wallet: add external_signer flag

Author: Sjors

src/wallet/wallet.cpp

@@ -259,6 +259,20 @@ std::shared_ptr<CWallet> CreateWallet(interfaces::Chain& chain, const std::strin
         wallet_creation_flags |= WALLET_FLAG_BLANK_WALLET;
     }
 
+    // Private keys must be disabled for an external signer wallet
+    if ((wallet_creation_flags & WALLET_FLAG_EXTERNAL_SIGNER) && !(wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
+        error = Untranslated("Private keys must be disabled when using an external signer");
+        status = DatabaseStatus::FAILED_CREATE;
+        return nullptr;
+    }
+
+    // Descriptor support must be enabled for an external signer wallet
+    if ((wallet_creation_flags & WALLET_FLAG_EXTERNAL_SIGNER) && !(wallet_creation_flags & WALLET_FLAG_DESCRIPTORS)) {
+        error = Untranslated("Descriptor support must be enabled when using an external signer");
+        status = DatabaseStatus::FAILED_CREATE;
+        return nullptr;
+    }
+
     // Wallet::Verify will check if we're trying to create a wallet with a duplicate name.
     std::unique_ptr<WalletDatabase> database = MakeWalletDatabase(name, options, status, error);
     if (!database) {

src/wallet/wallet.h

@@ -115,7 +115,8 @@ static constexpr uint64_t KNOWN_WALLET_FLAGS =
     |   WALLET_FLAG_BLANK_WALLET
     |   WALLET_FLAG_KEY_ORIGIN_METADATA
     |   WALLET_FLAG_DISABLE_PRIVATE_KEYS
-    |   WALLET_FLAG_DESCRIPTORS;
+    |   WALLET_FLAG_DESCRIPTORS
+    |   WALLET_FLAG_EXTERNAL_SIGNER;
 
 static constexpr uint64_t MUTABLE_WALLET_FLAGS =
         WALLET_FLAG_AVOID_REUSE;
@@ -126,6 +127,7 @@ static const std::map<std::string,WalletFlags> WALLET_FLAG_MAP{
     {"key_origin_metadata", WALLET_FLAG_KEY_ORIGIN_METADATA},
     {"disable_private_keys", WALLET_FLAG_DISABLE_PRIVATE_KEYS},
     {"descriptor_wallet", WALLET_FLAG_DESCRIPTORS},
+    {"external_signer", WALLET_FLAG_EXTERNAL_SIGNER}
 };
 
 extern const std::map<uint64_t,std::string> WALLET_FLAG_CAVEATS;

src/wallet/walletutil.h

@@ -60,6 +60,9 @@ enum WalletFlags : uint64_t {
 
     //! Indicate that this wallet supports DescriptorScriptPubKeyMan
     WALLET_FLAG_DESCRIPTORS = (1ULL << 34),
+
+    //! Indicates that the wallet needs an external signer
+    WALLET_FLAG_EXTERNAL_SIGNER = (1ULL << 35),
 };
 
 //! Get the path of the wallet directory.