From 7612cb4c31fadd7ccaa7672cf551b9d21d7884b4 Mon Sep 17 00:00:00 2001
From: Ryan Lahfa <tvl@lahfa.xyz>
Date: Mon, 12 Aug 2024 18:15:11 +0200
Subject: feat(tvix/nix-compat): add a basic listing deserializer

.ls files are useful to seek in a NAR without parsing it entirely.

The responsibility of validating the files is on the caller.

Change-Id: I5d1da28b5479c38f20ca5babe60e362a2217c9ea
Signed-off-by: Ryan Lahfa <tvl@lahfa.xyz>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12196
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
---
 tvix/nix-compat/src/nar/listing/mod.rs | 65 ++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 tvix/nix-compat/src/nar/listing/mod.rs

(limited to 'tvix/nix-compat/src/nar/listing/mod.rs')

diff --git a/tvix/nix-compat/src/nar/listing/mod.rs b/tvix/nix-compat/src/nar/listing/mod.rs
new file mode 100644
index 000000000000..c1119a0199f4
--- /dev/null
+++ b/tvix/nix-compat/src/nar/listing/mod.rs
@@ -0,0 +1,65 @@
+//! Parser for the Nix archive listing format, aka .ls.
+//!
+//! LS files are produced by the C++ Nix implementation via `write-nar-listing=1` query parameter
+//! passed to a store implementation when transferring store paths.
+//!
+//! Listing files contains metadata about a file and its offset in the corresponding NAR.
+//!
+//! NOTE: LS entries does not offer any integrity field to validate the retrieved file at the provided
+//! offset. Validating the contents is the caller's responsibility.
+
+use std::collections::HashMap;
+
+use serde::Deserialize;
+
+#[cfg(test)]
+mod test;
+
+#[derive(Debug, Deserialize)]
+#[serde(tag = "type", rename_all = "lowercase")]
+pub enum ListingEntry {
+    Regular {
+        size: u64,
+        #[serde(default)]
+        executable: bool,
+        #[serde(rename = "narOffset")]
+        nar_offset: u64,
+    },
+    Directory {
+        entries: HashMap<String, ListingEntry>,
+    },
+    Symlink {
+        target: String,
+    },
+}
+
+#[derive(Debug)]
+pub struct ListingVersion<const V: u8>;
+
+#[derive(Debug, thiserror::Error)]
+#[error("Invalid version: {0}")]
+struct ListingVersionError(u8);
+
+impl<'de, const V: u8> Deserialize<'de> for ListingVersion<V> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let value = u8::deserialize(deserializer)?;
+        if value == V {
+            Ok(ListingVersion::<V>)
+        } else {
+            Err(serde::de::Error::custom(ListingVersionError(value)))
+        }
+    }
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(untagged)]
+#[non_exhaustive]
+pub enum Listing {
+    V1 {
+        root: ListingEntry,
+        version: ListingVersion<1>,
+    },
+}
-- 
cgit 1.4.1