tx send: allow to re-send + error signaling. Fixes #49, #51

data/static-nodes.json

@@ -3,5 +3,5 @@
   "enode://3c0ab251e18c979a3358644f49bcadf264186847aeee4fe80de60da0d196ce879c913bc1c9b5e750847c0d7e63a707a1cf5153c4f242da0d058e42fdf985ef62@198.199.105.122:30303",
   "enode://fc3065bb80bfced98a01441718e2b70a0353f023b9da3d57beb8f96a827402d23702b3a461e1c1b6c7a208cb09cc0aea9b7c42bf953bb8f732529c198b158db4@95.85.40.211:30303",
   "enode://5ffa3a39f95614d881e07d24e265865218c45fe73b3a5f5d05868190e385cbf60d03ac8beaa4c31b7ee84a0ec947f22c969e2dd1783041a4d7381f7774c74526@188.166.229.119:30303",
-  "enode://3b020a1fd6ab980a5670975e8a7361af1732fa3fa1819b751a94b6a4265e8c52b02c608c0de1347784b834b298280b018bcf6547f47bbba63612cba0e4707ec1@139.59.212.114:30303"
+  "enode://3c0ab251e18c979a3358644f49bcadf264186847aeee4fe80de60da0d196ce879c913bc1c9b5e750847c0d7e63a707a1cf5153c4f242da0d058e42fdf985ef62@139.59.212.114:30303"
 ]

geth/node.go

@@ -165,6 +165,7 @@ func (m *NodeManager) RunNode() {
 		// setup handlers
 		m.lightEthereum.StatusBackend.SetTransactionQueueHandler(onSendTransactionRequest)
 		m.lightEthereum.StatusBackend.SetAccountsFilterHandler(onAccountsListRequest)
+		m.lightEthereum.StatusBackend.SetTransactionReturnHandler(onSendTransactionReturn)
 
 		var err error
 		m.client, err = m.currentNode.Attach()

geth/txqueue.go

@@ -13,6 +13,7 @@ import (
 	"math/big"
 	"strconv"
 
+	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/les/status"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -21,8 +22,15 @@ import (
 
 const (
 	EventTransactionQueued = "transaction.queued"
+	EventTransactionFailed = "transaction.failed"
 	SendTransactionRequest = "eth_sendTransaction"
 	MessageIdKey           = "message_id"
+
+	// tx error codes
+	SendTransactionNoErrorCode       = "0"
+	SendTransactionDefaultErrorCode  = "1"
+	SendTransactionPasswordErrorCode = "2"
+	SendTransactionTimeoutErrorCode  = "3"
 )
 
 func onSendTransactionRequest(queuedTx status.QueuedTx) {
@@ -39,6 +47,43 @@ func onSendTransactionRequest(queuedTx status.QueuedTx) {
 	C.StatusServiceSignalEvent(C.CString(string(body)))
 }
 
+func onSendTransactionReturn(queuedTx status.QueuedTx, err error) {
+	if err == nil {
+		return
+	}
+
+	// error occurred, signal up to application
+	event := GethEvent{
+		Type: EventTransactionFailed,
+		Event: ReturnSendTransactionEvent{
+			Id:           string(queuedTx.Id),
+			Args:         queuedTx.Args,
+			MessageId:    messageIdFromContext(queuedTx.Context),
+			ErrorMessage: err.Error(),
+			ErrorCode:    sendTransactionErrorCode(err),
+		},
+	}
+
+	body, _ := json.Marshal(&event)
+	C.StatusServiceSignalEvent(C.CString(string(body)))
+}
+
+func sendTransactionErrorCode(err error) string {
+	if err == nil {
+		return SendTransactionNoErrorCode
+	}
+
+	if err == accounts.ErrDecrypt {
+		return SendTransactionPasswordErrorCode
+	}
+
+	if err == status.ErrQueuedTxTimedOut {
+		return SendTransactionTimeoutErrorCode
+	}
+
+	return SendTransactionDefaultErrorCode
+}
+
 func CompleteTransaction(id, password string) (common.Hash, error) {
 	lightEthereum, err := GetNodeManager().LightEthereumService()
 	if err != nil {

geth/txqueue_test.go

@@ -10,8 +10,6 @@ import (
 	"github.com/ethereum/go-ethereum/cmd/utils"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/les/status"
-	"github.com/ethereum/go-ethereum/logger"
-	"github.com/ethereum/go-ethereum/logger/glog"
 	"github.com/ethereum/go-ethereum/rpc"
 	"github.com/status-im/status-go/geth"
 )
@@ -36,7 +34,7 @@ func TestQueuedTransactions(t *testing.T) {
 		return
 	}
 
