Use as_parts to encode Block<Unchecked> without cloning

Add an as_parts method to Block<Unchecked> that returns references to
the header and transactions. Use it in the Encodable impl to avoid
the clone we were doing previously.

Author: Alkamal01

api/primitives/all-features.txt

@@ -1465,6 +1465,7 @@ pub fn bitcoin_primitives::block::Block<V>::fmt(&self, f: &mut core::fmt::Format
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>::cached_witness_root(&self) -> core::option::Option<bitcoin_primitives::WitnessMerkleNode>
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>::header(&self) -> &bitcoin_primitives::block::Header
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>::transactions(&self) -> &[bitcoin_primitives::transaction::Transaction]
+pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::as_parts(&self) -> (&bitcoin_primitives::block::Header, &[bitcoin_primitives::transaction::Transaction])
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::assume_checked(self, witness_root: core::option::Option<bitcoin_primitives::WitnessMerkleNode>) -> bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::check_merkle_root(&self) -> bool
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::check_witness_commitment(&self) -> (bool, core::option::Option<bitcoin_primitives::WitnessMerkleNode>)

api/primitives/alloc-only.txt

@@ -1276,6 +1276,7 @@ pub fn bitcoin_primitives::block::Block<V>::fmt(&self, f: &mut core::fmt::Format
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>::cached_witness_root(&self) -> core::option::Option<bitcoin_primitives::WitnessMerkleNode>
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>::header(&self) -> &bitcoin_primitives::block::Header
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>::transactions(&self) -> &[bitcoin_primitives::transaction::Transaction]
+pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::as_parts(&self) -> (&bitcoin_primitives::block::Header, &[bitcoin_primitives::transaction::Transaction])
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::assume_checked(self, witness_root: core::option::Option<bitcoin_primitives::WitnessMerkleNode>) -> bitcoin_primitives::block::Block<bitcoin_primitives::block::Checked>
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::check_merkle_root(&self) -> bool
 pub fn bitcoin_primitives::block::Block<bitcoin_primitives::block::Unchecked>::check_witness_commitment(&self) -> (bool, core::option::Option<bitcoin_primitives::WitnessMerkleNode>)

bitcoin/src/blockdata/block.rs

@@ -236,10 +236,14 @@ fn block_base_size(transactions: &[Transaction]) -> usize {
 impl Encodable for Block<Unchecked> {
     #[inline]
     fn consensus_encode<W: io::Write + ?Sized>(&self, w: &mut W) -> Result<usize, io::Error> {
-        // TODO: Should we be able to encode without cloning?
-        // This is ok, we decode as unchecked anyway.
-        let block = self.clone().assume_checked(None);
-        block.consensus_encode(w)
+        let (header, transactions) = self.as_parts();
+        let mut len = 0;
+        len += header.consensus_encode(w)?;
+        len += w.emit_compact_size(transactions.len())?;
+        for tx in transactions.iter() {
+            len += tx.consensus_encode(w)?;
+        }
+        Ok(len)
     }
 }
 

primitives/src/block.rs

@@ -113,6 +113,10 @@ impl Block<Unchecked> {
     #[inline]
     pub fn into_parts(self) -> (Header, Vec<Transaction>) { (self.header, self.transactions) }
 
+    /// Returns the constituent parts of the block by reference.
+    #[inline]
+    pub fn as_parts(&self) -> (&Header, &[Transaction]) { (&self.header, &self.transactions) }
+
     /// Validates (or checks) a block.
     ///
     /// We define valid as: