allow configurable in-memory buffer size for SeekableStream

SeekableStream makes use of an in-memory buffer during reads.  Right
now, this is currently set to 64k.  This change allows the buffer size
to be configurable.

sdk/core/src/seekable_stream.rs

@@ -1,20 +1,21 @@
 use bytes::Bytes;
-use futures::io::AsyncRead;
-use futures::stream::Stream;
-use futures::task::Poll;
+use dyn_clone::DynClone;
+use futures::{io::AsyncRead, stream::Stream, task::Poll};
+use std::{pin::Pin, task::Context};
+
+/// Amount of the stream to buffer in memory during streaming uploads
+pub(crate) const DEFAULT_BUFFER_SIZE: usize = 1024 * 64;
 
 /// Enable a type implementing `AsyncRead` to be consumed as if it were
 /// a `Stream` of `Bytes`.
 #[cfg_attr(target_arch = "wasm32", async_trait::async_trait(?Send))]
 #[cfg_attr(not(target_arch = "wasm32"), async_trait::async_trait)]
-pub trait SeekableStream:
-    AsyncRead + Unpin + std::fmt::Debug + Send + Sync + dyn_clone::DynClone
-{
+pub trait SeekableStream: AsyncRead + Unpin + std::fmt::Debug + Send + Sync + DynClone {
     async fn reset(&mut self) -> crate::error::Result<()>;
     fn len(&self) -> usize;
 
-    fn is_empty(&self) -> bool {
-        self.len() == 0
+    fn buffer_size(&self) -> usize {
+        DEFAULT_BUFFER_SIZE
     }
 }
 
@@ -23,11 +24,8 @@ dyn_clone::clone_trait_object!(SeekableStream);
 impl Stream for dyn SeekableStream {
     type Item = crate::error::Result<Bytes>;
 
-    fn poll_next(
-        self: std::pin::Pin<&mut Self>,
-        cx: &mut std::task::Context<'_>,
-    ) -> std::task::Poll<Option<Self::Item>> {
-        let mut buffer = vec![0_u8; 1024 * 64];
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut buffer = vec![0_u8; self.buffer_size()];
 
         match self.poll_read(cx, &mut buffer) {
             Poll::Ready(Ok(0)) => Poll::Ready(None),