feat!: add burned outputs (#4364)

Description
---
This Pr adds in the ability to create burned outputs. 
There will be a follow-up PR addressing the kernel mutability as currently the fields are mutable and need to be signed to block mutability, see: #4365. 

For added reasoning why this is needed see RFC: tari-project/rfcs#10

Full testing of this is also blocked by: #4360

How Has This Been Tested?
---
Unit and integration tests.

applications/tari_app_grpc/proto/types.proto

@@ -151,6 +151,8 @@ message TransactionKernel {
     bytes hash = 8;
     // Version
     uint32 version = 9;
+    // Optional burned commitment
+    bytes burn_commitment = 10;
 }
 
 // A transaction input.

applications/tari_app_grpc/proto/wallet.proto

@@ -62,6 +62,8 @@ service Wallet {
     rpc RevalidateAllTransactions (RevalidateRequest) returns (RevalidateResponse);
     // This will send a XTR SHA Atomic swap transaction
     rpc SendShaAtomicSwapTransaction(SendShaAtomicSwapRequest) returns (SendShaAtomicSwapResponse);
+    // This will create a burn transaction
+    rpc CreateBurnTransaction(CreateBurnTransactionRequest) returns (CreateBurnTransactionResponse);
     // This will claim a XTR SHA Atomic swap transaction
     rpc ClaimShaAtomicSwapTransaction(ClaimShaAtomicSwapRequest) returns (ClaimShaAtomicSwapResponse);
     // This will claim a HTLC refund transaction
@@ -106,6 +108,12 @@ message SendShaAtomicSwapRequest {
     PaymentRecipient recipient = 1;
 }
 
+message CreateBurnTransactionRequest{
+    uint64 amount = 1;
+    uint64 fee_per_gram = 2;
+    string message = 3;
+}
+
 message PaymentRecipient {
     string address = 1;
     uint64 amount = 2;
@@ -131,6 +139,12 @@ message SendShaAtomicSwapResponse {
     string failure_message = 5;
 }
 
+message CreateBurnTransactionResponse{
+    uint64 transaction_id = 1;
+    bool is_success = 2;
+    string failure_message = 3;
+}
+
 message TransferResult {
     string address = 1;
     uint64 transaction_id = 2;

applications/tari_app_grpc/src/conversions/transaction_kernel.rs

@@ -45,6 +45,14 @@ impl TryFrom<grpc::TransactionKernel> for TransactionKernel {
             .map_err(|_| "excess_sig could not be converted".to_string())?;
 
         let kernel_features = u8::try_from(kernel.features).map_err(|_| "kernel features must be a single byte")?;
+        let commitment = if kernel.burn_commitment.is_empty() {
+            None
+        } else {
+            Some(
+                Commitment::from_bytes(&kernel.burn_commitment)
+                    .map_err(|err| format!("Burn commitment could not be converted:{}", err))?,
+            )
+        };
 
         Ok(Self::new(
             TransactionKernelVersion::try_from(
@@ -56,13 +64,18 @@ impl TryFrom<grpc::TransactionKernel> for TransactionKernel {
             kernel.lock_height,
             excess,
             excess_sig,
+            commitment,
         ))
     }
 }
 
 impl From<TransactionKernel> for grpc::TransactionKernel {
     fn from(kernel: TransactionKernel) -> Self {
         let hash = kernel.hash();
+        let commitment = match kernel.burn_commitment {
+            Some(c) => c.as_bytes().to_vec(),
+            None => vec![],
+        };
 
         grpc::TransactionKernel {
             features: u32::from(kernel.features.bits()),
@@ -75,6 +88,7 @@ impl From<TransactionKernel> for grpc::TransactionKernel {
             }),
             hash,
             version: kernel.version as u32,
+            burn_commitment: commitment,
         }
     }
 }

applications/tari_console_wallet/src/grpc/wallet_grpc_server.rs

@@ -45,6 +45,8 @@ use tari_app_grpc::{
         ClaimShaAtomicSwapResponse,
         CoinSplitRequest,
         CoinSplitResponse,
+        CreateBurnTransactionRequest,
+        CreateBurnTransactionResponse,
         CreateConstitutionDefinitionRequest,
         CreateConstitutionDefinitionResponse,
         CreateFollowOnAssetCheckpointRequest,
@@ -560,6 +562,39 @@ impl wallet_server::Wallet for WalletGrpcServer {
         Ok(Response::new(TransferResponse { results }))
     }
 
