feat(tvix/nix-compat): introduce ExportedPathInfo struct

This is another representation about information Nix has on a Store
Path. It's encountered in the exportReferencesGraph feature.

Change-Id: Ia0c08c369f4af9e50ebe3a5053bd98fadaa0003d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11396
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/nix-compat/src/lib.rs

@@ -4,5 +4,6 @@ pub mod nar;
 pub mod narinfo;
 pub mod nixbase32;
 pub mod nixhash;
+pub mod path_info;
 pub mod store_path;
 pub mod wire;

tvix/nix-compat/src/path_info.rs

@@ -0,0 +1,121 @@
+use crate::{nixbase32, nixhash::NixHash, store_path::StorePathRef};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeSet;
+
+/// Represents information about a Store Path that Nix provides inside the build
+/// if the exportReferencesGraph feature is used.
+/// This is not to be confused with the format Nix uses in its `nix path-info` command.
+/// It includes some more fields, like `registrationTime`, `signatures` and `ultimate`,
+/// does not include the `closureSize` and encodes `narHash` as SRI.
+#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
+pub struct ExportedPathInfo<'a> {
+    #[serde(rename = "closureSize")]
+    pub closure_size: u64,
+
+    #[serde(
+        rename = "narHash",
+        serialize_with = "to_nix_nixbase32_string",
+        deserialize_with = "from_nix_nixbase32_string"
+    )]
+    pub nar_sha256: [u8; 32],
+
+    #[serde(rename = "narSize")]
+    pub nar_size: u64,
+
+    #[serde(borrow)]
+    pub path: StorePathRef<'a>,
+
+    /// The list of other Store Paths this Store Path refers to.
+    /// StorePathRef does Ord by the nixbase32-encoded string repr, so this is correct.
+    pub references: BTreeSet<StorePathRef<'a>>,
+    // more recent versions of Nix also have a `valid: true` field here, Nix 2.3 doesn't,
+    // and nothing seems to use it.
+}
+
+/// ExportedPathInfo are ordered by their `path` field.
+impl Ord for ExportedPathInfo<'_> {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.path.cmp(&other.path)
+    }
+}
+
+impl PartialOrd for ExportedPathInfo<'_> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+fn to_nix_nixbase32_string<S>(v: &[u8; 32], serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: serde::Serializer,
+{
+    let string = NixHash::Sha256(*v).to_nix_nixbase32_string();
+    string.serialize(serializer)
+}
+
+/// The length of a sha256 digest, nixbase32-encoded.
+const NIXBASE32_SHA256_ENCODE_LEN: usize = nixbase32::encode_len(32);
+
+fn from_nix_nixbase32_string<'de, D>(deserializer: D) -> Result<[u8; 32], D::Error>
+where
+    D: serde::Deserializer<'de>,
+{
+    let str: &'de str = Deserialize::deserialize(deserializer)?;
+
+    let digest_str = str.strip_prefix("sha256:").ok_or_else(|| {
+        serde::de::Error::invalid_value(serde::de::Unexpected::Str(str), &"sha256:…")
+    })?;
+
+    let digest_str: [u8; NIXBASE32_SHA256_ENCODE_LEN] =
+        digest_str.as_bytes().try_into().map_err(|_| {
+            serde::de::Error::invalid_value(serde::de::Unexpected::Str(str), &"valid digest len")
+        })?;
+
+    let digest: [u8; 32] = nixbase32::decode_fixed(digest_str).map_err(|_| {
