feat(nix-compat): Add NixDeserialize and NixRead traits r/8585

Add a trait for deserializing a type from a daemon worker connection.
This adds the NixDeserialize trait which is kind of like the serde
Deserialize trait in that individual types are meant to implement it
and it can potentially be derived in the future.

The NixDeserialize trait takes something that implements NixRead as
input so that you can among other things mock the reader.

Change-Id: Ibb59e3562dfc822652f7d18039f00a1c0d422997
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11990
Autosubmit: Brian Olsen <me@griff.name>
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

1 files changed, 70 insertions, 0 deletions

diff --git a/tvix/nix-compat/src/nix_daemon/de/bytes.rs b/tvix/nix-compat/src/nix_daemon/de/bytes.rs
new file mode 100644
index 000000000000..7daced54eef7
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/de/bytes.rs
@@ -0,0 +1,70 @@
+use bytes::Bytes;
+
+use super::{Error, NixDeserialize, NixRead};
+
+impl NixDeserialize for Bytes {
+    async fn try_deserialize<R>(reader: &mut R) -> Result<Option<Self>, R::Error>
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        reader.try_read_bytes().await
+    }
+}
+
+impl NixDeserialize for String {
+    async fn try_deserialize<R>(reader: &mut R) -> Result<Option<Self>, R::Error>
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        if let Some(buf) = reader.try_read_bytes().await? {
+            String::from_utf8(buf.to_vec())
+                .map_err(R::Error::invalid_data)
+                .map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::io;
+
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio_test::io::Builder;
+
+    use crate::nix_daemon::de::{NixRead, NixReader};
+
+    #[rstest]
+    #[case::empty("", &hex!("0000 0000 0000 0000"))]
+    #[case::one(")", &hex!("0100 0000 0000 0000 2900 0000 0000 0000"))]
+    #[case::two("it", &hex!("0200 0000 0000 0000 6974 0000 0000 0000"))]
+    #[case::three("tea", &hex!("0300 0000 0000 0000 7465 6100 0000 0000"))]
+    #[case::four("were", &hex!("0400 0000 0000 0000 7765 7265 0000 0000"))]
+    #[case::five("where", &hex!("0500 0000 0000 0000 7768 6572 6500 0000"))]
+    #[case::six("unwrap", &hex!("0600 0000 0000 0000 756E 7772 6170 0000"))]
+    #[case::seven("where's", &hex!("0700 0000 0000 0000 7768 6572 6527 7300"))]
+    #[case::aligned("read_tea", &hex!("0800 0000 0000 0000 7265 6164 5F74 6561"))]
+    #[case::more_bytes("read_tess", &hex!("0900 0000 0000 0000 7265 6164 5F74 6573 7300 0000 0000 0000"))]
+    #[case::utf8("The quick brown 🦊 jumps over 13 lazy 🐶.", &hex!("2D00 0000 0000 0000  5468 6520 7175 6963  6b20 6272 6f77 6e20  f09f a68a 206a 756d  7073 206f 7665 7220  3133 206c 617a 7920  f09f 90b6 2e00 0000"))]
+    #[tokio::test]
+    async fn test_read_string(#[case] expected: &str, #[case] data: &[u8]) {
+        let mock = Builder::new().read(data).build();
+        let mut reader = NixReader::new(mock);
+        let actual: String = reader.read_value().await.unwrap();
+        assert_eq!(actual, expected);
+    }
+
+    #[tokio::test]
+    async fn test_read_string_invalid() {
+        let mock = Builder::new()
+            .read(&hex!("0300 0000 0000 0000 EDA0 8000 0000 0000"))
+            .build();
+        let mut reader = NixReader::new(mock);
+        assert_eq!(
+            io::ErrorKind::InvalidData,
+            reader.read_value::<String>().await.unwrap_err().kind()
+        );
+    }
+}