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-rw-r--r--tvix/Cargo.lock2
-rw-r--r--tvix/Cargo.nix12
-rw-r--r--tvix/nix-compat-derive-tests/tests/write_derive.rs370
-rw-r--r--tvix/nix-compat-derive/Cargo.toml1
-rw-r--r--tvix/nix-compat-derive/src/de.rs5
-rw-r--r--tvix/nix-compat-derive/src/internal/attrs.rs148
-rw-r--r--tvix/nix-compat-derive/src/internal/mod.rs4
-rw-r--r--tvix/nix-compat-derive/src/internal/symbol.rs3
-rw-r--r--tvix/nix-compat-derive/src/lib.rs175
-rw-r--r--tvix/nix-compat-derive/src/ser.rs227
-rw-r--r--tvix/nix-compat/Cargo.toml1
-rw-r--r--tvix/nix-compat/src/nix_daemon/mod.rs1
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/bytes.rs89
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/collections.rs94
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/display.rs8
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/int.rs108
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/mock.rs672
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/mod.rs124
-rw-r--r--tvix/nix-compat/src/nix_daemon/ser/writer.rs308
-rw-r--r--tvix/nix-compat/src/wire/bytes/mod.rs2
20 files changed, 2339 insertions, 15 deletions
diff --git a/tvix/Cargo.lock b/tvix/Cargo.lock
index 2984479c18ef..73badc2af496 100644
--- a/tvix/Cargo.lock
+++ b/tvix/Cargo.lock
@@ -2302,6 +2302,7 @@ dependencies = [
  "num-traits",
  "pin-project-lite",
  "pretty_assertions",
+ "proptest",
  "rstest",
  "serde",
  "serde_json",
@@ -2322,6 +2323,7 @@ dependencies = [
  "nix-compat",
  "pretty_assertions",
  "proc-macro2",
+ "proptest",
  "quote",
  "rstest",
  "syn 2.0.79",
diff --git a/tvix/Cargo.nix b/tvix/Cargo.nix
index 749f39fb93cc..a09cbc016a23 100644
--- a/tvix/Cargo.nix
+++ b/tvix/Cargo.nix
@@ -7299,6 +7299,12 @@ rec {
             packageId = "pretty_assertions";
           }
           {
+            name = "proptest";
+            packageId = "proptest";
+            usesDefaultFeatures = false;
+            features = [ "std" "alloc" "tempfile" ];
+          }
+          {
             name = "rstest";
             packageId = "rstest";
           }
@@ -7370,6 +7376,12 @@ rec {
             packageId = "pretty_assertions";
           }
           {
+            name = "proptest";
+            packageId = "proptest";
+            usesDefaultFeatures = false;
+            features = [ "std" "alloc" "tempfile" ];
+          }
+          {
             name = "rstest";
             packageId = "rstest";
           }
diff --git a/tvix/nix-compat-derive-tests/tests/write_derive.rs b/tvix/nix-compat-derive-tests/tests/write_derive.rs
new file mode 100644
index 000000000000..1ed5dbf7e735
--- /dev/null
+++ b/tvix/nix-compat-derive-tests/tests/write_derive.rs
@@ -0,0 +1,370 @@
+use std::fmt;
+
+use nix_compat::nix_daemon::ser::{
+    mock::{Builder, Error},
+    NixWrite as _,
+};
+use nix_compat_derive::NixSerialize;
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct UnitTest;
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct EmptyTupleTest();
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct StructTest {
+    first: u64,
+    second: String,
+}
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct TupleTest(u64, String);
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct StructVersionTest {
+    test: u64,
+    #[nix(version = "20..")]
+    hello: String,
+}
+
+fn default_test() -> StructVersionTest {
+    StructVersionTest {
+        test: 89,
+        hello: String::from("klomp"),
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct TupleVersionTest(u64, #[nix(version = "25..")] String);
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+pub struct TupleVersionDefaultTest(u64, #[nix(version = "..25")] StructVersionTest);
+
+#[tokio::test]
+async fn write_unit() {
+    let mut mock = Builder::new().build();
+    mock.write_value(&UnitTest).await.unwrap();
+}
+
+#[tokio::test]
+async fn write_empty_tuple() {
+    let mut mock = Builder::new().build();
+    mock.write_value(&EmptyTupleTest()).await.unwrap();
+}
+
+#[tokio::test]
+async fn write_struct() {
+    let mut mock = Builder::new()
+        .write_number(89)
+        .write_slice(b"klomp")
+        .build();
+    mock.write_value(&StructTest {
+        first: 89,
+        second: String::from("klomp"),
+    })
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_tuple() {
+    let mut mock = Builder::new()
+        .write_number(89)
+        .write_slice(b"klomp")
+        .build();
+    mock.write_value(&TupleTest(89, String::from("klomp")))
+        .await
+        .unwrap();
+}
+
+#[tokio::test]
+async fn write_struct_version() {
+    let mut mock = Builder::new()
+        .version((1, 20))
+        .write_number(89)
+        .write_slice(b"klomp")
+        .build();
+    mock.write_value(&default_test()).await.unwrap();
+}
+
+#[tokio::test]
+async fn write_struct_without_version() {
+    let mut mock = Builder::new().version((1, 19)).write_number(89).build();
+    mock.write_value(&StructVersionTest {
+        test: 89,
+        hello: String::new(),
+    })
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_tuple_version() {
+    let mut mock = Builder::new()
+        .version((1, 26))
+        .write_number(89)
+        .write_slice(b"klomp")
+        .build();
+    mock.write_value(&TupleVersionTest(89, "klomp".into()))
+        .await
+        .unwrap();
+}
+
+#[tokio::test]
+async fn write_tuple_without_version() {
+    let mut mock = Builder::new().version((1, 19)).write_number(89).build();
+    mock.write_value(&TupleVersionTest(89, String::new()))
+        .await
+        .unwrap();
+}
+
+#[tokio::test]
+async fn write_complex_1() {
+    let mut mock = Builder::new()
+        .version((1, 19))
+        .write_number(999)
+        .write_number(666)
+        .build();
+    mock.write_value(&TupleVersionDefaultTest(
+        999,
+        StructVersionTest {
+            test: 666,
+            hello: String::new(),
+        },
+    ))
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_complex_2() {
+    let mut mock = Builder::new()
+        .version((1, 20))
+        .write_number(999)
+        .write_number(666)
+        .write_slice(b"The quick brown \xF0\x9F\xA6\x8A jumps over 13 lazy \xF0\x9F\x90\xB6.")
+        .build();
+    mock.write_value(&TupleVersionDefaultTest(
+        999,
+        StructVersionTest {
+            test: 666,
+            hello: String::from("The quick brown 🦊 jumps over 13 lazy 🐶."),
+        },
+    ))
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_complex_3() {
+    let mut mock = Builder::new().version((1, 25)).write_number(999).build();
+    mock.write_value(&TupleVersionDefaultTest(
+        999,
+        StructVersionTest {
+            test: 89,
+            hello: String::from("klomp"),
+        },
+    ))
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_complex_4() {
+    let mut mock = Builder::new().version((1, 26)).write_number(999).build();
+    mock.write_value(&TupleVersionDefaultTest(
+        999,
+        StructVersionTest {
+            test: 89,
+            hello: String::from("klomp"),
+        },
+    ))
+    .await
+    .unwrap();
+}
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+#[nix(display)]
+struct TestFromStr;
+
+impl fmt::Display for TestFromStr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "test")
+    }
+}
+
+#[tokio::test]
+async fn write_display() {
+    let mut mock = Builder::new().write_display("test").build();
+    mock.write_value(&TestFromStr).await.unwrap();
+}
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+#[nix(display = "TestFromStr2::display")]
+struct TestFromStr2;
+struct TestFromStrDisplay;
+
+impl fmt::Display for TestFromStrDisplay {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "test")
+    }
+}
+impl TestFromStr2 {
+    fn display(&self) -> TestFromStrDisplay {
+        TestFromStrDisplay
+    }
+}
+
+#[tokio::test]
+async fn write_display_path() {
+    let mut mock = Builder::new().write_display("test").build();
+    mock.write_value(&TestFromStr2).await.unwrap();
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, NixSerialize)]
+#[nix(try_into = "u64")]
+struct TestTryFromU64(u64);
+
+impl TryFrom<TestTryFromU64> for u64 {
+    type Error = u64;
+
+    fn try_from(value: TestTryFromU64) -> Result<Self, Self::Error> {
+        if value.0 != 42 {
+            Ok(value.0)
+        } else {
+            Err(value.0)
+        }
+    }
+}
+
+#[tokio::test]
+async fn write_try_into_u64() {
+    let mut mock = Builder::new().write_number(666).build();
+    mock.write_value(&TestTryFromU64(666)).await.unwrap();
+}
+
+#[tokio::test]
+async fn write_try_into_u64_invalid_data() {
+    let mut mock = Builder::new().build();
+    let err = mock.write_value(&TestTryFromU64(42)).await.unwrap_err();
+    assert_eq!(Error::UnsupportedData("42".into()), err);
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, NixSerialize)]
+#[nix(into = "u64")]
+struct TestFromU64;
+
+impl From<TestFromU64> for u64 {
+    fn from(_value: TestFromU64) -> u64 {
+        42
+    }
+}
+
+#[tokio::test]
+async fn write_into_u64() {
+    let mut mock = Builder::new().write_number(42).build();
+    mock.write_value(&TestFromU64).await.unwrap();
+}
+
+#[derive(Debug, PartialEq, Eq, NixSerialize)]
+enum TestEnum {
+    #[nix(version = "..=19")]
+    Pre20(TestFromU64, #[nix(version = "10..")] u64),
+    #[nix(version = "20..=29")]
+    Post20(StructVersionTest),
+    #[nix(version = "30..=39")]
+    Post30,
+    #[nix(version = "40..")]
+    Post40 {
+        msg: String,
+        #[nix(version = "45..")]
