SegWit wallet support

This introduces two command line flags (-addresstype and -changetype) which control
the type of addresses/outputs created by the GUI and RPCs. Certain RPCs allow
overriding these (`getnewaddress` and `getrawchangeaddress`). Supported types
are "legacy" (P2PKH and P2SH-multisig), "p2sh-segwit" (P2SH-P2WPKH and P2SH-P2WSH-multisig),
and "bech32" (P2WPKH and P2WSH-multisig).

A few utility functions are added to the wallet to construct different address type
and to add the necessary entries to the wallet file to be compatible with earlier
versions (see `CWallet::LearnRelatedScripts`, `GetDestinationForKey`,
`GetAllDestinationsForKey`, `CWallet::AddAndGetDestinationForScript`).

6 files changed, 217 insertions, 21 deletions

diff --git a/src/wallet/init.cpp b/src/wallet/init.cpp
index 67c46df87d..8da99f2f7e 100644
--- a/src/wallet/init.cpp
+++ b/src/wallet/init.cpp
@@ -16,6 +16,8 @@
 std::string GetWalletHelpString(bool showDebug)
 {
     std::string strUsage = HelpMessageGroup(_("Wallet options:"));
+    strUsage += HelpMessageOpt("-addresstype", strprintf(_("What type of addresses to use (\"legacy\", \"p2sh-segwit\", or \"bech32\", default: \"%s\")"), FormatOutputType(OUTPUT_TYPE_DEFAULT)));
+    strUsage += HelpMessageOpt("-changetype", _("What type of change to use (\"legacy\", \"p2sh-segwit\", or \"bech32\", default is same as -addresstype)"));
     strUsage += HelpMessageOpt("-disablewallet", _("Do not load the wallet and disable wallet RPC calls"));
     strUsage += HelpMessageOpt("-keypool=<n>", strprintf(_("Set key pool size to <n> (default: %u)"), DEFAULT_KEYPOOL_SIZE));
     strUsage += HelpMessageOpt("-fallbackfee=<amt>", strprintf(_("A fee rate (in %s/kB) that will be used when fee estimation has insufficient data (default: %s)"),
@@ -175,6 +177,16 @@ bool WalletParameterInteraction()
     bSpendZeroConfChange = gArgs.GetBoolArg("-spendzeroconfchange", DEFAULT_SPEND_ZEROCONF_CHANGE);
     fWalletRbf = gArgs.GetBoolArg("-walletrbf", DEFAULT_WALLET_RBF);
 
+    g_address_type = ParseOutputType(gArgs.GetArg("-addresstype", ""));
+    if (g_address_type == OUTPUT_TYPE_NONE) {
+        return InitError(strprintf(_("Unknown address type '%s'"), gArgs.GetArg("-addresstype", "")));
+    }
+
+    g_change_type = ParseOutputType(gArgs.GetArg("-changetype", ""), g_address_type);
+    if (g_change_type == OUTPUT_TYPE_NONE) {
+        return InitError(strprintf(_("Unknown change type '%s'"), gArgs.GetArg("-changetype", "")));
+    }
+
     return true;
 }
 
diff --git a/src/wallet/rpcdump.cpp b/src/wallet/rpcdump.cpp
index 81922c5848..17d81a5e39 100644
--- a/src/wallet/rpcdump.cpp
+++ b/src/wallet/rpcdump.cpp
@@ -131,7 +131,11 @@ UniValue importprivkey(const JSONRPCRequest& request)
     CKeyID vchAddress = pubkey.GetID();
     {
         pwallet->MarkDirty();
-        pwallet->SetAddressBook(vchAddress, strLabel, "receive");
+
+        // We don't know which corresponding address will be used; label them all
+        for (const auto& dest : GetAllDestinationsForKey(pubkey)) {
+            pwallet->SetAddressBook(dest, strLabel, "receive");
+        }
 
         // Don't throw error in case a key is already there
         if (pwallet->HaveKey(vchAddress)) {
@@ -143,6 +147,7 @@ UniValue importprivkey(const JSONRPCRequest& request)
         if (!pwallet->AddKeyPubKey(key, pubkey)) {
             throw JSONRPCError(RPC_WALLET_ERROR, "Error adding key to wallet");
         }
+        pwallet->LearnAllRelatedScripts(pubkey);
 
