Refactor analyzepsbt for use outside RPC code

Refactor the analyzepsbt RPC into (1) an AnalyzePSBT function, which returns
its output as a new strongly-typed PSBTAnalysis struct, and (2) a thin wrapper
which converts the struct into a UniValue for RPC use.

3 files changed, 213 insertions, 130 deletions

diff --git a/src/psbt.cpp b/src/psbt.cpp
index 734e7897ec..184129e330 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -2,9 +2,14 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <coins.h>
+#include <consensus/tx_verify.h>
+#include <policy/policy.h>
 #include <psbt.h>
 #include <util/strencodings.h>
 
+#include <numeric>
+
 PartiallySignedTransaction::PartiallySignedTransaction(const CMutableTransaction& tx) : tx(tx)
 {
     inputs.resize(tx.vin.size());
@@ -205,7 +210,7 @@ void PSBTOutput::Merge(const PSBTOutput& output)
     if (redeem_script.empty() && !output.redeem_script.empty()) redeem_script = output.redeem_script;
     if (witness_script.empty() && !output.witness_script.empty()) witness_script = output.witness_script;
 }
-bool PSBTInputSigned(PSBTInput& input)
+bool PSBTInputSigned(const PSBTInput& input)
 {
     return !input.final_script_sig.empty() || !input.final_script_witness.IsNull();
 }
@@ -326,6 +331,138 @@ TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector
     return TransactionError::OK;
 }
 
+std::string PSBTRoleName(PSBTRole role) {
+    switch (role) {
+    case PSBTRole::UPDATER: return "updater";
+    case PSBTRole::SIGNER: return "signer";
+    case PSBTRole::FINALIZER: return "finalizer";
+    case PSBTRole::EXTRACTOR: return "extractor";
+    }
+}
+
+PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
+{
+    // Go through each input and build status
+    PSBTAnalysis result;
+
+    bool calc_fee = true;
+    bool all_final = true;
+    bool only_missing_sigs = true;
+    bool only_missing_final = false;
+    CAmount in_amt = 0;
+
+    result.inputs.resize(psbtx.tx->vin.size());
+
+    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
+        PSBTInput& input = psbtx.inputs[i];
+        PSBTInputAnalysis& input_analysis = result.inputs[i];
+
+        // Check for a UTXO
+        CTxOut utxo;
+        if (psbtx.GetInputUTXO(utxo, i)) {
+            in_amt += utxo.nValue;
+            input_analysis.has_utxo = true;
+        } else {
+            input_analysis.has_utxo = false;
+            input_analysis.is_final = false;
+            input_analysis.next = PSBTRole::UPDATER;
+            calc_fee = false;
+        }
+
+        // Check if it is final
+        if (!utxo.IsNull() && !PSBTInputSigned(input)) {
+            input_analysis.is_final = false;
+            all_final = false;
+
+            // Figure out what is missing
+            SignatureData outdata;
+            bool complete = SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, 1, &outdata);
+
+            // Things are missing
+            if (!complete) {
+                input_analysis.missing_pubkeys = outdata.missing_pubkeys;
+                input_analysis.missing_redeem_script = outdata.missing_redeem_script;
+                input_analysis.missing_witness_script = outdata.missing_witness_script;
+                input_analysis.missing_sigs = outdata.missing_sigs;
+
+                // If we are only missing signatures and nothing else, then next is signer
+                if (outdata.missing_pubkeys.empty() && outdata.missing_redeem_script.IsNull() && outdata.missing_witness_script.IsNull() && !outdata.missing_sigs.empty()) {
+                    input_analysis.next = PSBTRole::SIGNER;
+                } else {
+                    only_missing_sigs = false;
+                    input_analysis.next = PSBTRole::UPDATER;
+                }
+            } else {
+                only_missing_final = true;
+                input_analysis.next = PSBTRole::FINALIZER;
+            }
+        } else if (!utxo.IsNull()){
+            input_analysis.is_final = true;
+        }
+    }
+
+    if (all_final) {
+        only_missing_sigs = false;
+        result.next = PSBTRole::EXTRACTOR;
+    }
+    if (calc_fee) {
+        // Get the output amount
+        CAmount out_amt = std::accumulate(psbtx.tx->vout.begin(), psbtx.tx->vout.end(), CAmount(0),
+            [](CAmount a, const CTxOut& b) {
+                return a += b.nValue;
+            }
+        );
+
+        // Get the fee
+        CAmount fee = in_amt - out_amt;
+        result.fee = fee;
+
+        // Estimate the size
+        CMutableTransaction mtx(*psbtx.tx);
+        CCoinsView view_dummy;
+        CCoinsViewCache view(&view_dummy);
+        bool success = true;
+
+        for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
+            PSBTInput& input = psbtx.inputs[i];
+            Coin newcoin;
+
+            if (!SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, 1, nullptr, true) || !psbtx.GetInputUTXO(newcoin.out, i)) {
+                success = false;
+                break;
+            } else {
+                mtx.vin[i].scriptSig = input.final_script_sig;
+                mtx.vin[i].scriptWitness = input.final_script_witness;
+                newcoin.nHeight = 1;
+                view.AddCoin(psbtx.tx->vin[i].prevout, std::move(newcoin), true);
+            }
+        }
+
+        if (success) {
+            CTransaction ctx = CTransaction(mtx);
+            size_t size = GetVirtualTransactionSize(ctx, GetTransactionSigOpCost(ctx, view, STANDARD_SCRIPT_VERIFY_FLAGS));
+            result.estimated_vsize = size;
+            // Estimate fee rate
+            CFeeRate feerate(fee, size);
+            result.estimated_feerate = feerate;
+        }
+
+        if (only_missing_sigs) {
+            result.next = PSBTRole::SIGNER;
+        } else if (only_missing_final) {
+            result.next = PSBTRole::FINALIZER;
+        } else if (all_final) {
+            result.next = PSBTRole::EXTRACTOR;
+        } else {
+            result.next = PSBTRole::UPDATER;
+        }
+    } else {
+        result.next = PSBTRole::UPDATER;
+    }
+
+    return result;
+}
+
 bool DecodeBase64PSBT(PartiallySignedTransaction& psbt, const std::string& base64_tx, std::string& error)
 {
     bool invalid;
diff --git a/src/psbt.h b/src/psbt.h
index d89fd68c21..0f17a71a44 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -7,6 +7,8 @@
 
