New createmultisig rpc command

This is to support the signrawtransaction API call; given the public
keys involved in a multisig transaction, this gives back the redeemScript
needed to sign it.

src/bitcoinrpc.cpp

@@ -234,6 +234,7 @@ static const CRPCCommand vRPCCommands[] =
     { "sendfrom",               &sendfrom,               false,  false },
     { "sendmany",               &sendmany,               false,  false },
     { "addmultisigaddress",     &addmultisigaddress,     false,  false },
+    { "createmultisig",         &createmultisig,         true,   true  },
     { "getrawmempool",          &getrawmempool,          true,   false },
     { "getblock",               &getblock,               false,  false },
     { "getblockhash",           &getblockhash,           false,  false },
@@ -1160,6 +1161,8 @@ Array RPCConvertValues(const std::string &strMethod, const std::vector<std::stri
     if (strMethod == "sendmany"               && n > 2) ConvertTo<boost::int64_t>(params[2]);
     if (strMethod == "addmultisigaddress"     && n > 0) ConvertTo<boost::int64_t>(params[0]);
     if (strMethod == "addmultisigaddress"     && n > 1) ConvertTo<Array>(params[1]);
+    if (strMethod == "createmultisig"         && n > 0) ConvertTo<boost::int64_t>(params[0]);
+    if (strMethod == "createmultisig"         && n > 1) ConvertTo<Array>(params[1]);
     if (strMethod == "listunspent"            && n > 0) ConvertTo<boost::int64_t>(params[0]);
     if (strMethod == "listunspent"            && n > 1) ConvertTo<boost::int64_t>(params[1]);
     if (strMethod == "listunspent"            && n > 2) ConvertTo<Array>(params[2]);

src/bitcoinrpc.h

@@ -158,6 +158,7 @@ extern json_spirit::Value movecmd(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value sendfrom(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value sendmany(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value addmultisigaddress(const json_spirit::Array& params, bool fHelp);
+extern json_spirit::Value createmultisig(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value listreceivedbyaddress(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value listreceivedbyaccount(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value listtransactions(const json_spirit::Array& params, bool fHelp);

src/rpcwallet.cpp

@@ -702,22 +702,13 @@ Value sendmany(const Array& params, bool fHelp)
     return wtx.GetHash().GetHex();
 }
 
-Value addmultisigaddress(const Array& params, bool fHelp)
+//
+// Used by addmultisigaddress / createmultisig:
+//
+static CScript _createmultisig(const Array& params)
 {
-    if (fHelp || params.size() < 2 || params.size() > 3)
-    {
-        string msg = "addmultisigaddress <nrequired> <'[\"key\",\"key\"]'> [account]\n"
-            "Add a nrequired-to-sign multisignature address to the wallet\"\n"
-            "each key is a Bitcoin address or hex-encoded public key\n"
-            "If [account] is specified, assign address to [account].";
-        throw runtime_error(msg);
-    }
-
     int nRequired = params[0].get_int();
     const Array& keys = params[1].get_array();
-    string strAccount;
-    if (params.size() > 2)
-        strAccount = AccountFromValue(params[2]);
 
     // Gather public keys
     if (nRequired < 1)
@@ -760,10 +751,28 @@ Value addmultisigaddress(const Array& params, bool fHelp)
             throw runtime_error(" Invalid public key: "+ks);
         }
     }
+    CScript result;
+    result.SetMultisig(nRequired, pubkeys);
+    return result;
+}
+
+Value addmultisigaddress(const Array& params, bool fHelp)
+{
+    if (fHelp || params.size() < 2 || params.size() > 3)
+    {
+        string msg = "addmultisigaddress <nrequired> <'[\"key\",\"key\"]'> [account]\n"
+            "Add a nrequired-to-sign multisignature address to the wallet\"\n"
+            "each key is a Bitcoin address or hex-encoded public key\n"
+            "If [account] is specified, assign address to [account].";
+        throw runtime_error(msg);
+    }
+
+    string strAccount;
+    if (params.size() > 2)
+        strAccount = AccountFromValue(params[2]);
 
     // Construct using pay-to-script-hash:
-    CScript inner;
-    inner.SetMultisig(nRequired, pubkeys);
+    CScript inner = _createmultisig(params);
     CScriptID innerID = inner.GetID();
     pwalletMain->AddCScript(inner);
 
@@ -771,6 +780,30 @@ Value addmultisigaddress(const Array& params, bool fHelp)
     return CBitcoinAddress(innerID).ToString();
 }
 
+Value createmultisig(const Array& params, bool fHelp)
+{
+    if (fHelp || params.size() < 2 || params.size() > 2)
+    {
+        string msg = "createmultisig <nrequired> <'[\"key\",\"key\"]'>\n"
+            "Creates a multi-signature address and returns a json object\n"
+            "with keys:\n"
+            "address : bitcoin address\n"
+            "redeemScript : hex-encoded redemption script";
+        throw runtime_error(msg);
+    }
+
+    // Construct using pay-to-script-hash:
+    CScript inner = _createmultisig(params);
+    CScriptID innerID = inner.GetID();
+    CBitcoinAddress address(innerID);
+
+    Object result;
+    result.push_back(Pair("address", address.ToString()));
+    result.push_back(Pair("redeemScript", HexStr(inner.begin(), inner.end())));
+
+    return result;
+}
+
 
 struct tallyitem
 {