Merge bitcoin/bitcoin#24313: Improve display address handling for external signer

4357158 wallet: return and display signer error (Sjors Provoost)
dc55531 wallet: compare address returned by displayaddress (Sjors Provoost)
6c1a2cc test: use h marker for external signer mock (Sjors Provoost)

Pull request description:

  * HWI returns the requested address: as a sanity check, we now compare that to what we expected
     * external signer documentation now reflects that HWI alternatives must implement this check
  * both RPC and GUI will now return an error text, rather than just fail (the GUI even failed silently in some cases)

ACKs for top commit:
  brunoerg:
    ACK 4357158
  achow101:
    ACK 4357158

Tree-SHA512: 4f56edf3846745c8e7d08ef55cf29e8bb468256457149377c5f02da097931f9ca0c06bdbd856dc2385cde4fd11e4dc3b634c5a48814ff27f5562c8a25d43da93

Author: achow101

doc/external-signer.md

@@ -150,6 +150,9 @@ Example, display the first native SegWit receive address on Testnet:
 
 The command MUST be able to figure out the address type from the descriptor.
 
+The command MUST return an object containing `{"address": "[the address]"}`.
+As a sanity check, for devices that support this, it SHOULD ask the device to derive the address.
+
 If <descriptor> contains a master key fingerprint, the command MUST fail if it does not match the fingerprint known by the device.
 
 If <descriptor> contains an xpub, the command MUST fail if it does not match the xpub known by the device.

src/interfaces/wallet.h

@@ -127,7 +127,7 @@ class Wallet
     virtual bool setAddressReceiveRequest(const CTxDestination& dest, const std::string& id, const std::string& value) = 0;
 
     //! Display address on external signer
-    virtual bool displayAddress(const CTxDestination& dest) = 0;
+    virtual util::Result<void> displayAddress(const CTxDestination& dest) = 0;
 
     //! Lock coin.
     virtual bool lockCoin(const COutPoint& output, const bool write_to_db) = 0;

src/qt/walletmodel.cpp

@@ -569,16 +569,17 @@ bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
     return true;
 }
 
-bool WalletModel::displayAddress(std::string sAddress) const
+void WalletModel::displayAddress(std::string sAddress) const
 {
     CTxDestination dest = DecodeDestination(sAddress);
-    bool res = false;
     try {
-        res = m_wallet->displayAddress(dest);
+        util::Result<void> result = m_wallet->displayAddress(dest);
+        if (!result) {
+            QMessageBox::warning(nullptr, tr("Signer error"), QString::fromStdString(util::ErrorString(result).translated));
+        }
     } catch (const std::runtime_error& e) {
         QMessageBox::critical(nullptr, tr("Can't display address"), e.what());
     }
-    return res;
 }
 
 bool WalletModel::isWalletEnabled()

src/qt/walletmodel.h

@@ -130,7 +130,7 @@ class WalletModel : public QObject
     UnlockContext requestUnlock();
 
     bool bumpFee(uint256 hash, uint256& new_hash);
-    bool displayAddress(std::string sAddress) const;
+    void displayAddress(std::string sAddress) const;
 
     static bool isWalletEnabled();
 

src/wallet/external_signer_scriptpubkeyman.cpp

@@ -9,9 +9,11 @@
 #include <wallet/external_signer_scriptpubkeyman.h>
 
 #include <iostream>
+#include <key_io.h>
 #include <memory>
 #include <stdexcept>
 #include <string>
+#include <univalue.h>
 #include <utility>
 #include <vector>
 
@@ -51,15 +53,26 @@ ExternalSigner ExternalSignerScriptPubKeyMan::GetExternalSigner() {
     return signers[0];
 }
 
-bool ExternalSignerScriptPubKeyMan::DisplayAddress(const CScript scriptPubKey, const ExternalSigner &signer) const
+util::Result<void> ExternalSignerScriptPubKeyMan::DisplayAddress(const CTxDestination& dest, const ExternalSigner &signer) const
 {
     // TODO: avoid the need to infer a descriptor from inside a descriptor wallet
+    const CScript& scriptPubKey = GetScriptForDestination(dest);
     auto provider = GetSolvingProvider(scriptPubKey);
     auto descriptor = InferDescriptor(scriptPubKey, *provider);
 