+        level: u64,
+    },
+}
+
+#[tokio::test]
+async fn write_enum_9() {
+    let mut mock = Builder::new().version((1, 9)).write_number(42).build();
+    mock.write_value(&TestEnum::Pre20(TestFromU64, 666))
+        .await
+        .unwrap();
+}
+
+#[tokio::test]
+async fn write_enum_19() {
+    let mut mock = Builder::new()
+        .version((1, 19))
+        .write_number(42)
+        .write_number(666)
+        .build();
+    mock.write_value(&TestEnum::Pre20(TestFromU64, 666))
+        .await
+        .unwrap();
+}
+
+#[tokio::test]
+async fn write_enum_20() {
+    let mut mock = Builder::new()
+        .version((1, 20))
+        .write_number(666)
+        .write_slice(b"klomp")
+        .build();
+    mock.write_value(&TestEnum::Post20(StructVersionTest {
+        test: 666,
+        hello: "klomp".into(),
+    }))
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_enum_30() {
+    let mut mock = Builder::new().version((1, 30)).build();
+    mock.write_value(&TestEnum::Post30).await.unwrap();
+}
+
+#[tokio::test]
+async fn write_enum_40() {
+    let mut mock = Builder::new()
+        .version((1, 40))
+        .write_slice(b"hello world")
+        .build();
+    mock.write_value(&TestEnum::Post40 {
+        msg: "hello world".into(),
+        level: 9001,
+    })
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_enum_45() {
+    let mut mock = Builder::new()
+        .version((1, 45))
+        .write_slice(b"hello world")
+        .write_number(9001)
+        .build();
+    mock.write_value(&TestEnum::Post40 {
+        msg: "hello world".into(),
+        level: 9001,
+    })
+    .await
+    .unwrap();
+}
+
+#[tokio::test]
+async fn write_wrong_enum() {
+    let mut mock = Builder::new().version((1, 30)).build();
+    let err = mock
+        .write_value(&TestEnum::Post40 {
+            msg: "hello world".into(),
+            level: 9001,
+        })
+        .await
+        .unwrap_err();
+    assert_eq!(
+        err,
+        Error::InvalidEnum("Post40 is not valid for version 1.30".into())
+    )
+}
diff --git a/tvix/nix-compat-derive/Cargo.toml b/tvix/nix-compat-derive/Cargo.toml
index da6d6744e650..bc656b42842c 100644
--- a/tvix/nix-compat-derive/Cargo.toml
+++ b/tvix/nix-compat-derive/Cargo.toml
@@ -14,6 +14,7 @@ syn = { version = "2.0.76", features = ["full", "extra-traits"] }
 [dev-dependencies]
 hex-literal = { workspace = true }
 pretty_assertions = { workspace = true }
+proptest = { workspace = true, features = ["std", "alloc", "tempfile"] }
 rstest = { workspace = true }
 tokio-test = { workspace = true }
 tokio = { workspace = true, features = ["io-util", "macros"] }
diff --git a/tvix/nix-compat-derive/src/de.rs b/tvix/nix-compat-derive/src/de.rs
index 2214254e2b32..e678b50b0533 100644
--- a/tvix/nix-compat-derive/src/de.rs
+++ b/tvix/nix-compat-derive/src/de.rs
@@ -34,6 +34,11 @@ pub fn expand_nix_deserialize_remote(
 ) -> syn::Result<TokenStream> {
     let cx = Context::new();
     let remote = Remote::from_ast(&cx, crate_path, input);
+    if let Some(attrs) = remote.as_ref().map(|r| &r.attrs) {
+        if attrs.from_str.is_none() && attrs.type_from.is_none() && attrs.type_try_from.is_none() {
+            cx.error_spanned(input, "Missing from_str, from or try_from attribute");
+        }
+    }
     cx.check()?;
     let remote = remote.unwrap();
 
diff --git a/tvix/nix-compat-derive/src/internal/attrs.rs b/tvix/nix-compat-derive/src/internal/attrs.rs
index 9ed84aaf8745..d0fa3b008e22 100644
--- a/tvix/nix-compat-derive/src/internal/attrs.rs
+++ b/tvix/nix-compat-derive/src/internal/attrs.rs
@@ -3,7 +3,9 @@ use syn::meta::ParseNestedMeta;
 use syn::parse::Parse;
 use syn::{parse_quote, Attribute, Expr, ExprLit, ExprPath, Lit, Token};
 
-use super::symbol::{Symbol, CRATE, DEFAULT, FROM, FROM_STR, NIX, TRY_FROM, VERSION};
+use super::symbol::{
+    Symbol, CRATE, DEFAULT, DISPLAY, FROM, FROM_STR, INTO, NIX, TRY_FROM, TRY_INTO, VERSION,
+};
 use super::Context;
 
 #[derive(Debug, PartialEq, Eq)]
@@ -104,6 +106,9 @@ pub struct Container {
     pub from_str: Option<syn::Path>,
     pub type_from: Option<syn::Type>,
     pub type_try_from: Option<syn::Type>,
+    pub type_into: Option<syn::Type>,
+    pub type_try_into: Option<syn::Type>,
+    pub display: Default,
     pub crate_path: Option<syn::Path>,
 }
 
@@ -113,6 +118,9 @@ impl Container {
         let mut type_try_from = None;
         let mut crate_path = None;
         let mut from_str = None;
+        let mut type_into = None;
+        let mut type_try_into = None;
+        let mut display = Default::None;
 
         for attr in attrs {
             if attr.path() != NIX {
@@ -125,6 +133,18 @@ impl Container {
                     type_try_from = parse_lit(ctx, &meta, TRY_FROM)?;
                 } else if meta.path == FROM_STR {
                     from_str = Some(meta.path);
+                } else if meta.path == INTO {
+                    type_into = parse_lit(ctx, &meta, INTO)?;
+                } else if meta.path == TRY_INTO {
+                    type_try_into = parse_lit(ctx, &meta, TRY_INTO)?;
+                } else if meta.path == DISPLAY {
+                    if meta.input.peek(Token![=]) {
+                        if let Some(path) = parse_lit(ctx, &meta, DISPLAY)? {
+                            display = Default::Path(path);
+                        }
+                    } else {
+                        display = Default::Default(meta.path);
+                    }
                 } else if meta.path == CRATE {
                     crate_path = parse_lit(ctx, &meta, CRATE)?;
                 } else {
@@ -144,6 +164,9 @@ impl Container {
             from_str,
             type_from,
             type_try_from,
+            type_into,
+            type_try_into,
+            display,
             crate_path,
         }
     }
@@ -342,6 +365,46 @@ mod test {
     }
 
     #[test]
+    fn parse_container_from_str() {
+        let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(from_str)])];
+        let ctx = Context::new();
+        let container = Container::from_ast(&ctx, &attrs);
+        ctx.check().unwrap();
+        assert_eq!(
+            container,
+            Container {
+                from_str: Some(parse_quote!(from_str)),
+                type_from: None,
+                type_try_from: None,
+                type_into: None,
+                type_try_into: None,
+                display: Default::None,
+                crate_path: None,
+            }
+        );
+    }
+
+    #[test]
+    fn parse_container_from() {
+        let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(from="u64")])];
+        let ctx = Context::new();
+        let container = Container::from_ast(&ctx, &attrs);
+        ctx.check().unwrap();
+        assert_eq!(
+            container,
+            Container {
+                from_str: None,
+                type_from: Some(parse_quote!(u64)),
+                type_try_from: None,
+                type_into: None,
+                type_try_into: None,
+                display: Default::None,
+                crate_path: None,
+            }
+        );
+    }
+
+    #[test]
     fn parse_container_try_from() {
         let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(try_from="u64")])];
         let ctx = Context::new();
@@ -353,6 +416,89 @@ mod test {
                 from_str: None,
                 type_from: None,
                 type_try_from: Some(parse_quote!(u64)),
+                type_into: None,
+                type_try_into: None,
+                display: Default::None,
+                crate_path: None,
+            }
+        );
+    }
+
+    #[test]
+    fn parse_container_into() {
+        let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(into="u64")])];
+        let ctx = Context::new();
+        let container = Container::from_ast(&ctx, &attrs);
+        ctx.check().unwrap();
+        assert_eq!(
+            container,
+            Container {
+                from_str: None,
+                type_from: None,
+                type_try_from: None,
+                type_into: Some(parse_quote!(u64)),
+                type_try_into: None,
+                display: Default::None,
+                crate_path: None,
+            }
+        );
+    }
+
+    #[test]
+    fn parse_container_try_into() {
+        let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(try_into="u64")])];
+        let ctx = Context::new();
+        let container = Container::from_ast(&ctx, &attrs);
+        ctx.check().unwrap();
+        assert_eq!(
+            container,
+            Container {
+                from_str: None,
+                type_from: None,
+                type_try_from: None,
+                type_into: None,
+                type_try_into: Some(parse_quote!(u64)),
+                display: Default::None,
+                crate_path: None,
+            }
+        );
+    }
+
+    #[test]
+    fn parse_container_display() {
+        let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(display)])];
+        let ctx = Context::new();
+        let container = Container::from_ast(&ctx, &attrs);
+        ctx.check().unwrap();
+        assert_eq!(
+            container,
+            Container {
+                from_str: None,
+                type_from: None,
+                type_try_from: None,
+                type_into: None,
+                type_try_into: None,
+                display: Default::Default(parse_quote!(display)),
+                crate_path: None,
+            }
+        );
+    }
+
+    #[test]
+    fn parse_container_display_path() {
+        let attrs: Vec<Attribute> = vec![parse_quote!(#[nix(display="Path::display")])];
+        let ctx = Context::new();
+        let container = Container::from_ast(&ctx, &attrs);
+        ctx.check().unwrap();
+        assert_eq!(
+            container,
+            Container {
+                from_str: None,
+                type_from: None,
+                type_try_from: None,
+                type_into: None,
+                type_try_into: None,
+                display: Default::Path(parse_quote!(Path::display)),
                 crate_path: None,
             }
         );
diff --git a/tvix/nix-compat-derive/src/internal/mod.rs b/tvix/nix-compat-derive/src/internal/mod.rs
index 07ef43b6e0bb..aa42d904718d 100644
--- a/tvix/nix-compat-derive/src/internal/mod.rs
+++ b/tvix/nix-compat-derive/src/internal/mod.rs
@@ -154,10 +154,6 @@ impl<'a> Remote<'a> {
         input: &'a inputs::RemoteInput,
     ) -> Option<Remote<'a>> {
         let attrs = attrs::Container::from_ast(ctx, &input.attrs);
-        if attrs.from_str.is_none() && attrs.type_from.is_none() && attrs.type_try_from.is_none() {
-            ctx.error_spanned(input, "Missing from_str, from or try_from attribute");
-            return None;
-        }
         Some(Remote {
             ty: &input.ident,
             attrs,
diff --git a/tvix/nix-compat-derive/src/internal/symbol.rs b/tvix/nix-compat-derive/src/internal/symbol.rs
index ed3fe304eb5d..2bbdc069aa0f 100644
--- a/tvix/nix-compat-derive/src/internal/symbol.rs
+++ b/tvix/nix-compat-derive/src/internal/symbol.rs
@@ -11,6 +11,9 @@ pub const DEFAULT: Symbol = Symbol("default");
 pub const FROM: Symbol = Symbol("from");
 pub const TRY_FROM: Symbol = Symbol("try_from");
 pub const FROM_STR: Symbol = Symbol("from_str");
+pub const INTO: Symbol = Symbol("into");
+pub const TRY_INTO: Symbol = Symbol("try_into");
+pub const DISPLAY: Symbol = Symbol("display");
 pub const CRATE: Symbol = Symbol("crate");
 
 impl PartialEq<Symbol> for Path {
diff --git a/tvix/nix-compat-derive/src/lib.rs b/tvix/nix-compat-derive/src/lib.rs
index 89735cadf315..394473b1cbf8 100644
--- a/tvix/nix-compat-derive/src/lib.rs
+++ b/tvix/nix-compat-derive/src/lib.rs
@@ -6,7 +6,11 @@
 //!         1. [`#[nix(from_str)]`](#nixfrom_str)
 //!         2. [`#[nix(from = "FromType")]`](#nixfrom--fromtype)
 //!         3. [`#[nix(try_from = "FromType")]`](#nixtry_from--fromtype)
-//!         4. [`#[nix(crate = "...")]`](#nixcrate--)
+//!         4. [`#[nix(into = "IntoType")]`](#nixinto--intotype)
+//!         5. [`#[nix(try_into = "IntoType")]`](#nixtry_into--intotype)
+//!         6. [`#[nix(display)]`](#nixdisplay)
+//!         7. [`#[nix(display = "path")]`](#nixdisplay--path)
+//!         8. [`#[nix(crate = "...")]`](#nixcrate--)
 //!     2. [Variant attributes](#variant-attributes)
 //!         1. [`#[nix(version = "range")]`](#nixversion--range)
 //!     3. [Field attributes](#field-attributes)
@@ -17,20 +21,21 @@
 //! ## Overview
 //!
