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// Copyright 2022 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::Context;
use anyhow::Result;
use base::info;
use base::AsRawDescriptor;
use base::SafeDescriptor;
use cros_async::AsyncWrapper;
use cros_async::Executor;
use vmm_vhost::BackendServer;
use vmm_vhost::Error as VhostError;

/// Performs the run loop for an already-constructor request handler.
pub async fn run_handler<S>(mut backend_server: BackendServer<S>, ex: &Executor) -> Result<()>
where
    S: vmm_vhost::Backend,
{
    let h = SafeDescriptor::try_from(&backend_server as &dyn AsRawDescriptor)
        .map(AsyncWrapper::new)
        .context("failed to get safe descriptor for handler")?;
    let handler_source = ex
        .async_from(h)
        .context("failed to create an async source")?;

    loop {
        handler_source
            .wait_readable()
            .await
            .context("failed to wait for the handler to become readable")?;
        let (hdr, files) = match backend_server.recv_header() {
            Ok((hdr, files)) => (hdr, files),
            Err(VhostError::ClientExit) => {
                info!("vhost-user connection closed");
                // Exit as the client closed the connection.
                return Ok(());
            }
            Err(e) => {
                return Err(e.into());
            }
        };

        if backend_server.needs_wait_for_payload(&hdr) {
            handler_source
                .wait_readable()
                .await
                .context("failed to wait for the handler to become readable")?;
        }
        backend_server.process_message(hdr, files)?;
    }
}