Add data as output (via OP_RETURN)

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 - BIP39 implementation dependency, in `keys::bip39` changed from tiny-bip39 to rust-bip39.
+- Add new method on the `TxBuilder` to embed data in the transaction via `OP_RETURN`. To allow that a fix to check the dust only on spendable output has been introduced.
 
 ## [v0.13.0] - [v0.12.0]
 

src/testutils/blockchain_tests.rs

@@ -849,6 +849,37 @@ macro_rules! bdk_blockchain_tests {
                 assert_eq!(new_details.received, 0, "incorrect received after add input");
             }
 
+
+            #[test]
+            fn test_add_data() {
+                let (wallet, descriptors, mut test_client) = init_single_sig();
+                let node_addr = test_client.get_node_address(None);
+                let _ = test_client.receive(testutils! {
+                    @tx ( (@external descriptors, 0) => 50_000 )
+                });
+
+                wallet.sync(noop_progress(), None).unwrap();
+                assert_eq!(wallet.get_balance().unwrap(), 50_000, "incorrect balance");
+
+                let mut builder = wallet.build_tx();
+                let data = [42u8;80];
+                builder.add_data(&data);
+                let (mut psbt, details) = builder.finish().unwrap();
+
+                let finalized = wallet.sign(&mut psbt, Default::default()).unwrap();
+                assert!(finalized, "Cannot finalize transaction");
+                let tx = psbt.extract_tx();
+                let serialized_tx = bitcoin::consensus::encode::serialize(&tx);
+                assert!(serialized_tx.windows(data.len()).any(|e| e==data), "cannot find op_return data in transaction");
+                let sent_txid = wallet.broadcast(&tx).unwrap();
+                test_client.generate(1, Some(node_addr));
+                wallet.sync(noop_progress(), None).unwrap();
+                assert_eq!(wallet.get_balance().unwrap(), 50_000 - details.fee.unwrap_or(0), "incorrect balance after send");
+
+                let tx_map = wallet.list_transactions(false).unwrap().into_iter().map(|tx| (tx.txid, tx)).collect::<std::collections::HashMap<_, _>>();
+                let _ = tx_map.get(&sent_txid).unwrap();
+            }
+
             #[test]
             fn test_sync_receive_coinbase() {
                 let (wallet, _, mut test_client) = init_single_sig();

src/wallet/mod.rs

@@ -601,7 +601,7 @@ where
         let recipients = params.recipients.iter().map(|(r, v)| (r, *v));
 
         for (index, (script_pubkey, value)) in recipients.enumerate() {
-            if value.is_dust() {
+            if value.is_dust() && !script_pubkey.is_provably_unspendable() {
                 return Err(Error::OutputBelowDustLimit(index));
             }
 

src/wallet/tx_builder.rs

@@ -560,6 +560,13 @@ impl<'a, B, D: BatchDatabase, Cs: CoinSelectionAlgorithm<D>> TxBuilder<'a, B, D,
         self
     }
 
+    /// Add data as an output, using OP_RETURN
+    pub fn add_data(&mut self, data: &[u8]) -> &mut Self {
+        let script = Script::new_op_return(data);
+        self.add_recipient(script, 0u64);
+        self
+    }
+
     /// Sets the address to *drain* excess coins to.
     ///
     /// Usually, when there are excess coins they are sent to a change address generated by the