fix: range request (#44)

close #43

src/streamer.rs

@@ -0,0 +1,68 @@
+use async_stream::stream;
+use futures::{Stream, StreamExt};
+use std::io::Error;
+use std::pin::Pin;
+use tokio::io::{AsyncRead, AsyncReadExt};
+
+pub struct Streamer<R>
+where
+    R: AsyncRead + Unpin + Send + 'static,
+{
+    reader: R,
+    buf_size: usize,
+}
+
+impl<R> Streamer<R>
+where
+    R: AsyncRead + Unpin + Send + 'static,
+{
+    #[inline]
+    pub fn new(reader: R, buf_size: usize) -> Self {
+        Self { reader, buf_size }
+    }
+    pub fn into_stream(
+        mut self,
+    ) -> Pin<Box<impl ?Sized + Stream<Item = Result<Vec<u8>, Error>> + 'static>> {
+        let stream = stream! {
+            loop {
+                let mut buf = vec![0; self.buf_size];
+                let r = self.reader.read(&mut buf).await?;
+                if r == 0 {
+                    break
+                }
+                buf.truncate(r);
+                yield Ok(buf);
+            }
+        };
+        stream.boxed()
+    }
+    // allow truncation as truncated remaining is always less than buf_size: usize
+    pub fn into_stream_sized(
+        mut self,
+        max_length: u64,
+    ) -> Pin<Box<impl ?Sized + Stream<Item = Result<Vec<u8>, Error>> + 'static>> {
+        let stream = stream! {
+        let mut remaining = max_length;
+            loop {
+                if remaining == 0 {
+                    break;
+                }
+                let bs = if remaining >= self.buf_size as u64 {
+                    self.buf_size
+                } else {
+                    remaining as usize
+                };
+                let mut buf = vec![0; bs];
+                let r = self.reader.read(&mut buf).await?;
+                if r == 0 {
+                    break;
+                } else {
+                    buf.truncate(r);
+                    yield Ok(buf);
+                }
+                remaining -= r as u64;
+            }
+        };
+        stream.boxed()
+    }
+}