 //! This crate contains derive macros and function-like macros for implementing
-//! `NixDeserialize` with less boilerplate.
+//! `NixDeserialize` and `NixSerialize` with less boilerplate.
 //!
 //! ### Examples
+//!
 //! ```rust
-//! # use nix_compat_derive::NixDeserialize;
+//! # use nix_compat_derive::{NixDeserialize, NixSerialize};
 //! #
-//! #[derive(NixDeserialize)]
+//! #[derive(NixDeserialize, NixSerialize)]
 //! struct Unnamed(u64, String);
 //! ```
 //!
 //! ```rust
-//! # use nix_compat_derive::NixDeserialize;
+//! # use nix_compat_derive::{NixDeserialize, NixSerialize};
 //! #
-//! #[derive(NixDeserialize)]
+//! #[derive(NixDeserialize, NixSerialize)]
 //! struct Fields {
 //!     number: u64,
 //!     message: String,
@@ -38,9 +43,9 @@
 //! ```
 //!
 //! ```rust
-//! # use nix_compat_derive::NixDeserialize;
+//! # use nix_compat_derive::{NixDeserialize, NixSerialize};
 //! #
-//! #[derive(NixDeserialize)]
+//! #[derive(NixDeserialize, NixSerialize)]
 //! struct Ignored;
 //! ```
 //!
@@ -64,7 +69,7 @@
 //! #[derive(NixDeserialize)]
 //! #[nix(crate="nix_compat")] // <-- This is also a container attribute
 //! enum E {
-//!     #[nix(version="..=9")] // <-- This is a variant attribute
+//!     #[nix(version="..10")] // <-- This is a variant attribute
 //!     A(u64),
 //!     #[nix(version="10..")] // <-- This is also a variant attribute
 //!     B(String),
@@ -156,6 +161,114 @@
 //! }
 //! ```
 //!
+//! ##### `#[nix(into = "IntoType")]`
+//!
+//! When `into` is specified the fields are all ignored and instead the
+//! container type is converted to `IntoType` using `Into::into` and
+//! `IntoType` is then serialized. Before converting `Clone::clone` is
+//! called.
+//!
+//! This means that the container must implement `Into<IntoType>` and `Clone`
+//! and `IntoType` must implement `NixSerialize`.
+//!
+//! ###### Example
+//!
+//! ```rust
+//! # use nix_compat_derive::NixSerialize;
+//! #
+//! #[derive(Clone, NixSerialize)]
+//! #[nix(into="usize")]
+//! struct MyValue(usize);
+//! impl From<MyValue> for usize {
+//!     fn from(val: MyValue) -> Self {
+//!         val.0
+//!     }
+//! }
+//! ```
+//!
+//! ##### `#[nix(try_into = "IntoType")]`
+//!
+//! When `try_into` is specified the fields are all ignored and instead the
+//! container type is converted to `IntoType` using `TryInto::try_into` and
+//! `IntoType` is then serialized. Before converting `Clone::clone` is
+//! called.
+//!
+//! This means that the container must implement `TryInto<IntoType>` and
+//! `Clone` and `IntoType` must implement `NixSerialize`.
+//! The error returned from `try_into` also needs to implement `Display`.
+//!
+//! ###### Example
+//!
+//! ```rust
+//! # use nix_compat_derive::NixSerialize;
+//! #
+//! #[derive(Clone, NixSerialize)]
+//! #[nix(try_into="usize")]
+//! struct WrongAnswer(usize);
+//! impl TryFrom<WrongAnswer> for usize {
+//!     type Error = String;
+//!     fn try_from(val: WrongAnswer) -> Result<Self, Self::Error> {
+//!         if val.0 != 42 {
+//!             Ok(val.0)
+//!         } else {
+//!             Err("Got the answer to life the universe and everything".to_string())
+//!         }
+//!     }
+//! }
+//! ```
+//!
+//! ##### `#[nix(display)]`
+//!
+//! When `display` is specified the fields are all ignored and instead the
+//! container must implement `Display` and `NixWrite::write_display` is used to
+//! write the container.
+//!
+//! ###### Example
+//!
+//! ```rust
+//! # use nix_compat_derive::NixSerialize;
+//! # use std::fmt::{Display, Result, Formatter};
+//! #
+//! #[derive(NixSerialize)]
+//! #[nix(display)]
+//! struct WrongAnswer(usize);
+//! impl Display for WrongAnswer {
+//!     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+//!         write!(f, "Wrong Answer = {}", self.0)
+//!     }
+//! }
+//! ```
+//!
+//! ##### `#[nix(display = "path")]`
+//!
+//! When `display` is specified the fields are all ignored and instead the
+//! container the specified path must point to a function that is callable as
+//! `fn(&T) -> impl Display`. The result from this call is then written with
+//! `NixWrite::write_display`.
+//! For example `default = "my_value"` would call `my_value(&self)` and `display =
+//! "AType::empty"` would call `AType::empty(&self)`.
+//!
+//! ###### Example
+//!
+//! ```rust
+//! # use nix_compat_derive::NixSerialize;
+//! # use std::fmt::{Display, Result, Formatter};
+//! #
+//! #[derive(NixSerialize)]
+//! #[nix(display = "format_it")]
+//! struct WrongAnswer(usize);
+//! struct WrongDisplay<'a>(&'a WrongAnswer);
+//! impl<'a> Display for WrongDisplay<'a> {
+//!     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+//!         write!(f, "Wrong Answer = {}", self.0.0)
+//!     }
+//! }
+//!
+//! fn format_it(value: &WrongAnswer) -> impl Display + '_ {
+//!     WrongDisplay(value)
+//! }
+//! ```
+//!
 //! ##### `#[nix(crate = "...")]`
 //!
 //! Specify the path to the `nix-compat` crate instance to use when referring
@@ -175,6 +288,7 @@
 //!
 //! ```rust
 //! # use nix_compat_derive::NixDeserialize;
+//! #
 //! #[derive(NixDeserialize)]
 //! enum Testing {
 //!     #[nix(version="..=18")]
@@ -260,6 +374,7 @@ use syn::{parse_quote, DeriveInput};
 
 mod de;
 mod internal;
+mod ser;
 
 #[proc_macro_derive(NixDeserialize, attributes(nix))]
 pub fn derive_nix_deserialize(item: TokenStream) -> TokenStream {
@@ -270,6 +385,15 @@ pub fn derive_nix_deserialize(item: TokenStream) -> TokenStream {
         .into()
 }
 
+#[proc_macro_derive(NixSerialize, attributes(nix))]
+pub fn derive_nix_serialize(item: TokenStream) -> TokenStream {
+    let mut input = syn::parse_macro_input!(item as DeriveInput);
+    let crate_path: syn::Path = parse_quote!(::nix_compat);
+    ser::expand_nix_serialize(crate_path, &mut input)
+        .unwrap_or_else(syn::Error::into_compile_error)
+        .into()
+}
+
 /// Macro to implement `NixDeserialize` on a type.
 /// Sometimes you can't use the deriver to implement `NixDeserialize`
 /// (like when dealing with types in Rust standard library) but don't want
@@ -301,3 +425,36 @@ pub fn nix_deserialize_remote(item: TokenStream) -> TokenStream {
         .unwrap_or_else(syn::Error::into_compile_error)
         .into()
 }
+
+/// Macro to implement `NixSerialize` on a type.
+/// Sometimes you can't use the deriver to implement `NixSerialize`
+/// (like when dealing with types in Rust standard library) but don't want
+/// to implement it yourself. So this macro can be used for those situations
+/// where you would derive using `#[nix(display)]`, `#[nix(display = "path")]`,
+/// `#[nix(store_dir_display)]`, `#[nix(into = "IntoType")]` or
+/// `#[nix(try_into = "IntoType")]` if you could.