-	// test transaction queueing
+	// obtain reference to status backend
 	lightEthereum, err := geth.GetNodeManager().LightEthereumService()
 	if err != nil {
 		t.Errorf("Test failed: LES service is not running: %v", err)
@@ -58,7 +56,7 @@ func TestQueuedTransactions(t *testing.T) {
 		}
 		if envelope.Type == geth.EventTransactionQueued {
 			event := envelope.Event.(map[string]interface{})
-			glog.V(logger.Info).Infof("Transaction queued (will be completed in 5 secs): {id: %s}\n", event["id"].(string))
+			t.Logf("transaction queued (will be completed in 5 secs): {id: %s}\n", event["id"].(string))
 			time.Sleep(5 * time.Second)
 
 			if txHash, err = geth.CompleteTransaction(event["id"].(string), testAddressPassword); err != nil {
@@ -66,18 +64,12 @@ func TestQueuedTransactions(t *testing.T) {
 				return
 			}
 
-			glog.V(logger.Info).Infof("Transaction complete: https://testnet.etherscan.io/tx/%s", txHash.Hex())
+			t.Logf("transaction complete: https://testnet.etherscan.io/tx/%s", txHash.Hex())
 			completeQueuedTransaction <- struct{}{} // so that timeout is aborted
 		}
 	})
 
-	// try completing non-existing transaction
-	if _, err := geth.CompleteTransaction("some-bad-transaction-id", testAddressPassword); err == nil {
-		t.Error("error expected and not recieved")
-		return
-	}
-
-	// send normal transaction
+	// send from the same test account (which is guaranteed to have ether)
 	from, err := utils.MakeAddress(accountManager, testAddress)
 	if err != nil {
 		t.Errorf("could not retrieve account from address: %v", err)
@@ -112,11 +104,254 @@ func TestQueuedTransactions(t *testing.T) {
 		return
 	}
 
