rpc: clarify ALREADY_IN_CHAIN rpc errors

When using `sendrawtransaction` the ALREADY_IN_CHAIN error help string
may be confusing.

Rename TransactionError::ALREADY_IN_CHAIN to
TransactionError::ALREADY_IN_UTXO_SET and update the rpc help string.

Remove backwards compatibility alias as no longer required.

src/common/messages.cpp

@@ -100,8 +100,8 @@ bilingual_str TransactionErrorString(const TransactionError err)
             return Untranslated("No error");
         case TransactionError::MISSING_INPUTS:
             return Untranslated("Inputs missing or spent");
-        case TransactionError::ALREADY_IN_CHAIN:
-            return Untranslated("Transaction already in block chain");
+        case TransactionError::ALREADY_IN_UTXO_SET:
+            return Untranslated("Transaction outputs already in utxo set");
         case TransactionError::MEMPOOL_REJECTED:
             return Untranslated("Transaction rejected by mempool");
         case TransactionError::MEMPOOL_ERROR:

src/node/transaction.cpp

@@ -55,7 +55,7 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
             const Coin& existingCoin = view.AccessCoin(COutPoint(txid, o));
             // IsSpent doesn't mean the coin is spent, it means the output doesn't exist.
             // So if the output does exist, then this transaction exists in the chain.
-            if (!existingCoin.IsSpent()) return TransactionError::ALREADY_IN_CHAIN;
+            if (!existingCoin.IsSpent()) return TransactionError::ALREADY_IN_UTXO_SET;
         }
 
         if (auto mempool_tx = node.mempool->get(txid); mempool_tx) {

src/node/types.h

@@ -19,7 +19,7 @@ namespace node {
 enum class TransactionError {
     OK, //!< No error
     MISSING_INPUTS,
-    ALREADY_IN_CHAIN,
+    ALREADY_IN_UTXO_SET,
     MEMPOOL_REJECTED,
     MEMPOOL_ERROR,
     MAX_FEE_EXCEEDED,

src/rpc/mempool.cpp

@@ -43,7 +43,7 @@ static RPCHelpMan sendrawtransaction()
         "\nThe transaction will be sent unconditionally to all peers, so using sendrawtransaction\n"
         "for manual rebroadcast may degrade privacy by leaking the transaction's origin, as\n"
         "nodes will normally not rebroadcast non-wallet transactions already in their mempool.\n"
-        "\nA specific exception, RPC_TRANSACTION_ALREADY_IN_CHAIN, may throw if the transaction cannot be added to the mempool.\n"
+        "\nA specific exception, RPC_TRANSACTION_ALREADY_IN_UTXO_SET, may throw if the transaction cannot be added to the mempool.\n"
         "\nRelated RPCs: createrawtransaction, signrawtransactionwithkey\n",
         {
             {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of the raw transaction"},

src/rpc/protocol.h

@@ -46,14 +46,13 @@ enum RPCErrorCode
     RPC_DESERIALIZATION_ERROR       = -22, //!< Error parsing or validating structure in raw format
     RPC_VERIFY_ERROR                = -25, //!< General error during transaction or block submission
     RPC_VERIFY_REJECTED             = -26, //!< Transaction or block was rejected by network rules
-    RPC_VERIFY_ALREADY_IN_CHAIN     = -27, //!< Transaction already in chain
+    RPC_VERIFY_ALREADY_IN_UTXO_SET  = -27, //!< Transaction already in utxo set
     RPC_IN_WARMUP                   = -28, //!< Client still warming up
     RPC_METHOD_DEPRECATED           = -32, //!< RPC method is deprecated
 
     //! Aliases for backward compatibility
     RPC_TRANSACTION_ERROR           = RPC_VERIFY_ERROR,
     RPC_TRANSACTION_REJECTED        = RPC_VERIFY_REJECTED,
-    RPC_TRANSACTION_ALREADY_IN_CHAIN= RPC_VERIFY_ALREADY_IN_CHAIN,
 
     //! P2P client errors
     RPC_CLIENT_NOT_CONNECTED        = -9,  //!< Bitcoin is not connected

src/rpc/util.cpp

@@ -399,8 +399,8 @@ RPCErrorCode RPCErrorFromTransactionError(TransactionError terr)
     switch (terr) {
         case TransactionError::MEMPOOL_REJECTED:
             return RPC_TRANSACTION_REJECTED;
-        case TransactionError::ALREADY_IN_CHAIN:
-            return RPC_TRANSACTION_ALREADY_IN_CHAIN;
+        case TransactionError::ALREADY_IN_UTXO_SET:
+            return RPC_VERIFY_ALREADY_IN_UTXO_SET;
         default: break;
     }
     return RPC_TRANSACTION_ERROR;

src/test/fuzz/kitchen_sink.cpp

@@ -23,7 +23,7 @@ using node::TransactionError;
 namespace {
 constexpr TransactionError ALL_TRANSACTION_ERROR[] = {
     TransactionError::MISSING_INPUTS,
-    TransactionError::ALREADY_IN_CHAIN,
+    TransactionError::ALREADY_IN_UTXO_SET,
     TransactionError::MEMPOOL_REJECTED,
     TransactionError::MEMPOOL_ERROR,
     TransactionError::MAX_FEE_EXCEEDED,

test/functional/rpc_rawtransaction.py

@@ -430,13 +430,13 @@ class RawTransactionsTest(BitcoinTestFramework):
         assert_equal(testres['allowed'], True)
         self.nodes[2].sendrawtransaction(hexstring=tx['hex'], maxfeerate='0.20000000')
 
-        self.log.info("Test sendrawtransaction/testmempoolaccept with tx already in the chain")
+        self.log.info("Test sendrawtransaction/testmempoolaccept with tx outputs already in the utxo set")
         self.generate(self.nodes[2], 1)
         for node in self.nodes:
             testres = node.testmempoolaccept([tx['hex']])[0]
             assert_equal(testres['allowed'], False)
             assert_equal(testres['reject-reason'], 'txn-already-known')
-            assert_raises_rpc_error(-27, 'Transaction already in block chain', node.sendrawtransaction, tx['hex'])
+            assert_raises_rpc_error(-27, 'Transaction outputs already in utxo set', node.sendrawtransaction, tx['hex'])
 
     def decoderawtransaction_tests(self):
         self.log.info("Test decoderawtransaction")