+///
+/// #### Example
+///
+/// ```rust
+/// # use nix_compat_derive::nix_serialize_remote;
+/// #
+/// #[derive(Clone)]
+/// struct MyU64(u64);
+///
+/// impl From<MyU64> for u64 {
+///     fn from(value: MyU64) -> Self {
+///         value.0
+///     }
+/// }
+///
+/// nix_serialize_remote!(#[nix(into="u64")] MyU64);
+/// ```
+#[proc_macro]
+pub fn nix_serialize_remote(item: TokenStream) -> TokenStream {
+    let input = syn::parse_macro_input!(item as RemoteInput);
+    let crate_path = parse_quote!(::nix_compat);
+    ser::expand_nix_serialize_remote(crate_path, &input)
+        .unwrap_or_else(syn::Error::into_compile_error)
+        .into()
+}
diff --git a/tvix/nix-compat-derive/src/ser.rs b/tvix/nix-compat-derive/src/ser.rs
new file mode 100644
index 000000000000..47ddfa39366d
--- /dev/null
+++ b/tvix/nix-compat-derive/src/ser.rs
@@ -0,0 +1,227 @@
+use proc_macro2::{Span, TokenStream};
+use quote::{quote, quote_spanned};
+use syn::spanned::Spanned;
+use syn::{DeriveInput, Generics, Path, Type};
+
+use crate::internal::attrs::Default;
+use crate::internal::inputs::RemoteInput;
+use crate::internal::{attrs, Container, Context, Data, Field, Remote, Style, Variant};
+
+pub fn expand_nix_serialize(crate_path: Path, input: &mut DeriveInput) -> syn::Result<TokenStream> {
+    let cx = Context::new();
+    let cont = Container::from_ast(&cx, crate_path, input);
+    cx.check()?;
+    let cont = cont.unwrap();
+
+    let ty = cont.ident_type();
+    let body = nix_serialize_body(&cont);
+    let crate_path = cont.crate_path();
+
+    Ok(nix_serialize_impl(
+        crate_path,
+        &ty,
+        &cont.original.generics,
+        body,
+    ))
+}
+
+pub fn expand_nix_serialize_remote(
+    crate_path: Path,
+    input: &RemoteInput,
+) -> syn::Result<TokenStream> {
+    let cx = Context::new();
+    let remote = Remote::from_ast(&cx, crate_path, input);
+    if let Some(attrs) = remote.as_ref().map(|r| &r.attrs) {
+        if attrs.display.is_none() && attrs.type_into.is_none() && attrs.type_try_into.is_none() {
+            cx.error_spanned(input, "Missing into, try_into or display attribute");
+        }
+    }
+    cx.check()?;
+    let remote = remote.unwrap();
+
+    let crate_path = remote.crate_path();
+    let body = nix_serialize_body_into(crate_path, &remote.attrs).expect("From tokenstream");
+    let generics = Generics::default();
+    Ok(nix_serialize_impl(crate_path, remote.ty, &generics, body))
+}
+
+fn nix_serialize_impl(
+    crate_path: &Path,
+    ty: &Type,
+    generics: &Generics,
+    body: TokenStream,
+) -> TokenStream {
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+    quote! {
+        #[automatically_derived]
+        impl #impl_generics #crate_path::nix_daemon::ser::NixSerialize for #ty #ty_generics
+            #where_clause
+        {
+            async fn serialize<W>(&self, writer: &mut W) -> std::result::Result<(), W::Error>
+                where W: #crate_path::nix_daemon::ser::NixWrite
+            {
+                use #crate_path::nix_daemon::ser::Error as _;
+                #body
+            }
+        }
+    }
+}
+
+fn nix_serialize_body_into(
+    crate_path: &syn::Path,
+    attrs: &attrs::Container,
+) -> Option<TokenStream> {
+    if let Default::Default(span) = &attrs.display {
+        Some(nix_serialize_display(span.span()))
+    } else if let Default::Path(path) = &attrs.display {
+        Some(nix_serialize_display_path(path))
+    } else if let Some(type_into) = attrs.type_into.as_ref() {
+        Some(nix_serialize_into(type_into))
+    } else {
+        attrs
+            .type_try_into
+            .as_ref()
+            .map(|type_try_into| nix_serialize_try_into(crate_path, type_try_into))
+    }
+}
+
+fn nix_serialize_body(cont: &Container) -> TokenStream {
+    if let Some(tokens) = nix_serialize_body_into(cont.crate_path(), &cont.attrs) {
+        tokens
+    } else {
+        match &cont.data {
+            Data::Struct(_style, fields) => nix_serialize_struct(fields),
+            Data::Enum(variants) => nix_serialize_enum(variants),
+        }
+    }
+}
+
+fn nix_serialize_struct(fields: &[Field<'_>]) -> TokenStream {
+    let write_fields = fields.iter().map(|f| {
+        let field = &f.member;
+        let ty = f.ty;
+        let write_value = quote_spanned! {
+            ty.span()=> writer.write_value(&self.#field).await?
+        };
+        if let Some(version) = f.attrs.version.as_ref() {
+            quote! {
+                if (#version).contains(&writer.version().minor()) {
+                    #write_value;
+                }
+            }
+        } else {
+            quote! {
+                #write_value;
+            }
+        }
+    });
+
+    quote! {
+        #(#write_fields)*
+        Ok(())
+    }
+}
+
+fn nix_serialize_variant(variant: &Variant<'_>) -> TokenStream {
+    let ident = variant.ident;
+    let write_fields = variant.fields.iter().map(|f| {
+        let field = f.var_ident();
+        let ty = f.ty;
+        let write_value = quote_spanned! {
+            ty.span()=> writer.write_value(#field).await?
+        };
+        if let Some(version) = f.attrs.version.as_ref() {
+            quote! {
+                if (#version).contains(&writer.version().minor()) {
+                    #write_value;
+                }
+            }
+        } else {
+            quote! {
+                #write_value;
+            }
+        }
+    });
+    let field_names = variant.fields.iter().map(|f| f.var_ident());
+    let destructure = match variant.style {
+        Style::Struct => {
+            quote! {
+                Self::#ident { #(#field_names),* }
+            }
+        }
+        Style::Tuple => {
+            quote! {
+                Self::#ident(#(#field_names),*)
+            }
+        }
+        Style::Unit => quote!(Self::#ident),
+    };
+    let ignore = match variant.style {
+        Style::Struct => {
+            quote! {
+                Self::#ident { .. }
+            }
+        }
+        Style::Tuple => {
+            quote! {
+                Self::#ident(_, ..)
+            }
+        }
+        Style::Unit => quote!(Self::#ident),
+    };
+    let version = &variant.attrs.version;
+    quote! {
+        #destructure if (#version).contains(&writer.version().minor()) => {
+            #(#write_fields)*
+        }
+        #ignore => {
+            return Err(W::Error::invalid_enum(format!("{} is not valid for version {}", stringify!(#ident), writer.version())));
+        }
+    }
+}
+
+fn nix_serialize_enum(variants: &[Variant<'_>]) -> TokenStream {
+    let match_variant = variants
+        .iter()
+        .map(|variant| nix_serialize_variant(variant));
+    quote! {
+        match self {
+            #(#match_variant)*
+        }
+        Ok(())
+    }
+}
+
+fn nix_serialize_into(ty: &Type) -> TokenStream {
+    quote_spanned! {
+        ty.span() =>
+        {
+            let other : #ty = <Self as Clone>::clone(self).into();
+            writer.write_value(&other).await
+        }
+    }
+}
+
+fn nix_serialize_try_into(crate_path: &Path, ty: &Type) -> TokenStream {
+    quote_spanned! {
+        ty.span() =>
+        {
+            use #crate_path::nix_daemon::ser::Error;
+            let other : #ty = <Self as Clone>::clone(self).try_into().map_err(Error::unsupported_data)?;
+            writer.write_value(&other).await
+        }
+    }
+}
+
+fn nix_serialize_display(span: Span) -> TokenStream {
+    quote_spanned! {
+        span => writer.write_display(self).await
+    }
+}
+
+fn nix_serialize_display_path(path: &syn::ExprPath) -> TokenStream {
+    quote_spanned! {
+        path.span() => writer.write_display(#path(self)).await
+    }
+}
diff --git a/tvix/nix-compat/Cargo.toml b/tvix/nix-compat/Cargo.toml
index f430a5461829..cbbf97175d14 100644
--- a/tvix/nix-compat/Cargo.toml
+++ b/tvix/nix-compat/Cargo.toml
@@ -43,6 +43,7 @@ futures = { workspace = true }
 hex-literal = { workspace = true }
 mimalloc = { workspace = true }
 pretty_assertions = { workspace = true }
+proptest = { workspace = true, features = ["std", "alloc", "tempfile"] }
 rstest = { workspace = true }
 serde_json = { workspace = true }
 smol_str = { workspace = true }
diff --git a/tvix/nix-compat/src/nix_daemon/mod.rs b/tvix/nix-compat/src/nix_daemon/mod.rs
index 11413e85fd1b..a943b279f891 100644
--- a/tvix/nix-compat/src/nix_daemon/mod.rs
+++ b/tvix/nix-compat/src/nix_daemon/mod.rs
@@ -4,3 +4,4 @@ mod protocol_version;
 pub use protocol_version::ProtocolVersion;
 
 pub mod de;
+pub mod ser;
diff --git a/tvix/nix-compat/src/nix_daemon/ser/bytes.rs b/tvix/nix-compat/src/nix_daemon/ser/bytes.rs
new file mode 100644
index 000000000000..19494934ff32
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/bytes.rs
@@ -0,0 +1,89 @@
+use bytes::Bytes;
+
+use super::{NixSerialize, NixWrite};
+
+impl NixSerialize for Bytes {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        writer.write_slice(self).await
+    }
+}
+
+impl<'a> NixSerialize for &'a [u8] {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        writer.write_slice(self).await
+    }
+}
+
+impl NixSerialize for String {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        writer.write_slice(self.as_bytes()).await
+    }
+}
+
+impl NixSerialize for str {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        writer.write_slice(self.as_bytes()).await
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio::io::AsyncWriteExt as _;
+    use tokio_test::io::Builder;
+
+    use crate::nix_daemon::ser::{NixWrite, NixWriter};
+
+    #[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_write_str(#[case] value: &str, #[case] data: &[u8]) {
+        let mock = Builder::new().write(data).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(value).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+
+    #[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_write_string(#[case] value: &str, #[case] data: &[u8]) {
+        let mock = Builder::new().write(data).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(&value.to_string()).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+}
diff --git a/tvix/nix-compat/src/nix_daemon/ser/collections.rs b/tvix/nix-compat/src/nix_daemon/ser/collections.rs
new file mode 100644
index 000000000000..70c32e1c79ac
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/collections.rs
@@ -0,0 +1,94 @@
+use std::collections::BTreeMap;
+use std::future::Future;
+
+use super::{NixSerialize, NixWrite};
+
+impl<T> NixSerialize for Vec<T>