-	// now test eviction queue
+	if backend.TransactionQueue().Count() != 0 {
+		t.Error("tx queue must be empty at this point")
+		return
+	}
+}
+
+func TestDoubleCompleteQueuedTransactions(t *testing.T) {
+	err := geth.PrepareTestNode()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	accountManager, err := geth.GetNodeManager().AccountManager()
+	if err != nil {
+		t.Errorf(err.Error())
+		return
+	}
+
+	// create an account
+	address, _, _, err := geth.CreateAccount(newAccountPassword)
+	if err != nil {
+		t.Errorf("could not create account: %v", err)
+		return
+	}
+
+	// obtain reference to status backend
+	lightEthereum, err := geth.GetNodeManager().LightEthereumService()
+	if err != nil {
+		t.Errorf("Test failed: LES service is not running: %v", err)
+		return
+	}
+	backend := lightEthereum.StatusBackend
+
+	// make sure you panic if transaction complete doesn't return
+	completeQueuedTransaction := make(chan struct{}, 1)
+	geth.PanicAfter(20*time.Second, completeQueuedTransaction, "TestQueuedTransactions")
+
+	// replace transaction notification handler
+	var txId string
+	txFailedEventCalled := false
+	txHash := common.Hash{}
+	geth.SetDefaultNodeNotificationHandler(func(jsonEvent string) {
+		var envelope geth.GethEvent
+		if err := json.Unmarshal([]byte(jsonEvent), &envelope); err != nil {
+			t.Errorf("cannot unmarshal event's JSON: %s", jsonEvent)
+			return
+		}
+		if envelope.Type == geth.EventTransactionQueued {
+			event := envelope.Event.(map[string]interface{})
+			txId = event["id"].(string)
+			t.Logf("transaction queued (will be failed and completed on the second call): {id: %s}\n", txId)
+
+			// try with wrong password
+			// make sure that tx is NOT removed from the queue (by re-trying with the correct password)
+			if _, err = geth.CompleteTransaction(txId, testAddressPassword+"wrong"); err == nil {
+				t.Error("expects wrong password error, but call succeeded")
+				return
+			}
+
+			time.Sleep(1 * time.Second) // make sure that tx complete signal propagates
+			if txCount := backend.TransactionQueue().Count(); txCount != 1 {
+				t.Errorf("txqueue cannot be empty, as tx has failed: expected = 1, got = %d", txCount)
+				return
+			}
+
+			// now try to complete transaction, but with the correct password
+			t.Log("allow 5 seconds before sedning the second CompleteTransaction")
+			time.Sleep(5 * time.Second)
+			if txHash, err = geth.CompleteTransaction(event["id"].(string), testAddressPassword); err != nil {
+				t.Errorf("cannot complete queued transation[%v]: %v", event["id"], err)
+				return
+			}
+
+			time.Sleep(1 * time.Second) // make sure that tx complete signal propagates
+			if txCount := backend.TransactionQueue().Count(); txCount != 0 {
+				t.Errorf("txqueue must be empty, as tx has completed: expected = 0, got = %d", txCount)
+				return
+			}
+
+			t.Logf("transaction complete: https://testnet.etherscan.io/tx/%s", txHash.Hex())
+			completeQueuedTransaction <- struct{}{} // so that timeout is aborted
+		}
+
+		if envelope.Type == geth.EventTransactionFailed {
+			event := envelope.Event.(map[string]interface{})
+			t.Logf("transaction return event received: {id: %s}\n", event["id"].(string))
+
+			receivedErrMessage := event["error_message"].(string)
+			expectedErrMessage := "could not decrypt key with given passphrase"
+			if receivedErrMessage != expectedErrMessage {
+				t.Errorf("unexpected error message received: got %v", receivedErrMessage)
+				return
+			}
+
+			receivedErrCode := event["error_code"].(string)
+			if receivedErrCode != geth.SendTransactionPasswordErrorCode {
+				t.Errorf("unexpected error code received: got %v", receivedErrCode)
+				return
+			}
+
+			txFailedEventCalled = true
+		}
+	})
+
+	// send from the same test account (which is guaranteed to have ether)
+	from, err := utils.MakeAddress(accountManager, testAddress)
+	if err != nil {
+		t.Errorf("could not retrieve account from address: %v", err)
+		return
+	}
+
+	to, err := utils.MakeAddress(accountManager, address)
+	if err != nil {
+		t.Errorf("could not retrieve account from address: %v", err)
+		return
+	}
+
+	//  this call blocks, and should return on *second* attempt to CompleteTransaction (w/ the correct password)
+	txHashCheck, err := backend.SendTransaction(nil, status.SendTxArgs{
+		From:  from.Address,
+		To:    &to.Address,
+		Value: rpc.NewHexNumber(big.NewInt(1000000000000)),
+	})
+	if err != nil {
