Obtain simulation protocol version dynamically

cmd/soroban-rpc/internal/jsonrpc.go

@@ -208,7 +208,7 @@ func NewJSONRPCHandler(cfg *config.Config, params HandlerParams) Handler {
 		},
 		{
 			methodName:           "simulateTransaction",
-			underlyingHandler:    methods.NewSimulateTransactionHandler(params.Logger, params.LedgerEntryReader, params.LedgerReader, params.PreflightGetter),
+			underlyingHandler:    methods.NewSimulateTransactionHandler(params.Logger, params.LedgerEntryReader, params.LedgerReader, params.Daemon, params.PreflightGetter),
 			longName:             "simulate_transaction",
 			queueLimit:           cfg.RequestBacklogSimulateTransactionQueueLimit,
 			requestDurationLimit: cfg.MaxSimulateTransactionExecutionDuration,

cmd/soroban-rpc/internal/methods/simulate_transaction.go

@@ -7,11 +7,13 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+	"sync/atomic"
 
 	"github.com/creachadair/jrpc2"
 	"github.com/stellar/go/support/log"
 	"github.com/stellar/go/xdr"
 
+	"github.com/stellar/soroban-rpc/cmd/soroban-rpc/internal/daemon/interfaces"
 	"github.com/stellar/soroban-rpc/cmd/soroban-rpc/internal/db"
 	"github.com/stellar/soroban-rpc/cmd/soroban-rpc/internal/preflight"
 )
@@ -156,7 +158,7 @@ type PreflightGetter interface {
 }
 
 // NewSimulateTransactionHandler returns a json rpc handler to run preflight simulations
-func NewSimulateTransactionHandler(logger *log.Entry, ledgerEntryReader db.LedgerEntryReader, ledgerReader db.LedgerReader, getter PreflightGetter) jrpc2.Handler {
+func NewSimulateTransactionHandler(logger *log.Entry, ledgerEntryReader db.LedgerEntryReader, ledgerReader db.LedgerReader, daemon interfaces.Daemon, getter PreflightGetter) jrpc2.Handler {
 
 	return NewHandler(func(ctx context.Context, request SimulateTransactionRequest) SimulateTransactionResponse {
 		var txEnvelope xdr.TransactionEnvelope
@@ -223,13 +225,20 @@ func NewSimulateTransactionHandler(logger *log.Entry, ledgerEntryReader db.Ledge
 		if request.ResourceConfig != nil {
 			resource_config = *request.ResourceConfig
 		}
+		protocolVersion, err := getProtocolVersion(ctx, daemon.CoreClient())
+		if err != nil {
+			return SimulateTransactionResponse{
+				Error: fmt.Sprintf("cannot obtain protocol version from core: %s", err),
+			}
+		}
 		params := preflight.PreflightGetterParameters{
 			LedgerEntryReadTx: readTx,
 			BucketListSize:    bucketListSize,
 			SourceAccount:     sourceAccount,
 			OperationBody:     op.Body,
 			Footprint:         footprint,
 			ResourceConfig:    resource_config,
+			ProtocolVersion:   protocolVersion,
 		}
 		result, err := getter.GetPreflight(ctx, params)
 		if err != nil {
@@ -298,3 +307,19 @@ func getBucketListSize(ctx context.Context, ledgerReader db.LedgerReader, latest
 	}
 	return uint64(closeMeta.V1.TotalByteSizeOfBucketList), nil
 }
+
+var cachedCoreProtocolVersion atomic.Int32
+
+// getProtocolVersion obtains the memoized protocol version from a core client
+func getProtocolVersion(ctx context.Context, client interfaces.CoreClient) (int, error) {
+	version := cachedCoreProtocolVersion.Load()
+	if version != 0 {
+		return int(version), nil
+	}
+	info, err := client.Info(ctx)
+	if err != nil {
+		return 0, err
+	}
+	cachedCoreProtocolVersion.CompareAndSwap(0, int32(info.Info.ProtocolVersion))
+	return info.Info.ProtocolVersion, nil
+}

cmd/soroban-rpc/internal/preflight/pool.go

@@ -156,6 +156,7 @@ func (pwp *PreflightWorkerPool) GetPreflight(ctx context.Context, params Preflig
 		Footprint:         params.Footprint,
 		ResourceConfig:    params.ResourceConfig,
 		EnableDebug:       pwp.enableDebug,
+		ProtocolVersion:   params.ProtocolVersion,
 	}
 	resultC := make(chan workerResult)
 	select {

cmd/soroban-rpc/internal/preflight/preflight.go

@@ -91,6 +91,7 @@ type PreflightGetterParameters struct {
 	OperationBody     xdr.OperationBody
 	Footprint         xdr.LedgerFootprint
 	ResourceConfig    ResourceConfig
+	ProtocolVersion   int
 }
 
 type PreflightParameters struct {
@@ -103,6 +104,7 @@ type PreflightParameters struct {
 	BucketListSize    uint64
 	ResourceConfig    ResourceConfig
 	EnableDebug       bool
+	ProtocolVersion   int
 }
 
 type XDRDiff struct {
@@ -174,7 +176,7 @@ func getLedgerInfo(params PreflightParameters) (C.ledger_info_t, error) {
 	li := C.ledger_info_t{
 		network_passphrase: C.CString(params.NetworkPassphrase),
 		sequence_number:    C.uint32_t(simulationLedgerSeq),
-		protocol_version:   20,
+		protocol_version:   C.uint32_t(params.ProtocolVersion),
 		timestamp:          C.uint64_t(time.Now().Unix()),
 		// Current base reserve is 0.5XLM (in stroops)
 		base_reserve: 5_000_000,

cmd/soroban-rpc/internal/preflight/preflight_test.go

@@ -361,6 +361,7 @@ func getPreflightParameters(t testing.TB, dbConfig *preflightParametersDBConfig)
 		NetworkPassphrase: "foo",
 		LedgerEntryReadTx: ledgerEntryReadTx,
 		BucketListSize:    200,
+		ProtocolVersion:   20,
 	}
 	return params
 }