 #include <attributes.h>
 #include <node/transaction.h>
+#include <optional.h>
+#include <policy/feerate.h>
 #include <primitives/transaction.h>
 #include <pubkey.h>
 #include <script/sign.h>
@@ -548,8 +550,36 @@ struct PartiallySignedTransaction
     }
 };
 
+enum class PSBTRole {
+    UPDATER,
+    SIGNER,
+    FINALIZER,
+    EXTRACTOR
+};
+
+struct PSBTInputAnalysis {
+    bool has_utxo;
+    bool is_final;
+    PSBTRole next;
+
+    std::vector<CKeyID> missing_pubkeys;
+    std::vector<CKeyID> missing_sigs;
+    uint160 missing_redeem_script;
+    uint256 missing_witness_script;
+};
+
+struct PSBTAnalysis {
+    Optional<size_t> estimated_vsize;
+    Optional<CFeeRate> estimated_feerate;
+    Optional<CAmount> fee;
+    std::vector<PSBTInputAnalysis> inputs;
+    PSBTRole next;
+};
+
+std::string PSBTRoleName(PSBTRole role);
+
 /** Checks whether a PSBTInput is already signed. */
-bool PSBTInputSigned(PSBTInput& input);
+bool PSBTInputSigned(const PSBTInput& input);
 
 /** Signs a PSBTInput, verifying that all provided data matches what is being signed. */
 bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction& psbt, int index, int sighash = SIGHASH_ALL, SignatureData* out_sigdata = nullptr, bool use_dummy = false);
@@ -580,6 +610,14 @@ bool FinalizeAndExtractPSBT(PartiallySignedTransaction& psbtx, CMutableTransacti
  */
 NODISCARD TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector<PartiallySignedTransaction>& psbtxs);
 
