Move external signer out of wallet module

This commit moves the ExternalSigner class and RPC methods out of the wallet module.

The enumeratesigners RPC can be used without a wallet since #21417.
With additional modifications external signers could be used without a wallet in general, e.g. via signrawtransaction.

The signerdisplayaddress RPC is ranamed to walletdisplayaddress because it requires wallet context.
A future displayaddress RPC call without wallet context could take a descriptor argument.

This commit fixes a rpc_help.py failure when configured with --disable-wallet.

9 files changed, 48 insertions, 340 deletions

diff --git a/src/wallet/external_signer.cpp b/src/wallet/external_signer.cpp
deleted file mode 100644
index 3396111760..0000000000
--- a/src/wallet/external_signer.cpp
+++ /dev/null
@@ -1,119 +0,0 @@
-// Copyright (c) 2018-2021 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#include <chainparams.h>
-#include <core_io.h>
-#include <psbt.h>
-#include <util/strencodings.h>
-#include <util/system.h>
-#include <wallet/external_signer.h>
-
-ExternalSigner::ExternalSigner(const std::string& command, const std::string& fingerprint, std::string chain, std::string name): m_command(command), m_fingerprint(fingerprint), m_chain(chain), m_name(name) {}
-
-const std::string ExternalSigner::NetworkArg() const
-{
-    return " --chain " + m_chain;
-}
-
-#ifdef ENABLE_EXTERNAL_SIGNER
-
-bool ExternalSigner::Enumerate(const std::string& command, std::vector<ExternalSigner>& signers, std::string chain, bool ignore_errors)
-{
-    // Call <command> enumerate
-    const UniValue result = RunCommandParseJSON(command + " enumerate");
-    if (!result.isArray()) {
-        if (ignore_errors) return false;
-        throw ExternalSignerException(strprintf("'%s' received invalid response, expected array of signers", command));
-    }
-    for (UniValue signer : result.getValues()) {
-        // Check for error
-        const UniValue& error = find_value(signer, "error");
-        if (!error.isNull()) {
-            if (ignore_errors) return false;
-            if (!error.isStr()) {
-                throw ExternalSignerException(strprintf("'%s' error", command));
-            }
-            throw ExternalSignerException(strprintf("'%s' error: %s", command, error.getValStr()));
-        }
-        // Check if fingerprint is present
-        const UniValue& fingerprint = find_value(signer, "fingerprint");
-        if (fingerprint.isNull()) {
-            if (ignore_errors) return false;
-            throw ExternalSignerException(strprintf("'%s' received invalid response, missing signer fingerprint", command));
-        }
-        std::string fingerprintStr = fingerprint.get_str();
-        // Skip duplicate signer
-        bool duplicate = false;
-        for (ExternalSigner signer : signers) {
-            if (signer.m_fingerprint.compare(fingerprintStr) == 0) duplicate = true;
-        }
-        if (duplicate) break;
-        std::string name = "";
-        const UniValue& model_field = find_value(signer, "model");
-        if (model_field.isStr() && model_field.getValStr() != "") {
-            name += model_field.getValStr();
-        }
-        signers.push_back(ExternalSigner(command, fingerprintStr, chain, name));
-    }
-    return true;
-}
-
-UniValue ExternalSigner::DisplayAddress(const std::string& descriptor) const
-{
-    return RunCommandParseJSON(m_command + " --fingerprint \"" + m_fingerprint + "\"" + NetworkArg() + " displayaddress --desc \"" + descriptor + "\"");
-}
-
-UniValue ExternalSigner::GetDescriptors(int account)
-{
-    return RunCommandParseJSON(m_command + " --fingerprint \"" + m_fingerprint + "\"" + NetworkArg() + " getdescriptors --account " + strprintf("%d", account));
-}
-
-bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::string& error)
-{
-    // Serialize the PSBT
-    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
-    ssTx << psbtx;
-
-    // Check if signer fingerprint matches any input master key fingerprint
-    bool match = false;
-    for (unsigned int i = 0; i < psbtx.inputs.size(); ++i) {
-        const PSBTInput& input = psbtx.inputs[i];
-        for (auto entry : input.hd_keypaths) {
-            if (m_fingerprint == strprintf("%08x", ReadBE32(entry.second.fingerprint))) match = true;
-        }
-    }
-
-    if (!match) {
-        error = "Signer fingerprint " + m_fingerprint + " does not match any of the inputs:\n" + EncodeBase64(ssTx.str());