+    async fn create_burn_transaction(
+        &self,
+        request: Request<CreateBurnTransactionRequest>,
+    ) -> Result<Response<CreateBurnTransactionResponse>, Status> {
+        let message = request.into_inner();
+
+        let mut transaction_service = self.get_transaction_service();
+        debug!(target: LOG_TARGET, "Trying to burn {} Tari", message.amount);
+        let response = match transaction_service
+            .burn_tari(message.amount.into(), message.fee_per_gram.into(), message.message)
+            .await
+        {
+            Ok(tx_id) => {
+                debug!(target: LOG_TARGET, "Transaction broadcast: {}", tx_id,);
+                CreateBurnTransactionResponse {
+                    transaction_id: tx_id.as_u64(),
+                    is_success: true,
+                    failure_message: Default::default(),
+                }
+            },
+            Err(e) => {
+                warn!(target: LOG_TARGET, "Failed to burn Tarid: {}", e);
+                CreateBurnTransactionResponse {
+                    transaction_id: Default::default(),
+                    is_success: false,
+                    failure_message: e.to_string(),
+                }
+            },
+        };
+
+        Ok(Response::new(response))
+    }
+
     async fn get_transaction_info(
         &self,
         request: Request<GetTransactionInfoRequest>,

applications/test_faucet/src/main.rs

@@ -123,7 +123,8 @@ async fn write_keys(mut rx: mpsc::Receiver<(TransactionOutput, PrivateKey, Micro
     }
     let (pk, sig) = test_helpers::create_random_signature_from_s_key(key_sum, 0.into(), 0);
     let excess = Commitment::from_public_key(&pk);
-    let kernel = TransactionKernel::new_current_version(KernelFeatures::empty(), MicroTari::from(0), 0, excess, sig);
+    let kernel =
+        TransactionKernel::new_current_version(KernelFeatures::empty(), MicroTari::from(0), 0, excess, sig, None);
     let kernel = serde_json::to_string(&kernel).unwrap();
     let _result = utxo_file.write_all(format!("{}\n", kernel).as_bytes());
 

base_layer/core/src/base_node/sync/horizon_state_sync/error.rs

@@ -53,6 +53,8 @@ pub enum HorizonSyncError {
     JoinError(#[from] task::JoinError),
     #[error("A range proof verification has produced an error: {0}")]
     RangeProofError(#[from] RangeProofError),
+    #[error("An invalid transaction has been encountered: {0}")]
+    TransactionError(#[from] TransactionError),
     #[error("Invalid kernel signature: {0}")]
     InvalidKernelSignature(TransactionError),
     #[error("MMR did not match for {mmr_tree} at height {at_height}. Expected {actual_hex} to equal {expected_hex}")]

base_layer/core/src/base_node/sync/horizon_state_sync/synchronizer.rs

@@ -743,14 +743,15 @@ impl<'a, B: BlockchainBackend + 'static> HorizonStateSynchronization<'a, B> {
         ));
 
         let header = self.db().fetch_chain_header(self.horizon_sync_height).await?;
-        let (calc_utxo_sum, calc_kernel_sum) = self.calculate_commitment_sums(&header).await?;
+        let (calc_utxo_sum, calc_kernel_sum, calc_burned_sum) = self.calculate_commitment_sums(&header).await?;
 
         self.final_state_validator
             .validate(
                 &*self.db().inner().db_read_access()?,
                 header.height(),
                 &calc_utxo_sum,
                 &calc_kernel_sum,
+                &calc_burned_sum,
             )
             .map_err(HorizonSyncError::FinalStateValidationFailed)?;
 
