[wallet] Add a flag to fill-in PSBT_GLOBAL_XPUB

src/wallet/mod.rs

@@ -35,7 +35,9 @@ use std::sync::Arc;
 use bitcoin::secp256k1::Secp256k1;
 
 use bitcoin::consensus::encode::serialize;
+use bitcoin::util::base58;
 use bitcoin::util::bip32::ChildNumber;
+use bitcoin::util::psbt::raw::Key as PSBTKey;
 use bitcoin::util::psbt::PartiallySignedTransaction as PSBT;
 use bitcoin::{Address, Network, OutPoint, Script, Transaction, TxOut, Txid};
 
@@ -63,7 +65,7 @@ use crate::blockchain::{Blockchain, BlockchainMarker, OfflineBlockchain, Progres
 use crate::database::{BatchDatabase, BatchOperations, DatabaseUtils};
 use crate::descriptor::{
     get_checksum, DescriptorMeta, DescriptorScripts, ExtendedDescriptor, ExtractPolicy, Policy,
-    ToWalletDescriptor,
+    ToWalletDescriptor, XKeyUtils,
 };
 use crate::error::Error;
 use crate::psbt::PSBTUtils;
@@ -1157,7 +1159,36 @@ where
         selected: Vec<UTXO>,
         builder: TxBuilder<D, Cs, Ctx>,
     ) -> Result<PSBT, Error> {
+        use bitcoin::util::psbt::serialize::Serialize;
+
         let mut psbt = PSBT::from_unsigned_tx(tx)?;
+
+        if builder.add_global_xpubs {
+            let mut all_xpubs = self.descriptor.get_extended_keys()?;
+            if let Some(change_descriptor) = &self.change_descriptor {
+                all_xpubs.extend(change_descriptor.get_extended_keys()?);
+            }
+
+            for xpub in all_xpubs {
+                let serialized_xpub = base58::from_check(&xpub.xkey.to_string())
+                    .expect("Internal serialization error");
+                let key = PSBTKey {
+                    type_value: 0x01,
+                    key: serialized_xpub,
+                };
+
+                let origin = match xpub.origin {
+                    Some(origin) => origin,
+                    None if xpub.xkey.depth == 0 => {
+                        (xpub.root_fingerprint(&self.secp), vec![].into())
+                    }
+                    _ => return Err(Error::MissingKeyOrigin(xpub.xkey.to_string())),
+                };
+
+                psbt.global.unknown.insert(key, origin.serialize());
+            }
+        }
+
         let lookup_output = selected
             .into_iter()
             .map(|utxo| (utxo.outpoint, utxo))

src/wallet/tx_builder.rs

@@ -89,6 +89,7 @@ pub struct TxBuilder<D: Database, Cs: CoinSelectionAlgorithm<D>, Ctx: TxBuilderC
     pub(crate) version: Option<Version>,
     pub(crate) change_policy: ChangeSpendPolicy,
     pub(crate) force_non_witness_utxo: bool,
+    pub(crate) add_global_xpubs: bool,
     pub(crate) coin_selection: Cs,
     pub(crate) include_output_redeem_witness_script: bool,
 
@@ -131,6 +132,7 @@ where
             version: Default::default(),
             change_policy: Default::default(),
             force_non_witness_utxo: Default::default(),
+            add_global_xpubs: Default::default(),
             coin_selection: Default::default(),
             include_output_redeem_witness_script: Default::default(),
 
@@ -345,6 +347,25 @@ impl<D: Database, Cs: CoinSelectionAlgorithm<D>, Ctx: TxBuilderContext> TxBuilde
         self
     }
 
+    /// Fill-in the [`psbt::Output::redeem_script`](bitcoin::util::psbt::Output::redeem_script) and
+    /// [`psbt::Output::witness_script`](bitcoin::util::psbt::Output::witness_script) fields.
+    ///
+    /// This is useful for signers which always require it, like ColdCard hardware wallets.
+    pub fn include_output_redeem_witness_script(mut self) -> Self {
+        self.include_output_redeem_witness_script = true;
+        self
+    }
+
+    /// Fill-in the `PSBT_GLOBAL_XPUB` field with the extended keys contained in both the external
+    /// and internal descriptors
+    ///
+    /// This is useful for offline signers that take part to a multisig. Some hardware wallets like
+    /// BitBox and ColdCard are known to require this.
+    pub fn add_global_xpubs(mut self) -> Self {
+        self.add_global_xpubs = true;
+        self
+    }
+
     /// Spend all the available inputs. This respects filters like [`unspendable`] and the change policy.
     pub fn drain_wallet(mut self) -> Self {
         self.drain_wallet = true;
@@ -375,21 +396,13 @@ impl<D: Database, Cs: CoinSelectionAlgorithm<D>, Ctx: TxBuilderContext> TxBuilde
             version: self.version,
             change_policy: self.change_policy,
             force_non_witness_utxo: self.force_non_witness_utxo,
-            coin_selection,
+            add_global_xpubs: self.add_global_xpubs,
             include_output_redeem_witness_script: self.include_output_redeem_witness_script,
+            coin_selection,
 
             phantom: PhantomData,
         }
     }
-
-    /// Fill-in the [`psbt::Output::redeem_script`](bitcoin::util::psbt::Output::redeem_script) and
-    /// [`psbt::Output::witness_script`](bitcoin::util::psbt::Output::witness_script) fields.
-    ///
-    /// This is useful for signers which always require it, like ColdCard hardware wallets.
-    pub fn include_output_redeem_witness_script(mut self) -> Self {
-        self.include_output_redeem_witness_script = true;
-        self
-    }
 }
 
 // methods supported only by create_tx, and only for `DefaultCoinSelectionAlgorithm`