[pbs-devel] [PATCH proxmox-backup v3 2/3] tools: add AsyncChannelWriter

[Dominik Csapak]

similar to StdChannelWriter, but implements AsyncWrite and sends
to a tokio::sync::mpsc::Sender

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
changes from v2:
* use ByteBuffer instead of Vec<u8> (nicer interface)
 src/tools.rs                      |   4 ++
 src/tools/async_channel_writer.rs | 106 ++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 src/tools/async_channel_writer.rs

diff --git a/src/tools.rs b/src/tools.rs
index 5a9f020a..22d6c344 100644
--- a/src/tools.rs
+++ b/src/tools.rs
@@ -44,6 +44,10 @@ pub use parallel_handler::*;
 mod wrapped_reader_stream;
 pub use wrapped_reader_stream::*;
 
+mod async_channel_writer;
+pub use async_channel_writer::*;
+
+
 mod std_channel_writer;
 pub use std_channel_writer::*;
 
diff --git a/src/tools/async_channel_writer.rs b/src/tools/async_channel_writer.rs
new file mode 100644
index 00000000..4bb56ac5
--- /dev/null
+++ b/src/tools/async_channel_writer.rs
@@ -0,0 +1,106 @@
+use std::future::Future;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use anyhow::{Error, Result};
+use futures::{future::FutureExt, ready};
+use tokio::io::AsyncWrite;
+use tokio::sync::mpsc::Sender;
+
+use proxmox::io_format_err;
+use proxmox::tools::byte_buffer::ByteBuffer;
+use proxmox::sys::error::io_err_other;
+
+/// Wrapper around tokio::sync::mpsc::Sender, which implements Write
+pub struct AsyncChannelWriter {
+    sender: Option<Sender<Result<Vec<u8>, Error>>>,
+    buf: ByteBuffer,
+    state: WriterState,
+}
+
+type SendResult = io::Result<Sender<Result<Vec<u8>>>>;
+
+enum WriterState {
+    Ready,
+    Sending(Pin<Box<dyn Future<Output = SendResult> + Send + 'static>>),
+}
+
+impl AsyncChannelWriter {
+    pub fn new(sender: Sender<Result<Vec<u8>, Error>>, buf_size: usize) -> Self {
+        Self {
+            sender: Some(sender),
+            buf: ByteBuffer::with_capacity(buf_size),
+            state: WriterState::Ready,
+        }
+    }
+
+    fn poll_write_impl(
+        &mut self,
+        cx: &mut Context,
+        buf: &[u8],
+        flush: bool,
+    ) -> Poll<io::Result<usize>> {
+        loop {
+            match &mut self.state {
+                WriterState::Ready => {
+                    if flush {
+                        if self.buf.is_empty() {
+                            return Poll::Ready(Ok(0));
+                        }
+                    } else {
+                        let free_size = self.buf.free_size();
+                        if free_size > buf.len() || self.buf.is_empty() {
+                            let count = free_size.min(buf.len());
+                            self.buf.get_free_mut_slice()[..count].copy_from_slice(&buf[..count]);
+                            self.buf.add_size(count);
+                            return Poll::Ready(Ok(count));
+                        }
+                    }
+
+                    let mut sender = match self.sender.take() {
+                        Some(sender) => sender,
+                        None => return Poll::Ready(Err(io_err_other("no sender"))),
+                    };
+
+                    let data = self.buf.remove_data(self.buf.len()).to_vec();
+                    let future = async move {
+                        sender
+                            .send(Ok(data))
+                            .await
+                            .map(move |_| sender)
+                            .map_err(|err| io_format_err!("could not send: {}", err))
+                    };
+
+                    self.state = WriterState::Sending(future.boxed());
+                }
+                WriterState::Sending(ref mut future) => match ready!(future.as_mut().poll(cx)) {
+                    Ok(sender) => {
+                        self.sender = Some(sender);
+                        self.state = WriterState::Ready;
+                    }
+                    Err(err) => return Poll::Ready(Err(err)),
+                },
+            }
+        }
+    }
+}
+
+impl AsyncWrite for AsyncChannelWriter {
+    fn poll_write(self: Pin<&mut Self>, cx: &mut Context, buf: &[u8]) -> Poll<io::Result<usize>> {
+        let this = self.get_mut();
+        this.poll_write_impl(cx, buf, false)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
+        let this = self.get_mut();
+        match ready!(this.poll_write_impl(cx, &[], true)) {
+            Ok(_) => Poll::Ready(Ok(())),
+            Err(err) => Poll::Ready(Err(err)),
+        }
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
-- 
2.20.1