Create utility RPCs for PSBT

decodepsbt takes a PSBT and decodes it to JSON

combinepsbt takes multiple PSBTs for the same tx and combines them.

finalizepsbt takes a PSBT and finalizes the inputs. If all inputs
are final, it extracts the network serialized transaction and returns
that instead of a PSBT unless instructed otherwise.

createpsbt is like createrawtransaction but for PSBTs instead of
raw transactions.

convertpsbt takes a network serialized transaction and converts it
into a psbt. The resulting psbt will lose all signature data and
an explicit flag must be set to allow transactions with signature
data to be converted.

Author: achow101

src/core_io.h

@@ -14,6 +14,7 @@ class CBlock;
 class CScript;
 class CTransaction;
 struct CMutableTransaction;
+struct PartiallySignedTransaction;
 class uint256;
 class UniValue;
 
@@ -24,12 +25,15 @@ bool DecodeHexTx(CMutableTransaction& tx, const std::string& hex_tx, bool try_no
 bool DecodeHexBlk(CBlock&, const std::string& strHexBlk);
 uint256 ParseHashStr(const std::string&, const std::string& strName);
 std::vector<unsigned char> ParseHexUV(const UniValue& v, const std::string& strName);
+bool DecodePSBT(PartiallySignedTransaction& psbt, const std::string& base64_tx, std::string& error);
 
 // core_write.cpp
 UniValue ValueFromAmount(const CAmount& amount);
 std::string FormatScript(const CScript& script);
 std::string EncodeHexTx(const CTransaction& tx, const int serializeFlags = 0);
+std::string SighashToStr(unsigned char sighash_type);
 void ScriptPubKeyToUniv(const CScript& scriptPubKey, UniValue& out, bool fIncludeHex);
+void ScriptToUniv(const CScript& script, UniValue& out, bool include_address);
 void TxToUniv(const CTransaction& tx, const uint256& hashBlock, UniValue& entry, bool include_hex = true, int serialize_flags = 0);
 
 #endif // BITCOIN_CORE_IO_H

src/core_read.cpp

@@ -7,6 +7,7 @@
 #include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <script/script.h>
+#include <script/sign.h>
 #include <serialize.h>
 #include <streams.h>
 #include <univalue.h>
@@ -160,6 +161,23 @@ bool DecodeHexBlk(CBlock& block, const std::string& strHexBlk)
     return true;
 }
 
+bool DecodePSBT(PartiallySignedTransaction& psbt, const std::string& base64_tx, std::string& error)
+{
+    std::vector<unsigned char> tx_data = DecodeBase64(base64_tx.c_str());
+    CDataStream ss_data(tx_data, SER_NETWORK, PROTOCOL_VERSION);
+    try {
+        ss_data >> psbt;
+        if (!ss_data.empty()) {
+            error = "extra data after PSBT";
+            return false;
+        }
+    } catch (const std::exception& e) {
+        error = e.what();
+        return false;
+    }
+    return true;
+}
+
 uint256 ParseHashStr(const std::string& strHex, const std::string& strName)
 {
     if (!IsHex(strHex)) // Note: IsHex("") is false

src/core_write.cpp

@@ -70,6 +70,13 @@ const std::map<unsigned char, std::string> mapSigHashTypes = {
     {static_cast<unsigned char>(SIGHASH_SINGLE|SIGHASH_ANYONECANPAY), std::string("SINGLE|ANYONECANPAY")},
 };
 
+std::string SighashToStr(unsigned char sighash_type)
+{
+    const auto& it = mapSigHashTypes.find(sighash_type);
+    if (it == mapSigHashTypes.end()) return "";
+    return it->second;
+}
+
 /**
  * Create the assembly string representation of a CScript object.
  * @param[in] script    CScript object to convert into the asm string representation.
@@ -128,6 +135,22 @@ std::string EncodeHexTx(const CTransaction& tx, const int serializeFlags)
     return HexStr(ssTx.begin(), ssTx.end());
 }
 
+void ScriptToUniv(const CScript& script, UniValue& out, bool include_address)
+{
+    out.pushKV("asm", ScriptToAsmStr(script));
+    out.pushKV("hex", HexStr(script.begin(), script.end()));
+
+    std::vector<std::vector<unsigned char>> solns;
+    txnouttype type;
+    Solver(script, type, solns);
+    out.pushKV("type", GetTxnOutputType(type));
+
+    CTxDestination address;
+    if (include_address && ExtractDestination(script, address)) {
+        out.pushKV("address", EncodeDestination(address));
+    }
+}
+
 void ScriptPubKeyToUniv(const CScript& scriptPubKey,
                         UniValue& out, bool fIncludeHex)
 {

src/rpc/client.cpp

@@ -109,6 +109,14 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "combinerawtransaction", 0, "txs" },
     { "fundrawtransaction", 1, "options" },
     { "fundrawtransaction", 2, "iswitness" },
+    { "createpsbt", 0, "inputs" },
+    { "createpsbt", 1, "outputs" },
+    { "createpsbt", 2, "locktime" },
+    { "createpsbt", 3, "replaceable" },
+    { "combinepsbt", 0, "txs"},
+    { "finalizepsbt", 1, "extract"},
+    { "converttopsbt", 1, "permitsigdata"},
+    { "converttopsbt", 2, "iswitness"},
     { "gettxout", 1, "n" },
     { "gettxout", 2, "include_mempool" },
     { "gettxoutproof", 0, "txids" },