From 9d5d781a15162f3a146da01e2d01940e0e9ba82f Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Fri, 4 Mar 2022 21:36:24 +0000
Subject: [PATCH] libzcash_script: Add more granular errors to the new APIs

---
 src/script/zcash_script.cpp | 42 +++++++++++++++++++++++--------------
 src/script/zcash_script.h   |  1 +
 2 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/src/script/zcash_script.cpp b/src/script/zcash_script.cpp
index ff71289a8..edd457d55 100644
--- a/src/script/zcash_script.cpp
+++ b/src/script/zcash_script.cpp
@@ -134,30 +134,30 @@ void* zcash_script_new_precomputed_tx_v5(
     unsigned int allPrevOutputsLen,
     zcash_script_error* err)
 {
+    CTransaction tx;
     try {
         TxInputStream stream(SER_NETWORK, PROTOCOL_VERSION, txTo, txToLen);
-        CTransaction tx;
         stream >> tx;
         if (GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION) != txToLen) {
             set_error(err, zcash_script_ERR_TX_SIZE_MISMATCH);
             return nullptr;
         }
-
-        try {
-            auto preTx = new PrecomputedTransaction(tx, allPrevOutputs, allPrevOutputsLen);
-            // Deserializing the tx did not error.
-            set_error(err, zcash_script_ERR_OK);
-            return preTx;
-        } catch (const std::exception&) {
-            // We had some error when parsing allPrevOutputs inside the
-            // PrecomputedTransactionData constructor.
-            set_error(err, zcash_script_ERR_ALL_PREV_OUTPUTS_DESERIALIZE);
-            return nullptr;
-        }
     } catch (const std::exception&) {
         set_error(err, zcash_script_ERR_TX_DESERIALIZE); // Error deserializing
         return nullptr;
     }
+
+    try {
+        auto preTx = new PrecomputedTransaction(tx, allPrevOutputs, allPrevOutputsLen);
+        // Deserializing the tx did not error.
+        set_error(err, zcash_script_ERR_OK);
+        return preTx;
+    } catch (const std::exception&) {
+        // We had some error when parsing allPrevOutputs inside the
+        // PrecomputedTransactionData constructor.
+        set_error(err, zcash_script_ERR_ALL_PREV_OUTPUTS_DESERIALIZE);
+        return nullptr;
+    }
 }
 
 void zcash_script_free_precomputed_tx(void* pre_preTx)
@@ -239,15 +239,20 @@ int zcash_script_verify_v5(
     uint32_t consensusBranchId,
     zcash_script_error* err)
 {
+    CTransaction tx;
     try {
         TxInputStream stream(SER_NETWORK, PROTOCOL_VERSION, txTo, txToLen);
-        CTransaction tx;
         stream >> tx;
         if (nIn >= tx.vin.size())
             return set_error(err, zcash_script_ERR_TX_INDEX);
         if (GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION) != txToLen)
             return set_error(err, zcash_script_ERR_TX_SIZE_MISMATCH);
+    } catch (const std::exception&) {
+        return set_error(err, zcash_script_ERR_TX_DESERIALIZE); // Error deserializing
+    }
 
+    std::vector<CTxOut> prevOutputs;
+    try {
         // TODO: we can swap this second deserialization for an FFI call by
         // fetching this through PrecomputedTransactionData. Simplicity for now.
         CDataStream sAllPrevOutputs(
@@ -255,12 +260,17 @@ int zcash_script_verify_v5(
             reinterpret_cast<const char*>(allPrevOutputs + allPrevOutputsLen),
             SER_NETWORK,
             PROTOCOL_VERSION);
-        std::vector<CTxOut> prevOutputs;
         sAllPrevOutputs >> prevOutputs;
         if (!(tx.IsCoinBase() ? prevOutputs.empty() : tx.vin.size() == prevOutputs.size())) {
             return set_error(err, zcash_script_ERR_ALL_PREV_OUTPUTS_SIZE_MISMATCH);
         }
+    } catch (const std::exception&) {
+        // We had some error when parsing allPrevOutputs inside the
+        // PrecomputedTransactionData constructor.
+        return set_error(err, zcash_script_ERR_ALL_PREV_OUTPUTS_DESERIALIZE);
+    }
 
+    try {
         // Regardless of the verification result, the tx did not error.
         set_error(err, zcash_script_ERR_OK);
         PrecomputedTransactionData txdata(tx, allPrevOutputs, allPrevOutputsLen);
@@ -272,7 +282,7 @@ int zcash_script_verify_v5(
             consensusBranchId,
             NULL);
     } catch (const std::exception&) {
-        return set_error(err, zcash_script_ERR_TX_DESERIALIZE); // Error deserializing
+        return set_error(err, zcash_script_ERR_VERIFY_SCRIPT); // Error during script verification
     }
 }
 
diff --git a/src/script/zcash_script.h b/src/script/zcash_script.h
index dd6bc4997..51ed657ea 100644
--- a/src/script/zcash_script.h
+++ b/src/script/zcash_script.h
@@ -45,6 +45,7 @@ typedef enum zcash_script_error_t
     zcash_script_ERR_TX_VERSION,
     zcash_script_ERR_ALL_PREV_OUTPUTS_SIZE_MISMATCH,
     zcash_script_ERR_ALL_PREV_OUTPUTS_DESERIALIZE,
+    zcash_script_ERR_VERIFY_SCRIPT,
 } zcash_script_error;
 
 /** Script verification flags */