-        return false;
-    }
-
-    std::string command = m_command + " --stdin --fingerprint \"" + m_fingerprint + "\"" + NetworkArg();
-    std::string stdinStr = "signtx \"" + EncodeBase64(ssTx.str()) + "\"";
-
-    const UniValue signer_result = RunCommandParseJSON(command, stdinStr);
-
-    if (find_value(signer_result, "error").isStr()) {
-        error = find_value(signer_result, "error").get_str();
-        return false;
-    }
-
-    if (!find_value(signer_result, "psbt").isStr()) {
-        error = "Unexpected result from signer";
-        return false;
-    }
-
-    PartiallySignedTransaction signer_psbtx;
-    std::string signer_psbt_error;
-    if (!DecodeBase64PSBT(signer_psbtx, find_value(signer_result, "psbt").get_str(), signer_psbt_error)) {
-        error = strprintf("TX decode failed %s", signer_psbt_error);
-        return false;
-    }
-
-    psbtx = signer_psbtx;
-
-    return true;
-}
-
-#endif
diff --git a/src/wallet/external_signer.h b/src/wallet/external_signer.h
deleted file mode 100644
index 4b9711107b..0000000000
--- a/src/wallet/external_signer.h
+++ /dev/null
@@ -1,73 +0,0 @@
-// Copyright (c) 2018-2021 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#ifndef BITCOIN_WALLET_EXTERNAL_SIGNER_H
-#define BITCOIN_WALLET_EXTERNAL_SIGNER_H
-
-#include <stdexcept>
-#include <string>
-#include <univalue.h>
-#include <util/system.h>
-
-struct PartiallySignedTransaction;
-
-class ExternalSignerException : public std::runtime_error {
-public:
-    using std::runtime_error::runtime_error;
-};
-
-//! Enables interaction with an external signing device or service, such as
-//! a hardware wallet. See doc/external-signer.md
-class ExternalSigner
-{
-private:
-    //! The command which handles interaction with the external signer.
-    std::string m_command;
-
-public:
-    //! @param[in] command      the command which handles interaction with the external signer
-    //! @param[in] fingerprint  master key fingerprint of the signer
-    //! @param[in] chain        "main", "test", "regtest" or "signet"
-    //! @param[in] name         device name
-    ExternalSigner(const std::string& command, const std::string& fingerprint, std::string chain, std::string name);
-
-    //! Master key fingerprint of the signer
-    std::string m_fingerprint;
-
-    //! Bitcoin mainnet, testnet, etc
-    std::string m_chain;
-
-    //! Name of signer
-    std::string m_name;
-
-    const std::string NetworkArg() const;
-
-#ifdef ENABLE_EXTERNAL_SIGNER
-    //! Obtain a list of signers. Calls `<command> enumerate`.
-    //! @param[in]              command the command which handles interaction with the external signer
-    //! @param[in,out] signers  vector to which new signers (with a unique master key fingerprint) are added
-    //! @param chain            "main", "test", "regtest" or "signet"
-    //! @param[out] success     Boolean
-    static bool Enumerate(const std::string& command, std::vector<ExternalSigner>& signers, std::string chain, bool ignore_errors = false);
-
-    //! Display address on the device. Calls `<command> displayaddress --desc <descriptor>`.
-    //! @param[in] descriptor Descriptor specifying which address to display.
-    //!            Must include a public key or xpub, as well as key origin.
-    UniValue DisplayAddress(const std::string& descriptor) const;
-
-    //! Get receive and change Descriptor(s) from device for a given account.
-    //! Calls `<command> getdescriptors --account <account>`
-    //! @param[in] account  which BIP32 account to use (e.g. `m/44'/0'/account'`)
-    //! @param[out] UniValue see doc/external-signer.md
-    UniValue GetDescriptors(int account);
-
-    //! Sign PartiallySignedTransaction on the device.
-    //! Calls `<command> signtransaction` and passes the PSBT via stdin.
-    //! @param[in,out] psbt  PartiallySignedTransaction to be signed
-    bool SignTransaction(PartiallySignedTransaction& psbt, std::string& error);
-
-#endif
-};
-
-#endif // BITCOIN_WALLET_EXTERNAL_SIGNER_H
diff --git a/src/wallet/external_signer_scriptpubkeyman.cpp b/src/wallet/external_signer_scriptpubkeyman.cpp
index a2071e521a..a113c128d7 100644
--- a/src/wallet/external_signer_scriptpubkeyman.cpp
+++ b/src/wallet/external_signer_scriptpubkeyman.cpp
@@ -3,7 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <chainparams.h>
-#include <wallet/external_signer.h>
+#include <external_signer.h>
 #include <wallet/external_signer_scriptpubkeyman.h>
 