-    signer.DisplayAddress(descriptor->ToString());
-    // TODO inspect result
-    return true;
+    const UniValue& result = signer.DisplayAddress(descriptor->ToString());
+
+    const UniValue& error = result.find_value("error");
+    if (error.isStr()) return util::Error{strprintf(_("Signer returned error: %s"), error.getValStr())};
+
+    const UniValue& ret_address = result.find_value("address");
+    if (!ret_address.isStr()) return util::Error{_("Signer did not echo address")};
+
+    if (ret_address.getValStr() != EncodeDestination(dest)) {
+        return util::Error{strprintf(_("Signer echoed unexpected address %s"), ret_address.getValStr())};
+    }
+
+    return util::Result<void>();
 }
 
 // If sign is true, transaction must previously have been filled

src/wallet/external_signer_scriptpubkeyman.h

@@ -9,6 +9,8 @@
 
 #include <memory>
 
+struct bilingual_str;
+
 namespace wallet {
 class ExternalSignerScriptPubKeyMan : public DescriptorScriptPubKeyMan
 {
@@ -27,7 +29,11 @@ class ExternalSignerScriptPubKeyMan : public DescriptorScriptPubKeyMan
 
   static ExternalSigner GetExternalSigner();
 
-  bool DisplayAddress(const CScript scriptPubKey, const ExternalSigner &signer) const;
+  /**
+  * Display address on the device and verify that the returned value matches.
+  * @returns nothing or an error message
+  */
+ util::Result<void> DisplayAddress(const CTxDestination& dest, const ExternalSigner& signer) const;
 
   TransactionError FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = 1 /* SIGHASH_ALL */, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const override;
 };

src/wallet/interfaces.cpp

@@ -247,7 +247,7 @@ class WalletImpl : public Wallet
         return value.empty() ? m_wallet->EraseAddressReceiveRequest(batch, dest, id)
                              : m_wallet->SetAddressReceiveRequest(batch, dest, id, value);
     }
-    bool displayAddress(const CTxDestination& dest) override
+    util::Result<void> displayAddress(const CTxDestination& dest) override
     {
         LOCK(m_wallet->cs_wallet);
         return m_wallet->DisplayAddress(dest);

src/wallet/rpc/addresses.cpp

@@ -789,9 +789,8 @@ RPCHelpMan walletdisplayaddress()
                 throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid address");
             }
 
-            if (!pwallet->DisplayAddress(dest)) {
-                throw JSONRPCError(RPC_MISC_ERROR, "Failed to display address");
-            }
+            util::Result<void> res = pwallet->DisplayAddress(dest);
+            if (!res) throw JSONRPCError(RPC_MISC_ERROR, util::ErrorString(res).original);
 
             UniValue result(UniValue::VOBJ);
             result.pushKV("address", request.params[0].get_str());

src/wallet/scriptpubkeyman.h

@@ -27,7 +27,6 @@
 #include <unordered_map>
 
 enum class OutputType;
-struct bilingual_str;
 
 namespace wallet {
 struct MigrationData;

src/wallet/wallet.cpp

@@ -2667,7 +2667,7 @@ void ReserveDestination::ReturnDestination()
     address = CNoDestination();
 }
 
-bool CWallet::DisplayAddress(const CTxDestination& dest)
+util::Result<void> CWallet::DisplayAddress(const CTxDestination& dest)
 {
     CScript scriptPubKey = GetScriptForDestination(dest);
     for (const auto& spk_man : GetScriptPubKeyMans(scriptPubKey)) {
@@ -2676,9 +2676,9 @@ bool CWallet::DisplayAddress(const CTxDestination& dest)
             continue;
         }
         ExternalSigner signer = ExternalSignerScriptPubKeyMan::GetExternalSigner();
-        return signer_spk_man->DisplayAddress(scriptPubKey, signer);
+        return signer_spk_man->DisplayAddress(dest, signer);
     }
-    return false;
+    return util::Error{_("There is no ScriptPubKeyManager for this address")};
 }
 
 bool CWallet::LockCoin(const COutPoint& output, WalletBatch* batch)