+        serde::de::Error::invalid_value(serde::de::Unexpected::Str(str), &"valid nixbase32")
+    })?;
+
+    Ok(digest)
+}
+
+#[cfg(test)]
+mod tests {
+    use hex_literal::hex;
+
+    use super::*;
+
+    /// Ensure we can create the same JSON as the exportReferencesGraph feature
+    #[test]
+    fn serialize_deserialize() {
+        // JSON extracted from a build of
+        // stdenv.mkDerivation { name = "hello"; __structuredAttrs = true; exportReferencesGraph.blub = [ pkgs.hello ]; nativeBuildInputs = [pkgs.jq]; buildCommand = "jq -rc .blub $NIX_ATTRS_JSON_FILE > $out"; }
+        let pathinfos_str_json = r#"[{"closureSize":1828984,"narHash":"sha256:11vm2x1ajhzsrzw7lsyss51mmr3b6yll9wdjn51bh7liwkpc8ila","narSize":1828984,"path":"/nix/store/7n0mbqydcipkpbxm24fab066lxk68aqk-libunistring-1.1","references":["/nix/store/7n0mbqydcipkpbxm24fab066lxk68aqk-libunistring-1.1"]},{"closureSize":32696176,"narHash":"sha256:0alzbhjxdcsmr1pk7z0bdh46r2xpq3xs3k9y82bi4bx5pklcvw5x","narSize":226560,"path":"/nix/store/dbghhbq1x39yxgkv3vkgfwbxrmw9nfzi-hello-2.12.1","references":["/nix/store/dbghhbq1x39yxgkv3vkgfwbxrmw9nfzi-hello-2.12.1","/nix/store/ddwyrxif62r8n6xclvskjyy6szdhvj60-glibc-2.39-5"]},{"closureSize":32469616,"narHash":"sha256:1zw5p05fh0k836ybfxkskv8apcv2m3pm2wa6y90wqn5w5kjyj13c","narSize":30119936,"path":"/nix/store/ddwyrxif62r8n6xclvskjyy6szdhvj60-glibc-2.39-5","references":["/nix/store/ddwyrxif62r8n6xclvskjyy6szdhvj60-glibc-2.39-5","/nix/store/rxganm4ibf31qngal3j3psp20mak37yy-xgcc-13.2.0-libgcc","/nix/store/s32cldbh9pfzd9z82izi12mdlrw0yf8q-libidn2-2.3.7"]},{"closureSize":159560,"narHash":"sha256:10q8iyvfmpfck3yiisnj1j8vp6lq3km17r26sr95zpdf9mgmk69s","narSize":159560,"path":"/nix/store/rxganm4ibf31qngal3j3psp20mak37yy-xgcc-13.2.0-libgcc","references":[]},{"closureSize":2190120,"narHash":"sha256:1cv997nzxbd91jhmzwnhxa1ahlzp5ffli8m4a5npcq8zg0vb1kwg","narSize":361136,"path":"/nix/store/s32cldbh9pfzd9z82izi12mdlrw0yf8q-libidn2-2.3.7","references":["/nix/store/7n0mbqydcipkpbxm24fab066lxk68aqk-libunistring-1.1","/nix/store/s32cldbh9pfzd9z82izi12mdlrw0yf8q-libidn2-2.3.7"]}]"#;
+
+        // We ensure it roundtrips (to check the sorting is correct)
+        let deserialized: BTreeSet<ExportedPathInfo> =
+            serde_json::from_str(pathinfos_str_json).expect("must serialize");
+
+        let serialized_again = serde_json::to_string(&deserialized).expect("must deserialize");
+        assert_eq!(pathinfos_str_json, serialized_again);
+
+        // Also compare one specific item to be populated as expected.
+        assert_eq!(
+            &ExportedPathInfo {
+                closure_size: 1828984,
+                nar_sha256: hex!(
+                    "8a46c4eee4911eb842b1b2f144a9376be45a43d1da6b7af8cffa43a942177587"
+                ),
+                nar_size: 1828984,
+                path: StorePathRef::from_bytes(
+                    b"7n0mbqydcipkpbxm24fab066lxk68aqk-libunistring-1.1"
+                )
+                .expect("must parse"),
+                references: BTreeSet::from_iter([StorePathRef::from_bytes(
+                    b"7n0mbqydcipkpbxm24fab066lxk68aqk-libunistring-1.1"
+                )
+                .unwrap()]),
+            },
+            deserialized.first().unwrap()
+        );
+    }
+}