 #ifdef ENABLE_EXTERNAL_SIGNER
diff --git a/src/wallet/interfaces.cpp b/src/wallet/interfaces.cpp
index 23bdaa671a..64ce09d1d1 100644
--- a/src/wallet/interfaces.cpp
+++ b/src/wallet/interfaces.cpp
@@ -22,7 +22,6 @@
 #include <wallet/fees.h>
 #include <wallet/ismine.h>
 #include <wallet/load.h>
-#include <wallet/rpcsigner.h>
 #include <wallet/rpcwallet.h>
 #include <wallet/wallet.h>
 
@@ -520,17 +519,6 @@ public:
             }, command.argNames, command.unique_id);
             m_rpc_handlers.emplace_back(m_context.chain->handleRpc(m_rpc_commands.back()));
         }
-
-#ifdef ENABLE_EXTERNAL_SIGNER
-        for (const CRPCCommand& command : GetSignerRPCCommands()) {
-            m_rpc_commands.emplace_back(command.category, command.name, [this, &command](const JSONRPCRequest& request, UniValue& result, bool last_handler) {
-                JSONRPCRequest wallet_request = request;
-                wallet_request.context = &m_context;
-                return command.actor(wallet_request, result, last_handler);
-            }, command.argNames, command.unique_id);
-            m_rpc_handlers.emplace_back(m_context.chain->handleRpc(m_rpc_commands.back()));
-        }
-#endif
     }
     bool verify() override { return VerifyWallets(*m_context.chain); }
     bool load() override { return LoadWallets(*m_context.chain); }
diff --git a/src/wallet/rpcsigner.cpp b/src/wallet/rpcsigner.cpp
deleted file mode 100644
index 696c74d665..0000000000
--- a/src/wallet/rpcsigner.cpp
+++ /dev/null
@@ -1,108 +0,0 @@
-// Copyright (c) 2018-2021 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#include <chainparamsbase.h>
-#include <key_io.h>
-#include <rpc/server.h>
-#include <rpc/util.h>
-#include <util/strencodings.h>
-#include <wallet/rpcsigner.h>
-#include <wallet/rpcwallet.h>
-#include <wallet/wallet.h>
-
-#ifdef ENABLE_EXTERNAL_SIGNER
-
-static RPCHelpMan enumeratesigners()
-{
-    return RPCHelpMan{
-        "enumeratesigners",
-        "Returns a list of external signers from -signer.",
-        {},
-        RPCResult{
-            RPCResult::Type::OBJ, "", "",
-            {
-                {RPCResult::Type::ARR, "signers", /* optional */ false, "",
-                {
-                    {RPCResult::Type::STR_HEX, "masterkeyfingerprint", "Master key fingerprint"},
-                    {RPCResult::Type::STR, "name", "Device name"},
-                },
-                }
-            }
-        },
-        RPCExamples{""},
-        [](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue {
-            const std::string command = gArgs.GetArg("-signer", "");
-            if (command == "") throw JSONRPCError(RPC_WALLET_ERROR, "Error: restart bitcoind with -signer=<cmd>");
-            std::string chain = gArgs.GetChainName();
-            UniValue signers_res = UniValue::VARR;
-            try {
-                std::vector<ExternalSigner> signers;
-                ExternalSigner::Enumerate(command, signers, chain);
-                for (ExternalSigner signer : signers) {
-                    UniValue signer_res = UniValue::VOBJ;
-                    signer_res.pushKV("fingerprint", signer.m_fingerprint);
-                    signer_res.pushKV("name", signer.m_name);
-                    signers_res.push_back(signer_res);
-                }
-            } catch (const ExternalSignerException& e) {
-                throw JSONRPCError(RPC_WALLET_ERROR, e.what());
-            }
-            UniValue result(UniValue::VOBJ);
-            result.pushKV("signers", signers_res);
-            return result;
-        }
-    };
-}
-
-static RPCHelpMan signerdisplayaddress()
-{
-    return RPCHelpMan{
-        "signerdisplayaddress",
-        "Display address on an external signer for verification.\n",
-        {
-            {"address",     RPCArg::Type::STR, RPCArg::Optional::NO, /* default_val */ "", "bitcoin address to display"},
-        },
-        RPCResult{RPCResult::Type::NONE,"",""},
-        RPCExamples{""},
-        [](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue {
-            std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
-            if (!wallet) return NullUniValue;
-            CWallet* const pwallet = wallet.get();
-
-            LOCK(pwallet->cs_wallet);
-
-            CTxDestination dest = DecodeDestination(request.params[0].get_str());
-
-            // Make sure the destination is valid
-            if (!IsValidDestination(dest)) {
-                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid address");
-            }
-
-            if (!pwallet->DisplayAddress(dest)) {
-                throw JSONRPCError(RPC_WALLET_ERROR, "Failed to display address");
-            }
-
-            UniValue result(UniValue::VOBJ);
-            result.pushKV("address", request.params[0].get_str());
-            return result;
-        }
-    };
-}
-
-Span<const CRPCCommand> GetSignerRPCCommands()
-{
-
-// clang-format off
-static const CRPCCommand commands[] =
-{ // category              actor (function)
-  // --------------------- ------------------------
-  { "signer",              &enumeratesigners,      },
-  { "signer",              &signerdisplayaddress,  },
-};
-// clang-format on
-    return MakeSpan(commands);
-}
-
-
-#endif // ENABLE_EXTERNAL_SIGNER
diff --git a/src/wallet/rpcsigner.h b/src/wallet/rpcsigner.h
deleted file mode 100644
index f3ab83c428..0000000000
--- a/src/wallet/rpcsigner.h
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright (c) 2018-2021 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#ifndef BITCOIN_WALLET_RPCSIGNER_H
-#define BITCOIN_WALLET_RPCSIGNER_H
-
-#include <span.h>
-#include <util/system.h>
-#include <vector>
-
-#ifdef ENABLE_EXTERNAL_SIGNER
-
-class CRPCCommand;
-
-namespace interfaces {
-class Chain;
-class Handler;
-}
-
-Span<const CRPCCommand> GetSignerRPCCommands();
-
-#endif // ENABLE_EXTERNAL_SIGNER
-
-#endif //BITCOIN_WALLET_RPCSIGNER_H
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 672ee3e7a4..dc821dc06d 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -4526,6 +4526,48 @@ static RPCHelpMan upgradewallet()
     };
 }
 
