use crate::nix_hash;
use crate::output::{Hash, Output};
use crate::write;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::{collections::BTreeMap, fmt, fmt::Write};
use tvix_store::nixbase32::NIXBASE32;
use tvix_store::store_path::{ParseStorePathError, StorePath, STORE_DIR};
#[derive(Clone, Debug, Default, Eq, PartialEq, Serialize, Deserialize)]
pub struct Derivation {
#[serde(rename = "args")]
pub arguments: Vec<String>,
pub builder: String,
#[serde(rename = "env")]
pub environment: BTreeMap<String, String>,
#[serde(rename = "inputDrvs")]
pub input_derivations: BTreeMap<String, Vec<String>>,
#[serde(rename = "inputSrcs")]
pub input_sources: Vec<String>,
pub outputs: BTreeMap<String, Output>,
pub system: String,
}
/// This returns a store path, either of a derivation or a regular output.
/// The path_hash is compressed to 20 bytes, and nixbase32-encoded (32 characters)
fn build_store_path(
is_derivation: bool,
path_hash: &[u8],
name: &str,
) -> Result<StorePath, ParseStorePathError> {
let compressed = nix_hash::compress_hash(path_hash, 20);
if is_derivation {
StorePath::from_string(
format!(
"{}-{}{}",
NIXBASE32.encode(&compressed),
name,
write::DOT_FILE_EXT,
)
.as_str(),
)
} else {
StorePath::from_string(format!("{}-{}", NIXBASE32.encode(&compressed), name,).as_str())
}
}
impl Derivation {
pub fn serialize(&self, writer: &mut impl Write) -> Result<(), fmt::Error> {
writer.write_str(write::DERIVATION_PREFIX)?;
writer.write_char(write::PAREN_OPEN)?;
write::write_outputs(writer, &self.outputs)?;
write::write_input_derivations(writer, &self.input_derivations)?;
write::write_input_sources(writer, &self.input_sources)?;
write::write_system(writer, &self.system)?;
write::write_builder(writer, &self.builder)?;
write::write_arguments(writer, &self.arguments)?;
write::write_enviroment(writer, &self.environment)?;
writer.write_char(write::PAREN_CLOSE)?;
Ok(())
}
/// Returns the fixed output path and its hash
// (if the Derivation is fixed output),
/// or None if there is no fixed output.
/// This takes some shortcuts in case more than one output exists, as this
/// can't be a valid fixed-output Derivation.
pub fn get_fixed_output(&self) -> Option<(&String, &Hash)> {
if self.outputs.len() != 1 {
return None;
}
match self.outputs.get("out") {
#[allow(clippy::manual_map)]
Some(out_output) => match &out_output.hash {
Some(out_output_hash) => Some((&out_output.path, out_output_hash)),
// There has to be a hash, otherwise it would not be FOD
None => None,
},
None => None,
}
}
/// Returns the drv path of a Derivation struct.
///
/// The drv path is calculated like this:
/// - Write the fingerprint of the Derivation to the sha256 hash function.
/// This is: `text:`,
/// all d.InputDerivations and d.InputSources (sorted, separated by a `:`),
/// a `:`,
/// a `sha256:`, followed by the sha256 digest of the ATerm representation (hex-encoded)
/// a `:`,
/// the storeDir, followed by a `:`,
/// the name of a derivation,
/// a `.drv`.
/// - Write the .drv A-Term contents to a hash function
/// - Take the digest, run hash.CompressHash(digest, 20) on it.
/// - Encode it with nixbase32
/// - Use it (and the name) to construct a [StorePath].
pub fn calculate_derivation_path(&self, name: &str) -> Result<StorePath, ParseStorePathError> {
let mut hasher = Sha256::new();
// collect the list of paths from input_sources and input_derivations
// into a sorted list, and join them by :
hasher.update(write::TEXT_COLON);
let concat_inputs: Vec<String> = {
let mut inputs = self.input_sources.clone();
let input_derivation_keys: Vec<String> =
self.input_derivations.keys().cloned().collect();
inputs.extend(input_derivation_keys);
inputs.sort();
inputs
};
for input in concat_inputs {
hasher.update(input);
hasher.update(write::COLON);
}
// calculate the sha256 hash of the ATerm representation, and represent
// it as a hex-encoded string (prefixed with sha256:).
hasher.update(write::SHA256_COLON);
let digest = {
let mut derivation_hasher = Sha256::new();
derivation_hasher.update(self.to_string());
derivation_hasher.finalize()
};
hasher.update(format!("{:x}", digest));
hasher.update(write::COLON);
hasher.update(STORE_DIR);
hasher.update(write::COLON);
hasher.update(name);
hasher.update(write::DOT_FILE_EXT);
build_store_path(true, &hasher.finalize(), name)
}
/// Calculate the drv replacement string for a given derivation.
///
/// This is either called on a struct without output paths populated,
/// to provide the `drv_replacement_str` value for the `calculate_output_paths`
/// function call, or called on a struct with output paths populated, to
/// calculate / cache lookups for calls to fn_get_drv_replacement.
