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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),
}
}
}
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