diff options
Diffstat (limited to 'tvix/nix-compat/src/nixhash/ca_hash.rs')
| -rw-r--r-- | tvix/nix-compat/src/nixhash/ca_hash.rs | 213 |
1 files changed, 213 insertions, 0 deletions
diff --git a/tvix/nix-compat/src/nixhash/ca_hash.rs b/tvix/nix-compat/src/nixhash/ca_hash.rs new file mode 100644 index 000000000000..0d6c68d7fa7f --- /dev/null +++ b/tvix/nix-compat/src/nixhash/ca_hash.rs @@ -0,0 +1,213 @@ +use crate::nixbase32; +use crate::nixhash::{self, HashAlgo, NixHash}; +use serde::de::Unexpected; +use serde::ser::SerializeMap; +use serde::{Deserialize, Deserializer, Serialize, Serializer}; +use serde_json::{Map, Value}; +use std::borrow::Cow; + +use super::algos::SUPPORTED_ALGOS; +use super::from_algo_and_digest; + +/// A Nix CAHash describes a content-addressed hash of a path. +/// +/// The way Nix prints it as a string is a bit confusing, but there's essentially +/// three modes, `Flat`, `Nar` and `Text`. +/// `Flat` and `Nar` support all 4 algos that [NixHash] supports +/// (sha1, md5, sha256, sha512), `Text` only supports sha256. +#[derive(Clone, Debug, Eq, PartialEq)] +pub enum CAHash { + Flat(NixHash), // "fixed flat" + Nar(NixHash), // "fixed recursive" + Text([u8; 32]), // "text", only supports sha256 +} + +impl CAHash { + pub fn digest(&self) -> Cow<NixHash> { + match *self { + CAHash::Flat(ref digest) => Cow::Borrowed(digest), + CAHash::Nar(ref digest) => Cow::Borrowed(digest), + CAHash::Text(digest) => Cow::Owned(NixHash::Sha256(digest)), + } + } + + /// Constructs a [CAHash] from the textual representation, + /// which is one of the three: + /// - `text:sha256:$nixbase32sha256digest` + /// - `fixed:r:$algo:$nixbase32digest` + /// - `fixed:$algo:$nixbase32digest` + /// which is the format that's used in the NARInfo for example. + pub fn from_nix_hex_str(s: &str) -> Option<Self> { + 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(s) = s.strip_prefix("r:") { + NixHash::from_nix_hex_str(s).map(CAHash::Nar) + } else { + NixHash::from_nix_hex_str(s).map(CAHash::Flat) + } + } + _ => None, + } + } + + /// Formats a [CAHash] in the Nix default hash format, which is the format + /// that's used in NARInfos for example. + pub fn to_nix_nixbase32_string(&self) -> String { + match self { + CAHash::Flat(nh) => format!("fixed:{}", nh.to_nix_nixbase32_string()), + CAHash::Nar(nh) => format!("fixed:r:{}", nh.to_nix_nixbase32_string()), + CAHash::Text(digest) => { + format!("text:sha256:{}", nixbase32::encode(digest)) + } + } + } + + /// This takes a serde_json::Map and turns it into this structure. This is necessary to do such + /// shenigans because we have external consumers, like the Derivation parser, who would like to + /// know whether we have a invalid or a missing NixHashWithMode structure in another structure, + /// e.g. Output. + /// This means we have this combinatorial situation: + /// - no hash, no hashAlgo: no [CAHash] so we return Ok(None). + /// - present hash, missing hashAlgo: invalid, we will return missing_field + /// - missing hash, present hashAlgo: same + /// - present hash, present hashAlgo: either we return ourselves or a type/value validation + /// error. + /// This function is for internal consumption regarding those needs until we have a better + /// solution. Now this is said, let's explain how this works. + /// + /// We want to map the serde data model into a [CAHash]. + /// + /// The serde data model has a `hash` field (containing a digest in nixbase32), + /// and a `hashAlgo` field, containing the stringified hash algo. + /// In case the hash is recursive, hashAlgo also has a `r:` prefix. + /// + /// This is to match how `nix show-derivation` command shows them in JSON + /// representation. + pub(crate) fn from_map<'de, D>(map: &Map<String, Value>) -> Result<Option<Self>, D::Error> + where + D: Deserializer<'de>, + { + // If we don't have hash neither hashAlgo, let's just return None. + if !map.contains_key("hash") && !map.contains_key("hashAlgo") { + return Ok(None); + } + + let digest: Vec<u8> = { + if let Some(v) = map.get("hash") { + if let Some(s) = v.as_str() { + data_encoding::HEXLOWER + .decode(s.as_bytes()) + .map_err(|e| serde::de::Error::custom(e.to_string()))? + } else { + return Err(serde::de::Error::invalid_type( + Unexpected::Other(&v.to_string()), + &"a string", + )); + } + } else { + return Err(serde::de::Error::missing_field( + "couldn't extract `hash` key but `hashAlgo` key present", + )); + } + }; + + if let Some(v) = map.get("hashAlgo") { + if let Some(s) = v.as_str() { + match s.strip_prefix("r:") { + Some(rest) => Ok(Some(Self::Nar( + from_algo_and_digest( + HashAlgo::try_from(rest).map_err(|e| { + serde::de::Error::invalid_value( + Unexpected::Other(&e.to_string()), + &format!("one of {}", SUPPORTED_ALGOS.join(",")).as_str(), + ) + })?, + &digest, + ) + .map_err(|e: nixhash::Error| { + serde::de::Error::invalid_value( + Unexpected::Other(&e.to_string()), + &"a digest with right length", + ) + })?, + ))), + None => Ok(Some(Self::Flat( + from_algo_and_digest( + HashAlgo::try_from(s).map_err(|e| { + serde::de::Error::invalid_value( + Unexpected::Other(&e.to_string()), + &format!("one of {}", SUPPORTED_ALGOS.join(",")).as_str(), + ) + })?, + &digest, + ) + .map_err(|e: nixhash::Error| { + serde::de::Error::invalid_value( + Unexpected::Other(&e.to_string()), + &"a digest with right length", + ) + })?, + ))), + } + } else { + Err(serde::de::Error::invalid_type( + Unexpected::Other(&v.to_string()), + &"a string", + )) + } + } else { + Err(serde::de::Error::missing_field( + "couldn't extract `hashAlgo` key, but `hash` key present", + )) + } + } +} + +impl Serialize for CAHash { + /// map a CAHash into the serde data model. + fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> + where + S: Serializer, + { + let mut map = serializer.serialize_map(Some(2))?; + match self { + CAHash::Flat(h) => { + map.serialize_entry("hash", &nixbase32::encode(h.digest_as_bytes()))?; + map.serialize_entry("hashAlgo", &h.algo())?; + } + CAHash::Nar(h) => { + map.serialize_entry("hash", &nixbase32::encode(h.digest_as_bytes()))?; + map.serialize_entry("hashAlgo", &format!("r:{}", &h.algo()))?; + } + // It is not legal for derivations to use this (which is where + // we're currently exercising [Serialize] mostly, + // but it's still good to be able to serialize other CA hashes too. + CAHash::Text(h) => { + map.serialize_entry("hash", &nixbase32::encode(h.as_ref()))?; + map.serialize_entry("hashAlgo", "text")?; + } + }; + map.end() + } +} + +impl<'de> Deserialize<'de> for CAHash { + fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> + where + D: Deserializer<'de>, + { + let value = Self::from_map::<D>(&Map::deserialize(deserializer)?)?; + + match value { + None => Err(serde::de::Error::custom("couldn't parse as map")), + Some(v) => Ok(v), + } + } +} |