Merge #17853: [0.19] psbt: handle unspendable psbts

ca5f8deefd778195cb10a3419d3b5c0693abb958 Mark PSBTs spending unspendable outputs as invalid in analysis (Andrew Chow)
551583398ba4fdae973c047bc60556ffa17c6431 Have a PSBTAnalysis state that indicates invalid PSBT (Andrew Chow)

Pull request description:

  Backport of #17524

ACKs for top commit:
  achow101:
    ACK ca5f8deefd778195cb10a3419d3b5c0693abb958

Tree-SHA512: b5f2b951beb9477ac3176a0aade845654d2108ca3a9fbc72097ba4b4797df5419053d6b489bbaa03be08cb8cfdc37a83db8b7642ffa52d42b7aa8ea14aff39cc

5 files changed, 24 insertions, 1 deletions

diff --git a/src/node/psbt.cpp b/src/node/psbt.cpp
index 12559c5a5f..9a30c3f083 100644
--- a/src/node/psbt.cpp
+++ b/src/node/psbt.cpp
@@ -7,6 +7,7 @@
 #include <node/psbt.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
+#include <tinyformat.h>
 
 #include <numeric>
 
@@ -39,6 +40,11 @@ PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
             calc_fee = false;
         }
 
+        if (!utxo.IsNull() && utxo.scriptPubKey.IsUnspendable()) {
+            result.SetInvalid(strprintf("PSBT is not valid. Input %u spends unspendable output", i));
+            return result;
+        }
+
         // Check if it is final
         if (!utxo.IsNull() && !PSBTInputSigned(input)) {
             input_analysis.is_final = false;
diff --git a/src/node/psbt.h b/src/node/psbt.h
index e04366a20f..7384dc415c 100644
--- a/src/node/psbt.h
+++ b/src/node/psbt.h
@@ -30,6 +30,17 @@ struct PSBTAnalysis {
     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
+    std::string error;                     //!< Error message
+
+    void SetInvalid(std::string err_msg)
+    {
+        estimated_vsize = nullopt;
+        estimated_feerate = nullopt;
+        fee = nullopt;
+        inputs.clear();
+        next = PSBTRole::CREATOR;
+        error = err_msg;
+    }
 };
 
 /**
diff --git a/src/psbt.cpp b/src/psbt.cpp
index fe74002e82..20473429a4 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -349,6 +349,7 @@ TransactionError CombinePSBTs(PartiallySignedTransaction& out, const std::vector
 
 std::string PSBTRoleName(PSBTRole role) {
     switch (role) {
+    case PSBTRole::CREATOR: return "creator";
     case PSBTRole::UPDATER: return "updater";
     case PSBTRole::SIGNER: return "signer";
     case PSBTRole::FINALIZER: return "finalizer";
diff --git a/src/psbt.h b/src/psbt.h
index 6d77db0c6f..437b75d7cf 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -552,6 +552,7 @@ struct PartiallySignedTransaction
 };
 
 enum class PSBTRole {
+    CREATOR,
     UPDATER,
     SIGNER,
     FINALIZER,
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index f548d356cf..2fd6b9709f 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1671,6 +1671,7 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
                 "  \"estimated_feerate\" : feerate   (numeric, optional) Estimated feerate of the final signed transaction in " + CURRENCY_UNIT + "/kB. Shown only if all UTXO slots in the PSBT have been filled.\n"
                 "  \"fee\" : fee                     (numeric, optional) The transaction fee paid. Shown only if all UTXO slots in the PSBT have been filled.\n"
                 "  \"next\" : \"role\"                 (string) Role of the next person that this psbt needs to go to\n"
+                "  \"error\" : \"error\"               (string) Error message if there is one"
                 "}\n"
             },
             RPCExamples {
@@ -1723,7 +1724,7 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
         }
         inputs_result.push_back(input_univ);
     }
-    result.pushKV("inputs", inputs_result);
+    if (!inputs_result.empty()) result.pushKV("inputs", inputs_result);
 
     if (psbta.estimated_vsize != nullopt) {
         result.pushKV("estimated_vsize", (int)*psbta.estimated_vsize);
@@ -1735,6 +1736,9 @@ UniValue analyzepsbt(const JSONRPCRequest& request)
         result.pushKV("fee", ValueFromAmount(*psbta.fee));
     }
     result.pushKV("next", PSBTRoleName(psbta.next));
+    if (!psbta.error.empty()) {
+        result.pushKV("error", psbta.error);
+    }
 
     return result;
 }