///
/// `fn_get_drv_replacement` is used to look up the drv replacement strings
/// for input_derivations the Derivation refers to.
pub fn calculate_drv_replacement_str<F>(&self, fn_get_drv_replacement: F) -> String
where
F: Fn(&str) -> String,
{
let mut hasher = Sha256::new();
let digest = match self.get_fixed_output() {
Some((fixed_output_path, fixed_output_hash)) => {
hasher.update("fixed:out:");
hasher.update(&fixed_output_hash.algo);
hasher.update(":");
hasher.update(&fixed_output_hash.digest);
hasher.update(":");
hasher.update(fixed_output_path);
hasher.finalize()
}
None => {
let mut replaced_input_derivations: BTreeMap<String, Vec<String>> = BTreeMap::new();
// For each input_derivation, look up the replacement.
for (drv_path, input_derivation) in &self.input_derivations {
replaced_input_derivations.insert(
fn_get_drv_replacement(drv_path).to_string(),
input_derivation.to_vec(),
);
}
// construct a new derivation struct with these replaced input derivation strings
let replaced_derivation = Derivation {
input_derivations: replaced_input_derivations,
..self.clone()
};
// write the ATerm of that to the hash function
hasher.update(replaced_derivation.to_string());
hasher.finalize()
}
};
format!("{:x}", digest)
}
/// This calculates all output paths of a Derivation and updates the struct.
/// It requires the struct to be initially without output paths.
/// This means, self.outputs[$outputName].path needs to be an empty string,
/// and self.environment[$outputName] needs to be an empty string.
///
/// Output path calculation requires knowledge of "drv replacement
/// strings", and in case of non-fixed-output derivations, also knowledge
/// of "drv replacement" strings (recursively) of all input derivations.
///
/// We solve this by asking the caller of this function to provide
/// the drv replacement string of the current derivation itself,
/// which is ran on the struct without output paths.
///
/// This sound terribly ugly, but won't be too much of a concern later on, as
/// naming fixed-output paths once uploaded will be a tvix-store concern,
/// so there's no need to calculate them here anymore.
///
/// On completion, self.environment[$outputName] and
/// self.outputs[$outputName].path are set to the calculated output path for all
/// outputs.
pub fn calculate_output_paths(
&mut self,
name: &str,
drv_replacement_str: &str,
) -> Result<(), ParseStorePathError> {
let mut hasher = Sha256::new();
// Check if the Derivation is fixed output, because they cause
// different fingerprints to be hashed.
match self.get_fixed_output() {
None => {
// The fingerprint and hash differs per output
for (output_name, output) in self.outputs.iter_mut() {
// Assert that outputs are not yet populated, to avoid using this function wrongly.
// We don't also go over self.environment, but it's a sufficient
// footgun prevention mechanism.
assert!(output.path.is_empty());
hasher.update("output:");
hasher.update(output_name);
hasher.update(":sha256:");
hasher.update(drv_replacement_str);
hasher.update(":");
hasher.update(STORE_DIR);
hasher.update(":");
// calculate the output_name_path, which is the part of the NixPath after the digest.
let mut output_path_name = name.to_string();
if output_name != "out" {
output_path_name.push('-');
output_path_name.push_str(output_name);
}
hasher.update(output_path_name.as_str());
let digest = hasher.finalize_reset();
let abs_store_path =
build_store_path(false, &digest, &output_path_name)?.to_absolute_path();
output.path = abs_store_path.clone();
self.environment
.insert(output_name.to_string(), abs_store_path);
}
}
Some((fixed_output_path, fixed_output_hash)) => {
// Assert that outputs are not yet populated, to avoid using this function wrongly.
// We don't also go over self.environment, but it's a sufficient
// footgun prevention mechanism.
assert!(fixed_output_path.is_empty());
let digest = {
// Fixed-output derivation.
// There's two different hashing strategies in place, depending on the value of hash.algo.
// This code is _weird_ but it is what Nix is doing. See:
// https://github.com/NixOS/nix/blob/1385b2007804c8a0370f2a6555045a00e34b07c7/src/libstore/store-api.cc#L178-L196
if fixed_output_hash.algo == "r:sha256" {
hasher.update("source:");
hasher.update("sha256");
hasher.update(":");
hasher.update(fixed_output_hash.digest.clone()); // nixbase32
} else {
hasher.update("output:out:sha256:");
// This is drv_replacement for FOD, with an empty fixed_output_path.
hasher.update(drv_replacement_str);
}
hasher.update(":");
hasher.update(STORE_DIR);
hasher.update(":");
hasher.update(name);
hasher.finalize()
};
let abs_store_path = build_store_path(false, &digest, name)?.to_absolute_path();
self.outputs.insert(
"out".to_string(),
Output {
path: abs_store_path.clone(),
hash: Some(fixed_output_hash.clone()),
},
);
self.environment.insert("out".to_string(), abs_store_path);
}
};
Ok(())
}
}
impl fmt::Display for Derivation {
/// Formats the Derivation in ATerm representation.
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.serialize(f)
}
}