+#ifdef ENABLE_EXTERNAL_SIGNER
+static RPCHelpMan walletdisplayaddress()
+{
+    return RPCHelpMan{
+        "walletdisplayaddress",
+        "Display address on an external signer for verification.\n",
+        {
+            {"address",     RPCArg::Type::STR, RPCArg::Optional::NO, /* default_val */ "", "bitcoin address to display"},
+        },
+        RPCResult{
+            RPCResult::Type::OBJ,"","",
+            {
+                {RPCResult::Type::STR, "address", "The address as confirmed by the signer"},
+            }
+        },
+        RPCExamples{""},
+        [](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue {
+            std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
+            if (!wallet) return NullUniValue;
+            CWallet* const pwallet = wallet.get();
+
+            LOCK(pwallet->cs_wallet);
+
+            CTxDestination dest = DecodeDestination(request.params[0].get_str());
+
+            // Make sure the destination is valid
+            if (!IsValidDestination(dest)) {
+                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid address");
+            }
+
+            if (!pwallet->DisplayAddress(dest)) {
+                throw JSONRPCError(RPC_MISC_ERROR, "Failed to display address");
+            }
+
+            UniValue result(UniValue::VOBJ);
+            result.pushKV("address", request.params[0].get_str());
+            return result;
+        }
+    };
+}
+#endif // ENABLE_EXTERNAL_SIGNER
+
 RPCHelpMan abortrescan();
 RPCHelpMan dumpprivkey();
 RPCHelpMan importprivkey();
@@ -4602,6 +4644,9 @@ static const CRPCCommand commands[] =
     { "wallet",             &unloadwallet,                   },
     { "wallet",             &upgradewallet,                  },
     { "wallet",             &walletcreatefundedpsbt,         },
+#ifdef ENABLE_EXTERNAL_SIGNER
+    { "wallet",             &walletdisplayaddress,           },
+#endif // ENABLE_EXTERNAL_SIGNER
     { "wallet",             &walletlock,                     },
     { "wallet",             &walletpassphrase,               },
     { "wallet",             &walletpassphrasechange,         },
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 9a75002b6c..149549410c 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -13,7 +13,7 @@
 #include <util/system.h>
 #include <util/time.h>
 #include <util/translation.h>
-#include <wallet/external_signer.h>
+#include <external_signer.h>
 #include <wallet/scriptpubkeyman.h>
 
 #include <optional>
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 192fd60dc2..5bf3c91bec 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -22,7 +22,7 @@
 #include <wallet/coinselection.h>
 #include <wallet/crypter.h>
 #include <wallet/scriptpubkeyman.h>
-#include <wallet/external_signer.h>
+#include <external_signer.h>
 #include <wallet/walletdb.h>
 #include <wallet/walletutil.h>