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, 100 insertions, 0 deletions

diff --git a/tvix/nix-compat/src/nix_daemon/de/int.rs b/tvix/nix-compat/src/nix_daemon/de/int.rs
new file mode 100644
index 000000000000..eecf641cfe99
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/de/int.rs
@@ -0,0 +1,100 @@
+use super::{Error, NixDeserialize, NixRead};
+
+impl NixDeserialize for u64 {
+    async fn try_deserialize<R>(reader: &mut R) -> Result<Option<Self>, R::Error>
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        reader.try_read_number().await
+    }
+}
+
+impl NixDeserialize for usize {
+    async fn try_deserialize<R>(reader: &mut R) -> Result<Option<Self>, R::Error>
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        if let Some(value) = reader.try_read_number().await? {
+            value.try_into().map_err(R::Error::invalid_data).map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+}
+
+impl NixDeserialize for bool {
+    async fn try_deserialize<R>(reader: &mut R) -> Result<Option<Self>, R::Error>
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        Ok(reader.try_read_number().await?.map(|v| v != 0))
+    }
+}
+impl NixDeserialize for i64 {
+    async fn try_deserialize<R>(reader: &mut R) -> Result<Option<Self>, R::Error>
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        Ok(reader.try_read_number().await?.map(|v| v as i64))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio_test::io::Builder;
+
+    use crate::nix_daemon::de::{NixRead, NixReader};
+
+    #[rstest]
+    #[case::simple_false(false, &hex!("0000 0000 0000 0000"))]
+    #[case::simple_true(true, &hex!("0100 0000 0000 0000"))]
+    #[case::other_true(true, &hex!("1234 5600 0000 0000"))]
+    #[case::max_true(true, &hex!("FFFF FFFF FFFF FFFF"))]
+    #[tokio::test]
+    async fn test_read_bool(#[case] expected: bool, #[case] data: &[u8]) {
+        let mock = Builder::new().read(data).build();
+        let mut reader = NixReader::new(mock);
+        let actual: bool = reader.read_value().await.unwrap();
+        assert_eq!(actual, expected);
+    }
+
+    #[rstest]
+    #[case::zero(0, &hex!("0000 0000 0000 0000"))]
+    #[case::one(1, &hex!("0100 0000 0000 0000"))]
+    #[case::other(0x563412, &hex!("1234 5600 0000 0000"))]
+    #[case::max_value(u64::MAX, &hex!("FFFF FFFF FFFF FFFF"))]
+    #[tokio::test]
+    async fn test_read_u64(#[case] expected: u64, #[case] data: &[u8]) {
+        let mock = Builder::new().read(data).build();
+        let mut reader = NixReader::new(mock);
+        let actual: u64 = reader.read_value().await.unwrap();
+        assert_eq!(actual, expected);
+    }
+
+    #[rstest]
+    #[case::zero(0, &hex!("0000 0000 0000 0000"))]
+    #[case::one(1, &hex!("0100 0000 0000 0000"))]
+    #[case::other(0x563412, &hex!("1234 5600 0000 0000"))]
+    #[case::max_value(usize::MAX, &usize::MAX.to_le_bytes())]
+    #[tokio::test]
+    async fn test_read_usize(#[case] expected: usize, #[case] data: &[u8]) {
+        let mock = Builder::new().read(data).build();
+        let mut reader = NixReader::new(mock);
+        let actual: usize = reader.read_value().await.unwrap();
+        assert_eq!(actual, expected);
+    }
+
+    // FUTUREWORK: Test this on supported hardware
+    #[tokio::test]
+    #[cfg(any(target_pointer_width = "16", target_pointer_width = "32"))]
+    async fn test_read_usize_overflow() {
+        let mock = Builder::new().read(&u64::MAX.to_le_bytes()).build();
+        let mut reader = NixReader::new(mock);
+        assert_eq!(
+            std::io::ErrorKind::InvalidData,
+            reader.read_value::<usize>().await.unwrap_err().kind()
+        );
+    }
+}