         // whenever a key is imported, we need to scan the whole chain
         pwallet->UpdateTimeFirstKey(1);
@@ -433,8 +438,11 @@ UniValue importpubkey(const JSONRPCRequest& request)
 
     LOCK2(cs_main, pwallet->cs_wallet);
 
-    ImportAddress(pwallet, pubKey.GetID(), strLabel);
+    for (const auto& dest : GetAllDestinationsForKey(pubKey)) {
+        ImportAddress(pwallet, dest, strLabel);
+    }
     ImportScript(pwallet, GetScriptForRawPubKey(pubKey), strLabel, false);
+    pwallet->LearnAllRelatedScripts(pubKey);
 
     if (fRescan)
     {
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index e4b2b020b7..447dd794ae 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -136,14 +136,15 @@ UniValue getnewaddress(const JSONRPCRequest& request)
         return NullUniValue;
     }
 
-    if (request.fHelp || request.params.size() > 1)
+    if (request.fHelp || request.params.size() > 2)
         throw std::runtime_error(
-            "getnewaddress ( \"account\" )\n"
+            "getnewaddress ( \"account\" \"address_type\" )\n"
             "\nReturns a new Bitcoin address for receiving payments.\n"
             "If 'account' is specified (DEPRECATED), it is added to the address book \n"
             "so payments received with the address will be credited to 'account'.\n"
             "\nArguments:\n"
             "1. \"account\"        (string, optional) DEPRECATED. The account name for the address to be linked to. If not provided, the default account \"\" is used. It can also be set to the empty string \"\" to represent the default account. The account does not need to exist, it will be created if there is no account by the given name.\n"
+            "2. \"address_type\"   (string, optional) The address type to use. Options are \"legacy\", \"p2sh\", and \"bech32\". Default is set by -addresstype.\n"
             "\nResult:\n"
             "\"address\"    (string) The new bitcoin address\n"
             "\nExamples:\n"
@@ -158,6 +159,14 @@ UniValue getnewaddress(const JSONRPCRequest& request)
     if (!request.params[0].isNull())
         strAccount = AccountFromValue(request.params[0]);
 
+    OutputType output_type = g_address_type;
+    if (!request.params[1].isNull()) {
+        output_type = ParseOutputType(request.params[1].get_str(), g_address_type);
+        if (output_type == OUTPUT_TYPE_NONE) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[1].get_str()));
+        }
+    }
+
     if (!pwallet->IsLocked()) {
         pwallet->TopUpKeyPool();
     }
@@ -167,11 +176,12 @@ UniValue getnewaddress(const JSONRPCRequest& request)
     if (!pwallet->GetKeyFromPool(newKey)) {
         throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, "Error: Keypool ran out, please call keypoolrefill first");
     }
-    CKeyID keyID = newKey.GetID();
+    pwallet->LearnRelatedScripts(newKey, output_type);
+    CTxDestination dest = GetDestinationForKey(newKey, output_type);
 
-    pwallet->SetAddressBook(keyID, strAccount, "receive");
+    pwallet->SetAddressBook(dest, strAccount, "receive");
 
-    return EncodeDestination(keyID);
+    return EncodeDestination(dest);
 }
 
 
@@ -226,11 +236,13 @@ UniValue getrawchangeaddress(const JSONRPCRequest& request)
         return NullUniValue;
     }
 
-    if (request.fHelp || request.params.size() > 0)
+    if (request.fHelp || request.params.size() > 1)
         throw std::runtime_error(
-            "getrawchangeaddress\n"
+            "getrawchangeaddress ( \"address_type\" )\n"
             "\nReturns a new Bitcoin address, for receiving change.\n"
             "This is for use with raw transactions, NOT normal use.\n"
+            "\nArguments:\n"
+            "1. \"address_type\"           (string, optional) The address type to use. Options are \"legacy\", \"p2sh\", and \"bech32\". Default is set by -changetype.\n"
             "\nResult:\n"
             "\"address\"    (string) The address\n"
             "\nExamples:\n"
@@ -244,6 +256,14 @@ UniValue getrawchangeaddress(const JSONRPCRequest& request)
         pwallet->TopUpKeyPool();
     }
 
+    OutputType output_type = g_change_type;
+    if (!request.params[0].isNull()) {
+        output_type = ParseOutputType(request.params[0].get_str(), g_change_type);
+        if (output_type == OUTPUT_TYPE_NONE) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[0].get_str()));
+        }
+    }
+
     CReserveKey reservekey(pwallet);
     CPubKey vchPubKey;
     if (!reservekey.GetReservedKey(vchPubKey, true))
@@ -251,9 +271,10 @@ UniValue getrawchangeaddress(const JSONRPCRequest& request)
 
     reservekey.KeepKey();
 