@@ -793,9 +794,10 @@ impl<'a, B: BlockchainBackend + 'static> HorizonStateSynchronization<'a, B> {
     async fn calculate_commitment_sums(
         &mut self,
         header: &ChainHeader,
-    ) -> Result<(Commitment, Commitment), HorizonSyncError> {
+    ) -> Result<(Commitment, Commitment, Commitment), HorizonSyncError> {
         let mut utxo_sum = HomomorphicCommitment::default();
         let mut kernel_sum = HomomorphicCommitment::default();
+        let mut burned_sum = HomomorphicCommitment::default();
 
         let mut prev_mmr = 0;
         let mut prev_kernel_mmr = 0;
@@ -810,7 +812,6 @@ impl<'a, B: BlockchainBackend + 'static> HorizonStateSynchronization<'a, B> {
 
             for h in 0..=height {
                 let curr_header = db.fetch_chain_header(h)?;
-
                 trace!(
                     target: LOG_TARGET,
                     "Fetching utxos from db: height:{}, header.output_mmr:{}, prev_mmr:{}, end:{}",
@@ -866,6 +867,9 @@ impl<'a, B: BlockchainBackend + 'static> HorizonStateSynchronization<'a, B> {
                 trace!(target: LOG_TARGET, "Number of kernels returned: {}", kernels.len());
                 for k in kernels {
                     kernel_sum = &k.excess + &kernel_sum;
+                    if k.is_burned() {
+                        burned_sum = k.get_burn_commitment()? + &burned_sum;
+                    }
                 }
                 prev_kernel_mmr = curr_header.header().kernel_mmr_size;
 
@@ -888,7 +892,7 @@ impl<'a, B: BlockchainBackend + 'static> HorizonStateSynchronization<'a, B> {
                 db.write(txn)?;
             }
 
-            Ok((utxo_sum, kernel_sum))
+            Ok((utxo_sum, kernel_sum, burned_sum))
         })
         .await?
     }

base_layer/core/src/blocks/genesis_block.rs

@@ -128,7 +128,8 @@ fn get_igor_genesis_block_raw() -> Block {
                 "9474ba70976e2fa06f970bb83f7d0a4d4b45e6e29f834847b659d32102f90b51",
             )
                 .unwrap(),
-            sig,
+            sig,None
+
         )],
     );
     body.sort();
@@ -216,7 +217,7 @@ pub fn get_dibbler_genesis_block() -> ChainBlock {
     // println!("output mr: {}", block.header.output_mr.to_hex());
 
     // Hardcode the Merkle roots once they've been computed above
-    block.header.kernel_mr = from_hex("8bec1140bfac718ab3acd8a5e19c1bb28e0e4a57663c2fc7e8c7155cc355aac3").unwrap();
+    block.header.kernel_mr = from_hex("51acb4b74cc2e43a11be4f283b653a6fc95666dcf90f66f0c32742c5fb77e640").unwrap();
     block.header.witness_mr = from_hex("1df4a4200338686763c784187f7077148986e088586cf4839147a3f56adc4af6").unwrap();
     block.header.output_mr = from_hex("f9616ca84e798022f638546e6ce372d1344eee56e5cf47ba7e2bf58b5e28bf45").unwrap();
 
@@ -274,6 +275,7 @@ fn get_dibbler_genesis_block_raw() -> Block {
         0,
         Commitment::from_hex("0cff7e89fa0468aa68f777cf600ae6f9e46fdc6e4e33540077e7303e8929295c").unwrap(),
         excess_sig,
+        None,
     );
     let mut body = AggregateBody::new(vec![], vec![coinbase], vec![kernel]);
     body.sort();
@@ -314,7 +316,7 @@ fn get_dibbler_genesis_block_raw() -> Block {
 #[cfg(test)]
 mod test {
     use croaring::Bitmap;
-    use tari_common_types::types::HashDigest;
+    use tari_common_types::types::{Commitment, HashDigest};
     use tari_mmr::{MerkleMountainRange, MutableMmr};
 
     use super::*;
@@ -385,7 +387,7 @@ mod test {
 
         let lock = db.db_read_access().unwrap();
         ChainBalanceValidator::new(ConsensusManager::builder(Network::Dibbler).build(), Default::default())
-            .validate(&*lock, 0, &utxo_sum, &kernel_sum)
+            .validate(&*lock, 0, &utxo_sum, &kernel_sum, &Commitment::default())
             .unwrap();
     }
 }

base_layer/core/src/chain_storage/lmdb_db/lmdb_db.rs

@@ -1302,12 +1302,35 @@ impl LMDBDatabase {
         let leaf_count = witness_mmr.get_leaf_count()?;
 