+		t.Errorf("cannot send transaction: %v", err)
+		return
+	}
+
+	if !reflect.DeepEqual(txHash, txHashCheck) {
+		t.Errorf("tx hash returned from SendTransaction is invalid: expected %s, got %s", txHashCheck, txHash)
+		return
+	}
+
+	if reflect.DeepEqual(txHashCheck, common.Hash{}) {
+		t.Error("transaction was never queued or completed")
+		return
+	}
+
+	if backend.TransactionQueue().Count() != 0 {
+		t.Error("tx queue must be empty at this point")
+		return
+	}
+
+	if !txFailedEventCalled {
+		t.Error("expected tx failure signal is not received")
+		return
+	}
+
+	t.Log("sleep extra time, to allow sync")
+	time.Sleep(5 * time.Second)
+}
+
+func TestNonExistentQueuedTransactions(t *testing.T) {
+	err := geth.PrepareTestNode()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	// make sure you panic if transaction complete doesn't return
+	completeQueuedTransaction := make(chan struct{}, 1)
+	geth.PanicAfter(20*time.Second, completeQueuedTransaction, "TestQueuedTransactions")
+
+	// replace transaction notification handler
+	var txHash = common.Hash{}
+	geth.SetDefaultNodeNotificationHandler(func(jsonEvent string) {
+		var envelope geth.GethEvent
+		if err := json.Unmarshal([]byte(jsonEvent), &envelope); err != nil {
+			t.Errorf("cannot unmarshal event's JSON: %s", jsonEvent)
+			return
+		}
+		if envelope.Type == geth.EventTransactionQueued {
+			event := envelope.Event.(map[string]interface{})
+			t.Logf("Transaction queued (will be completed in 5 secs): {id: %s}\n", event["id"].(string))
+			time.Sleep(5 * time.Second)
+
+			// next call is the very same one, but with the correct password
+			if txHash, err = geth.CompleteTransaction(event["id"].(string), testAddressPassword); err != nil {
+				t.Errorf("cannot complete queued transation[%v]: %v", event["id"], err)
+				return
+			}
+
+			t.Logf("Transaction complete: https://testnet.etherscan.io/tx/%s", txHash.Hex())
+			completeQueuedTransaction <- struct{}{} // so that timeout is aborted
+		}
+	})
+
+	// try completing non-existing transaction
+	if _, err = geth.CompleteTransaction("some-bad-transaction-id", testAddressPassword); err == nil {
+		t.Error("error expected and not recieved")
+		return
+	}
+	if err != status.ErrQueuedTxIdNotFound {
+		t.Errorf("unexpected error recieved: expected '%s', got: '%s'", status.ErrQueuedTxIdNotFound.Error(), err.Error())
+		return
+	}
+}
+
+func TestEvictionOfQueuedTransactions(t *testing.T) {
+	err := geth.PrepareTestNode()
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	// obtain reference to status backend
+	lightEthereum, err := geth.GetNodeManager().LightEthereumService()
+	if err != nil {
+		t.Errorf("Test failed: LES service is not running: %v", err)
+		return
+	}
+	backend := lightEthereum.StatusBackend
+
+	// make sure you panic if transaction complete doesn't return
+	completeQueuedTransaction := make(chan struct{}, 1)
+	geth.PanicAfter(20*time.Second, completeQueuedTransaction, "TestQueuedTransactions")
+
+	// replace transaction notification handler
+	var txHash = common.Hash{}
+	geth.SetDefaultNodeNotificationHandler(func(jsonEvent string) {
+		var envelope geth.GethEvent
+		if err := json.Unmarshal([]byte(jsonEvent), &envelope); err != nil {
+			t.Errorf("cannot unmarshal event's JSON: %s", jsonEvent)
+			return
+		}
+		if envelope.Type == geth.EventTransactionQueued {
+			event := envelope.Event.(map[string]interface{})
+			t.Logf("Transaction queued (will be completed in 5 secs): {id: %s}\n", event["id"].(string))
+			time.Sleep(5 * time.Second)
+
+			// next call is the very same one, but with the correct password
+			if txHash, err = geth.CompleteTransaction(event["id"].(string), testAddressPassword); err != nil {
+				t.Errorf("cannot complete queued transation[%v]: %v", event["id"], err)
+				return
+			}
+
+			t.Logf("Transaction complete: https://testnet.etherscan.io/tx/%s", txHash.Hex())
+			completeQueuedTransaction <- struct{}{} // so that timeout is aborted
+		}
+	})
+
 	txQueue := backend.TransactionQueue()
 	var i = 0
+	txIds := [status.DefaultTxQueueCap + 5 + 10]status.QueuedTxId{}
 	backend.SetTransactionQueueHandler(func(queuedTx status.QueuedTx) {
-		//glog.V(logger.Info).Infof("%d. Transaction queued (queue size: %d): {id: %v}\n", i, txQueue.Count(), queuedTx.Id)
+		t.Logf("%d. Transaction queued (queue size: %d): {id: %v}\n", i, txQueue.Count(), queuedTx.Id)
+		txIds[i] = queuedTx.Id
 		i++
 	})
 
