diff options
Diffstat (limited to 'tvix/nix-compat/src/derivation/derivation.rs')
| -rw-r--r-- | tvix/nix-compat/src/derivation/derivation.rs | 347 |
1 files changed, 347 insertions, 0 deletions
diff --git a/tvix/nix-compat/src/derivation/derivation.rs b/tvix/nix-compat/src/derivation/derivation.rs new file mode 100644 index 000000000000..c9a45d9c9bd2 --- /dev/null +++ b/tvix/nix-compat/src/derivation/derivation.rs @@ -0,0 +1,347 @@ +use crate::derivation::output::{Hash, Output}; +use crate::derivation::write; +use crate::derivation::DerivationError; +use crate::nixbase32; +use crate::store_path::{StorePath, STORE_DIR}; +use serde::{Deserialize, Serialize}; +use sha2::{Digest, Sha256}; +use std::collections::BTreeSet; +use std::{collections::BTreeMap, fmt, fmt::Write}; + +#[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, BTreeSet<String>>, + + #[serde(rename = "inputSrcs")] + pub input_sources: BTreeSet<String>, + + pub outputs: BTreeMap<String, Output>, + + pub system: String, +} + +/// 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) +fn build_store_path( + is_derivation: bool, + 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); + if is_derivation { + StorePath::from_string(format!("{}-{}.drv", nixbase32::encode(&compressed), name).as_str()) + } else { + 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 mut s = String::from("text"); + + for reference in references { + s.push(':'); + s.push_str(reference.as_ref()); + } + + let content_digest = { + let mut hasher = Sha256::new(); + hasher.update(content); + hasher.finalize() + }; + + s.push_str(&format!( + ":sha256:{:x}:{}:{}", + content_digest, STORE_DIR, name + )); + + build_store_path(false, &s, name) +} + +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, DerivationError> { + let mut s = String::from("text:"); + + // collect the list of paths from input_sources and input_derivations + // into a (sorted, guaranteed by BTreeSet) list, and join them by : + let concat_inputs: BTreeSet<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 + }; + + for input in concat_inputs { + s.push_str(&input); + s.push(':'); + } + + // calculate the sha256 hash of the ATerm representation, and represent + // it as a hex-encoded string (prefixed with sha256:). + let aterm_digest = { + let mut derivation_hasher = Sha256::new(); + derivation_hasher.update(self.to_string()); + derivation_hasher.finalize() + }; + + s.push_str(&format!( + "sha256:{:x}:{}:{}.drv", + aterm_digest, STORE_DIR, name, + )); + + build_store_path(true, &s, 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(format!( + "fixed:out:{}:{}:{}", + &fixed_output_hash.algo, &fixed_output_hash.digest, fixed_output_path, + )); + hasher.finalize() + } + None => { + let mut replaced_input_derivations: BTreeMap<String, BTreeSet<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.clone(), + ); + } + + // 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<(), DerivationError> { + // 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()); + + // 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); + } + + let s = &format!( + "output:{}:sha256:{}:{}:{}", + output_name, drv_replacement_str, STORE_DIR, output_path_name, + ); + + let abs_store_path = + build_store_path(false, s, &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 s = { + let mut s = String::new(); + // 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" { + s.push_str(&format!( + "source:sha256:{}", + fixed_output_hash.digest, // nixbase32 + )); + } else { + s.push_str("output:out:sha256:"); + // This is drv_replacement for FOD, with an empty fixed_output_path. + s.push_str(drv_replacement_str); + } + s.push_str(&format!(":{}:{}", STORE_DIR, name)); + s + }; + + let abs_store_path = build_store_path(false, &s, 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) + } +} |