use crate::nixbase32;
use crate::nixhash::{CAHash, NixHash};
use crate::store_path::{Error, StorePath, STORE_DIR};
use data_encoding::HEXLOWER;
use sha2::{Digest, Sha256};
use thiserror;
/// Errors that can occur when creating a content-addressed store path.
///
/// This wraps the main [crate::store_path::Error]..
#[derive(Debug, PartialEq, Eq, thiserror::Error)]
pub enum BuildStorePathError {
#[error("Invalid Store Path: {0}")]
InvalidStorePath(Error),
/// This error occurs when we have references outside the SHA-256 +
/// Recursive case. The restriction comes from upstream Nix. It may be
/// lifted at some point but there isn't a pressing need to anticipate that.
#[error("References were not supported as much as requested")]
InvalidReference(),
}
/// compress_hash takes an arbitrarily long sequence of bytes (usually
/// a hash digest), and returns a sequence of bytes of length
/// OUTPUT_SIZE.
///
/// It's calculated by rotating through the bytes in the output buffer
/// (zero- initialized), and XOR'ing with each byte of the passed
/// input. It consumes 1 byte at a time, and XOR's it with the current
/// value in the output buffer.
///
/// This mimics equivalent functionality in C++ Nix.
pub fn compress_hash<const OUTPUT_SIZE: usize>(input: &[u8]) -> [u8; OUTPUT_SIZE] {
let mut output = [0; OUTPUT_SIZE];
for (ii, ch) in input.iter().enumerate() {
output[ii % OUTPUT_SIZE] ^= ch;
}
output
}
/// This builds a store path, by calculating the text_hash_string of either a
/// derivation or a literal text file that may contain references.
/// If you don't want to have to pass the entire contents, you might want to use
/// [build_ca_path] instead.
pub fn build_text_path<'a, S, SP, I, C>(
name: &'a str,
content: C,
references: I,
) -> Result<StorePath<SP>, BuildStorePathError>
where
S: AsRef<str>,
SP: AsRef<str> + std::convert::From<&'a str>,
I: IntoIterator<Item = S>,
C: AsRef<[u8]>,
{
// produce the sha256 digest of the contents
let content_digest = Sha256::new_with_prefix(content).finalize().into();
build_ca_path(name, &CAHash::Text(content_digest), references, false)
}
/// This builds a store path from a [CAHash] and a list of references.
pub fn build_ca_path<'a, S, SP, I>(
name: &'a str,
ca_hash: &CAHash,
references: I,
self_reference: bool,
) -> Result<StorePath<SP>, BuildStorePathError>
where
S: AsRef<str>,
SP: AsRef<str> + std::convert::From<&'a str>,
I: IntoIterator<Item = S>,
{
// self references are only allowed for CAHash::Nar(NixHash::Sha256(_)).
if self_reference && matches!(ca_hash, CAHash::Nar(NixHash::Sha256(_))) {
return Err(BuildStorePathError::InvalidReference());
}
/// Helper function, used for the non-sha256 [CAHash::Nar] and all [CAHash::Flat].
fn fixed_out_digest(prefix: &str, hash: &NixHash) -> [u8; 32] {
Sha256::new_with_prefix(format!("{}:{}:", prefix, hash.to_nix_hex_string()))
.finalize()
.into()
}
let (ty, inner_digest) = match &ca_hash {
CAHash::Text(ref digest) => (make_references_string("text", references, false), *digest),
CAHash::Nar(NixHash::Sha256(ref digest)) => (
make_references_string("source", references, self_reference),
*digest,
),
// for all other CAHash::Nar, another custom scheme is used.
CAHash::Nar(ref hash) => {
if references.into_iter().next().is_some() {
return Err(BuildStorePathError::InvalidReference());
}
(
"output:out".to_string(),
fixed_out_digest("fixed:out:r", hash),
)
}
// CaHash::Flat is using something very similar, except the `r:` prefix.
CAHash::Flat(ref hash) => {
if references.into_iter().next().is_some() {
return Err(BuildStorePathError::InvalidReference());
}
(
"output:out".to_string(),
fixed_out_digest("fixed:out", hash),
)
}
};
build_store_path_from_fingerprint_parts(&ty, &inner_digest, name)
.map_err(BuildStorePathError::InvalidStorePath)
}
/// This builds an input-addressed store path.
///
/// Input-addresed store paths are always derivation outputs, the "input" in question is the
/// derivation and its closure.
pub fn build_output_path<'a, SP>(
drv_sha256: &[u8; 32],
output_name: &str,
output_path_name: &'a str,
) -> Result<StorePath<SP>, Error>
where
SP: AsRef<str> + std::convert::From<&'a str>,
{
build_store_path_from_fingerprint_parts(
&(String::from("output:") + output_name),
drv_sha256,
output_path_name,
)
}
/// This builds a store path from fingerprint parts.
/// Usually, that function is used from [build_text_path] and
/// passed a "text hash string" (starting with "text:" as fingerprint),
/// but other fingerprints starting with "output:" are also used in Derivation
/// output path calculation.
///
/// The fingerprint is hashed with sha256, and its digest is compressed to 20
/// bytes.