+where
+    T: NixSerialize + Send + Sync,
+{
+    #[allow(clippy::manual_async_fn)]
+    fn serialize<W>(&self, writer: &mut W) -> impl Future<Output = Result<(), W::Error>> + Send
+    where
+        W: NixWrite,
+    {
+        async move {
+            writer.write_value(&self.len()).await?;
+            for value in self.iter() {
+                writer.write_value(value).await?;
+            }
+            Ok(())
+        }
+    }
+}
+
+impl<K, V> NixSerialize for BTreeMap<K, V>
+where
+    K: NixSerialize + Ord + Send + Sync,
+    V: NixSerialize + Send + Sync,
+{
+    #[allow(clippy::manual_async_fn)]
+    fn serialize<W>(&self, writer: &mut W) -> impl Future<Output = Result<(), W::Error>> + Send
+    where
+        W: NixWrite,
+    {
+        async move {
+            writer.write_value(&self.len()).await?;
+            for (key, value) in self.iter() {
+                writer.write_value(key).await?;
+                writer.write_value(value).await?;
+            }
+            Ok(())
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::collections::BTreeMap;
+    use std::fmt;
+
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio::io::AsyncWriteExt as _;
+    use tokio_test::io::Builder;
+
+    use crate::nix_daemon::ser::{NixSerialize, NixWrite, NixWriter};
+
+    #[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_write_small_vec(#[case] value: Vec<usize>, #[case] data: &[u8]) {
+        let mock = Builder::new().write(data).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(&value).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+
+    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_write_small_btree_map<E>(#[case] value: E, #[case] data: &[u8])
+    where
+        E: NixSerialize + Send + PartialEq + fmt::Debug,
+    {
+        let mock = Builder::new().write(data).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(&value).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+}
diff --git a/tvix/nix-compat/src/nix_daemon/ser/display.rs b/tvix/nix-compat/src/nix_daemon/ser/display.rs
new file mode 100644
index 000000000000..a3438d50d8ff
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/display.rs
@@ -0,0 +1,8 @@
+use nix_compat_derive::nix_serialize_remote;
+
+use crate::nixhash;
+
+nix_serialize_remote!(
+    #[nix(display)]
+    nixhash::HashAlgo
+);
diff --git a/tvix/nix-compat/src/nix_daemon/ser/int.rs b/tvix/nix-compat/src/nix_daemon/ser/int.rs
new file mode 100644
index 000000000000..1be06442e322
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/int.rs
@@ -0,0 +1,108 @@
+#[cfg(feature = "nix-compat-derive")]
+use nix_compat_derive::nix_serialize_remote;
+
+use super::{Error, NixSerialize, NixWrite};
+
+impl NixSerialize for u64 {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        writer.write_number(*self).await
+    }
+}
+
+impl NixSerialize for usize {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        let v = (*self).try_into().map_err(W::Error::unsupported_data)?;
+        writer.write_number(v).await
+    }
+}
+
+#[cfg(feature = "nix-compat-derive")]
+nix_serialize_remote!(
+    #[nix(into = "u64")]
+    u8
+);
+#[cfg(feature = "nix-compat-derive")]
+nix_serialize_remote!(
+    #[nix(into = "u64")]
+    u16
+);
+#[cfg(feature = "nix-compat-derive")]
+nix_serialize_remote!(
+    #[nix(into = "u64")]
+    u32
+);
+
+impl NixSerialize for bool {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        if *self {
+            writer.write_number(1).await
+        } else {
+            writer.write_number(0).await
+        }
+    }
+}
+
+impl NixSerialize for i64 {
+    async fn serialize<W>(&self, writer: &mut W) -> Result<(), W::Error>
+    where
+        W: NixWrite,
+    {
+        writer.write_number(*self as u64).await
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio::io::AsyncWriteExt as _;
+    use tokio_test::io::Builder;
+
+    use crate::nix_daemon::ser::{NixWrite, NixWriter};
+
+    #[rstest]
+    #[case::simple_false(false, &hex!("0000 0000 0000 0000"))]
+    #[case::simple_true(true, &hex!("0100 0000 0000 0000"))]
+    #[tokio::test]
+    async fn test_write_bool(#[case] value: bool, #[case] expected: &[u8]) {
+        let mock = Builder::new().write(expected).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(&value).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+
+    #[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_write_u64(#[case] value: u64, #[case] expected: &[u8]) {
+        let mock = Builder::new().write(expected).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(&value).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+
+    #[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_write_usize(#[case] value: usize, #[case] expected: &[u8]) {
+        let mock = Builder::new().write(expected).build();
+        let mut writer = NixWriter::new(mock);
+        writer.write_value(&value).await.unwrap();
+        writer.flush().await.unwrap();
+    }
+}
diff --git a/tvix/nix-compat/src/nix_daemon/ser/mock.rs b/tvix/nix-compat/src/nix_daemon/ser/mock.rs
new file mode 100644
index 000000000000..1319a8da3228
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/mock.rs
@@ -0,0 +1,672 @@
+use std::collections::VecDeque;
+use std::fmt;
+use std::io;
+use std::thread;
+
+#[cfg(test)]
+use ::proptest::prelude::TestCaseError;
+use thiserror::Error;
+
+use crate::nix_daemon::ProtocolVersion;
+
+use super::NixWrite;
+
+#[derive(Debug, Error, PartialEq, Eq, Clone)]
+pub enum Error {
+    #[error("custom error '{0}'")]
+    Custom(String),
+    #[error("unsupported data error '{0}'")]
+    UnsupportedData(String),
+    #[error("Invalid enum: {0}")]
+    InvalidEnum(String),
+    #[error("IO error {0} '{1}'")]
+    IO(io::ErrorKind, String),
+    #[error("wrong write: expected {0} got {1}")]
+    WrongWrite(OperationType, OperationType),
+    #[error("unexpected write: got an extra {0}")]
+    ExtraWrite(OperationType),
+    #[error("got an unexpected number {0} in write_number")]
+    UnexpectedNumber(u64),
+    #[error("got an unexpected slice '{0:?}' in write_slice")]
+    UnexpectedSlice(Vec<u8>),
+    #[error("got an unexpected display '{0:?}' in write_slice")]
+    UnexpectedDisplay(String),
+}
+
+impl Error {
+    pub fn unexpected_write_number(expected: OperationType) -> Error {
+        Error::WrongWrite(expected, OperationType::WriteNumber)
+    }
+
+    pub fn extra_write_number() -> Error {
+        Error::ExtraWrite(OperationType::WriteNumber)
+    }
+
+    pub fn unexpected_write_slice(expected: OperationType) -> Error {
+        Error::WrongWrite(expected, OperationType::WriteSlice)
+    }
+
+    pub fn unexpected_write_display(expected: OperationType) -> Error {
+        Error::WrongWrite(expected, OperationType::WriteDisplay)
+    }
+}
+
+impl super::Error for Error {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        Self::Custom(msg.to_string())
+    }
+
+    fn io_error(err: std::io::Error) -> Self {
+        Self::IO(err.kind(), err.to_string())
+    }
+
+    fn unsupported_data<T: fmt::Display>(msg: T) -> Self {
+        Self::UnsupportedData(msg.to_string())
+    }
+
+    fn invalid_enum<T: fmt::Display>(msg: T) -> Self {
+        Self::InvalidEnum(msg.to_string())
+    }
+}
+
+#[allow(clippy::enum_variant_names)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum OperationType {
+    WriteNumber,
+    WriteSlice,
+    WriteDisplay,
+}
+
+impl fmt::Display for OperationType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::WriteNumber => write!(f, "write_number"),
+            Self::WriteSlice => write!(f, "write_slice"),
+            Self::WriteDisplay => write!(f, "write_display"),
+        }
+    }
+}
+
+#[allow(clippy::enum_variant_names)]
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum Operation {
+    WriteNumber(u64, Result<(), Error>),
+    WriteSlice(Vec<u8>, Result<(), Error>),
+    WriteDisplay(String, Result<(), Error>),
+}
+
+impl From<Operation> for OperationType {
+    fn from(value: Operation) -> Self {
+        match value {
+            Operation::WriteNumber(_, _) => OperationType::WriteNumber,
+            Operation::WriteSlice(_, _) => OperationType::WriteSlice,
+            Operation::WriteDisplay(_, _) => OperationType::WriteDisplay,
+        }
+    }
+}
+
+pub struct Builder {
+    version: ProtocolVersion,
+    ops: VecDeque<Operation>,
+}
+
+impl Builder {
+    pub fn new() -> Builder {
+        Builder {
+            version: Default::default(),
+            ops: VecDeque::new(),
+        }
+    }
+
+    pub fn version<V: Into<ProtocolVersion>>(&mut self, version: V) -> &mut Self {
+        self.version = version.into();
+        self
+    }
+
+    pub fn write_number(&mut self, value: u64) -> &mut Self {
+        self.ops.push_back(Operation::WriteNumber(value, Ok(())));
+        self
+    }
+
+    pub fn write_number_error(&mut self, value: u64, err: Error) -> &mut Self {
+        self.ops.push_back(Operation::WriteNumber(value, Err(err)));
+        self
+    }
+
+    pub fn write_slice(&mut self, value: &[u8]) -> &mut Self {
+        self.ops
+            .push_back(Operation::WriteSlice(value.to_vec(), Ok(())));
+        self
+    }
+
+    pub fn write_slice_error(&mut self, value: &[u8], err: Error) -> &mut Self {
+        self.ops
+            .push_back(Operation::WriteSlice(value.to_vec(), Err(err)));
+        self
+    }
+
+    pub fn write_display<D>(&mut self, value: D) -> &mut Self
+    where
+        D: fmt::Display,
+    {
+        let msg = value.to_string();
+        self.ops.push_back(Operation::WriteDisplay(msg, Ok(())));
+        self
+    }
+
+    pub fn write_display_error<D>(&mut self, value: D, err: Error) -> &mut Self
+    where
+        D: fmt::Display,
+    {
+        let msg = value.to_string();
+        self.ops.push_back(Operation::WriteDisplay(msg, Err(err)));
+        self
+    }
+
+    #[cfg(test)]
+    fn write_operation_type(&mut self, op: OperationType) -> &mut Self {
+        match op {
+            OperationType::WriteNumber => self.write_number(10),
+            OperationType::WriteSlice => self.write_slice(b"testing"),
+            OperationType::WriteDisplay => self.write_display("testing"),
+        }
+    }
+
+    #[cfg(test)]
+    fn write_operation(&mut self, op: &Operation) -> &mut Self {
+        match op {
+            Operation::WriteNumber(value, Ok(_)) => self.write_number(*value),
+            Operation::WriteNumber(value, Err(Error::UnexpectedNumber(_))) => {
+                self.write_number(*value)
