Move transaction combining from signrawtransaction to new RPC

Create a combinerawtransaction RPC which accepts a json array of hex raw
transactions to combine them into one transaction. Signrawtransaction is changed
to no longer combine transactions and only accept one transaction at a time.

2 files changed, 101 insertions, 35 deletions

diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index 775ad4b6c9..d82e85f825 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -95,6 +95,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "signrawtransaction", 1, "prevtxs" },
     { "signrawtransaction", 2, "privkeys" },
     { "sendrawtransaction", 1, "allowhighfees" },
+    { "combinerawtransaction", 0, "txs" },
     { "fundrawtransaction", 1, "options" },
     { "gettxout", 1, "n" },
     { "gettxout", 2, "include_mempool" },
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index b878624df8..10886fea9f 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -554,6 +554,93 @@ static void TxInErrorToJSON(const CTxIn& txin, UniValue& vErrorsRet, const std::
     vErrorsRet.push_back(entry);
 }
 
+UniValue combinerawtransaction(const JSONRPCRequest& request)
+{
+
+    if (request.fHelp || request.params.size() != 1)
+        throw std::runtime_error(
+            "combinerawtransaction [\"hexstring\",...]\n"
+            "\nCombine multiple partially signed transactions into one transaction.\n"
+            "The combined transaction may be another partially signed transaction or a \n"
+            "fully signed transaction."
+
+            "\nArguments:\n"
+            "1. \"txs\"         (string) A json array of hex strings of partially signed transactions\n"
+            "    [\n"
+            "      \"hexstring\"     (string) A transaction hash\n"
+            "      ,...\n"
+            "    ]\n"
+
+            "\nResult:\n"
+            "\"hex\" : \"value\",           (string) The hex-encoded raw transaction with signature(s)\n"
+
+            "\nExamples:\n"
+            + HelpExampleCli("combinerawtransaction", "[\"myhex1\", \"myhex2\", \"myhex3\"]")
+        );
+
+
+    UniValue txs = request.params[0].get_array();
+    std::vector<CMutableTransaction> txVariants(txs.size());
+
+    for (unsigned int idx = 0; idx < txs.size(); idx++) {
+        if (!DecodeHexTx(txVariants[idx], txs[idx].get_str(), true)) {
+            throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed for tx %d", idx));
+        }
+    }
+
+    if (txVariants.empty()) {
+        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "Missing transactions");
+    }
+
+    // mergedTx will end up with all the signatures; it
+    // starts as a clone of the rawtx:
+    CMutableTransaction mergedTx(txVariants[0]);
+
+    // Fetch previous transactions (inputs):
+    CCoinsView viewDummy;
+    CCoinsViewCache view(&viewDummy);
+    {
+        LOCK(cs_main);
+        LOCK(mempool.cs);
+        CCoinsViewCache &viewChain = *pcoinsTip;
+        CCoinsViewMemPool viewMempool(&viewChain, mempool);
+        view.SetBackend(viewMempool); // temporarily switch cache backend to db+mempool view
+
+        for (const CTxIn& txin : mergedTx.vin) {
+            view.AccessCoin(txin.prevout); // Load entries from viewChain into view; can fail.
+        }
+
+        view.SetBackend(viewDummy); // switch back to avoid locking mempool for too long
+    }
+
+    // Use CTransaction for the constant parts of the
+    // transaction to avoid rehashing.
+    const CTransaction txConst(mergedTx);
+    // Sign what we can:
+    for (unsigned int i = 0; i < mergedTx.vin.size(); i++) {
+        CTxIn& txin = mergedTx.vin[i];
+        const Coin& coin = view.AccessCoin(txin.prevout);
+        if (coin.IsSpent()) {
+            throw JSONRPCError(RPC_VERIFY_ERROR, "Input not found or already spent");
+        }
+        const CScript& prevPubKey = coin.out.scriptPubKey;
+        const CAmount& amount = coin.out.nValue;
+
+        SignatureData sigdata;
+
+        // ... and merge in other signatures:
+        for (const CMutableTransaction& txv : txVariants) {
+            if (txv.vin.size() > i) {
+                sigdata = CombineSignatures(prevPubKey, TransactionSignatureChecker(&txConst, i, amount), sigdata, DataFromTransaction(txv, i));
+            }
+        }
+
+        UpdateTransaction(mergedTx, i, sigdata);
+    }
+
+    return EncodeHexTx(mergedTx);
+}
+
 UniValue signrawtransaction(const JSONRPCRequest& request)
 {
 #ifdef ENABLE_WALLET
@@ -626,26 +713,9 @@ UniValue signrawtransaction(const JSONRPCRequest& request)
 #endif
     RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VARR, UniValue::VARR, UniValue::VSTR}, true);
 
