feat: scaffold Byron phase-1 validations (#300)

Co-authored-by: Santiago Carmuega <santiago@carmuega.me>

pallas-applying/src/byron.rs

@@ -0,0 +1,14 @@
+//! Utilities required for Byron-era transaction validation.
+
+use crate::types::{ByronProtParams, UTxOs, ValidationResult};
+
+use pallas_primitives::byron::MintedTxPayload;
+
+// TODO: implement each of the validation rules.
+pub fn validate_byron_tx(
+    _mtxp: &MintedTxPayload,
+    _utxos: &UTxOs,
+    _prot_pps: &ByronProtParams,
+) -> ValidationResult {
+    Ok(())
+}

pallas-applying/src/lib.rs

@@ -0,0 +1,24 @@
+//! Logic for validating and applying new blocks and txs to the chain state
+
+pub mod byron;
+pub mod types;
+
+use byron::validate_byron_tx;
+
+use pallas_traverse::{MultiEraTx, MultiEraTx::Byron as ByronTxPayload};
+
+pub use types::{
+    MultiEraProtParams, MultiEraProtParams::Byron as ByronProtParams, UTxOs, ValidationResult,
+};
+
+pub fn validate(
+    metx: &MultiEraTx,
+    utxos: &UTxOs,
+    prot_pps: &MultiEraProtParams,
+) -> ValidationResult {
+    match (metx, prot_pps) {
+        (ByronTxPayload(mtxp), ByronProtParams(bpp)) => validate_byron_tx(mtxp, utxos, bpp),
+        // TODO: implement the rest of the eras.
+        _ => Ok(()),
+    }
+}

pallas-applying/src/types.rs

@@ -0,0 +1,27 @@
+//! Base types used for validating transactions in each era.
+
+use std::{borrow::Cow, collections::HashMap};
+
+pub use pallas_traverse::{MultiEraInput, MultiEraOutput};
+
+pub type UTxOs<'b> = HashMap<MultiEraInput<'b>, MultiEraOutput<'b>>;
+
+// TODO: add a field for each protocol parameter in the Byron era.
+#[derive(Debug, Clone)]
+pub struct ByronProtParams;
+
+// TODO: add variants for the other eras.
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum MultiEraProtParams<'b> {
+    Byron(Box<Cow<'b, ByronProtParams>>),
+}
+
+// TODO: replace this generic variant with validation-rule-specific ones.
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum ValidationError {
+    ValidationError,
+}
+
+pub type ValidationResult = Result<(), ValidationError>;