+            }
+            Operation::WriteNumber(_, Err(Error::ExtraWrite(OperationType::WriteNumber))) => self,
+            Operation::WriteNumber(_, Err(Error::WrongWrite(op, OperationType::WriteNumber))) => {
+                self.write_operation_type(*op)
+            }
+            Operation::WriteNumber(value, Err(Error::Custom(msg))) => {
+                self.write_number_error(*value, Error::Custom(msg.clone()))
+            }
+            Operation::WriteNumber(value, Err(Error::IO(kind, msg))) => {
+                self.write_number_error(*value, Error::IO(*kind, msg.clone()))
+            }
+            Operation::WriteSlice(value, Ok(_)) => self.write_slice(value),
+            Operation::WriteSlice(value, Err(Error::UnexpectedSlice(_))) => self.write_slice(value),
+            Operation::WriteSlice(_, Err(Error::ExtraWrite(OperationType::WriteSlice))) => self,
+            Operation::WriteSlice(_, Err(Error::WrongWrite(op, OperationType::WriteSlice))) => {
+                self.write_operation_type(*op)
+            }
+            Operation::WriteSlice(value, Err(Error::Custom(msg))) => {
+                self.write_slice_error(value, Error::Custom(msg.clone()))
+            }
+            Operation::WriteSlice(value, Err(Error::IO(kind, msg))) => {
+                self.write_slice_error(value, Error::IO(*kind, msg.clone()))
+            }
+            Operation::WriteDisplay(value, Ok(_)) => self.write_display(value),
+            Operation::WriteDisplay(value, Err(Error::Custom(msg))) => {
+                self.write_display_error(value, Error::Custom(msg.clone()))
+            }
+            Operation::WriteDisplay(value, Err(Error::IO(kind, msg))) => {
+                self.write_display_error(value, Error::IO(*kind, msg.clone()))
+            }
+            Operation::WriteDisplay(value, Err(Error::UnexpectedDisplay(_))) => {
+                self.write_display(value)
+            }
+            Operation::WriteDisplay(_, Err(Error::ExtraWrite(OperationType::WriteDisplay))) => self,
+            Operation::WriteDisplay(_, Err(Error::WrongWrite(op, OperationType::WriteDisplay))) => {
+                self.write_operation_type(*op)
+            }
+            s => panic!("Invalid operation {:?}", s),
+        }
+    }
+
+    pub fn build(&mut self) -> Mock {
+        Mock {
+            version: self.version,
+            ops: self.ops.clone(),
+        }
+    }
+}
+
+impl Default for Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+pub struct Mock {
+    version: ProtocolVersion,
+    ops: VecDeque<Operation>,
+}
+
+impl Mock {
+    #[cfg(test)]
+    #[allow(dead_code)]
+    async fn assert_operation(&mut self, op: Operation) {
+        match op {
+            Operation::WriteNumber(_, Err(Error::UnexpectedNumber(value))) => {
+                assert_eq!(
+                    self.write_number(value).await,
+                    Err(Error::UnexpectedNumber(value))
+                );
+            }
+            Operation::WriteNumber(value, res) => {
+                assert_eq!(self.write_number(value).await, res);
+            }
+            Operation::WriteSlice(_, ref res @ Err(Error::UnexpectedSlice(ref value))) => {
+                assert_eq!(self.write_slice(value).await, res.clone());
+            }
+            Operation::WriteSlice(value, res) => {
+                assert_eq!(self.write_slice(&value).await, res);
+            }
+            Operation::WriteDisplay(_, ref res @ Err(Error::UnexpectedDisplay(ref value))) => {
+                assert_eq!(self.write_display(value).await, res.clone());
+            }
+            Operation::WriteDisplay(value, res) => {
+                assert_eq!(self.write_display(value).await, res);
+            }
+        }
+    }
+
+    #[cfg(test)]
+    async fn prop_assert_operation(&mut self, op: Operation) -> Result<(), TestCaseError> {
+        use ::proptest::prop_assert_eq;
+
+        match op {
+            Operation::WriteNumber(_, Err(Error::UnexpectedNumber(value))) => {
+                prop_assert_eq!(
+                    self.write_number(value).await,
+                    Err(Error::UnexpectedNumber(value))
+                );
+            }
+            Operation::WriteNumber(value, res) => {
+                prop_assert_eq!(self.write_number(value).await, res);
+            }
+            Operation::WriteSlice(_, ref res @ Err(Error::UnexpectedSlice(ref value))) => {
+                prop_assert_eq!(self.write_slice(value).await, res.clone());
+            }
+            Operation::WriteSlice(value, res) => {
+                prop_assert_eq!(self.write_slice(&value).await, res);
+            }
+            Operation::WriteDisplay(_, ref res @ Err(Error::UnexpectedDisplay(ref value))) => {
+                prop_assert_eq!(self.write_display(&value).await, res.clone());
+            }
+            Operation::WriteDisplay(value, res) => {
+                prop_assert_eq!(self.write_display(&value).await, res);
+            }
+        }
+        Ok(())
+    }
+}
+
+impl NixWrite for Mock {
+    type Error = Error;
+
+    fn version(&self) -> ProtocolVersion {
+        self.version
+    }
+
+    async fn write_number(&mut self, value: u64) -> Result<(), Self::Error> {
+        match self.ops.pop_front() {
+            Some(Operation::WriteNumber(expected, ret)) => {
+                if value != expected {
+                    return Err(Error::UnexpectedNumber(value));
+                }
+                ret
+            }
+            Some(op) => Err(Error::unexpected_write_number(op.into())),
+            _ => Err(Error::ExtraWrite(OperationType::WriteNumber)),
+        }
+    }
+
+    async fn write_slice(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
+        match self.ops.pop_front() {
+            Some(Operation::WriteSlice(expected, ret)) => {
+                if buf != expected {
+                    return Err(Error::UnexpectedSlice(buf.to_vec()));
+                }
+                ret
+            }
+            Some(op) => Err(Error::unexpected_write_slice(op.into())),
+            _ => Err(Error::ExtraWrite(OperationType::WriteSlice)),
+        }
+    }
+
+    async fn write_display<D>(&mut self, msg: D) -> Result<(), Self::Error>
+    where
+        D: fmt::Display + Send,
+        Self: Sized,
+    {
+        let value = msg.to_string();
+        match self.ops.pop_front() {
+            Some(Operation::WriteDisplay(expected, ret)) => {
+                if value != expected {
+                    return Err(Error::UnexpectedDisplay(value));
+                }
+                ret
+            }
+            Some(op) => Err(Error::unexpected_write_display(op.into())),
+            _ => Err(Error::ExtraWrite(OperationType::WriteDisplay)),
+        }
+    }
+}
+
+impl Drop for Mock {
+    fn drop(&mut self) {
+        // No need to panic again
+        if thread::panicking() {
+            return;
+        }
+        if let Some(op) = self.ops.front() {
+            panic!("reader dropped with {op:?} operation still unread")
+        }
+    }
+}
+
+#[cfg(test)]
+mod proptest {
+    use std::io;
+
+    use proptest::{
+        prelude::{any, Arbitrary, BoxedStrategy, Just, Strategy},
+        prop_oneof,
+    };
+
+    use super::{Error, Operation, OperationType};
+
+    pub fn arb_write_number_operation() -> impl Strategy<Value = Operation> {
+        (
+            any::<u64>(),
+            prop_oneof![
+                Just(Ok(())),
+                any::<u64>().prop_map(|v| Err(Error::UnexpectedNumber(v))),
+                Just(Err(Error::WrongWrite(
+                    OperationType::WriteSlice,
+                    OperationType::WriteNumber
+                ))),
+                Just(Err(Error::WrongWrite(
+                    OperationType::WriteDisplay,
+                    OperationType::WriteNumber
+                ))),
+                any::<String>().prop_map(|s| Err(Error::Custom(s))),
+                (any::<io::ErrorKind>(), any::<String>())
+                    .prop_map(|(kind, msg)| Err(Error::IO(kind, msg))),
+            ],
+        )
+            .prop_filter("same number", |(v, res)| match res {
+                Err(Error::UnexpectedNumber(exp_v)) => v != exp_v,
+                _ => true,
+            })
+            .prop_map(|(v, res)| Operation::WriteNumber(v, res))
+    }
+
+    pub fn arb_write_slice_operation() -> impl Strategy<Value = Operation> {
+        (
+            any::<Vec<u8>>(),
+            prop_oneof![
+                Just(Ok(())),
+                any::<Vec<u8>>().prop_map(|v| Err(Error::UnexpectedSlice(v))),
+                Just(Err(Error::WrongWrite(
+                    OperationType::WriteNumber,
+                    OperationType::WriteSlice
+                ))),
+                Just(Err(Error::WrongWrite(
+                    OperationType::WriteDisplay,
+                    OperationType::WriteSlice
+                ))),
+                any::<String>().prop_map(|s| Err(Error::Custom(s))),
+                (any::<io::ErrorKind>(), any::<String>())
+                    .prop_map(|(kind, msg)| Err(Error::IO(kind, msg))),
+            ],
+        )
+            .prop_filter("same slice", |(v, res)| match res {
+                Err(Error::UnexpectedSlice(exp_v)) => v != exp_v,
+                _ => true,
+            })
+            .prop_map(|(v, res)| Operation::WriteSlice(v, res))
+    }
+
+    #[allow(dead_code)]
+    pub fn arb_extra_write() -> impl Strategy<Value = Operation> {
+        prop_oneof![
+            any::<u64>().prop_map(|msg| {
+                Operation::WriteNumber(msg, Err(Error::ExtraWrite(OperationType::WriteNumber)))
+            }),
+            any::<Vec<u8>>().prop_map(|msg| {
+                Operation::WriteSlice(msg, Err(Error::ExtraWrite(OperationType::WriteSlice)))
+            }),
+            any::<String>().prop_map(|msg| {
+                Operation::WriteDisplay(msg, Err(Error::ExtraWrite(OperationType::WriteDisplay)))
+            }),
+        ]
+    }
+
+    pub fn arb_write_display_operation() -> impl Strategy<Value = Operation> {
+        (
+            any::<String>(),
+            prop_oneof![
+                Just(Ok(())),
+                any::<String>().prop_map(|v| Err(Error::UnexpectedDisplay(v))),
+                Just(Err(Error::WrongWrite(
+                    OperationType::WriteNumber,
+                    OperationType::WriteDisplay
+                ))),
+                Just(Err(Error::WrongWrite(
