maintain switch_commit_hashes in the output pmmr (not used yet) (#583)

core/src/core/transaction.rs

@@ -467,6 +467,11 @@ impl SwitchCommitHash {
 		}
 		SwitchCommitHash { hash: h }
 	}
+
+	/// Build an "zero" switch commitment hash
+	pub fn zero() -> SwitchCommitHash {
+		SwitchCommitHash { hash: [0; SWITCH_COMMIT_HASH_SIZE] }
+	}
 }
 
 /// Output for a transaction, defining the new ownership of coins that are being
@@ -571,6 +576,19 @@ impl Output {
 pub struct SumCommit {
 	/// Output commitment
 	pub commit: Commitment,
+	/// The corresponding "switch commit hash"
+	pub switch_commit_hash: SwitchCommitHash,
+}
+
+impl SumCommit {
+	/// For when we do not care about the switch_commit_hash
+	/// for example when comparing sum_commit hashes
+	pub fn from_commit(commit: &Commitment) -> SumCommit {
+		SumCommit {
+			commit: commit.clone(),
+			switch_commit_hash: SwitchCommitHash::zero(),
+		}
+	}
 }
 
 /// Outputs get summed through their commitments.
@@ -578,17 +596,23 @@ impl Summable for SumCommit {
 	type Sum = SumCommit;
 
 	fn sum(&self) -> SumCommit {
-		SumCommit { commit: self.commit.clone() }
+		SumCommit {
+			commit: self.commit.clone(),
+			switch_commit_hash: self.switch_commit_hash.clone(),
+		}
 	}
 
 	fn sum_len() -> usize {
-		secp::constants::PEDERSEN_COMMITMENT_SIZE
+		secp::constants::PEDERSEN_COMMITMENT_SIZE + SWITCH_COMMIT_HASH_SIZE
 	}
 }
 
 impl Writeable for SumCommit {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
 		self.commit.write(writer)?;
+		if writer.serialization_mode() == ser::SerializationMode::Full {
+			self.switch_commit_hash.write(writer)?;
+		}
 		Ok(())
 	}
 }
@@ -596,8 +620,12 @@ impl Writeable for SumCommit {
 impl Readable for SumCommit {
 	fn read(reader: &mut Reader) -> Result<SumCommit, ser::Error> {
 		let commit = Commitment::read(reader)?;
+		let switch_commit_hash = SwitchCommitHash::read(reader)?;
 
-		Ok(SumCommit { commit: commit })
+		Ok(SumCommit {
+			commit: commit,
+			switch_commit_hash: switch_commit_hash,
+		})
 	}
 }
 
@@ -616,7 +644,7 @@ impl ops::Add for SumCommit {
 			Ok(s) => s,
 			Err(_) => Commitment::from_vec(vec![1; 33]),
 		};
-		SumCommit { commit: sum }
+		SumCommit::from_commit(&sum)
 	}
 }