Allow creating partially signed bitcoin transactions

src/bdk.udl

@@ -105,3 +105,8 @@ interface OnlineWallet {
     [Throws=BdkError]
     u64 get_balance();
 };
+
+interface PartiallySignedBitcoinTransaction {
+  [Throws=BdkError]
+  constructor([ByRef] OnlineWallet wallet, string recipient, u64 amount);
+};

src/lib.rs

@@ -1,4 +1,6 @@
-use bdk::bitcoin::Network;
+use bdk::address_validator::AddressValidatorError;
+use bdk::bitcoin::util::psbt::PartiallySignedTransaction;
+use bdk::bitcoin::{Address, Network};
 use bdk::blockchain::any::{AnyBlockchain, AnyBlockchainConfig};
 use bdk::blockchain::Progress;
 use bdk::blockchain::{
@@ -7,9 +9,9 @@ use bdk::blockchain::{
 use bdk::database::any::{AnyDatabase, SledDbConfiguration};
 use bdk::database::{AnyDatabaseConfig, ConfigurableDatabase};
 use bdk::wallet::AddressIndex;
-use bdk::Error;
-use bdk::Wallet;
+use bdk::{Error, Wallet};
 use std::convert::TryFrom;
+use std::str::FromStr;
 use std::sync::{Mutex, MutexGuard};
 
 uniffi_macros::include_scaffolding!("bdk");
@@ -103,6 +105,29 @@ impl Progress for BdkProgressHolder {
     }
 }
 
+struct PartiallySignedBitcoinTransaction {
+    internal: Mutex<PartiallySignedTransaction>,
+}
+
+impl PartiallySignedBitcoinTransaction {
+    fn new(online_wallet: &OnlineWallet, recipient: String, amount: u64) -> Result<Self, Error> {
+        let wallet = online_wallet.get_wallet();
+        match Address::from_str(&recipient) {
+            Ok(address) => {
+                let mut builder = wallet.build_tx();
+                builder.add_recipient(address.script_pubkey(), amount);
+                let (pst, ..) = builder.finish()?;
+                Ok(PartiallySignedBitcoinTransaction {
+                    internal: Mutex::new(pst),
+                })
+            }
+            Err(..) => Err(BdkError::AddressValidator(
+                AddressValidatorError::InvalidScript,
+            )),
+        }
+    }
+}
+
 impl OnlineWallet {
     fn new(
         descriptor: String,