+                    OperationType::WriteSlice,
+                    OperationType::WriteDisplay
+                ))),
+                any::<String>().prop_map(|s| Err(Error::Custom(s))),
+                (any::<io::ErrorKind>(), any::<String>())
+                    .prop_map(|(kind, msg)| Err(Error::IO(kind, msg))),
+            ],
+        )
+            .prop_filter("same string", |(v, res)| match res {
+                Err(Error::UnexpectedDisplay(exp_v)) => v != exp_v,
+                _ => true,
+            })
+            .prop_map(|(v, res)| Operation::WriteDisplay(v, res))
+    }
+
+    pub fn arb_operation() -> impl Strategy<Value = Operation> {
+        prop_oneof![
+            arb_write_number_operation(),
+            arb_write_slice_operation(),
+            arb_write_display_operation(),
+        ]
+    }
+
+    impl Arbitrary for Operation {
+        type Parameters = ();
+        type Strategy = BoxedStrategy<Operation>;
+
+        fn arbitrary_with(_args: Self::Parameters) -> Self::Strategy {
+            arb_operation().boxed()
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use hex_literal::hex;
+    use proptest::prelude::any;
+    use proptest::prelude::TestCaseError;
+    use proptest::proptest;
+
+    use crate::nix_daemon::ser::mock::proptest::arb_extra_write;
+    use crate::nix_daemon::ser::mock::Operation;
+    use crate::nix_daemon::ser::mock::OperationType;
+    use crate::nix_daemon::ser::Error as _;
+    use crate::nix_daemon::ser::NixWrite;
+
+    use super::{Builder, Error};
+
+    #[tokio::test]
+    async fn write_number() {
+        let mut mock = Builder::new().write_number(10).build();
+        mock.write_number(10).await.unwrap();
+    }
+
+    #[tokio::test]
+    async fn write_number_error() {
+        let mut mock = Builder::new()
+            .write_number_error(10, Error::custom("bad number"))
+            .build();
+        assert_eq!(
+            Err(Error::custom("bad number")),
+            mock.write_number(10).await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_number_unexpected() {
+        let mut mock = Builder::new().write_slice(b"").build();
+        assert_eq!(
+            Err(Error::unexpected_write_number(OperationType::WriteSlice)),
+            mock.write_number(11).await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_number_unexpected_number() {
+        let mut mock = Builder::new().write_number(10).build();
+        assert_eq!(
+            Err(Error::UnexpectedNumber(11)),
+            mock.write_number(11).await
+        );
+    }
+
+    #[tokio::test]
+    async fn extra_write_number() {
+        let mut mock = Builder::new().build();
+        assert_eq!(
+            Err(Error::ExtraWrite(OperationType::WriteNumber)),
+            mock.write_number(11).await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_slice() {
+        let mut mock = Builder::new()
+            .write_slice(&[])
+            .write_slice(&hex!("0000 1234 5678 9ABC DEFF"))
+            .build();
+        mock.write_slice(&[]).await.expect("write_slice empty");
+        mock.write_slice(&hex!("0000 1234 5678 9ABC DEFF"))
+            .await
+            .expect("write_slice");
+    }
+
+    #[tokio::test]
+    async fn write_slice_error() {
+        let mut mock = Builder::new()
+            .write_slice_error(&[], Error::custom("bad slice"))
+            .build();
+        assert_eq!(Err(Error::custom("bad slice")), mock.write_slice(&[]).await);
+    }
+
+    #[tokio::test]
+    async fn write_slice_unexpected() {
+        let mut mock = Builder::new().write_number(10).build();
+        assert_eq!(
+            Err(Error::unexpected_write_slice(OperationType::WriteNumber)),
+            mock.write_slice(b"").await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_slice_unexpected_slice() {
+        let mut mock = Builder::new().write_slice(b"").build();
+        assert_eq!(
+            Err(Error::UnexpectedSlice(b"bad slice".to_vec())),
+            mock.write_slice(b"bad slice").await
+        );
+    }
+
+    #[tokio::test]
+    async fn extra_write_slice() {
+        let mut mock = Builder::new().build();
+        assert_eq!(
+            Err(Error::ExtraWrite(OperationType::WriteSlice)),
+            mock.write_slice(b"extra slice").await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_display() {
+        let mut mock = Builder::new().write_display("testing").build();
+        mock.write_display("testing").await.unwrap();
+    }
+
+    #[tokio::test]
+    async fn write_display_error() {
+        let mut mock = Builder::new()
+            .write_display_error("testing", Error::custom("bad number"))
+            .build();
+        assert_eq!(
+            Err(Error::custom("bad number")),
+            mock.write_display("testing").await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_display_unexpected() {
+        let mut mock = Builder::new().write_number(10).build();
+        assert_eq!(
+            Err(Error::unexpected_write_display(OperationType::WriteNumber)),
+            mock.write_display("").await
+        );
+    }
+
+    #[tokio::test]
+    async fn write_display_unexpected_display() {
+        let mut mock = Builder::new().write_display("").build();
+        assert_eq!(
+            Err(Error::UnexpectedDisplay("bad display".to_string())),
+            mock.write_display("bad display").await
+        );
+    }
+
+    #[tokio::test]
+    async fn extra_write_display() {
+        let mut mock = Builder::new().build();
+        assert_eq!(
+            Err(Error::ExtraWrite(OperationType::WriteDisplay)),
+            mock.write_display("extra slice").await
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn operations_left() {
+        let _ = Builder::new().write_number(10).build();
+    }
+
+    #[test]
+    fn proptest_mock() {
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+        proptest!(|(
+            operations in any::<Vec<Operation>>(),
+            extra_operations in proptest::collection::vec(arb_extra_write(), 0..3)
+            )| {
+            rt.block_on(async {
+                let mut builder = Builder::new();
+                for op in operations.iter() {
+                    builder.write_operation(op);
+                }
+                for op in extra_operations.iter() {
+                    builder.write_operation(op);
+                }
+                let mut mock = builder.build();
+                for op in operations {
+                    mock.prop_assert_operation(op).await?;
+                }
+                for op in extra_operations {
+                    mock.prop_assert_operation(op).await?;
+                }
+                Ok(()) as Result<(), TestCaseError>
+            })?;
+        });
+    }
+}
diff --git a/tvix/nix-compat/src/nix_daemon/ser/mod.rs b/tvix/nix-compat/src/nix_daemon/ser/mod.rs
new file mode 100644
index 000000000000..5860226f39eb
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/mod.rs
@@ -0,0 +1,124 @@
+use std::error::Error as StdError;
+use std::future::Future;
+use std::{fmt, io};
+
+use super::ProtocolVersion;
+
+mod bytes;
+mod collections;
+#[cfg(feature = "nix-compat-derive")]
+mod display;
+mod int;
+#[cfg(any(test, feature = "test"))]
+pub mod mock;
+mod writer;
+
+pub use writer::{NixWriter, NixWriterBuilder};
+
+pub trait Error: Sized + StdError {
+    fn custom<T: fmt::Display>(msg: T) -> Self;
+
+    fn io_error(err: std::io::Error) -> Self {
+        Self::custom(format_args!("There was an I/O error {}", err))
+    }
+
+    fn unsupported_data<T: fmt::Display>(msg: T) -> Self {
+        Self::custom(msg)
+    }
+
+    fn invalid_enum<T: fmt::Display>(msg: T) -> Self {
+        Self::custom(msg)
+    }
+}
+
+impl Error for io::Error {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        io::Error::new(io::ErrorKind::Other, msg.to_string())
+    }
+
+    fn io_error(err: std::io::Error) -> Self {
+        err
+    }
+
+    fn unsupported_data<T: fmt::Display>(msg: T) -> Self {
+        io::Error::new(io::ErrorKind::InvalidData, msg.to_string())
+    }
+}
+
+pub trait NixWrite: Send {
+    type Error: Error;
+
+    /// Some types are serialized differently depending on the version
+    /// of the protocol and so this can be used for implementing that.
+    fn version(&self) -> ProtocolVersion;
+
+    /// Write a single u64 to the protocol.
+    fn write_number(&mut self, value: u64) -> impl Future<Output = Result<(), Self::Error>> + Send;
+
+    /// Write a slice of bytes to the protocol.
+    fn write_slice(&mut self, buf: &[u8]) -> impl Future<Output = Result<(), Self::Error>> + Send;
+
+    /// Write a value that implements `std::fmt::Display` to the protocol.
+    /// The protocol uses many small string formats and instead of allocating
+    /// a `String` each time we want to write one an implementation of `NixWrite`
+    /// can instead use `Display` to dump these formats to a reusable buffer.
+    fn write_display<D>(&mut self, msg: D) -> impl Future<Output = Result<(), Self::Error>> + Send
+    where
+        D: fmt::Display + Send,
+        Self: Sized,
+    {
+        async move {
+            let s = msg.to_string();
+            self.write_slice(s.as_bytes()).await
+        }
+    }
+
+    /// Write a value to the protocol.
+    /// Uses `NixSerialize::serialize` to write the value.
+    fn write_value<V>(&mut self, value: &V) -> impl Future<Output = Result<(), Self::Error>> + Send
+    where
+        V: NixSerialize + Send + ?Sized,
+        Self: Sized,
+    {
+        value.serialize(self)
+    }
+}
+
+impl<T: NixWrite> NixWrite for &mut T {
+    type Error = T::Error;
+
+    fn version(&self) -> ProtocolVersion {
+        (**self).version()
+    }
+
+    fn write_number(&mut self, value: u64) -> impl Future<Output = Result<(), Self::Error>> + Send {
+        (**self).write_number(value)
+    }
+
+    fn write_slice(&mut self, buf: &[u8]) -> impl Future<Output = Result<(), Self::Error>> + Send {
+        (**self).write_slice(buf)
+    }
+
+    fn write_display<D>(&mut self, msg: D) -> impl Future<Output = Result<(), Self::Error>> + Send
+    where
+        D: fmt::Display + Send,
+        Self: Sized,
+    {
+        (**self).write_display(msg)
+    }
+
+    fn write_value<V>(&mut self, value: &V) -> impl Future<Output = Result<(), Self::Error>> + Send
+    where
+        V: NixSerialize + Send + ?Sized,
+        Self: Sized,
+    {
+        (**self).write_value(value)
+    }
+}
+
+pub trait NixSerialize {
+    /// Write a value to the writer.