+/**
+ * Provides helpful miscellaneous information about where a PSBT is in the signing workflow.
+ *
+ * @param[in] psbtx the PSBT to analyze
+ * @return A PSBTAnalysis with information about the provided PSBT.
+ */
+PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx);
+
 //! Decode a base64ed PSBT into a PartiallySignedTransaction
 NODISCARD bool DecodeBase64PSBT(PartiallySignedTransaction& decoded_psbt, const std::string& base64_psbt, std::string& error);
 //! Decode a raw (binary blob) PSBT into a PartiallySignedTransaction
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index 71acdbfb99..7dd8abc193 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1895,148 +1895,56 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
     }
 
-    // Go through each input and build status
+    PSBTAnalysis psbta = AnalyzePSBT(psbtx);
+
     UniValue result(UniValue::VOBJ);
     UniValue inputs_result(UniValue::VARR);
-    bool calc_fee = true;
-    bool all_final = true;
-    bool only_missing_sigs = true;
-    bool only_missing_final = false;
-    CAmount in_amt = 0;
-    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
-        PSBTInput& input = psbtx.inputs[i];
+    for (const auto& input : psbta.inputs) {
         UniValue input_univ(UniValue::VOBJ);
         UniValue missing(UniValue::VOBJ);
 
-        // Check for a UTXO
-        CTxOut utxo;
-        if (psbtx.GetInputUTXO(utxo, i)) {
-            in_amt += utxo.nValue;
-            input_univ.pushKV("has_utxo", true);
-        } else {
-            input_univ.pushKV("has_utxo", false);
-            input_univ.pushKV("is_final", false);
-            input_univ.pushKV("next", "updater");
-            calc_fee = false;
-        }
+        input_univ.pushKV("has_utxo", input.has_utxo);
+        input_univ.pushKV("is_final", input.is_final);
+        input_univ.pushKV("next", PSBTRoleName(input.next));
 
-        // Check if it is final
-        if (!utxo.IsNull() && !PSBTInputSigned(input)) {
-            input_univ.pushKV("is_final", false);
-            all_final = false;
-
-            // Figure out what is missing
-            SignatureData outdata;
-            bool complete = SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, 1, &outdata);
-
-            // Things are missing
-            if (!complete) {
-                if (!outdata.missing_pubkeys.empty()) {
-                    // Missing pubkeys
-                    UniValue missing_pubkeys_univ(UniValue::VARR);
-                    for (const CKeyID& pubkey : outdata.missing_pubkeys) {
-                        missing_pubkeys_univ.push_back(HexStr(pubkey));
-                    }
-                    missing.pushKV("pubkeys", missing_pubkeys_univ);
-                }
-                if (!outdata.missing_redeem_script.IsNull()) {
-                    // Missing redeemScript
-                    missing.pushKV("redeemscript", HexStr(outdata.missing_redeem_script));
-                }
-                if (!outdata.missing_witness_script.IsNull()) {
-                    // Missing witnessScript
-                    missing.pushKV("witnessscript", HexStr(outdata.missing_witness_script));
-                }
-                if (!outdata.missing_sigs.empty()) {
-                    // Missing sigs
-                    UniValue missing_sigs_univ(UniValue::VARR);
-                    for (const CKeyID& pubkey : outdata.missing_sigs) {
-                        missing_sigs_univ.push_back(HexStr(pubkey));
-                    }
-                    missing.pushKV("signatures", missing_sigs_univ);
-                }
-                input_univ.pushKV("missing", missing);
-
-                // If we are only missing signatures and nothing else, then next is signer
-                if (outdata.missing_pubkeys.empty() && outdata.missing_redeem_script.IsNull() && outdata.missing_witness_script.IsNull() && !outdata.missing_sigs.empty()) {
-                    input_univ.pushKV("next", "signer");
-                } else {
-                    only_missing_sigs = false;
-                    input_univ.pushKV("next", "updater");
-                }
-            } else {
-                only_missing_final = true;
-                input_univ.pushKV("next", "finalizer");
+        if (!input.missing_pubkeys.empty()) {
+            UniValue missing_pubkeys_univ(UniValue::VARR);
+            for (const CKeyID& pubkey : input.missing_pubkeys) {
+                missing_pubkeys_univ.push_back(HexStr(pubkey));
             }
-        } else if (!utxo.IsNull()){
-            input_univ.pushKV("is_final", true);
+            missing.pushKV("pubkeys", missing_pubkeys_univ);
+        }
+        if (!input.missing_redeem_script.IsNull()) {
+            missing.pushKV("redeemscript", HexStr(input.missing_redeem_script));
+        }
+        if (!input.missing_witness_script.IsNull()) {
+            missing.pushKV("witnessscript", HexStr(input.missing_witness_script));
+        }
+        if (!input.missing_sigs.empty()) {
+            UniValue missing_sigs_univ(UniValue::VARR);
+            for (const CKeyID& pubkey : input.missing_sigs) {
+                missing_sigs_univ.push_back(HexStr(pubkey));
+            }
+            missing.pushKV("signatures", missing_sigs_univ);
+        }
+        if (!missing.getKeys().empty()) {
+            input_univ.pushKV("missing", missing);
         }
         inputs_result.push_back(input_univ);
     }
     result.pushKV("inputs", inputs_result);
 
