Impl helpers::AsyncFileWriter

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

src/helpers.rs

@@ -1,9 +1,10 @@
 use std::{
     fs,
-    io::{stderr, stdin, Write},
+    io::{self, stderr, stdin, Write},
     path::{Path, PathBuf},
 };
 
+use bytes::Bytes;
 use cargo_toml::Manifest;
 use flate2::read::GzDecoder;
 use log::{debug, info};
@@ -11,6 +12,7 @@ use reqwest::Method;
 use serde::Serialize;
 use tar::Archive;
 use tinytemplate::TinyTemplate;
+use tokio::{sync::mpsc, task};
 use url::Url;
 use xz2::read::XzDecoder;
 use zip::read::ZipArchive;
@@ -210,3 +212,49 @@ pub trait Template: Serialize {
         Ok(tt.render("path", self)?)
     }
 }
+
+#[derive(Debug)]
+pub struct AsyncFileWriter {
+    handle: task::JoinHandle<io::Result<()>>,
+    tx: mpsc::Sender<Bytes>,
+}
+
+impl AsyncFileWriter {
+    pub fn new(path: &Path) -> io::Result<Self> {
+        fs::create_dir_all(path.parent().unwrap())?;
+
+        let mut file = fs::File::create(path)?;
+        let (tx, mut rx) = mpsc::channel::<Bytes>(100);
+
+        let handle = task::spawn_blocking(move || {
+            while let Some(bytes) = rx.blocking_recv() {
+                file.write_all(&*bytes)?;
+            }
+
+            rx.close();
+            file.flush()?;
+
+            Ok(())
+        });
+
+        Ok(Self { handle, tx })
+    }
+
+    pub async fn write(&self, bytes: Bytes) {
+        self.tx
+            .send(bytes)
+            .await
+            .expect("Implementation bug: rx is closed before tx is dropped")
+    }
+
+    pub async fn done(self) -> io::Result<()> {
+        // Drop tx as soon as possible so that the task would wrap up what it
+        // was doing and flush out all the pending data.
+        drop(self.tx);
+
+        match self.handle.await {
+            Ok(res) => res,
+            Err(join_err) => Err(io::Error::new(io::ErrorKind::Other, join_err)),
+        }
+    }
+}