+    fn serialize<W>(&self, writer: &mut W) -> impl Future<Output = Result<(), W::Error>> + Send
+    where
+        W: NixWrite;
+}
diff --git a/tvix/nix-compat/src/nix_daemon/ser/writer.rs b/tvix/nix-compat/src/nix_daemon/ser/writer.rs
new file mode 100644
index 000000000000..87e30580af34
--- /dev/null
+++ b/tvix/nix-compat/src/nix_daemon/ser/writer.rs
@@ -0,0 +1,308 @@
+use std::fmt::{self, Write as _};
+use std::future::poll_fn;
+use std::io::{self, Cursor};
+use std::pin::Pin;
+use std::task::{ready, Context, Poll};
+
+use bytes::{Buf, BufMut, BytesMut};
+use pin_project_lite::pin_project;
+use tokio::io::{AsyncWrite, AsyncWriteExt};
+
+use crate::nix_daemon::ProtocolVersion;
+use crate::wire::padding_len;
+use crate::wire::EMPTY_BYTES;
+
+use super::{Error, NixWrite};
+
+pub struct NixWriterBuilder {
+    buf: Option<BytesMut>,
+    reserved_buf_size: usize,
+    max_buf_size: usize,
+    version: ProtocolVersion,
+}
+
+impl Default for NixWriterBuilder {
+    fn default() -> Self {
+        Self {
+            buf: Default::default(),
+            reserved_buf_size: 8192,
+            max_buf_size: 8192,
+            version: Default::default(),
+        }
+    }
+}
+
+impl NixWriterBuilder {
+    pub fn set_buffer(mut self, buf: BytesMut) -> Self {
+        self.buf = Some(buf);
+        self
+    }
+
+    pub fn set_reserved_buf_size(mut self, size: usize) -> Self {
+        self.reserved_buf_size = size;
+        self
+    }
+
+    pub fn set_max_buf_size(mut self, size: usize) -> Self {
+        self.max_buf_size = size;
+        self
+    }
+
+    pub fn set_version(mut self, version: ProtocolVersion) -> Self {
+        self.version = version;
+        self
+    }
+
+    pub fn build<W>(self, writer: W) -> NixWriter<W> {
+        let buf = self
+            .buf
+            .unwrap_or_else(|| BytesMut::with_capacity(self.max_buf_size));
+        NixWriter {
+            buf,
+            inner: writer,
+            reserved_buf_size: self.reserved_buf_size,
+            max_buf_size: self.max_buf_size,
+            version: self.version,
+        }
+    }
+}
+
+pin_project! {
+    pub struct NixWriter<W> {
+        #[pin]
+        inner: W,
+        buf: BytesMut,
+        reserved_buf_size: usize,
+        max_buf_size: usize,
+        version: ProtocolVersion,
+    }
+}
+
+impl NixWriter<Cursor<Vec<u8>>> {
+    pub fn builder() -> NixWriterBuilder {
+        NixWriterBuilder::default()
+    }
+}
+
+impl<W> NixWriter<W>
+where
+    W: AsyncWriteExt,
+{
+    pub fn new(writer: W) -> NixWriter<W> {
+        NixWriter::builder().build(writer)
+    }
+
+    pub fn buffer(&self) -> &[u8] {
+        &self.buf[..]
+    }
+
+    pub fn set_version(&mut self, version: ProtocolVersion) {
+        self.version = version;
+    }
+
+    /// Remaining capacity in internal buffer
+    pub fn remaining_mut(&self) -> usize {
+        self.buf.capacity() - self.buf.len()
+    }
+
+    fn poll_flush_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        let mut this = self.project();
+        while !this.buf.is_empty() {
+            let n = ready!(this.inner.as_mut().poll_write(cx, &this.buf[..]))?;
+            if n == 0 {
+                return Poll::Ready(Err(io::Error::new(
+                    io::ErrorKind::WriteZero,
+                    "failed to write the buffer",
+                )));
+            }
+            this.buf.advance(n);
+        }
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<W> NixWriter<W>
+where
+    W: AsyncWriteExt + Unpin,
+{
+    async fn flush_buf(&mut self) -> Result<(), io::Error> {
+        let mut s = Pin::new(self);
+        poll_fn(move |cx| s.as_mut().poll_flush_buf(cx)).await
+    }
+}
+
+impl<W> AsyncWrite for NixWriter<W>
+where
+    W: AsyncWrite,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        // Flush
+        if self.remaining_mut() < buf.len() {
+            ready!(self.as_mut().poll_flush_buf(cx))?;
+        }
+        let this = self.project();
+        if buf.len() > this.buf.capacity() {
+            this.inner.poll_write(cx, buf)
+        } else {
+            this.buf.put_slice(buf);
+            Poll::Ready(Ok(buf.len()))
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        ready!(self.as_mut().poll_flush_buf(cx))?;
+        self.project().inner.poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        ready!(self.as_mut().poll_flush_buf(cx))?;
+        self.project().inner.poll_shutdown(cx)
+    }
+}
+
+impl<W> NixWrite for NixWriter<W>
+where
+    W: AsyncWrite + Send + Unpin,
+{
+    type Error = io::Error;
+
+    fn version(&self) -> ProtocolVersion {
+        self.version
+    }
+
+    async fn write_number(&mut self, value: u64) -> Result<(), Self::Error> {
+        let mut buf = [0u8; 8];
+        BufMut::put_u64_le(&mut &mut buf[..], value);
+        self.write_all(&buf).await
+    }
+
+    async fn write_slice(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
+        let padding = padding_len(buf.len() as u64) as usize;
+        self.write_value(&buf.len()).await?;
+        self.write_all(buf).await?;
+        if padding > 0 {
+            self.write_all(&EMPTY_BYTES[..padding]).await
+        } else {
+            Ok(())
+        }
+    }
+
+    async fn write_display<D>(&mut self, msg: D) -> Result<(), Self::Error>
+    where
+        D: fmt::Display + Send,
+        Self: Sized,
+    {
+        // Ensure that buffer has space for at least reserved_buf_size bytes
+        if self.remaining_mut() < self.reserved_buf_size && !self.buf.is_empty() {
+            self.flush_buf().await?;
+        }
+        let offset = self.buf.len();
+        self.buf.put_u64_le(0);
+        if let Err(err) = write!(self.buf, "{}", msg) {
+            self.buf.truncate(offset);
+            return Err(Self::Error::unsupported_data(err));
+        }
+        let len = self.buf.len() - offset - 8;
+        BufMut::put_u64_le(&mut &mut self.buf[offset..(offset + 8)], len as u64);
+        let padding = padding_len(len as u64) as usize;
+        self.write_all(&EMPTY_BYTES[..padding]).await
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::time::Duration;
+
+    use hex_literal::hex;
+    use rstest::rstest;
+    use tokio::io::AsyncWriteExt as _;
+    use tokio_test::io::Builder;
+
+    use crate::nix_daemon::ser::NixWrite;
+
+    use super::NixWriter;
+
+    #[rstest]
+    #[case(1, &hex!("0100 0000 0000 0000"))]
+    #[case::evil(666, &hex!("9A02 0000 0000 0000"))]
+    #[case::max(u64::MAX, &hex!("FFFF FFFF FFFF FFFF"))]
+    #[tokio::test]
+    async fn test_write_number(#[case] number: u64, #[case] buf: &[u8]) {
+        let mock = Builder::new().write(buf).build();
+        let mut writer = NixWriter::new(mock);
+
+        writer.write_number(number).await.unwrap();
+        assert_eq!(writer.buffer(), buf);
+        writer.flush().await.unwrap();
+        assert_eq!(writer.buffer(), b"");
+    }
+
+    #[rstest]
+    #[case::empty(b"", &hex!("0000 0000 0000 0000"))]
+    #[case::one(b")", &hex!("0100 0000 0000 0000 2900 0000 0000 0000"))]
+    #[case::two(b"it", &hex!("0200 0000 0000 0000 6974 0000 0000 0000"))]
+    #[case::three(b"tea", &hex!("0300 0000 0000 0000 7465 6100 0000 0000"))]
+    #[case::four(b"were", &hex!("0400 0000 0000 0000 7765 7265 0000 0000"))]
+    #[case::five(b"where", &hex!("0500 0000 0000 0000 7768 6572 6500 0000"))]
+    #[case::six(b"unwrap", &hex!("0600 0000 0000 0000 756E 7772 6170 0000"))]
+    #[case::seven(b"where's", &hex!("0700 0000 0000 0000 7768 6572 6527 7300"))]
+    #[case::aligned(b"read_tea", &hex!("0800 0000 0000 0000 7265 6164 5F74 6561"))]
+    #[case::more_bytes(b"read_tess", &hex!("0900 0000 0000 0000 7265 6164 5F74 6573 7300 0000 0000 0000"))]
+    #[tokio::test]
+    async fn test_write_slice(
+        #[case] value: &[u8],
+        #[case] buf: &[u8],
+        #[values(1, 2, 3, 4, 5, 6, 7, 8, 9, 1024)] chunks_size: usize,
+        #[values(1, 2, 3, 4, 5, 6, 7, 8, 9, 1024)] buf_size: usize,
+    ) {
+        let mut builder = Builder::new();
+        for chunk in buf.chunks(chunks_size) {
+            builder.write(chunk);
+            builder.wait(Duration::ZERO);
+        }
+        let mock = builder.build();
+        let mut writer = NixWriter::builder().set_max_buf_size(buf_size).build(mock);
+
+        writer.write_slice(value).await.unwrap();
+        writer.flush().await.unwrap();
+        assert_eq!(writer.buffer(), b"");
+    }
+
+    #[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"))]
+    #[tokio::test]
+    async fn test_write_display(
+        #[case] value: &str,
+        #[case] buf: &[u8],
+        #[values(1, 2, 3, 4, 5, 6, 7, 8, 9, 1024)] chunks_size: usize,
+    ) {
+        let mut builder = Builder::new();
+        for chunk in buf.chunks(chunks_size) {
+            builder.write(chunk);
+            builder.wait(Duration::ZERO);
+        }
+        let mock = builder.build();
+        let mut writer = NixWriter::builder().build(mock);
+
+        writer.write_display(value).await.unwrap();
+        assert_eq!(writer.buffer(), buf);
+        writer.flush().await.unwrap();
+        assert_eq!(writer.buffer(), b"");
+    }
+}
diff --git a/tvix/nix-compat/src/wire/bytes/mod.rs b/tvix/nix-compat/src/wire/bytes/mod.rs
index 74adfb49b6a4..9b981fbbd2c0 100644
--- a/tvix/nix-compat/src/wire/bytes/mod.rs
+++ b/tvix/nix-compat/src/wire/bytes/mod.rs
@@ -181,7 +181,7 @@ pub async fn write_bytes<W: AsyncWriteExt + Unpin, B: AsRef<[u8]>>(
 
 /// Computes the number of bytes we should add to len (a length in
 /// bytes) to be aligned on 64 bits (8 bytes).
-fn padding_len(len: u64) -> u8 {
+pub(crate) fn padding_len(len: u64) -> u8 {
     let aligned = len.wrapping_add(7) & !7;
     aligned.wrapping_sub(len) as u8
 }