add better reject reason for immature peg-in, with test

qa/rpc-tests/pegging.py

@@ -169,12 +169,22 @@ try:
     addrs = sidechain.getpeginaddress()
     txid1 = bitcoin.sendtoaddress(addrs["mainchain_address"], 24)
     # 10+2 confirms required to get into mempool and confirm
-    bitcoin.generate(11)
+    bitcoin.generate(1)
     time.sleep(2)
     proof = bitcoin.gettxoutproof([txid1])
     raw = bitcoin.getrawtransaction(txid1)
 
     print("Attempting peg-in")
+    # First attempt fails the consensus check but gives useful result
+    try:
+        pegtxid = sidechain.claimpegin(raw, proof)
+        raise Exception("Peg-in should not mature enough yet, need another block.")
+    except JSONRPCException as e:
+        assert("Peg-in Bitcoin transaction needs more confirmations to be sent." in e.error["message"])
+        pass
+
+    # Second attempt simply doesn't hit mempool bar
+    bitcoin.generate(10)
     try:
         pegtxid = sidechain.claimpegin(raw, proof)
         raise Exception("Peg-in should not mature enough yet, need another block.")

src/wallet/rpcwallet.cpp

@@ -3660,7 +3660,11 @@ UniValue createrawpegin(const JSONRPCRequest& request)
     stack.push_back(txData);
     stack.push_back(txOutProofData);
 
-    if (!IsValidPeginWitness(pegin_witness, mtx.vin[0].prevout)) {
+    // Peg-in witness isn't valid, even though the block header is(without depth check)
+    // We re-check depth before returning with more descriptive result
+    if (GetBoolArg("-validatepegin", DEFAULT_VALIDATE_PEGIN) &&
+            !IsConfirmedBitcoinBlock(merkleBlock.header.GetHash(), 0) &&
+    !IsValidPeginWitness(pegin_witness, mtx.vin[0].prevout)) {
         throw JSONRPCError(RPC_INVALID_PARAMETER, "Constructed peg-in witness is invalid.");
     }