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use crate::derivation::DerivationError;
use crate::nixbase32;
use crate::store_path::StorePath;
use crate::texthash::text_hash_string;
use sha2::{Digest, Sha256};
/// 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.
fn compress_hash(input: &[u8], output_size: usize) -> Vec<u8> {
let mut output: Vec<u8> = vec![0; output_size];
for (ii, ch) in input.iter().enumerate() {
output[ii % output_size] ^= ch;
}
output
}
/// This returns a store path, either of a derivation or a regular output.
/// The string is hashed with sha256, its digest is compressed to 20 bytes, and
/// nixbase32-encoded (32 characters)
pub(super) fn build_store_path(
fingerprint: &str,
name: &str,
) -> Result<StorePath, DerivationError> {
let digest = {
let mut hasher = Sha256::new();
hasher.update(fingerprint);
hasher.finalize()
};
let compressed = compress_hash(&digest, 20);
StorePath::from_string(format!("{}-{}", nixbase32::encode(&compressed), name,).as_str())
.map_err(|_e| DerivationError::InvalidOutputName(name.to_string()))
// Constructing the StorePath can only fail if the passed output name was
// invalid, so map errors to a [DerivationError::InvalidOutputName].
}
/// Build a store path for a literal text file in the store that may
/// contain references.
pub fn path_with_references<S: AsRef<str>, I: IntoIterator<Item = S>, C: AsRef<[u8]>>(
name: &str,
content: C,
references: I,
) -> Result<StorePath, DerivationError> {
let text_hash_str = text_hash_string(name, content, references);
build_store_path(&text_hash_str, name)
}
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