-    if (all_final) {
-        only_missing_sigs = false;
-        result.pushKV("next", "extractor");
+    if (psbta.estimated_vsize != nullopt) {
+        result.pushKV("estimated_vsize", (int)*psbta.estimated_vsize);
     }
-    if (calc_fee) {
-        // Get the output amount
-        CAmount out_amt = std::accumulate(psbtx.tx->vout.begin(), psbtx.tx->vout.end(), CAmount(0),
-            [](CAmount a, const CTxOut& b) {
-                return a += b.nValue;
-            }
-        );
-
-        // Get the fee
-        CAmount fee = in_amt - out_amt;
-
-        // Estimate the size
-        CMutableTransaction mtx(*psbtx.tx);
-        CCoinsView view_dummy;
-        CCoinsViewCache view(&view_dummy);
-        bool success = true;
-
-        for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
-            PSBTInput& input = psbtx.inputs[i];
-            if (SignPSBTInput(DUMMY_SIGNING_PROVIDER, psbtx, i, 1, nullptr, true)) {
-                mtx.vin[i].scriptSig = input.final_script_sig;
-                mtx.vin[i].scriptWitness = input.final_script_witness;
-
-                Coin newcoin;
-                if (!psbtx.GetInputUTXO(newcoin.out, i)) {
-                    success = false;
-                    break;
-                }
-                newcoin.nHeight = 1;
-                view.AddCoin(psbtx.tx->vin[i].prevout, std::move(newcoin), true);
-            } else {
-                success = false;
-                break;
-            }
-        }
-
-        if (success) {
-            CTransaction ctx = CTransaction(mtx);
-            size_t size = GetVirtualTransactionSize(ctx, GetTransactionSigOpCost(ctx, view, STANDARD_SCRIPT_VERIFY_FLAGS));
-            result.pushKV("estimated_vsize", (int)size);
-            // Estimate fee rate
-            CFeeRate feerate(fee, size);
-            result.pushKV("estimated_feerate", ValueFromAmount(feerate.GetFeePerK()));
-        }
-        result.pushKV("fee", ValueFromAmount(fee));
-
-        if (only_missing_sigs) {
-            result.pushKV("next", "signer");
-        } else if (only_missing_final) {
-            result.pushKV("next", "finalizer");
-        } else if (all_final) {
-            result.pushKV("next", "extractor");
-        } else {
-            result.pushKV("next", "updater");
-        }
-    } else {
-        result.pushKV("next", "updater");
+    if (psbta.estimated_feerate != nullopt) {
+        result.pushKV("estimated_feerate", ValueFromAmount(psbta.estimated_feerate->GetFeePerK()));
     }
+    if (psbta.fee != nullopt) {
+        result.pushKV("fee", ValueFromAmount(*psbta.fee));
+    }
+    result.pushKV("next", PSBTRoleName(psbta.next));
+
     return result;
 }