/// Inside a StorePath, that digest is printed nixbase32-encoded
/// (32 characters).
fn build_store_path_from_fingerprint_parts<'a, SP>(
ty: &str,
inner_digest: &[u8; 32],
name: &'a str,
) -> Result<StorePath<SP>, Error>
where
SP: AsRef<str> + std::convert::From<&'a str>,
{
let fingerprint = format!(
"{ty}:sha256:{}:{STORE_DIR}:{name}",
HEXLOWER.encode(inner_digest)
);
// name validation happens in here.
StorePath::from_name_and_digest_fixed(
name,
compress_hash(&Sha256::new_with_prefix(fingerprint).finalize()),
)
}
/// This contains the Nix logic to create "text hash strings", which are used
/// in `builtins.toFile`, as well as in Derivation Path calculation.
///
/// A text hash is calculated by concatenating the following fields, separated by a `:`:
///
/// - text
/// - references, individually joined by `:`
/// - the nix_hash_string representation of the sha256 digest of some contents
/// - the value of `storeDir`
/// - the name
fn make_references_string<S: AsRef<str>, I: IntoIterator<Item = S>>(
ty: &str,
references: I,
self_ref: bool,
) -> String {
let mut s = String::from(ty);
for reference in references {
s.push(':');
s.push_str(reference.as_ref());
}
if self_ref {
s.push_str(":self");
}
s
}
/// Nix placeholders (i.e. values returned by `builtins.placeholder`)
/// are used to populate outputs with paths that must be
/// string-replaced with the actual placeholders later, at runtime.
///
/// The actual placeholder is basically just a SHA256 hash encoded in
/// cppnix format.
pub fn hash_placeholder(name: &str) -> String {
let digest = Sha256::new_with_prefix(format!("nix-output:{}", name)).finalize();
format!("/{}", nixbase32::encode(&digest))
}
#[cfg(test)]
mod test {
use hex_literal::hex;
use super::*;
use crate::{
nixhash::{CAHash, NixHash},
store_path::StorePathRef,
};
#[test]
fn build_text_path_with_zero_references() {
// This hash should match `builtins.toFile`, e.g.:
//
// nix-repl> builtins.toFile "foo" "bar"
// "/nix/store/vxjiwkjkn7x4079qvh1jkl5pn05j2aw0-foo"
let store_path: StorePathRef = build_text_path("foo", "bar", Vec::<String>::new())
.expect("build_store_path() should succeed");
assert_eq!(
store_path.to_absolute_path().as_str(),
"/nix/store/vxjiwkjkn7x4079qvh1jkl5pn05j2aw0-foo"
);
}
#[test]
fn build_text_path_with_non_zero_references() {
// This hash should match:
//
// nix-repl> builtins.toFile "baz" "${builtins.toFile "foo" "bar"}"
// "/nix/store/5xd714cbfnkz02h2vbsj4fm03x3f15nf-baz"
let inner: StorePathRef = build_text_path("foo", "bar", Vec::<String>::new())
.expect("path_with_references() should succeed");
let inner_path = inner.to_absolute_path();
let outer: StorePathRef = build_text_path("baz", &inner_path, vec![inner_path.as_str()])
.expect("path_with_references() should succeed");
assert_eq!(
outer.to_absolute_path().as_str(),
"/nix/store/5xd714cbfnkz02h2vbsj4fm03x3f15nf-baz"
);
}
#[test]
fn build_sha1_path() {
let outer: StorePathRef = build_ca_path(
"bar",
&CAHash::Nar(NixHash::Sha1(hex!(
"0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"
))),
Vec::<String>::new(),
false,
)
.expect("path_with_references() should succeed");
assert_eq!(
outer.to_absolute_path().as_str(),
"/nix/store/mp57d33657rf34lzvlbpfa1gjfv5gmpg-bar"
);
}
#[test]
fn build_store_path_with_non_zero_references() {
// This hash should match:
//
// nix-repl> builtins.toFile "baz" "${builtins.toFile "foo" "bar"}"
// "/nix/store/5xd714cbfnkz02h2vbsj4fm03x3f15nf-baz"
//
// $ nix store make-content-addressed /nix/store/5xd714cbfnkz02h2vbsj4fm03x3f15nf-baz
// rewrote '/nix/store/5xd714cbfnkz02h2vbsj4fm03x3f15nf-baz' to '/nix/store/s89y431zzhmdn3k8r96rvakryddkpv2v-baz'
let outer: StorePathRef = build_ca_path(
"baz",
&CAHash::Nar(NixHash::Sha256(
nixbase32::decode(b"1xqkzcb3909fp07qngljr4wcdnrh1gdam1m2n29i6hhrxlmkgkv1")
.expect("nixbase32 should decode")
.try_into()
.expect("should have right len"),
)),
vec!["/nix/store/dxwkwjzdaq7ka55pkk252gh32bgpmql4-foo"],
false,
)
.expect("path_with_references() should succeed");
assert_eq!(
outer.to_absolute_path().as_str(),
"/nix/store/s89y431zzhmdn3k8r96rvakryddkpv2v-baz"
);
}
}
