From 709a917c26bf048de454760c7189278b965ca7f3 Mon Sep 17 00:00:00 2001
From: Andrew Chow <achow101-github@achow101.com>
Date: Mon, 1 Nov 2021 15:47:33 -0400
Subject: [PATCH] rpc: Add getxpub command

---
 src/wallet/keyman.cpp    |  8 +++++++
 src/wallet/keyman.h      |  1 +
 src/wallet/rpcwallet.cpp | 45 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+)

diff --git a/src/wallet/keyman.cpp b/src/wallet/keyman.cpp
index 978ea07b1c549..c77b85e42cdf7 100644
--- a/src/wallet/keyman.cpp
+++ b/src/wallet/keyman.cpp
@@ -74,6 +74,14 @@ std::optional<CExtKey> KeyManager::GetActiveHDKey() const
     return master_key;
 }
 
+std::optional<CExtPubKey> KeyManager::GetActiveHDPubKey() const
+{
+    if (!m_active_xpub.pubkey.IsValid()) {
+        return std::nullopt;
+    }
+    return m_active_xpub;
+}
+
 bool KeyManager::AddKeyInner(WalletBatch& batch, const CKey& key, const CPubKey& pubkey)
 {
     AssertLockHeld(cs_keyman);
diff --git a/src/wallet/keyman.h b/src/wallet/keyman.h
index cdebe232b85cd..03b369136f0b0 100644
--- a/src/wallet/keyman.h
+++ b/src/wallet/keyman.h
@@ -43,6 +43,7 @@ class KeyManager
 
     void GenerateAndSetHDKey();
     std::optional<CExtKey> GetActiveHDKey() const EXCLUSIVE_LOCKS_REQUIRED(cs_keyman);
+    std::optional<CExtPubKey> GetActiveHDPubKey() const EXCLUSIVE_LOCKS_REQUIRED(cs_keyman);
     void SetActiveHDKey(const CExtPubKey& extpub);
     void LoadActiveHDKey(const CExtPubKey& extpub);
 
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 86bfa10d888a7..62ba5b130758c 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -4839,6 +4839,50 @@ static RPCHelpMan walletdisplayaddress()
 }
 #endif // ENABLE_EXTERNAL_SIGNER
 
+static RPCHelpMan getxpub()
+{
+    return RPCHelpMan{"getxpub",
+                "Returns the xpub most recently used to generate descriptors for this descriptor wallet. "
+                "Not entirely useful right now as it returns the xpub of the root, and there are "
+                "hardened derivation steps involved in normal key derivation.\n",
+                {},
+                RPCResult{
+                    RPCResult::Type::OBJ, "", "",
+                    {
+                        {
+                        {RPCResult::Type::STR, "xpub", "The xpub"},
+                    }},
+                },
+                RPCExamples{
+                    HelpExampleCli("getxpub", "")
+            + HelpExampleRpc("getxpub", "")
+                },
+        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
+{
+    const std::shared_ptr<CWallet> pwallet = GetWalletForJSONRPCRequest(request);
+    if (!pwallet) return NullUniValue;
+
+    if (!pwallet->IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "getxpub is not available for non-descriptor wallets");
+    }
+
+    const KeyManager& keyman = pwallet->GetKeyManager();
+    LOCK2(pwallet->cs_wallet, keyman.cs_keyman);
+
+    std::optional<CExtPubKey> extpub = keyman.GetActiveHDPubKey();
+    if (extpub == std::nullopt) {
+        throw JSONRPCError(RPC_WALLET_ERROR, "This wallet does not have an active xpub");
+    }
+    std::string xpub = EncodeExtPubKey(*extpub);
+
+    UniValue obj(UniValue::VOBJ);
+    obj.pushKV("xpub", xpub);
+
+    return obj;
+},
+    };
+}
+
 RPCHelpMan abortrescan();
 RPCHelpMan dumpprivkey();
 RPCHelpMan importprivkey();
@@ -4880,6 +4924,7 @@ static const CRPCCommand commands[] =
     { "wallet",             &gettransaction,                 },
     { "wallet",             &getunconfirmedbalance,          },
     { "wallet",             &getbalances,                    },
+    { "wallet",             &getxpub,                        },
     { "wallet",             &getwalletinfo,                  },
     { "wallet",             &importaddress,                  },
     { "wallet",             &importdescriptors,              },