refactor(nix-compat): Move serialization machinery into wire. r/8898

This groups most `wire` feature gated logic into a single module.
The nix_daemon module will be gated by a feature that adds
nix-compat-derive as a dependency.

All of this is a way to break the crate2nix dependency cycle between
nix-compat and nix-compat-derive(which depends on nix-compat for its
doctests).

Change-Id: I95938a6f280c11967371ff21f8b5a19e6d3d3805
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12761
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

1 files changed, 105 insertions, 0 deletions

diff --git a/tvix/nix-compat/src/wire/de/collections.rs b/tvix/nix-compat/src/wire/de/collections.rs
new file mode 100644
index 000000000000..e1271635e4e6
--- /dev/null
+++ b/tvix/nix-compat/src/wire/de/collections.rs
@@ -0,0 +1,105 @@
+use std::{collections::BTreeMap, future::Future};
+
+use super::{NixDeserialize, NixRead};
+
+#[allow(clippy::manual_async_fn)]
+impl<T> NixDeserialize for Vec<T>
+where
+    T: NixDeserialize + Send,
+{
+    fn try_deserialize<R>(
+        reader: &mut R,
+    ) -> impl Future<Output = Result<Option<Self>, R::Error>> + Send + '_
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        async move {
+            if let Some(len) = reader.try_read_value::<usize>().await? {
+                let mut ret = Vec::with_capacity(len);
+                for _ in 0..len {
+                    ret.push(reader.read_value().await?);
+                }
+                Ok(Some(ret))
+            } else {
+                Ok(None)
+            }
+        }
+    }
+}
+
+#[allow(clippy::manual_async_fn)]
+impl<K, V> NixDeserialize for BTreeMap<K, V>
+where
+    K: NixDeserialize + Ord + Send,
+    V: NixDeserialize + Send,
+{
+    fn try_deserialize<R>(
+        reader: &mut R,
+    ) -> impl Future<Output = Result<Option<Self>, R::Error>> + Send + '_
+    where
+        R: ?Sized + NixRead + Send,
+    {
+        async move {
+            if let Some(len) = reader.try_read_value::<usize>().await? {
+                let mut ret = BTreeMap::new();
+                for _ in 0..len {
+                    let key = reader.read_value().await?;
+                    let value = reader.read_value().await?;
+                    ret.insert(key, value);
+                }
+                Ok(Some(ret))
+            } else {
+                Ok(None)
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::collections::BTreeMap;
+    use std::fmt;
+
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio_test::io::Builder;
+
+    use crate::wire::de::{NixDeserialize, NixRead, NixReader};
+
+    #[rstest]
+    #[case::empty(vec![], &hex!("0000 0000 0000 0000"))]
+    #[case::one(vec![0x29], &hex!("0100 0000 0000 0000 2900 0000 0000 0000"))]
+    #[case::two(vec![0x7469, 10], &hex!("0200 0000 0000 0000 6974 0000 0000 0000 0A00 0000 0000 0000"))]
+    #[tokio::test]
+    async fn test_read_small_vec(#[case] expected: Vec<usize>, #[case] data: &[u8]) {
+        let mock = Builder::new().read(data).build();
+        let mut reader = NixReader::new(mock);
+        let actual: Vec<usize> = reader.read_value().await.unwrap();
+        assert_eq!(actual, expected);
+    }
+
+    fn empty_map() -> BTreeMap<usize, u64> {
+        BTreeMap::new()
+    }
+    macro_rules! map {
+        ($($key:expr => $value:expr),*) => {{
+            let mut ret = BTreeMap::new();
+            $(ret.insert($key, $value);)*
+            ret
+        }};
+    }
+
+    #[rstest]
+    #[case::empty(empty_map(), &hex!("0000 0000 0000 0000"))]
+    #[case::one(map![0x7469usize => 10u64], &hex!("0100 0000 0000 0000 6974 0000 0000 0000 0A00 0000 0000 0000"))]
+    #[tokio::test]
+    async fn test_read_small_btree_map<E>(#[case] expected: E, #[case] data: &[u8])
+    where
+        E: NixDeserialize + PartialEq + fmt::Debug,
+    {
+        let mock = Builder::new().read(data).build();
+        let mut reader = NixReader::new(mock);
+        let actual: E = reader.read_value().await.unwrap();
+        assert_eq!(actual, expected);
+    }
+}