wallet: add ability for addhdkey to import a codex32 seed

Author: apoelstra

src/rpc/client.cpp

@@ -310,6 +310,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "stop", 0, "wait" },
     { "addnode", 2, "v2transport" },
     { "addconnection", 2, "v2transport" },
+    { "addhdkey", 1, "codex32" },
 };
 // clang-format on
 

src/wallet/rpc/wallet.cpp

@@ -5,6 +5,7 @@
 
 #include <bitcoin-build-config.h> // IWYU pragma: keep
 
+#include <codex32.h>
 #include <core_io.h>
 #include <key_io.h>
 #include <rpc/server.h>
@@ -938,9 +939,15 @@ RPCHelpMan addhdkey()
 {
     return RPCHelpMan{
         "addhdkey",
-        "\nAdd a BIP 32 HD key to the wallet that can be used with 'createwalletdescriptor'\n",
+        "Add a BIP 32 HD key to the wallet that can be used with 'createwalletdescriptor'.\n"
+        "If no argument is provided, a randomly generated one will be added.",
         {
-            {"hdkey", RPCArg::Type::STR, RPCArg::DefaultHint{"Automatically generated new key"}, "The BIP 32 extended private key to add. If none is provided, a randomly generated one will be added."},
+            {"hdkey", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "The BIP 32 extended private key to add."},
+            {"codex32", RPCArg::Type::ARR, RPCArg::Optional::OMITTED, "A codex32 (BIP 93) encoded seed, or list of codex32-encoded shares",
+             {
+                 {"share 1", RPCArg::Type::STR, RPCArg::Optional::OMITTED, ""},
+             },
+            },
         },
         RPCResult{
             RPCResult::Type::OBJ, "", "",
@@ -963,11 +970,13 @@ RPCHelpMan addhdkey()
             EnsureWalletIsUnlocked(*wallet);
 
             CExtKey hdkey;
-            if (request.params[0].isNull()) {
+            if (request.params[0].isNull() && request.params[1].isNull()) {
                 CKey seed_key;
                 seed_key.MakeNewKey(true);
                 hdkey.SetSeed(seed_key);
-            } else {
+            } else if (!request.params[0].isNull() && !request.params[1].isNull()) {
+                   throw JSONRPCError(RPC_WALLET_ERROR, "addhkey takes at most one key type");
+            } else if (!request.params[0].isNull()) {
                 hdkey = DecodeExtKey(request.params[0].get_str());
                 if (!hdkey.key.IsValid()) {
                     // Check if the user gave us an xpub and give a more descriptive error if so
@@ -978,6 +987,37 @@ RPCHelpMan addhdkey()
                         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Could not parse HD key");
                     }
                 }
+            } else {
+                const auto& req_shares = request.params[1].get_array();
+                std::vector<codex32::Result> shares;
+                shares.reserve(req_shares.size());
+                for (size_t j = 0; j < req_shares.size(); ++j) {
+                    if (!req_shares[j].isStr()) {
+                        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "codex32 shares must be strings");
+                    }
+                    codex32::Result key_res{req_shares[j].get_str()};
+                    if (!key_res.IsValid()) {
+                        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid codex32 share: " + codex32::ErrorString(key_res.error()));
+                    }
+                    shares.push_back(key_res);
+                }
+
+                // Recover seed
+                std::vector<unsigned char> seed;
+                if (shares.size() == 1) {
+                    if (shares[0].GetShareIndex() != 's') {
+                        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid codex32: single share must be the S share");
+                    }
+                    seed = shares[0].GetPayload();
+                } else {
+                    codex32::Result s{shares, 's'};
+                    if (!s.IsValid()) {
+                        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Failed to derive codex32 seed: " + codex32::ErrorString(s.error()));
+                    }
+                    seed = s.GetPayload();
+                }
+
+                hdkey.SetSeed(std::span{(std::byte*) seed.data(), seed.size()});
             }
 
             LOCK(wallet->cs_wallet);