From 9e35758653e28b896062295707c9215252e0b979 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Thu, 31 Dec 2020 13:54:42 +0300
Subject: [PATCH] rpc: fix gettxout result for already spent outputs

As per C# documentation [1]:
  If the transaction output is already spent, the result value will be null .

[1]: https://docs.neo.org/docs/en-us/reference/rpc/latest-version/api/gettxout.html
---
 pkg/core/state/unspent_coin.go      |  5 +++++
 pkg/core/state/unspent_coin_test.go |  2 ++
 pkg/rpc/server/server.go            | 14 ++++++++------
 pkg/rpc/server/server_test.go       | 12 ++++++++++--
 4 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/pkg/core/state/unspent_coin.go b/pkg/core/state/unspent_coin.go
index a0f1e635e..b474f1151 100644
--- a/pkg/core/state/unspent_coin.go
+++ b/pkg/core/state/unspent_coin.go
@@ -43,6 +43,11 @@ func (s *UnspentCoin) EncodeBinary(bw *io.BinWriter) {
 func (s *UnspentCoin) DecodeBinary(br *io.BinReader) {
 	s.Height = br.ReadU32LE()
 	br.ReadArray(&s.States)
+	if br.Err == nil {
+		for i := range s.States {
+			s.States[i].Output.Position = i
+		}
+	}
 }
 
 // EncodeBinary implements Serializable interface.
diff --git a/pkg/core/state/unspent_coin_test.go b/pkg/core/state/unspent_coin_test.go
index 51e778ab7..1904e5fd0 100644
--- a/pkg/core/state/unspent_coin_test.go
+++ b/pkg/core/state/unspent_coin_test.go
@@ -27,6 +27,7 @@ func TestDecodeEncodeUnspentCoin(t *testing.T) {
 					AssetID:    random.Uint256(),
 					Amount:     util.Fixed8(420),
 					ScriptHash: random.Uint160(),
+					Position:   1,
 				},
 				SpendHeight: 0,
 				State:       CoinConfirmed,
@@ -36,6 +37,7 @@ func TestDecodeEncodeUnspentCoin(t *testing.T) {
 					AssetID:    random.Uint256(),
 					Amount:     util.Fixed8(4200),
 					ScriptHash: random.Uint160(),
+					Position:   2,
 				},
 				SpendHeight: 111000,
 				State:       CoinSpent & CoinClaimed,
diff --git a/pkg/rpc/server/server.go b/pkg/rpc/server/server.go
index 6eabd408d..c2b6e3900 100644
--- a/pkg/rpc/server/server.go
+++ b/pkg/rpc/server/server.go
@@ -1207,17 +1207,19 @@ func (s *Server) getTxOut(ps request.Params) (interface{}, *response.Error) {
 		return nil, response.ErrInvalidParams
 	}
 
-	tx, _, err := s.chain.GetTransaction(h)
-	if err != nil {
-		return nil, response.NewInvalidParamsError(err.Error(), err)
+	ucs := s.chain.GetUnspentCoinState(h)
+	if ucs == nil {
+		return nil, response.NewInvalidParamsError("invalid tx hash", errors.New("unknown"))
 	}
 
-	if num >= len(tx.Outputs) {
+	if num >= len(ucs.States) {
 		return nil, response.NewInvalidParamsError("invalid index", errors.New("too big index"))
 	}
 
-	out := tx.Outputs[num]
-	return result.NewTxOutput(&out), nil
+	if ucs.States[num].State&state.CoinSpent != 0 {
+		return nil, nil
+	}
+	return result.NewTxOutput(&ucs.States[num].Output), nil
 }
 
 // getContractState returns contract state (contract information, according to the contract script hash).
diff --git a/pkg/rpc/server/server_test.go b/pkg/rpc/server/server_test.go
index fb49d19bf..4b544610c 100644
--- a/pkg/rpc/server/server_test.go
+++ b/pkg/rpc/server/server_test.go
@@ -1204,13 +1204,21 @@ func testRPCProtocol(t *testing.T, doRPCCall func(string, string, *testing.T) []
 			`"`+tx.Hash().StringLE()+`"`, 0)
 		body := doRPCCall(rpc, httpSrv.URL, t)
 		res := checkErrGetResult(t, body, false)
+		assert.Equal(t, "null", string(res)) // already spent
+
+		block, _ = chain.GetBlock(e.chain.GetHeaderHash(1))
+		tx = block.Transactions[1]
+		rpc = fmt.Sprintf(`{"jsonrpc": "2.0", "id": 1, "method": "gettxout", "params": [%s, %d]}"`,
+			`"`+tx.Hash().StringLE()+`"`, 1) // Neo remainder in txMoveNeo
+		body = doRPCCall(rpc, httpSrv.URL, t)
+		res = checkErrGetResult(t, body, false)
 
 		var txOut result.TransactionOutput
 		err := json.Unmarshal(res, &txOut)
 		require.NoErrorf(t, err, "could not parse response: %s", res)
-		assert.Equal(t, 0, txOut.N)
+		assert.Equal(t, 1, txOut.N)
 		assert.Equal(t, "0x9b7cffdaa674beae0f930ebe6085af9093e5fe56b34a5c220ccdcf6efc336fc5", txOut.Asset)
-		assert.Equal(t, util.Fixed8FromInt64(100000000), txOut.Value)
+		assert.Equal(t, util.Fixed8FromInt64(1000), txOut.Value)
 		assert.Equal(t, "AZ81H31DMWzbSnFDLFkzh9vHwaDLayV7fU", txOut.Address)
 	})