-    CKeyID keyID = vchPubKey.GetID();
+    pwallet->LearnRelatedScripts(vchPubKey, output_type);
+    CTxDestination dest = GetDestinationForKey(vchPubKey, output_type);
 
-    return EncodeDestination(keyID);
+    return EncodeDestination(dest);
 }
 
 
@@ -1184,11 +1205,12 @@ UniValue addmultisigaddress(const JSONRPCRequest& request)
 
     // Construct using pay-to-script-hash:
     CScript inner = _createmultisig_redeemScript(pwallet, request.params);
-    CScriptID innerID(inner);
     pwallet->AddCScript(inner);
 
-    pwallet->SetAddressBook(innerID, strAccount, "send");
-    return EncodeDestination(innerID);
+    CTxDestination dest = pwallet->AddAndGetDestinationForScript(inner, g_address_type);
+
+    pwallet->SetAddressBook(dest, strAccount, "send");
+    return EncodeDestination(dest);
 }
 
 class Witnessifier : public boost::static_visitor<bool>
@@ -3446,8 +3468,8 @@ static const CRPCCommand commands[] =
     { "wallet",             "getaccount",               &getaccount,               {"address"} },
     { "wallet",             "getaddressesbyaccount",    &getaddressesbyaccount,    {"account"} },
     { "wallet",             "getbalance",               &getbalance,               {"account","minconf","include_watchonly"} },
-    { "wallet",             "getnewaddress",            &getnewaddress,            {"account"} },
-    { "wallet",             "getrawchangeaddress",      &getrawchangeaddress,      {} },
+    { "wallet",             "getnewaddress",            &getnewaddress,            {"account","address_type"} },
+    { "wallet",             "getrawchangeaddress",      &getrawchangeaddress,      {"address_type"} },
     { "wallet",             "getreceivedbyaccount",     &getreceivedbyaccount,     {"account","minconf"} },
     { "wallet",             "getreceivedbyaddress",     &getreceivedbyaddress,     {"address","minconf"} },
     { "wallet",             "gettransaction",           &gettransaction,           {"txid","include_watchonly"} },
diff --git a/src/wallet/test/wallet_test_fixture.cpp b/src/wallet/test/wallet_test_fixture.cpp
index 3ee83d2d7c..86f4df6008 100644
--- a/src/wallet/test/wallet_test_fixture.cpp
+++ b/src/wallet/test/wallet_test_fixture.cpp
@@ -13,6 +13,8 @@ WalletTestingSetup::WalletTestingSetup(const std::string& chainName):
     bitdb.MakeMock();
 
     bool fFirstRun;
+    g_address_type = OUTPUT_TYPE_DEFAULT;
+    g_change_type = OUTPUT_TYPE_DEFAULT;
     std::unique_ptr<CWalletDBWrapper> dbw(new CWalletDBWrapper(&bitdb, "wallet_test.dat"));
     pwalletMain = MakeUnique<CWallet>(std::move(dbw));
     pwalletMain->LoadWallet(fFirstRun);
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index f73f787259..ff052c75be 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -42,6 +42,8 @@ CFeeRate payTxFee(DEFAULT_TRANSACTION_FEE);
 unsigned int nTxConfirmTarget = DEFAULT_TX_CONFIRM_TARGET;
 bool bSpendZeroConfChange = DEFAULT_SPEND_ZEROCONF_CHANGE;
 bool fWalletRbf = DEFAULT_WALLET_RBF;
+OutputType g_address_type = OUTPUT_TYPE_NONE;
+OutputType g_change_type = OUTPUT_TYPE_NONE;
 
 const char * DEFAULT_WALLET_DAT = "wallet.dat";
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
@@ -832,8 +834,8 @@ bool CWallet::GetAccountDestination(CTxDestination &dest, std::string strAccount
         if (!account.vchPubKey.IsValid())
             bForceNew = true;
         else {
-            // Check if the current key has been used
-            CScript scriptPubKey = GetScriptForDestination(account.vchPubKey.GetID());
+            // Check if the current key has been used (TODO: check other addresses with the same key)
+            CScript scriptPubKey = GetScriptForDestination(GetDestinationForKey(account.vchPubKey, g_address_type));
             for (std::map<uint256, CWalletTx>::iterator it = mapWallet.begin();
                  it != mapWallet.end() && account.vchPubKey.IsValid();
                  ++it)
@@ -850,11 +852,12 @@ bool CWallet::GetAccountDestination(CTxDestination &dest, std::string strAccount
         if (!GetKeyFromPool(account.vchPubKey, false))
             return false;
 
