Compute hashes on dedicated threads

src/util/async_hash.rs

@@ -0,0 +1,55 @@
+use bytes::Bytes;
+use digest::Digest;
+
+use tokio::sync::mpsc;
+use tokio::task::JoinHandle;
+
+use crate::data::*;
+
+/// Compute the sha256 of a slice,
+/// spawning on a tokio thread for CPU-intensive processing
+/// The argument has to be an owned Bytes, as it is moved out to a new thread.
+pub async fn async_sha256sum(data: Bytes) -> Hash {
+	tokio::task::spawn_blocking(move || sha256sum(&data))
+		.await
+		.unwrap()
+}
+
+/// Compute the blake2sum of a slice,
+/// spawning on a tokio thread for CPU-intensive processing.
+/// The argument has to be an owned Bytes, as it is moved out to a new thread.
+pub async fn async_blake2sum(data: Bytes) -> Hash {
+	tokio::task::spawn_blocking(move || blake2sum(&data))
+		.await
+		.unwrap()
+}
+
+// ----
+
+pub struct AsyncHasher<D: Digest> {
+	sendblk: mpsc::UnboundedSender<Bytes>,
+	task: JoinHandle<digest::Output<D>>,
+}
+
+impl<D: Digest> AsyncHasher<D> {
+	pub fn new() -> Self {
+		let (sendblk, mut recvblk) = mpsc::unbounded_channel::<Bytes>();
+		let task = tokio::task::spawn_blocking(move || {
+			let mut digest = D::new();
+			while let Some(blk) = recvblk.blocking_recv() {
+				digest.update(&blk[..]);
+			}
+			digest.finalize()
+		});
+		Self { sendblk, task }
+	}
+
+	pub fn update(&self, b: Bytes) {
+		self.sendblk.send(b).unwrap()
+	}
+
+	pub async fn finalize(self) -> digest::Output<D> {
+		drop(self.sendblk);
+		self.task.await.unwrap()
+	}
+}