scientific_workflow/

rng_record.rs

//! Lightweight provenance records for application-owned random number generators.
//!
//! Workflow does not generate keys, derive streams, select algorithms, sample
//! distributions, or maintain RNG cursors. Applications perform those tasks
//! and use [`RngRecord`] only to persist enough exact identity for
//! reproducibility and continuation validation.

use serde::{Deserialize, Serialize};
use serde_json::{Map, Value};
use thiserror::Error;

/// Reserved user-metadata key containing records indexed by application namespace.
pub const RNG_RECORDS_METADATA_KEY: &str = "rng_records";

/// Immutable identity of one application-owned random source.
///
/// Keys are persisted as plain text and therefore must be reproducibility
/// material rather than secrets. `method` and `version` should identify every
/// implementation detail that affects the produced sequence, including a
/// distribution transform when relevant.
#[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
#[serde(deny_unknown_fields)]
pub struct RngRecord {
    namespace: String,
    method: String,
    version: String,
    key_encoding: String,
    key: String,
    #[serde(default, skip_serializing_if = "Map::is_empty")]
    parameters: Map<String, Value>,
}

impl RngRecord {
    /// Creates and validates one application-namespaced RNG record.
    pub fn new(
        namespace: impl Into<String>,
        method: impl Into<String>,
        version: impl Into<String>,
        key_encoding: impl Into<String>,
        key: impl Into<String>,
    ) -> Result<Self, RngRecordError> {
        let record = Self {
            namespace: namespace.into(),
            method: method.into(),
            version: version.into(),
            key_encoding: key_encoding.into(),
            key: key.into(),
            parameters: Map::new(),
        };
        record.validate()?;
        Ok(record)
    }

    /// Adds application-defined JSON parameters without assigning them RNG semantics.
    #[must_use]
    pub fn with_parameters(mut self, parameters: Map<String, Value>) -> Self {
        self.parameters = parameters;
        self
    }

    /// Returns the collision domain used inside recording metadata.
    pub fn namespace(&self) -> &str {
        &self.namespace
    }

    /// Returns the application-declared RNG or sampling method.
    pub fn method(&self) -> &str {
        &self.method
    }

    /// Returns the application-declared sequence-affecting version.
    pub fn version(&self) -> &str {
        &self.version
    }

    /// Returns the application-declared key representation.
    pub fn key_encoding(&self) -> &str {
        &self.key_encoding
    }

    /// Returns the persisted reproducibility key.
    pub fn key(&self) -> &str {
        &self.key
    }

    /// Borrows opaque application-defined method parameters.
    pub const fn parameters(&self) -> &Map<String, Value> {
        &self.parameters
    }

    /// Inserts this record beneath the reserved user-metadata object.
    ///
    /// Existing unrelated metadata is preserved. Reusing a namespace is
    /// rejected rather than overwritten.
    pub fn insert_into_metadata(
        &self,
        metadata: &mut Map<String, Value>,
    ) -> Result<(), RngRecordError> {
        self.validate()?;
        let records = metadata
            .entry(RNG_RECORDS_METADATA_KEY.to_owned())
            .or_insert_with(|| Value::Object(Map::new()))
            .as_object_mut()
            .ok_or(RngRecordError::InvalidMetadataShape)?;
        if records.contains_key(&self.namespace) {
            return Err(RngRecordError::DuplicateNamespace {
                namespace: self.namespace.clone(),
            });
        }
        records.insert(
            self.namespace.clone(),
            serde_json::to_value(self).expect("RNG records contain only JSON-compatible values"),
        );
        Ok(())
    }

    /// Reads and validates one namespaced record from user metadata.
    pub fn from_metadata(
        metadata: &Map<String, Value>,
        namespace: &str,
    ) -> Result<Option<Self>, RngRecordError> {
        let Some(value) = metadata.get(RNG_RECORDS_METADATA_KEY) else {
            return Ok(None);
        };
        let records = value
            .as_object()
            .ok_or(RngRecordError::InvalidMetadataShape)?;
        let Some(value) = records.get(namespace) else {
            return Ok(None);
        };
        let record: Self = serde_json::from_value(value.clone()).map_err(|source| {
            RngRecordError::InvalidStoredRecord {
                namespace: namespace.to_owned(),
                source,
            }
        })?;
        record.validate()?;
        if record.namespace != namespace {
            return Err(RngRecordError::NamespaceMismatch {
                index: namespace.to_owned(),
                record: record.namespace,
            });
        }
        Ok(Some(record))
    }

    fn validate(&self) -> Result<(), RngRecordError> {
        for (field, value) in [
            ("namespace", self.namespace.as_str()),
            ("method", self.method.as_str()),
            ("version", self.version.as_str()),
            ("key_encoding", self.key_encoding.as_str()),
            ("key", self.key.as_str()),
        ] {
            if value.trim().is_empty() {
                return Err(RngRecordError::EmptyField { field });
            }
        }
        Ok(())
    }
}

/// Rejection while constructing or embedding RNG provenance.
#[derive(Debug, Error)]
#[non_exhaustive]
pub enum RngRecordError {
    /// A required textual identity field is empty or whitespace-only.
    #[error("RNG record field `{field}` must not be empty")]
    EmptyField {
        /// Rejected stable field name.
        field: &'static str,
    },
    /// A metadata map already contains a record for the namespace.
    #[error("RNG namespace `{namespace}` is recorded more than once")]
    DuplicateNamespace {
        /// Repeated application namespace.
        namespace: String,
    },
    /// The reserved metadata entry is not an object indexed by namespace.
    #[error("user metadata `{RNG_RECORDS_METADATA_KEY}` entry must be an object")]
    InvalidMetadataShape,
    /// A stored namespaced value does not decode as an RNG record.
    #[error("invalid RNG record for namespace `{namespace}`")]
    InvalidStoredRecord {
        /// Namespace selected by the caller.
        namespace: String,
        /// JSON type or field failure.
        #[source]
        source: serde_json::Error,
    },
    /// The metadata index and embedded record namespace disagree.
    #[error("RNG metadata index `{index}` contains record namespace `{record}`")]
    NamespaceMismatch {
        /// Namespace used as the metadata object key.
        index: String,
        /// Namespace embedded in the record.
        record: String,
    },
}