = self.file().seek(SeekFrom::Start(file_position)).await?;
+        Ok(file_position)
+    }
+
+    // Start of the file i.e. the Header, not the entries.
+    async fn seek_to_start(&mut self) -> Result<FilePosition> {
+        let file_position = self.file().seek(SeekFrom::Start(0)).await?;
+        Ok(file_position)
+    }
+
+    async fn seek_to_end(&mut self) -> Result<FilePosition> {
+        let file_position = self.file().seek(SeekFrom::End(0)).await?;
+        Ok(file_position)
+    }
+
+    // Seeks from current position by offset and returns new file position
+    async fn seek_by(&mut self, offset: i64) -> Result<FilePosition> {
+        let file_position = self.file().seek(SeekFrom::Current(offset)).await?;
+        Ok(file_position)
+    }
+
+    async fn current_file_position(&mut self) -> Result<FilePosition> {
+        let next_file_position: FilePosition = self.file().stream_position().await?;
+        Ok(next_file_position)
+    }
+
+    async fn is_at_eof(&mut self) -> Result<bool> {
+        let current_file_position = self.current_file_position().await?;
+        let eof_file_position = self.eof_file_position();
+        Ok(current_file_position == eof_file_position)
+    }
+}
+
+#[async_trait]
+pub(crate) trait CursorCanWrite<T>: CursorCanRead<T> {
+    async fn write_bytes(&mut self, bytes: &[u8]) -> Result<usize> {
+        Ok(self.file().write(bytes).await?)
+    }
+}