@@ -142,8 +377,17 @@ func TestQueuedTransactions(t *testing.T) {
 	}
 	time.Sleep(5 * time.Second)
 
-	if txQueue.Count() != status.DefaultTxQueueCap && txQueue.Count() != (status.DefaultTxQueueCap-1) {
+	if txQueue.Count() > status.DefaultTxQueueCap {
 		t.Errorf("transaction count should be %d (or %d): got %d", status.DefaultTxQueueCap, status.DefaultTxQueueCap-1, txQueue.Count())
 		return
 	}
+
+	for _, txId := range txIds {
+		txQueue.Remove(txId)
+	}
+
+	if txQueue.Count() != 0 {
+		t.Errorf("transaction count should be zero: %d", txQueue.Count())
+		return
+	}
 }

geth/types.go

@@ -40,6 +40,14 @@ type SendTransactionEvent struct {
 	MessageId string            `json:"message_id"`
 }
 
+type ReturnSendTransactionEvent struct {
+	Id           string            `json:"id"`
+	Args         status.SendTxArgs `json:"args"`
+	MessageId    string            `json:"message_id"`
+	ErrorMessage string            `json:"error_message"`
+	ErrorCode    string            `json:"error_code"`
+}
+
 type CompleteTransactionResult struct {
 	Hash  string `json:"hash"`
 	Error string `json:"error"`

vendor/github.com/ethereum/go-ethereum/internal/ethapi/api.go

@@ -20,7 +20,6 @@ import (
 	"bytes"
 	"encoding/hex"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"math/big"
 	"strings"
@@ -1035,11 +1034,14 @@ func (s *PublicTransactionPoolAPI) SendTransaction(ctx context.Context, args Sen
 	s.txQueue <- queuedTx
 
 	// now wait up until transaction is complete (via call to CompleteQueuedTransaction) or timeout occurs
+	backend := GetStatusBackend()
 	select {
 	case <-queuedTx.Done:
+		backend.NotifyOnQueuedTxReturn(queuedTx.Id, queuedTx.Err)
 		return queuedTx.Hash, queuedTx.Err
 	case <-time.After(status.DefaultTxSendCompletionTimeout * time.Second):
-		return common.Hash{}, errors.New("transaction sending timed out")
+		backend.NotifyOnQueuedTxReturn(queuedTx.Id, status.ErrQueuedTxTimedOut)
+		return common.Hash{}, status.ErrQueuedTxTimedOut
 	}
 
 	return queuedTx.Hash, nil

vendor/github.com/ethereum/go-ethereum/internal/ethapi/status_backend.go

@@ -3,6 +3,7 @@ package ethapi
 import (
 	"sync"
 
+	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/les/status"
 	"github.com/ethereum/go-ethereum/logger"
@@ -46,6 +47,18 @@ func GetStatusBackend() *StatusBackend {
 	return statusBackend
 }
 
+func (b *StatusBackend) NotifyOnQueuedTxReturn(id status.QueuedTxId, err error) {
+	if b == nil {
+		return
+	}
+
+	b.txQueue.NotifyOnQueuedTxReturn(id, err)
+}
+
+func (b *StatusBackend) SetTransactionReturnHandler(fn status.EnqueuedTxReturnHandler) {
+	b.txQueue.SetTxReturnHandler(fn)
+}
+
 func (b *StatusBackend) SetTransactionQueueHandler(fn status.EnqueuedTxHandler) {
 	b.txQueue.SetEnqueueHandler(fn)
 }
@@ -79,6 +92,14 @@ func (b *StatusBackend) CompleteQueuedTransaction(id status.QueuedTxId, passphra
 	}
 
 	hash, err := b.txapi.CompleteQueuedTransaction(context.Background(), SendTxArgs(queuedTx.Args), passphrase)
+
+	// on password error, notify the app, and keep tx in queue (so that CompleteQueuedTransaction() can be resent)
+	if err == accounts.ErrDecrypt {
+		b.NotifyOnQueuedTxReturn(id, err)
+		return hash, err // SendTransaction is still blocked
+	}
+
+	// allow SendTransaction to return
 	queuedTx.Hash = hash
 	queuedTx.Err = err
 	queuedTx.Done <- struct{}{} // sendTransaction() waits on this, notify so that it can return

vendor/github.com/ethereum/go-ethereum/les/status/txqueue.go

@@ -2,6 +2,9 @@ package status
 
 import (
 	"errors"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/rpc"
 	"golang.org/x/net/context"
@@ -15,16 +18,21 @@ const (
 
 var (
 	ErrQueuedTxIdNotFound = errors.New("transaction hash not found")
+	ErrQueuedTxTimedOut   = errors.New("transaction sending timed out")
 )
 