         // Output hashes added before inputs so that inputs can spend outputs in this transaction (0-conf and combined)
+        let mut burned_outputs = Vec::new();
         let outputs = outputs
             .into_iter()
             .enumerate()
             .map(|(i, output)| {
                 output_mmr.push(output.hash())?;
                 witness_mmr.push(output.witness_hash())?;
+                // lets check burn
+                if output.is_burned() {
+                    let index = match output_mmr.find_leaf_index(&output.hash())? {
+                        Some(index) => {
+                            debug!(target: LOG_TARGET, "Output {} burned in current block", output);
+                            burned_outputs.push(output.commitment.clone());
+                            index
+                        },
+                        None => {
+                            return Err(ChainStorageError::UnexpectedResult(
+                                "Output MMR did not contain the expected output".to_string(),
+                            ))
+                        },
+                    };
+                    // We need to mark this as spent as well.
+                    if !output_mmr.delete(index) {
+                        return Err(ChainStorageError::InvalidOperation(format!(
+                            "Could not delete index {} from the output MMR",
+                            index
+                        )));
+                    }
+                };
                 Ok((output, leaf_count + i + 1))
             })
             .collect::<Result<Vec<_>, ChainStorageError>>()?;
@@ -1366,6 +1389,14 @@ impl LMDBDatabase {
                 "utxo_commitment_index",
             )?;
         }
+        for commitment in burned_outputs {
+            lmdb_delete(
+                txn,
+                &self.utxo_commitment_index,
+                commitment.as_bytes(),
+                "utxo_commitment_index",
+            )?;
+        }
         // Merge current deletions with the tip bitmap
         let deleted_at_current_height = output_mmr.deleted().clone();
         // Merge the new indexes with the blockchain deleted bitmap

base_layer/core/src/proto/transaction.proto

@@ -29,6 +29,8 @@ message TransactionKernel {
     Signature excess_sig = 7;
     // Version
     uint32 version = 8;
+    // Optional burned commitment
+    Commitment burn_commitment = 9;
 }
 
 // A transaction input.

base_layer/core/src/proto/transaction.rs

@@ -100,6 +100,10 @@ impl TryFrom<proto::types::TransactionKernel> for TransactionKernel {
             .ok_or_else(|| "excess_sig not provided".to_string())?
             .try_into()?;
         let kernel_features = u8::try_from(kernel.features).map_err(|_| "Kernel features must be a single byte")?;
+        let commitment = match kernel.burn_commitment {
+            Some(burn_commitment) => Some(Commitment::from_bytes(&burn_commitment.data).map_err(|e| e.to_string())?),
+            None => None,
+        };
 
         Ok(TransactionKernel::new(
             TransactionKernelVersion::try_from(
@@ -111,19 +115,22 @@ impl TryFrom<proto::types::TransactionKernel> for TransactionKernel {
             kernel.lock_height,
             excess,
             excess_sig,
+            commitment,
         ))
     }
 }
 
 impl From<TransactionKernel> for proto::types::TransactionKernel {
     fn from(kernel: TransactionKernel) -> Self {
+        let commitment = kernel.burn_commitment.map(|commitment| commitment.into());
         Self {
             features: u32::from(kernel.features.bits()),
             excess: Some(kernel.excess.into()),
             excess_sig: Some(kernel.excess_sig.into()),
             fee: kernel.fee.into(),
             lock_height: kernel.lock_height,
             version: kernel.version as u32,
+            burn_commitment: commitment,
         }
     }
 }

base_layer/core/src/transactions/aggregated_body.rs

@@ -264,7 +264,7 @@ impl AggregateBody {
         for kernel in self.kernels() {
             if kernel.lock_height > height {
                 warn!(target: LOG_TARGET, "Kernel lock height was not reached: {}", kernel);
-                return Err(TransactionError::InvalidKernel);
+                return Err(TransactionError::InvalidKernel("Invalid lock height".to_string()));
             }
         }
         Ok(())

base_layer/core/src/transactions/transaction_components/error.rs

@@ -45,8 +45,8 @@ pub enum TransactionError {
     RangeProofError(#[from] RangeProofError),
     #[error("An error occurred while performing a commitment signature: {0}")]
     SigningError(#[from] CommitmentSignatureError),
-    #[error("Invalid kernel in body")]
-    InvalidKernel,
+    #[error("Invalid kernel in body : {0}")]
+    InvalidKernel(String),
     #[error("Invalid coinbase in body")]
     InvalidCoinbase,
     #[error("Invalid coinbase maturity in body")]