Merge bitcoin#23499: multiprocess: Add interfaces::Node::broadCastTransaction method

0e0f4fd multiprocess: Add interfaces::Node::broadCastTransaction method (Russell Yanofsky)

Pull request description:

  This fixes a null pointer crash in the bitcoin-gui PSBT dialog. The bitcoin-gui interfaces::Node object has a null NodeContext pointer, and can't broadcast transactions directly. It needs to broadcast transactions through the bitcoin-node process instead.

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

ACKs for top commit:
  lsilva01:
    Code Review ACK 0e0f4fd

Tree-SHA512: cd2c1fe8dc15e7cecf01a21d64319d6add1124995305a9ef9cb72f8492dc692c62d4f846182567d47a5048a533178a925419250941a47cb39932467c36bea3e1

Author: MarcoFalke

src/interfaces/node.h

@@ -30,6 +30,7 @@ class RPCTimerInterface;
 class UniValue;
 class proxyType;
 enum class SynchronizationState;
+enum class TransactionError;
 struct CNodeStateStats;
 struct NodeContext;
 struct bilingual_str;
@@ -183,6 +184,9 @@ class Node
     //! Get unspent outputs associated with a transaction.
     virtual bool getUnspentOutput(const COutPoint& output, Coin& coin) = 0;
 
+    //! Broadcast transaction.
+    virtual TransactionError broadcastTransaction(CTransactionRef tx, CAmount max_tx_fee, std::string& err_string) = 0;
+
     //! Get wallet client.
     virtual WalletClient& walletClient() = 0;
 

src/node/interfaces.cpp

@@ -276,6 +276,10 @@ class NodeImpl : public Node
         LOCK(::cs_main);
         return chainman().ActiveChainstate().CoinsTip().GetCoin(output, coin);
     }
+    TransactionError broadcastTransaction(CTransactionRef tx, CAmount max_tx_fee, std::string& err_string) override
+    {
+        return BroadcastTransaction(*m_context, std::move(tx), err_string, max_tx_fee, /*relay=*/ true, /*wait_callback=*/ false);
+    }
     WalletClient& walletClient() override
     {
         return *Assert(m_context->wallet_client);

src/qt/psbtoperationsdialog.cpp

@@ -110,8 +110,8 @@ void PSBTOperationsDialog::broadcastTransaction()
 
     CTransactionRef tx = MakeTransactionRef(mtx);
     std::string err_string;
-    TransactionError error = BroadcastTransaction(
-        *m_client_model->node().context(), tx, err_string, DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK(), /* relay */ true, /* await_callback */ false);
+    TransactionError error =
+        m_client_model->node().broadcastTransaction(tx, DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK(), err_string);
 
     if (error == TransactionError::OK) {
         showStatus(tr("Transaction broadcast successfully! Transaction ID: %1")