fix: single allocation for block header consensus encoding (#4101)

Description
---
- implements `ConsensusEncodingSized` for `BlockHeader` to allow for single allocation when encoding to bytes
- uses `to_consensus_bytes` in `tari_mining_helper_ffi::inject_nonce`
- Use consensus encoding impl for EpochTime

Motivation and Context
---
Previously an unallocated Vec was passed into `consensus_encode` which leads to a number of allocations.
It is best practice, if the size is known, to allocate the vec once. This is implemented generically in `to_consensus_bytes`.

How Has This Been Tested?
---
Existing tests pass.

base_layer/core/src/blocks/block_header.rs

@@ -65,7 +65,7 @@ use thiserror::Error;
 #[cfg(feature = "base_node")]
 use crate::blocks::{BlockBuilder, NewBlockHeaderTemplate};
 use crate::{
-    consensus::{ConsensusDecoding, ConsensusEncoding, ConsensusHashWriter},
+    consensus::{ConsensusDecoding, ConsensusEncoding, ConsensusEncodingSized, ConsensusHashWriter},
     proof_of_work::{PowAlgorithm, PowError, ProofOfWork},
 };
 
@@ -398,7 +398,7 @@ impl ConsensusEncoding for BlockHeader {
         let mut written = self.version.consensus_encode(writer)?;
         written += self.height.consensus_encode(writer)?;
         written += copy_into_fixed_array_lossy::<_, 32>(&self.prev_hash).consensus_encode(writer)?;
-        written += self.timestamp.as_u64().consensus_encode(writer)?;
+        written += self.timestamp.consensus_encode(writer)?;
         written += copy_into_fixed_array_lossy::<_, 32>(&self.output_mr).consensus_encode(writer)?;
         written += copy_into_fixed_array_lossy::<_, 32>(&self.witness_mr).consensus_encode(writer)?;
         written += self.output_mmr_size.consensus_encode(writer)?;
@@ -413,13 +413,15 @@ impl ConsensusEncoding for BlockHeader {
     }
 }
 
+impl ConsensusEncodingSized for BlockHeader {}
+
 impl ConsensusDecoding for BlockHeader {
     fn consensus_decode<R: Read>(reader: &mut R) -> Result<Self, io::Error> {
         let version = u16::consensus_decode(reader)?;
         let mut header = BlockHeader::new(version);
         header.height = u64::consensus_decode(reader)?;
         header.prev_hash = <[u8; 32] as ConsensusDecoding>::consensus_decode(reader)?.to_vec();
-        header.timestamp = EpochTime::from(u64::consensus_decode(reader)?);
+        header.timestamp = EpochTime::consensus_decode(reader)?;
         header.output_mr = <[u8; 32] as ConsensusDecoding>::consensus_decode(reader)?.to_vec();
         header.witness_mr = <[u8; 32] as ConsensusDecoding>::consensus_decode(reader)?.to_vec();
         header.output_mmr_size = u64::consensus_decode(reader)?;

base_layer/tari_mining_helper_ffi/src/lib.rs

@@ -35,7 +35,7 @@ use std::{convert::TryFrom, ffi::CString, slice};
 use libc::{c_char, c_int, c_uchar, c_uint, c_ulonglong};
 use tari_core::{
     blocks::BlockHeader,
-    consensus::{ConsensusDecoding, ConsensusEncoding},
+    consensus::{ConsensusDecoding, ToConsensusBytes},
     proof_of_work::sha3_difficulty,
 };
 use tari_crypto::tari_utilities::hex::Hex;
@@ -236,15 +236,7 @@ pub unsafe extern "C" fn inject_nonce(header: *mut ByteVector, nonce: c_ulonglon
         },
     };
     block_header.nonce = nonce;
-    let mut header_bytes = Vec::new();
-    match block_header.consensus_encode(&mut header_bytes) {
-        Ok(_) => {},
-        Err(e) => {
-            error = MiningHelperError::from(InterfaceError::Conversion(e.to_string())).code;
-            ptr::swap(error_out, &mut error as *mut c_int);
-        },
-    };
-    (*header).0 = header_bytes;
+    (*header).0 = block_header.to_consensus_bytes();
 }
 
 /// Returns the difficulty of a share
@@ -357,7 +349,10 @@ pub unsafe extern "C" fn share_validate(
 mod tests {
     use libc::c_int;
     use tari_common::configuration::Network;
-    use tari_core::blocks::{genesis_block::get_genesis_block, Block};
+    use tari_core::{
+        blocks::{genesis_block::get_genesis_block, Block},
+        consensus::ConsensusEncoding,
+    };
 
     use super::*;
     use crate::{inject_nonce, public_key_hex_validate, share_difficulty, share_validate};