 // TxQueue is capped container that holds pending transactions
 type TxQueue struct {
 	transactions  map[QueuedTxId]*QueuedTx
+	mu            sync.RWMutex // to guard trasactions map
 	evictableIds  chan QueuedTxId
 	enqueueTicker chan struct{}
 
-	// when items are enqueued notify handlers
+	// when items are enqueued notify subscriber
 	txEnqueueHandler EnqueuedTxHandler
+
+	// when tx is returned (either successfully or with error) notify subscriber
+	txReturnHandler EnqueuedTxReturnHandler
 }
 
 // QueuedTx holds enough information to complete the queued transaction.
@@ -39,9 +47,12 @@ type QueuedTx struct {
 
 type QueuedTxId string
 
-// QueuedTxHandler is a function that receives queued/pending transactions, when they get queued
+// EnqueuedTxHandler is a function that receives queued/pending transactions, when they get queued
 type EnqueuedTxHandler func(QueuedTx)
 
+// EnqueuedTxReturnHandler is a function that receives response when tx is complete (both on success and error)
+type EnqueuedTxReturnHandler func(queuedTx QueuedTx, err error)
+
 // SendTxArgs represents the arguments to submbit a new transaction into the transaction pool.
 type SendTxArgs struct {
 	From     common.Address  `json:"from"`
@@ -68,7 +79,8 @@ func NewTransactionQueue() *TxQueue {
 func (q *TxQueue) evictionLoop() {
 	for range q.enqueueTicker {
 		if len(q.transactions) >= (DefaultTxQueueCap - 1) { // eviction is required to accommodate another/last item
-			delete(q.transactions, <-q.evictableIds)
+			q.Remove(<-q.evictableIds)
+			q.enqueueTicker <- struct{}{} // in case we pulled already removed item
 		}
 	}
 }
@@ -81,7 +93,9 @@ func (q *TxQueue) Enqueue(tx *QueuedTx) error {
 	q.enqueueTicker <- struct{}{} // notify eviction loop that we are trying to insert new item
 	q.evictableIds <- tx.Id       // this will block when we hit DefaultTxQueueCap
 
+	q.mu.Lock()
 	q.transactions[tx.Id] = tx
+	q.mu.Unlock()
 
 	// notify handler
 	q.txEnqueueHandler(*tx)
@@ -90,19 +104,34 @@ func (q *TxQueue) Enqueue(tx *QueuedTx) error {
 }
 
 func (q *TxQueue) Get(id QueuedTxId) (*QueuedTx, error) {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+
 	if tx, ok := q.transactions[id]; ok {
-		delete(q.transactions, id)
 		return tx, nil
 	}
 
 	return nil, ErrQueuedTxIdNotFound
 }
 
+func (q *TxQueue) Remove(id QueuedTxId) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+
+	delete(q.transactions, id)
+}
+
 func (q *TxQueue) Count() int {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+
 	return len(q.transactions)
 }
 
 func (q *TxQueue) Has(id QueuedTxId) bool {
+	q.mu.RLock()
+	defer q.mu.RUnlock()
+
 	_, ok := q.transactions[id]
 
 	return ok
@@ -111,3 +140,38 @@ func (q *TxQueue) Has(id QueuedTxId) bool {
 func (q *TxQueue) SetEnqueueHandler(fn EnqueuedTxHandler) {
 	q.txEnqueueHandler = fn
 }
+
+func (q *TxQueue) SetTxReturnHandler(fn EnqueuedTxReturnHandler) {
+	q.txReturnHandler = fn
+}
+
+func (q *TxQueue) NotifyOnQueuedTxReturn(id QueuedTxId, err error) {
+	if q == nil {
+		return
+	}
+
+	// on success, remove item from the queue and stop propagating
+	if err == nil {
+		q.Remove(id)
+		return
+	}
+
+	// error occurred, send upward notification
+	if q.txReturnHandler == nil { // discard, until handler is provided
+		return
+	}
+
+	// discard, if transaction is not found
+	tx, _ := q.Get(id)
+	if tx == nil {
+		return
+	}
+
+	// remove from queue on any error (except for password related one) and propagate
+	if err != accounts.ErrDecrypt {
+		q.Remove(id)
+	}
+
+	// notify handler
+	q.txReturnHandler(*tx, err)
+}