for #32: conditionally add Send requirement for AsyncRead/Write

Cargo.toml

@@ -20,7 +20,6 @@ bencher = "~0.1"
 
 [[example]]
 name = "encode_varint_from_stdin"
-required-features = ["tokio_async"]
 
 [[example]]
 name = "read_write_file"
@@ -31,11 +30,15 @@ name = "main"
 harness = false
 
 [features]
+default = ["sendable_io_traits"]
+
+# Requires that AsyncRead and AsyncWrite implementors are Send.
+sendable_io_traits = []
 # Enable one of these features if you want to use the AsyncRead/AsyncWrite traits from
 # the futures crate instead of those from tokio.
 tokio_async = ["tokio", "async-trait"]
 futures_async = ["futures-util", "async-trait"]
 
 [package.metadata.docs.rs]
-features = ["tokio_async"]
+features = ["tokio_async", "sendable_io_traits"]
 

src/reader.rs

@@ -5,10 +5,32 @@
 use crate::varint::{VarInt, VarIntMaxSize, MSB};
 
 #[cfg(feature = "tokio_async")]
-use tokio::io::{AsyncRead, AsyncReadExt};
-
+use tokio::io::AsyncReadExt;
 #[cfg(feature = "futures_async")]
-use futures_util::{io::AsyncRead, io::AsyncReadExt};
+use futures_util::io::AsyncReadExt;
+
+#[cfg(all(any(feature = "tokio_async", feature = "futures_async"), feature = "sendable_io_traits"))]
+mod helper_traits {
+    #[cfg(feature = "tokio_async")]
+    use tokio::io::AsyncRead;
+    #[cfg(feature = "futures_async")]
+    use futures_util::io::AsyncRead;
+    pub(crate) trait AsyncReader: AsyncRead + Unpin + Send {}
+    impl<T> AsyncReader for T where T : AsyncRead + Unpin + Send {}
+}
+
+#[cfg(all(any(feature = "tokio_async", feature = "futures_async"), not(feature = "sendable_io_traits")))]
+mod helper_traits {
+    #[cfg(feature = "tokio_async")]
+    use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite};
+    #[cfg(feature = "futures_async")]
+    use futures_util::{io::AsyncRead, io::AsyncReadExt, AsyncWrite};
+    pub(crate) trait AsyncReader: AsyncRead + Unpin {}
+    impl<T> AsyncReader for T where T : AsyncRead + Unpin {}
+}
+
+#[cfg(any(feature = "tokio_async", feature = "futures_async"))]
+use helper_traits::AsyncReader;
 
 /// A trait for reading VarInts from any other `Reader`.
 ///
@@ -66,7 +88,7 @@
 
 #[cfg(any(feature = "tokio_async", feature = "futures_async"))]
 #[async_trait::async_trait(?Send)]
-impl<AR: AsyncRead + Unpin> VarIntAsyncReader for AR {
+impl<AR: AsyncReader> VarIntAsyncReader for AR {
     async fn read_varint_async<VI: VarInt>(&mut self) -> Result<VI> {
         let mut buf = [0_u8; 1];
         let mut p = VarIntProcessor::new::<VI>();
@@ -131,7 +153,7 @@
 
 #[cfg(any(feature = "tokio_async", feature = "futures_async"))]
 #[async_trait::async_trait(?Send)]
-impl<AR: AsyncRead + Unpin> FixedIntAsyncReader for AR {
+impl<AR: AsyncReader> FixedIntAsyncReader for AR {
     async fn read_fixedint_async<FI: FixedInt>(&mut self) -> Result<FI> {
         let mut buf = [0_u8; 8];
         self.read_exact(&mut buf[0..std::mem::size_of::<FI>()])

src/writer.rs

@@ -4,11 +4,34 @@
 use crate::varint::VarInt;
 
 #[cfg(feature = "tokio_async")]
-use tokio::io::{AsyncWrite, AsyncWriteExt};
+use tokio::io::AsyncWriteExt;
 
 #[cfg(feature = "futures_async")]
 use futures_util::{io::AsyncWrite, io::AsyncWriteExt};
 
+#[cfg(all(any(feature = "tokio_async", feature = "futures_async"), feature = "sendable_io_traits"))]
+mod helper_traits {
+    #[cfg(feature = "tokio_async")]
+    use tokio::io::AsyncWrite;
+    #[cfg(feature = "futures_async")]
+    use futures_util::AsyncWrite;
+    pub(crate) trait AsyncWriter: AsyncWrite + Unpin + Send {}
+    impl<T> AsyncWriter for T where T : AsyncWrite + Unpin + Send {}
+}
+
+#[cfg(all(any(feature = "tokio_async", feature = "futures_async"), not(feature = "sendable_io_traits")))]
+mod helper_traits {
+    #[cfg(feature = "tokio_async")]
+    use tokio::io::AsyncWrite;
+    #[cfg(feature = "futures_async")]
+    use futures_util::AsyncWrite;
+    pub(crate) trait AsyncWriter: AsyncWrite + Unpin {}
+    impl<T> AsyncWriter for T where T : AsyncWrite + Unpin {}
+}
+
+#[cfg(any(feature = "tokio_async", feature = "futures_async"))]
+use helper_traits::AsyncWriter;
+
 /// A trait for writing integers in VarInt encoding to any `Write` type. This packs encoding and
 /// writing into one step.
 pub trait VarIntWriter {
@@ -25,7 +48,7 @@
 
 #[cfg(any(feature = "tokio_async", feature = "futures_async"))]
 #[async_trait::async_trait(?Send)]
-impl<AW: AsyncWrite + Unpin> VarIntAsyncWriter for AW {
+impl<AW: AsyncWriter> VarIntAsyncWriter for AW {
     async fn write_varint_async<VI: VarInt>(&mut self, n: VI) -> Result<usize> {
         let mut buf = [0_u8; 10];
         let b = n.encode_var(&mut buf);
@@ -57,7 +80,7 @@
 
 #[cfg(any(feature = "tokio_async", feature = "futures_async"))]
 #[async_trait::async_trait(?Send)]
-impl<AW: AsyncWrite + Unpin> FixedIntAsyncWriter for AW {
+impl<AW: AsyncWriter> FixedIntAsyncWriter for AW {
     async fn write_fixedint_async<FI: FixedInt>(&mut self, n: FI) -> Result<usize> {
         let mut buf = [0_u8; 8];
         n.encode_fixed(&mut buf[..std::mem::size_of::<FI>()]);