-    std::vector<unsigned char> txData(ParseHexV(request.params[0], "argument 1"));
-    CDataStream ssData(txData, SER_NETWORK, PROTOCOL_VERSION);
-    std::vector<CMutableTransaction> txVariants;
-    while (!ssData.empty()) {
-        try {
-            CMutableTransaction tx;
-            ssData >> tx;
-            txVariants.push_back(tx);
-        }
-        catch (const std::exception&) {
-            throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
-        }
-    }
-
-    if (txVariants.empty())
-        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "Missing transaction");
-
-    // mergedTx will end up with all the signatures; it
-    // starts as a clone of the rawtx:
-    CMutableTransaction mergedTx(txVariants[0]);
+    CMutableTransaction mtx;
+    if (!DecodeHexTx(mtx, request.params[0].get_str(), true))
+        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
 
     // Fetch previous transactions (inputs):
     CCoinsView viewDummy;
@@ -656,7 +726,7 @@ UniValue signrawtransaction(const JSONRPCRequest& request)
         CCoinsViewMemPool viewMempool(&viewChain, mempool);
         view.SetBackend(viewMempool); // temporarily switch cache backend to db+mempool view
 
-        for (const CTxIn& txin : mergedTx.vin) {
+        for (const CTxIn& txin : mtx.vin) {
             view.AccessCoin(txin.prevout); // Load entries from viewChain into view; can fail.
         }
 
@@ -781,10 +851,10 @@ UniValue signrawtransaction(const JSONRPCRequest& request)
 
     // Use CTransaction for the constant parts of the
     // transaction to avoid rehashing.
-    const CTransaction txConst(mergedTx);
+    const CTransaction txConst(mtx);
     // Sign what we can:
-    for (unsigned int i = 0; i < mergedTx.vin.size(); i++) {
-        CTxIn& txin = mergedTx.vin[i];
+    for (unsigned int i = 0; i < mtx.vin.size(); i++) {
+        CTxIn& txin = mtx.vin[i];
         const Coin& coin = view.AccessCoin(txin.prevout);
         if (coin.IsSpent()) {
             TxInErrorToJSON(txin, vErrors, "Input not found or already spent");
@@ -795,17 +865,11 @@ UniValue signrawtransaction(const JSONRPCRequest& request)
 
         SignatureData sigdata;
         // Only sign SIGHASH_SINGLE if there's a corresponding output:
-        if (!fHashSingle || (i < mergedTx.vout.size()))
-            ProduceSignature(MutableTransactionSignatureCreator(&keystore, &mergedTx, i, amount, nHashType), prevPubKey, sigdata);
+        if (!fHashSingle || (i < mtx.vout.size()))
+            ProduceSignature(MutableTransactionSignatureCreator(&keystore, &mtx, i, amount, nHashType), prevPubKey, sigdata);
+        sigdata = CombineSignatures(prevPubKey, TransactionSignatureChecker(&txConst, i, amount), sigdata, DataFromTransaction(mtx, i));
 
-        // ... and merge in other signatures:
-        for (const CMutableTransaction& txv : txVariants) {
-            if (txv.vin.size() > i) {
-                sigdata = CombineSignatures(prevPubKey, TransactionSignatureChecker(&txConst, i, amount), sigdata, DataFromTransaction(txv, i));
-            }
-        }
-
-        UpdateTransaction(mergedTx, i, sigdata);
+        UpdateTransaction(mtx, i, sigdata);
 
         ScriptError serror = SCRIPT_ERR_OK;
         if (!VerifyScript(txin.scriptSig, prevPubKey, &txin.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, TransactionSignatureChecker(&txConst, i, amount), &serror)) {
@@ -815,7 +879,7 @@ UniValue signrawtransaction(const JSONRPCRequest& request)
     bool fComplete = vErrors.empty();
 
     UniValue result(UniValue::VOBJ);
-    result.push_back(Pair("hex", EncodeHexTx(mergedTx)));
+    result.push_back(Pair("hex", EncodeHexTx(mtx)));
     result.push_back(Pair("complete", fComplete));
     if (!vErrors.empty()) {
         result.push_back(Pair("errors", vErrors));
@@ -905,6 +969,7 @@ static const CRPCCommand commands[] =
     { "rawtransactions",    "decoderawtransaction",   &decoderawtransaction,   true,  {"hexstring"} },
     { "rawtransactions",    "decodescript",           &decodescript,           true,  {"hexstring"} },
     { "rawtransactions",    "sendrawtransaction",     &sendrawtransaction,     false, {"hexstring","allowhighfees"} },
+    { "rawtransactions",    "combinerawtransaction",  &combinerawtransaction,  true,  {"txs"} },
     { "rawtransactions",    "signrawtransaction",     &signrawtransaction,     false, {"hexstring","prevtxs","privkeys","sighashtype"} }, /* uses wallet if enabled */
 
     { "blockchain",         "gettxoutproof",          &gettxoutproof,          true,  {"txids", "blockhash"} },