feat(tvix/nix-compat): add narinfo parsing and serialisation r/6897

Change-Id: I72c63414794642ca8d85c3f635f49db888420c40
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9852
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

1 files changed, 406 insertions, 0 deletions

diff --git a/tvix/nix-compat/src/narinfo.rs b/tvix/nix-compat/src/narinfo.rs
new file mode 100644
index 000000000000..a66709abfe79
--- /dev/null
+++ b/tvix/nix-compat/src/narinfo.rs
@@ -0,0 +1,406 @@
+//! NAR info files describe a store path in a traditional Nix binary cache.
+//! Over the wire, they are formatted as "Key: value" pairs separated by newlines.
+//!
+//! It contains four kinds of information:
+//! 1. the description of the store path itself
+//!    * store path prefix, digest, and name
+//!    * NAR hash and size
+//!    * references
+//! 2. authenticity information
+//!    * zero or more signatures over that description
+//!    * an optional [CAHash] for content-addressed paths (fixed outputs, sources, and derivations)
+//! 3. derivation metadata
+//!    * deriver (the derivation that produced this path)
+//!    * system (the system value of that derivation)
+//! 4. cache-specific information
+//!    * URL of the compressed NAR, relative to the NAR info file
+//!    * compression algorithm used for the NAR
+//!    * hash and size of the compressed NAR
+
+use data_encoding::BASE64;
+use std::{
+    fmt::{self, Display},
+    mem,
+};
+
+use crate::{
+    nixbase32,
+    nixhash::{CAHash, NixHash},
+    store_path::StorePathRef,
+};
+
+#[derive(Debug)]
+pub struct NarInfo<'a> {
+    // core (authenticated, but unverified here)
+    /// Store path described by this [NarInfo]
+    pub store_path: StorePathRef<'a>,
+    /// SHA-256 digest of the NAR file
+    pub nar_hash: [u8; 32],
+    /// Size of the NAR file in bytes
+    pub nar_size: u64,
+    /// Store paths known to be referenced by the contents
+    pub references: Vec<StorePathRef<'a>>,
+    // authenticity
+    /// Ed25519 signature over the path fingerprint
+    pub signatures: Vec<Signature<'a>>,
+    /// Content address (for content-defined paths)
+    pub ca: Option<CAHash>,
+    // derivation metadata
+    /// Nix system triple of [deriver]
+    pub system: Option<&'a str>,
+    /// Store path of the derivation that produced this
+    pub deriver: Option<StorePathRef<'a>>,
+    // cache-specific untrusted metadata
+    /// Relative URL of the compressed NAR file
+    pub url: &'a str,
+    /// Compression method of the NAR file
+    /// TODO(edef): default this to bzip2, and have None mean "none" (uncompressed)
+    pub compression: Option<&'a str>,
+    /// SHA-256 digest of the file at `url`
+    pub file_hash: Option<[u8; 32]>,
+    /// Size of the file at `url` in bytes
+    pub file_size: Option<u64>,
+}
+
+impl<'a> NarInfo<'a> {
+    pub fn parse(input: &'a str) -> Option<Self> {
+        let mut store_path = None;
+        let mut url = None;
+        let mut compression = None;
+        let mut file_hash = None;
+        let mut file_size = None;
+        let mut nar_hash = None;
+        let mut nar_size = None;
+        let mut references = None;
+        let mut system = None;
+        let mut deriver = None;
+        let mut signatures = vec![];
+        let mut ca = None;
+
+        for line in input.lines() {
+            let (tag, val) = line.split_once(':')?;
+            let val = val.strip_prefix(' ')?;
+
+            match tag {
+                "StorePath" => {
+                    let val = val.strip_prefix("/nix/store/")?;
+                    let val = StorePathRef::from_bytes(val.as_bytes()).ok()?;
+
+                    if store_path.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "URL" => {
+                    if val.is_empty() {
+                        return None;
+                    }
+
+                    if url.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "Compression" => {
+                    if val.is_empty() {
+                        return None;
+                    }
+
+                    if compression.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "FileHash" => {
+                    let val = val.strip_prefix("sha256:")?;
+                    let val = nixbase32::decode_fixed::<32>(val).ok()?;
+
+                    if file_hash.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "FileSize" => {
+                    let val = val.parse::<u64>().ok()?;
+
+                    if file_size.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "NarHash" => {
+                    let val = val.strip_prefix("sha256:")?;
+                    let val = nixbase32::decode_fixed::<32>(val).ok()?;
+
+                    if nar_hash.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "NarSize" => {
+                    let val = val.parse::<u64>().ok()?;
+
+                    if nar_size.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "References" => {
+                    let val: Vec<StorePathRef> = if !val.is_empty() {
+                        let mut prev = "";
+                        val.split(' ')
+                            .map(|s| {
+                                if mem::replace(&mut prev, s) < s {
+                                    StorePathRef::from_bytes(s.as_bytes()).ok()
+                                } else {
+                                    // references are out of order
+                                    None
+                                }
+                            })
+                            .collect::<Option<_>>()?
