core: unify Hashed and Writeable to simplify things and remove allocations

core/src/core/block.rs

@@ -26,7 +26,7 @@ use core::transaction::merkle_inputs_outputs;
 use core::{PROOFSIZE, REWARD};
 use core::hash::{Hash, Hashed, ZERO_HASH};
 use core::transaction::MAX_IN_OUT_LEN;
-use ser::{self, Readable, Reader, Writeable, Writer, ser_vec};
+use ser::{self, Readable, Reader, Writeable, Writer};
 
 /// Block header, fairly standard compared to other blockchains.
 pub struct BlockHeader {
@@ -79,13 +79,6 @@ impl Writeable for BlockHeader {
 	}
 }
 
-impl Hashed for BlockHeader {
-	fn bytes(&self) -> Vec<u8> {
-		// no serialization errors are applicable in this specific case
-		ser_vec(self).unwrap()
-	}
-}
-
 /// A block as expressed in the MimbleWimble protocol. The reward is
 /// non-explicit, assumed to be deductible from block height (similar to
 /// bitcoin's schedule) and expressed as a global transaction fee (added v.H),

core/src/core/hash.rs

@@ -17,10 +17,12 @@
 //! Primary hash function used in the protocol
 //!
 
+use byteorder::{ByteOrder, WriteBytesExt, BigEndian};
 use std::fmt;
-
 use tiny_keccak::Keccak;
 
+use ser::{self, AsFixedBytes};
+
 /// A hash to uniquely (or close enough) identify one of the main blockchain
 /// constructs. Used pervasively for blocks, transactions and ouputs.
 #[derive(Debug, Copy, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
@@ -56,27 +58,58 @@ impl Hash {
 
 pub const ZERO_HASH: Hash = Hash([0; 32]);
 
-/// A trait for types that get their hash (double SHA256) from their byte
-/// serialzation.
-pub trait Hashed {
-	fn hash(&self) -> Hash {
-		let data = self.bytes();
-		Hash(sha3(data))
-	}
-
-	fn bytes(&self) -> Vec<u8>;
+/// Serializer that outputs a hash of the serialized object
+pub struct HashWriter {
+	state: Keccak
 }
 
-fn sha3(data: Vec<u8>) -> [u8; 32] {
-	let mut sha3 = Keccak::new_sha3_256();
-	let mut buf = [0; 32];
-	sha3.update(&data);
-	sha3.finalize(&mut buf);
-	buf
+impl HashWriter {
+	fn finalize(self, output: &mut [u8]) {
+		self.state.finalize(output);
+	}
+}
+
+impl Default for HashWriter {
+	fn default() -> HashWriter {
+		HashWriter {
+			state: Keccak::new_sha3_256()
+		}
+	}
+}
+
+impl ser::Writer for HashWriter {
+	fn serialization_mode(&self) -> ser::SerializationMode {
+		ser::SerializationMode::Hash
+	}
+
+	fn write_fixed_bytes(&mut self, b32: &AsFixedBytes) -> Result<(), ser::Error> {
+		self.state.update(b32.as_fixed_bytes());
+		Ok(())
+	}
+}
+
+/// A trait for types that have a canonical hash
+pub trait Hashed {
+       fn hash(&self) -> Hash;
+}
+
+impl<W: ser::Writeable> Hashed for W {
+	fn hash(&self) -> Hash {
+		let mut hasher = HashWriter::default();
+		ser::Writeable::write(self, &mut hasher).unwrap();
+		let mut ret = [0; 32];
+		hasher.finalize(&mut ret);
+		Hash(ret)
+	}
 }
 
 impl Hashed for [u8] {
-	fn bytes(&self) -> Vec<u8> {
-		self.to_owned()
+	fn hash(&self) -> Hash {
+		let mut hasher = HashWriter::default();
+		let mut ret = [0; 32];
+		ser::Writer::write_bytes(&mut hasher, &self).unwrap();
+		hasher.finalize(&mut ret);
+		Hash(ret)
 	}
 }
+

core/src/core/mod.rs

@@ -154,12 +154,12 @@ impl Proof {
 /// Two hashes that will get hashed together in a Merkle tree to build the next
 /// level up.
 struct HPair(Hash, Hash);
-impl Hashed for HPair {
-	fn bytes(&self) -> Vec<u8> {
-		let mut data = Vec::with_capacity(64);
-		data.extend_from_slice(self.0.to_slice());
-		data.extend_from_slice(self.1.to_slice());
-		return data;
+
+impl Writeable for HPair {
+	fn write(&self, writer: &mut Writer) -> Result<(), Error> {
+		try!(writer.write_bytes(&self.0.to_slice()));
+		try!(writer.write_bytes(&self.1.to_slice()));
+		Ok(())
 	}
 }
 /// An iterator over hashes in a vector that pairs them to build a row in a

core/src/core/transaction.rs

@@ -16,7 +16,7 @@
 
 use core::Committed;
 use core::MerkleRow;
-use core::hash::{Hashed, Hash};
+use core::hash::{Hash, Hashed};
 use ser::{self, Reader, Writer, Readable, Writeable};
 
 use secp::{self, Secp256k1, Message, Signature};
@@ -283,13 +283,6 @@ impl Input {
 	}
 }
 
