feat(traverse): Add era-handling utilities (#123)

pallas-traverse/src/header.rs

@@ -0,0 +1,42 @@
+use pallas_codec::minicbor;
+use pallas_crypto::hash::Hash;
+use pallas_primitives::ToHash;
+
+use crate::{Error, MultiEraHeader};
+
+impl<'b> MultiEraHeader<'b> {
+    pub fn decode(tag: u8, subtag: Option<u8>, cbor: &'b [u8]) -> Result<Self, Error> {
+        match tag {
+            0 => match subtag {
+                Some(0) => {
+                    let header = minicbor::decode(cbor).map_err(Error::invalid_cbor)?;
+                    Ok(MultiEraHeader::EpochBoundary(header))
+                }
+                _ => {
+                    let header = minicbor::decode(cbor).map_err(Error::invalid_cbor)?;
+                    Ok(MultiEraHeader::Byron(header))
+                }
+            },
+            _ => {
+                let header = minicbor::decode(cbor).map_err(Error::invalid_cbor)?;
+                Ok(MultiEraHeader::AlonzoCompatible(header))
+            }
+        }
+    }
+
+    pub fn slot(&self) -> u64 {
+        match self {
+            MultiEraHeader::EpochBoundary(x) => x.to_abs_slot(),
+            MultiEraHeader::AlonzoCompatible(x) => x.header_body.slot,
+            MultiEraHeader::Byron(x) => x.consensus_data.0.to_abs_slot(),
+        }
+    }
+
+    pub fn hash(&self) -> Hash<32> {
+        match self {
+            MultiEraHeader::EpochBoundary(x) => x.to_hash(),
+            MultiEraHeader::AlonzoCompatible(x) => x.to_hash(),
+            MultiEraHeader::Byron(x) => x.to_hash(),
+        }
+    }
+}