-        dest = account.vchPubKey.GetID();
+        LearnRelatedScripts(account.vchPubKey, g_address_type);
+        dest = GetDestinationForKey(account.vchPubKey, g_address_type);
         SetAddressBook(dest, strAccount, "receive");
         walletdb.WriteAccount(strAccount, account);
     } else {
-        dest = account.vchPubKey.GetID();
+        dest = GetDestinationForKey(account.vchPubKey, g_address_type);
     }
 
     return true;
@@ -2743,7 +2746,8 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                     return false;
                 }
 
-                scriptChange = GetScriptForDestination(vchPubKey.GetID());
+                LearnRelatedScripts(vchPubKey, g_change_type);
+                scriptChange = GetScriptForDestination(GetDestinationForKey(vchPubKey, g_change_type));
             }
             CTxOut change_prototype_txout(0, scriptChange);
             size_t change_prototype_size = GetSerializeSize(change_prototype_txout, SER_DISK, 0);
@@ -4136,3 +4140,106 @@ bool CWalletTx::AcceptToMemoryPool(const CAmount& nAbsurdFee, CValidationState&
     fInMempool = ret;
     return ret;
 }
+
+static const std::string OUTPUT_TYPE_STRING_LEGACY = "legacy";
+static const std::string OUTPUT_TYPE_STRING_P2SH_SEGWIT = "p2sh-segwit";
+static const std::string OUTPUT_TYPE_STRING_BECH32 = "bech32";
+
+OutputType ParseOutputType(const std::string& type, OutputType default_type)
+{
+    if (type.empty()) {
+        return default_type;
+    } else if (type == OUTPUT_TYPE_STRING_LEGACY) {
+        return OUTPUT_TYPE_LEGACY;
+    } else if (type == OUTPUT_TYPE_STRING_P2SH_SEGWIT) {
+        return OUTPUT_TYPE_P2SH_SEGWIT;
+    } else if (type == OUTPUT_TYPE_STRING_BECH32) {
+        return OUTPUT_TYPE_BECH32;
+    } else {
+        return OUTPUT_TYPE_NONE;
+    }
+}
+
+const std::string& FormatOutputType(OutputType type)
+{
+    switch (type) {
+    case OUTPUT_TYPE_LEGACY: return OUTPUT_TYPE_STRING_LEGACY;
+    case OUTPUT_TYPE_P2SH_SEGWIT: return OUTPUT_TYPE_STRING_P2SH_SEGWIT;
+    case OUTPUT_TYPE_BECH32: return OUTPUT_TYPE_STRING_BECH32;
+    default: assert(false);
+    }
+}
+
+void CWallet::LearnRelatedScripts(const CPubKey& key, OutputType type)
+{
+    if (key.IsCompressed() && (type == OUTPUT_TYPE_P2SH_SEGWIT || type == OUTPUT_TYPE_BECH32)) {
+        CTxDestination witdest = WitnessV0KeyHash(key.GetID());
+        CScript witprog = GetScriptForDestination(witdest);
+        // Make sure the resulting program is solvable.
+        assert(IsSolvable(*this, witprog));
+        AddCScript(witprog);
+    }
+}
+
+void CWallet::LearnAllRelatedScripts(const CPubKey& key)
+{
+    // OUTPUT_TYPE_P2SH_SEGWIT always adds all necessary scripts for all types.
+    LearnRelatedScripts(key, OUTPUT_TYPE_P2SH_SEGWIT);
+}
+
+CTxDestination GetDestinationForKey(const CPubKey& key, OutputType type)
+{
+    switch (type) {
+    case OUTPUT_TYPE_LEGACY: return key.GetID();
+    case OUTPUT_TYPE_P2SH_SEGWIT:
+    case OUTPUT_TYPE_BECH32: {
+        if (!key.IsCompressed()) return key.GetID();
+        CTxDestination witdest = WitnessV0KeyHash(key.GetID());
+        CScript witprog = GetScriptForDestination(witdest);
+        if (type == OUTPUT_TYPE_P2SH_SEGWIT) {
+            return CScriptID(witprog);
+        } else {
+            return witdest;
+        }
+    }
+    default: assert(false);
+    }
+}
+
+std::vector<CTxDestination> GetAllDestinationsForKey(const CPubKey& key)
+{
+    CKeyID keyid = key.GetID();
+    if (key.IsCompressed()) {
+        CTxDestination segwit = WitnessV0KeyHash(keyid);
+        CTxDestination p2sh = CScriptID(GetScriptForDestination(segwit));
+        return std::vector<CTxDestination>{std::move(keyid), std::move(p2sh), std::move(segwit)};
+    } else {
+        return std::vector<CTxDestination>{std::move(keyid)};
+    }
+}
+
+CTxDestination CWallet::AddAndGetDestinationForScript(const CScript& script, OutputType type)
+{
+    // Note that scripts over 520 bytes are not yet supported.
+    switch (type) {
+    case OUTPUT_TYPE_LEGACY:
+        return CScriptID(script);
+    case OUTPUT_TYPE_P2SH_SEGWIT:
+    case OUTPUT_TYPE_BECH32: {
+        WitnessV0ScriptHash hash;
+        CSHA256().Write(script.data(), script.size()).Finalize(hash.begin());
+        CTxDestination witdest = hash;
+        CScript witprog = GetScriptForDestination(witdest);
+        // Check if the resulting program is solvable (i.e. doesn't use an uncompressed key)
+        if (!IsSolvable(*this, witprog)) return CScriptID(script);
+        // Add the redeemscript, so that P2WSH and P2SH-P2WSH outputs are recognized as ours.
+        AddCScript(witprog);
+        if (type == OUTPUT_TYPE_BECH32) {
+            return witdest;
+        } else {
+            return CScriptID(witprog);
+        }
+    }
+    default: assert(false);
+    }
+}
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index e64ea2534a..4088ed1985 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -99,6 +99,19 @@ enum WalletFeature
     FEATURE_LATEST = FEATURE_COMPRPUBKEY // HD is optional, use FEATURE_COMPRPUBKEY as latest version
 };
 
