async_db: add BufReader, BufReaderStream

for using as mutable reader

lib/src/async_db.rs

@@ -1,4 +1,5 @@
 use std::marker::PhantomData;
+use std::ops::Deref;
 use std::vec;
 use std::{path::Path, sync::Arc};
 
@@ -224,7 +225,7 @@ impl<T> Reader<T>
 where
     T: bincode::Decode,
 {
-    pub async fn new<P: AsRef<Path>>(path: P, _buf_size: usize) -> Result<Self, String> {
+    pub async fn new<P: AsRef<Path>>(path: P) -> Result<Self, String> {
         let mmap = AsyncOptions::new()
             .read(true)
             .open_mmap_file(path)
@@ -372,6 +373,145 @@ where
     }
 }
 
+pub struct BufReader<T>
+where
+    T: bincode::Decode,
+{
+    inner: Reader<T>,
+    buf: Vec<u8>,
+}
+
+impl<T> BufReader<T>
+where
+    T: bincode::Decode,
+{
+    pub async fn new<P: AsRef<Path>>(path: P, buf_size: usize) -> Result<Self, String> {
+        match Reader::<T>::new(path).await {
+            Ok(inner) => Ok(Self {
+                inner,
+                buf: Vec::with_capacity(buf_size),
+            }),
+            Err(e) => Err(e),
+        }
+    }
+
+    pub async fn get(&mut self, index: usize) -> Result<T, String> {
+        self.inner.get_with_buf(index, &mut self.buf).await
+    }
+
+    pub fn into_inner(self) -> Reader<T> {
+        self.inner
+    }
+
+    pub fn stream(self) -> BufReaderStream<T> {
+        BufReaderStream::new(self)
+    }
+}
+
+impl<T> From<Reader<T>> for BufReader<T>
+where
+    T: bincode::Decode,
+{
+    fn from(inner: Reader<T>) -> Self {
+        Self {
+            inner,
+            buf: Vec::new(),
+        }
+    }
+}
+
+impl<T> From<BufReader<T>> for Reader<T>
+where
+    T: bincode::Decode,
+{
+    fn from(value: BufReader<T>) -> Self {
+        value.into_inner()
+    }
+}
+
+impl<T> Deref for BufReader<T>
+where
+    T: bincode::Decode,
+{
+    type Target = Reader<T>;
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+pub struct BufReaderStream<T>
+where
+    T: bincode::Decode,
+{
+    reader: BufReader<T>,
+    index: Option<usize>,
+}
+
+impl<T> BufReaderStream<T>
+where
+    T: bincode::Decode,
+{
+    fn new(reader: BufReader<T>) -> Self {
+        BufReaderStream {
+            reader,
+            index: None,
+        }
+    }
+
+    async fn get_next(&mut self) -> Result<T, String> {
+        match self.index {
+            None => Err("index is None".into()),
+            Some(index) => {
+                let res = self.reader.get(index).await;
+                self.index = Some(index + 1);
+
+                res
+            }
+        }
+    }
+}
+
+impl<T> Stream for BufReaderStream<T>
+where
+    T: bincode::Decode,
+{
+    type Item = T;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        if self.index.is_none() && !self.reader.is_empty() {
+            self.index = Some(0);
+        }
+
+        if self.index.unwrap() == self.reader.len() {
+            return Poll::Ready(None);
+        }
+
+        // FIXME: mayby work only if reader.get().poll() return Ready immediately
+        let future = self.get_next();
+        pin_mut!(future);
+        match Pin::new(&mut future).poll(cx) {
+            Poll::Ready(Ok(item)) => Poll::Ready(Some(item)),
+            Poll::Ready(Err(_)) => Poll::Ready(None),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.reader.len();
+        if self.index.is_none() {
+            return (len, Some(len));
+        }
+
+        let index = self.index.unwrap();
+        let rem = if len > index + 1 {
+            len - (index + 1)
+        } else {
+            0
+        };
+        (rem, Some(rem))
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -438,7 +578,7 @@ mod test {
         writer.load(src).await.expect("load");
         writer.finish().await.expect("finish write");
 
-        let reader: Reader<TestData> = Reader::new(&tmpfile, 2048).await.expect("new reader");
+        let reader: Reader<TestData> = Reader::new(&tmpfile).await.expect("new reader");
         assert_eq!(items.len(), reader.len());
 
         for (idx, item) in items.iter().enumerate() {
@@ -466,7 +606,7 @@ mod test {
         src.forward(writer.sink()).await.expect("forward");
         writer.finish().await.expect("finish write");
 
-        let reader: Reader<TestData> = Reader::new(&tmpfile, 2048).await.expect("new reader");
+        let reader: Reader<TestData> = Reader::new(&tmpfile).await.expect("new reader");
         assert_eq!(items.len(), reader.len());
 
         for (idx, item) in items.iter().enumerate() {
@@ -494,7 +634,7 @@ mod test {
         writer.load(src).await.expect("load");
         writer.finish().await.expect("finish write");
 
-        let reader: Reader<TestData> = Reader::new(&tmpfile, 2048).await.expect("new reader");
+        let reader: Reader<TestData> = Reader::new(&tmpfile).await.expect("new reader");
         assert_eq!(items.len(), reader.len());
 
         for (idx, item) in items.iter().enumerate() {
@@ -523,7 +663,7 @@ mod test {
         writer.load(src).await.expect("load");
         writer.finish().await.expect("finish write");
 
-        let reader: Reader<TestData> = Reader::new(&tmpfile, 2048).await.expect("new reader");
+        let reader: Reader<TestData> = Reader::new(&tmpfile).await.expect("new reader");
         assert_eq!(items.len(), reader.len());
 
         let dst_stream = reader.stream();
@@ -560,7 +700,7 @@ mod test {
         writer.load(src).await.expect("load");
         writer.finish().await.expect("finish write");
 
-        let reader: Reader<TestData> = Reader::new(&tmpfile, 2048).await.expect("new reader");
+        let reader: Reader<TestData> = Reader::new(&tmpfile).await.expect("new reader");
         assert_eq!(items.len(), reader.len());
 
         let reader = Arc::new(reader);