+                    } else {
+                        vec![]
+                    };
+
+                    if references.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "System" => {
+                    if val.is_empty() {
+                        return None;
+                    }
+
+                    if system.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "Deriver" => {
+                    let val = StorePathRef::from_bytes(val.as_bytes()).ok()?;
+
+                    if !val.name().ends_with(".drv") {
+                        return None;
+                    }
+
+                    if deriver.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                "Sig" => {
+                    let val = Signature::parse(val)?;
+
+                    signatures.push(val);
+                }
+                "CA" => {
+                    let val = parse_ca(val)?;
+
+                    if ca.replace(val).is_some() {
+                        return None;
+                    }
+                }
+                _ => {
+                    // unknown field, ignore
+                }
+            }
+        }
+
+        Some(NarInfo {
+            store_path: store_path?,
+            nar_hash: nar_hash?,
+            nar_size: nar_size?,
+            references: references?,
+            signatures,
+            ca,
+            system,
+            deriver,
+            url: url?,
+            compression,
+            file_hash,
+            file_size,
+        })
+    }
+}
+
+impl Display for NarInfo<'_> {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        writeln!(w, "StorePath: /nix/store/{}", self.store_path)?;
+        writeln!(w, "URL: {}", self.url)?;
+
+        if let Some(compression) = self.compression {
+            writeln!(w, "Compression: {compression}")?;
+        }
+
+        if let Some(file_hash) = self.file_hash {
+            writeln!(w, "FileHash: {}", fmt_hash(&NixHash::Sha256(file_hash)))?;
+        }
+
+        if let Some(file_size) = self.file_size {
+            writeln!(w, "FileSize: {file_size}")?;
+        }
+
+        writeln!(w, "NarHash: {}", fmt_hash(&NixHash::Sha256(self.nar_hash)))?;
+        writeln!(w, "NarSize: {}", self.nar_size)?;
+
+        write!(w, "References:")?;
+        if self.references.is_empty() {
+            write!(w, " ")?;
+        } else {
+            for path in &self.references {
+                write!(w, " {path}")?;
+            }
+        }
+        writeln!(w)?;
+
+        if let Some(deriver) = &self.deriver {
+            writeln!(w, "Deriver: {deriver}")?;
+        }
+
+        if let Some(system) = self.system {
+            writeln!(w, "System: {system}")?;
+        }
+
+        for sig in &self.signatures {
+            writeln!(w, "Sig: {sig}")?;
+        }
+
+        if let Some(ca) = &self.ca {
+            writeln!(w, "CA: {}", fmt_ca(ca))?;
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct Signature<'a> {
+    name: &'a str,
+    bytes: [u8; 64],
+}
+
+impl<'a> Signature<'a> {
+    pub fn parse(input: &'a str) -> Option<Signature<'a>> {
+        let (name, bytes64) = input.split_once(':')?;
+
+        let mut buf = [0; 66];
+        let mut bytes = [0; 64];
+        match BASE64.decode_mut(bytes64.as_bytes(), &mut buf) {
+            Ok(64) => {
+                bytes.copy_from_slice(&buf[..64]);
+            }
+            _ => {
+                return None;
