proxmox-async: add SenderWriter helper

this wraps around a tokio Sender for Vec<u8>, but implements a blocking
write. We can use thas as an adapter for something that only takes a
writer, and can read from it asynchonously

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

proxmox-async/src/blocking/mod.rs

@@ -9,3 +9,6 @@ pub use tokio_writer_adapter::TokioWriterAdapter;
 
 mod wrapped_reader_stream;
 pub use wrapped_reader_stream::WrappedReaderStream;
+
+mod sender_writer;
+pub use sender_writer::SenderWriter;

proxmox-async/src/blocking/sender_writer.rs

@@ -0,0 +1,47 @@
+use std::io;
+
+use anyhow::Error;
+use tokio::sync::mpsc::Sender;
+
+/// Wrapper struct around [`tokio::sync::mpsc::Sender`] for `Result<Vec<u8>, Error>` that implements [`std::io::Write`]
+pub struct SenderWriter {
+    sender: Sender<Result<Vec<u8>, Error>>,
+}
+
+impl SenderWriter {
+    pub fn from_sender(sender: tokio::sync::mpsc::Sender<Result<Vec<u8>, Error>>) -> Self {
+        Self { sender }
+    }
+
+    fn write_impl(&mut self, buf: &[u8]) -> io::Result<usize> {
+        if let Err(err) = self.sender.blocking_send(Ok(buf.to_vec())) {
+            return Err(io::Error::new(
+                io::ErrorKind::UnexpectedEof,
+                format!("could not send: {}", err),
+            ));
+        }
+
+        Ok(buf.len())
+    }
+
+    fn flush_impl(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+impl io::Write for SenderWriter {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.write_impl(buf)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.flush_impl()
+    }
+}
+
+impl Drop for SenderWriter {
+    fn drop(&mut self) {
+        // ignore errors
+        let _ = self.flush_impl();
+    }
+}