feat(client): Invoke get_channel function in the contract without sen…

…ding a signed transaction - decode the result of the simulated transaction result

client/client.go

@@ -263,19 +263,12 @@ func (cb *ContractBackend) GetChannelInfo(ctx context.Context, perunAddr xdr.ScA
 	if err != nil {
 		return wire.Channel{}, errors.New("error while building get_channel tx")
 	}
-	txMeta, err := cb.InvokeSignedTx("get_channel", getchTxArgs, perunAddr)
+	chanInfo, err := cb.InvokeUnsignedTx("get_channel", getchTxArgs, perunAddr)
 	if err != nil {
 		return wire.Channel{}, errors.New("error while processing and submitting get_channel tx")
 	}
 
-	retVal := txMeta.V3.SorobanMeta.ReturnValue
-	var getChan wire.Channel
-
-	err = getChan.FromScVal(retVal)
-	if err != nil {
-		return wire.Channel{}, errors.New("error while decoding return value")
-	}
-	return getChan, nil
+	return chanInfo, nil
 }
 
 func (cb *ContractBackend) GetBalanceUser(cID xdr.ScAddress) (string, error) {

client/contractbackend.go

@@ -10,6 +10,7 @@ import (
 	"github.com/stellar/go/xdr"
 	"perun.network/go-perun/wallet"
 	"perun.network/perun-stellar-backend/wallet/types"
+	"perun.network/perun-stellar-backend/wire"
 	"sync"
 )
 
@@ -129,6 +130,30 @@ func (st *StellarSigner) GetHorizonClient() *horizonclient.Client {
 	return st.hzClient
 }
 
+func (c *ContractBackend) InvokeUnsignedTx(fname string, callTxArgs xdr.ScVec, contractAddr xdr.ScAddress) (wire.Channel, error) { //xdr.TransactionMeta, error
+	c.cbMutex.Lock()
+	defer c.cbMutex.Unlock()
+	fnameXdr := xdr.ScSymbol(fname)
+	hzAcc, err := c.tr.GetHorizonAccount()
+	if err != nil {
+		return wire.Channel{}, err
+	}
+
+	hzClient := c.tr.GetHorizonClient()
+
+	txSender, ok := c.tr.sender.(*TxSender)
+	if !ok {
+		return wire.Channel{}, errors.New("sender is not of type *TxSender")
+	}
+
+	txSender.SetHzClient(hzClient)
+
+	invokeHostFunctionOp := BuildContractCallOp(hzAcc, fnameXdr, callTxArgs, contractAddr)
+	chanInfo, _, _ := PreflightHostFunctionsResult(hzClient, &hzAcc, *invokeHostFunctionOp)
+
+	return chanInfo, nil
+}
+
 func (c *ContractBackend) InvokeSignedTx(fname string, callTxArgs xdr.ScVec, contractAddr xdr.ScAddress) (xdr.TransactionMeta, error) {
 	c.cbMutex.Lock()
 	defer c.cbMutex.Unlock()

client/transaction.go

@@ -8,6 +8,7 @@ import (
 	"github.com/stellar/go/protocols/horizon"
 	"github.com/stellar/go/txnbuild"
 	"github.com/stellar/go/xdr"
+	"perun.network/perun-stellar-backend/wire"
 	"strconv"
 	"time"
 )
@@ -96,6 +97,43 @@ func PreflightHostFunctions(hzClient *horizonclient.Client,
 	return function, result.MinResourceFee
 }
 
+func PreflightHostFunctionsResult(hzClient *horizonclient.Client,
+	sourceAccount txnbuild.Account, function txnbuild.InvokeHostFunction,
+) (wire.Channel, txnbuild.InvokeHostFunction, int64) {
+	result, transactionData := simulateTransaction(hzClient, sourceAccount, &function)
+
+	function.Ext = xdr.TransactionExt{
+		V:           1,
+		SorobanData: &transactionData,
+	}
+	var getChan wire.Channel
+
+	if len(result.Results) != 1 {
+		panic("expected one result")
+	}
+
+	var decodedXdr xdr.ScVal
+	err := xdr.SafeUnmarshalBase64(result.Results[0].XDR, &decodedXdr)
+	if err != nil {
+		panic(err)
+	}
+
+	decChanInfo := decodedXdr
+
+	if decChanInfo.Type != xdr.ScValTypeScvMap {
+		return getChan, function, result.MinResourceFee
+
+	}
+
+	err = getChan.FromScVal(decChanInfo)
+	if err != nil {
+
+		panic(err)
+	}
+
+	return getChan, function, result.MinResourceFee
+}
+
 func simulateTransaction(hzClient *horizonclient.Client,
 	sourceAccount txnbuild.Account, op txnbuild.Operation,
 ) (RPCSimulateTxResponse, xdr.SorobanTransactionData) {