+            }
+        }
+
+        Some(Signature { name, bytes })
+    }
+
+    pub fn name(&self) -> &'a str {
+        self.name
+    }
+
+    pub fn bytes(&self) -> &[u8; 64] {
+        &self.bytes
+    }
+}
+
+impl Display for Signature<'_> {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        write!(w, "{}:{}", self.name, BASE64.encode(&self.bytes))
+    }
+}
+
+pub fn parse_ca(s: &str) -> Option<CAHash> {
+    let (tag, s) = s.split_once(':')?;
+
+    match tag {
+        "text" => {
+            let digest = s.strip_prefix("sha256:")?;
+            let digest = nixbase32::decode_fixed(digest).ok()?;
+            Some(CAHash::Text(digest))
+        }
+        "fixed" => {
+            if let Some(digest) = s.strip_prefix("r:sha256:") {
+                let digest = nixbase32::decode_fixed(digest).ok()?;
+                Some(CAHash::Nar(NixHash::Sha256(digest)))
+            } else {
+                parse_hash(s).map(CAHash::Flat)
+            }
+        }
+        _ => None,
+    }
+}
+
+#[allow(non_camel_case_types)]
+struct fmt_ca<'a>(&'a CAHash);
+
+impl Display for fmt_ca<'_> {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        match self.0 {
+            CAHash::Flat(h) => {
+                write!(w, "fixed:{}", fmt_hash(h))
+            }
+            &CAHash::Text(d) => {
+                write!(w, "text:{}", fmt_hash(&NixHash::Sha256(d)))
+            }
+            CAHash::Nar(h) => {
+                write!(w, "fixed:r:{}", fmt_hash(h))
+            }
+        }
+    }
+}
+
+fn parse_hash(s: &str) -> Option<NixHash> {
+    let (tag, digest) = s.split_once(':')?;
+
+    (match tag {
+        "md5" => nixbase32::decode_fixed(digest).map(NixHash::Md5),
+        "sha1" => nixbase32::decode_fixed(digest).map(NixHash::Sha1),
+        "sha256" => nixbase32::decode_fixed(digest).map(NixHash::Sha256),
+        "sha512" => nixbase32::decode_fixed(digest)
+            .map(Box::new)
+            .map(NixHash::Sha512),
+        _ => return None,
+    })
+    .ok()
+}
+
+#[allow(non_camel_case_types)]
+struct fmt_hash<'a>(&'a NixHash);
+
+impl Display for fmt_hash<'_> {
+    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
+        let (tag, digest) = match self.0 {
+            NixHash::Md5(d) => ("md5", &d[..]),
+            NixHash::Sha1(d) => ("sha1", &d[..]),
+            NixHash::Sha256(d) => ("sha256", &d[..]),
+            NixHash::Sha512(d) => ("sha512", &d[..]),
+        };
+
+        write!(w, "{tag}:{}", nixbase32::encode(digest))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use lazy_static::lazy_static;
+    use pretty_assertions::assert_eq;
+    use std::{io, str};
+
+    use super::NarInfo;
+
+    lazy_static! {
+        static ref CASES: &'static [&'static str] = {
+            let data = zstd::decode_all(io::Cursor::new(include_bytes!("../testdata/narinfo.zst")))
+                .unwrap();
+            let data = str::from_utf8(Vec::leak(data)).unwrap();
+            Vec::leak(
+                data.split_inclusive("\n\n")
+                    .map(|s| s.strip_suffix('\n').unwrap())
+                    .collect::<Vec<_>>(),
+            )
+        };
+    }
+
+    #[test]
+    fn roundtrip() {
+        for &input in *CASES {
+            let parsed = NarInfo::parse(input).expect("should parse");
+            let output = format!("{parsed}");
+            assert_eq!(input, output, "should roundtrip");
+        }
+    }
+}