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-rw-r--r--tvix/nix-compat/src/derivation/mod.rs281
1 files changed, 278 insertions, 3 deletions
diff --git a/tvix/nix-compat/src/derivation/mod.rs b/tvix/nix-compat/src/derivation/mod.rs
index 1b82251bf672..cecaa3f42d80 100644
--- a/tvix/nix-compat/src/derivation/mod.rs
+++ b/tvix/nix-compat/src/derivation/mod.rs
@@ -1,7 +1,12 @@
-mod derivation;
+use crate::store_path::{self, StorePath};
+use serde::{Deserialize, Serialize};
+use sha2::{Digest, Sha256};
+use std::collections::{BTreeMap, BTreeSet};
+
 mod errors;
 mod output;
 mod string_escape;
+mod utils;
 mod validate;
 mod write;
 
@@ -9,7 +14,277 @@ mod write;
 mod tests;
 
 // Public API of the crate.
-
-pub use derivation::{path_with_references, Derivation};
 pub use errors::{DerivationError, OutputError};
 pub use output::{Hash, Output};
+pub use utils::path_with_references;
+
+#[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,
+}
+
+impl Derivation {
+    pub fn serialize(&self, writer: &mut impl std::fmt::Write) -> Result<(), std::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_path::STORE_DIR,
+            name,
+        ));
+
+        utils::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_path::STORE_DIR,
+                        output_path_name,
+                    );
+
+                    let abs_store_path =
+                        utils::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_path::STORE_DIR, name));
+                    s
+                };
+
+                let abs_store_path = utils::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 std::fmt::Display for Derivation {
+    /// Formats the Derivation in ATerm representation.
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.serialize(f)
+    }
+}