[build] Move AnalyzePSBT from psbt.cpp to node/psbt.cpp

psbt.cpp definitions except for AnalyzePSBT are used by the wallet and need to
be linked into the wallet binary. AnalyzePSBT is an exception in that it is not
used by the wallet, and depends on node classes like CCoinsViewCache, and on
node global variables like nBytesPerSigOp.

So AnalyzePSBT is more at home in libbitcoin_server than libbitcoin_common, and
in any case needs to be defined in a separate object file than other PSBT
utilities, to avoid dragging link dependencies on node functions and global
variables into the wallet.

2 files changed, 177 insertions, 0 deletions

diff --git a/src/node/psbt.cpp b/src/node/psbt.cpp
new file mode 100644
index 0000000000..12559c5a5f
--- /dev/null
+++ b/src/node/psbt.cpp
@@ -0,0 +1,134 @@
+// Copyright (c) 2009-2018 The Bitcoin Core developers
+// 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 <node/psbt.h>
+#include <policy/policy.h>
+#include <policy/settings.h>
+
+#include <numeric>
+
+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;
+}
diff --git a/src/node/psbt.h b/src/node/psbt.h
new file mode 100644
index 0000000000..e04366a20f
--- /dev/null
+++ b/src/node/psbt.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_NODE_PSBT_H
+#define BITCOIN_NODE_PSBT_H
+
+#include <psbt.h>
+
+/**
+ * Holds an analysis of one input from a PSBT
+ */
+struct PSBTInputAnalysis {
+    bool has_utxo; //!< Whether we have UTXO information for this input
+    bool is_final; //!< Whether the input has all required information including signatures
+    PSBTRole next; //!< Which of the BIP 174 roles needs to handle this input next
+
+    std::vector<CKeyID> missing_pubkeys; //!< Pubkeys whose BIP32 derivation path is missing
+    std::vector<CKeyID> missing_sigs;    //!< Pubkeys whose signatures are missing
+    uint160 missing_redeem_script;       //!< Hash160 of redeem script, if missing
+    uint256 missing_witness_script;      //!< SHA256 of witness script, if missing
+};
+
+/**
+ * Holds the results of AnalyzePSBT (miscellaneous information about a PSBT)
+ */
+struct PSBTAnalysis {
+    Optional<size_t> estimated_vsize;      //!< Estimated weight of the transaction
+    Optional<CFeeRate> estimated_feerate;  //!< Estimated feerate (fee / weight) of the transaction
+    Optional<CAmount> fee;                 //!< Amount of fee being paid by the transaction
+    std::vector<PSBTInputAnalysis> inputs; //!< More information about the individual inputs of the transaction
+    PSBTRole next;                         //!< Which of the BIP 174 roles needs to handle the transaction next
+};
+
+/**
+ * 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);
+
+#endif // BITCOIN_NODE_PSBT_H