+enum OutputType
+{
+    OUTPUT_TYPE_NONE,
+    OUTPUT_TYPE_LEGACY,
+    OUTPUT_TYPE_P2SH_SEGWIT,
+    OUTPUT_TYPE_BECH32,
+
+    OUTPUT_TYPE_DEFAULT = OUTPUT_TYPE_P2SH_SEGWIT
+};
+
+extern OutputType g_address_type;
+extern OutputType g_change_type;
+
 
 /** A key pool entry */
 class CKeyPool
@@ -1129,6 +1142,26 @@ public:
      * deadlock
      */
     void BlockUntilSyncedToCurrentChain();
+
+    /**
+     * Explicitly make the wallet learn the related scripts for outputs to the
+     * given key. This is purely to make the wallet file compatible with older
+     * software, as CBasicKeyStore automatically does this implicitly for all
+     * keys now.
+     */
+    void LearnRelatedScripts(const CPubKey& key, OutputType);
+
+    /**
+     * Same as LearnRelatedScripts, but when the OutputType is not known (and could
+     * be anything).
+     */
+    void LearnAllRelatedScripts(const CPubKey& key);
+
+    /**
+     * Get a destination of the requested type (if possible) to the specified script.
+     * This function will automatically add the necessary scripts to the wallet.
+     */
+    CTxDestination AddAndGetDestinationForScript(const CScript& script, OutputType);
 };
 
 /** A key allocated from the key pool. */
@@ -1218,4 +1251,16 @@ bool CWallet::DummySignTx(CMutableTransaction &txNew, const ContainerType &coins
     return true;
 }
 
+OutputType ParseOutputType(const std::string& str, OutputType default_type = OUTPUT_TYPE_DEFAULT);
+const std::string& FormatOutputType(OutputType type);
+
+/**
+ * Get a destination of the requested type (if possible) to the specified key.
+ * The caller must make sure LearnRelatedScripts has been called beforehand.
+ */
+CTxDestination GetDestinationForKey(const CPubKey& key, OutputType);
+
+/** Get all destinations (potentially) supported by the wallet for the given key. */
+std::vector<CTxDestination> GetAllDestinationsForKey(const CPubKey& key);
+
 #endif // BITCOIN_WALLET_WALLET_H