-/// The hash of an input is the hash of the output hash it references.
-impl Hashed for Input {
-	fn bytes(&self) -> Vec<u8> {
-		self.output_hash().to_vec()
-	}
-}
-
 #[derive(Debug, Copy, Clone)]
 pub enum Output {
 	BlindOutput {
@@ -303,8 +296,12 @@ pub enum Output {
 /// an Output as binary.
 impl Writeable for Output {
 	fn write(&self, writer: &mut Writer) -> Result<(), ser::Error> {
+		// The hash of an output is only the hash of its commitment.
 		try!(writer.write_fixed_bytes(&self.commitment().unwrap()));
-		writer.write_bytes(&self.proof().unwrap().bytes())
+		if writer.serialization_mode() == ser::SerializationMode::Full {
+			try!(writer.write_bytes(&self.proof().unwrap().bytes()))
+		}
+		Ok(())
 	}
 }
 
@@ -363,17 +360,6 @@ impl Output {
 	}
 }
 
-/// The hash of an output is the hash of its commitment.
-impl Hashed for Output {
-	fn bytes(&self) -> Vec<u8> {
-		if let &Output::BlindOutput { commit, .. } = self {
-			return commit.bytes().to_vec();
-		} else {
-			panic!("cannot hash an overt output");
-		}
-	}
-}
-
 /// Utility function to calculate the Merkle root of vectors of inputs and
 /// outputs.
 pub fn merkle_inputs_outputs(inputs: &Vec<Input>, outputs: &Vec<Output>) -> Hash {
@@ -418,12 +404,12 @@ mod test {
 		let ref secp = new_secp();
 
 		let tx = tx2i1o(secp, &mut rng);
-		let mut btx = tx.blind(&secp).unwrap();
+		let btx = tx.blind(&secp).unwrap();
 		let mut vec = Vec::new();
 		serialize(&mut vec, &btx).expect("serialization failed");
 		// let mut dtx = Transaction::read(&mut BinReader { source: &mut &vec[..]
 		// }).unwrap();
-		let mut dtx: Transaction = deserialize(&mut &vec[..]).unwrap();
+		let dtx: Transaction = deserialize(&mut &vec[..]).unwrap();
 		assert_eq!(dtx.fee, 1);
 		assert_eq!(dtx.inputs.len(), 2);
 		assert_eq!(dtx.outputs.len(), 1);
@@ -437,15 +423,15 @@ mod test {
 		let ref secp = new_secp();
 
 		let tx = tx2i1o(secp, &mut rng);
-		let mut btx = tx.blind(&secp).unwrap();
+		let btx = tx.blind(&secp).unwrap();
 
 		let mut vec = Vec::new();
 		assert!(serialize(&mut vec, &btx).is_ok());
-		let mut dtx: Transaction = deserialize(&mut &vec[..]).unwrap();
+		let dtx: Transaction = deserialize(&mut &vec[..]).unwrap();
 
 		let mut vec2 = Vec::new();
 		assert!(serialize(&mut vec2, &btx).is_ok());
-		let mut dtx2: Transaction = deserialize(&mut &vec2[..]).unwrap();
+		let dtx2: Transaction = deserialize(&mut &vec2[..]).unwrap();
 
 		assert_eq!(btx.hash(), dtx.hash());
 		assert_eq!(dtx.hash(), dtx2.hash());
@@ -532,10 +518,10 @@ mod test {
 		let mut rng = OsRng::new().unwrap();
 
 		let tx1 = tx2i1o(secp, &mut rng);
-		let mut btx1 = tx1.blind(&secp).unwrap();
+		let btx1 = tx1.blind(&secp).unwrap();
 
 		let tx2 = tx1i1o(secp, &mut rng);
-		let mut btx2 = tx2.blind(&secp).unwrap();
+		let btx2 = tx2.blind(&secp).unwrap();
 
 		if btx1.hash() == btx2.hash() {
 			panic!("diff txs have same hash")

core/src/pow/mod.rs

@@ -85,13 +85,6 @@ impl Writeable for PowHeader {
 	}
 }
 
-impl Hashed for PowHeader {
-	fn bytes(&self) -> Vec<u8> {
-		// no serialization errors are applicable in this specific case
-		ser_vec(self).unwrap()
-	}
-}
-
 impl PowHeader {
 	fn from_block(b: &Block) -> PowHeader {
 		let ref h = b.header;

core/src/ser.rs

@@ -81,9 +81,24 @@ pub trait AsFixedBytes {
 	fn as_fixed_bytes(&self) -> &[u8];
 }
 
+
+/// Signal to a serializable object how much of its data should be serialized
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub enum SerializationMode {
+	/// Serialize everything sufficiently to fully reconstruct the object
+	Full,
+	/// Serialize the data that defines the object
+	Hash,
+	/// Serialize everything that a signer of the object should know
+	SigHash
+}
+
 /// Implementations defined how different numbers and binary structures are
 /// written to an underlying stream or container (depending on implementation).
 pub trait Writer {
+	/// The mode this serializer is writing in
+	fn serialization_mode(&self) -> SerializationMode;
+
 	/// Writes a u8 as bytes
 	fn write_u8(&mut self, n: u8) -> Result<(), Error> {
 		self.write_fixed_bytes(&[n])
@@ -252,6 +267,10 @@ struct BinWriter<'a> {
 }
 
 impl<'a> Writer for BinWriter<'a> {
+	fn serialization_mode(&self) -> SerializationMode {
+		SerializationMode::Full
+	}
+
 	fn write_fixed_bytes(&mut self, fixed: &AsFixedBytes) -> Result<(), Error> {
 		let bs = fixed.as_fixed_bytes();
 		try!(self.sink.write_all(bs));