diff --git a/rpc/client.go b/rpc/client.go
index 0c52402ea65d6cf2edace49cc84ca948c4744148..6846e1ddafa680fd662cc59a4c052c4f0bf2a6f7 100644
--- a/rpc/client.go
+++ b/rpc/client.go
@@ -18,6 +18,7 @@ package rpc
import (
"bytes"
+ "container/list"
"encoding/json"
"errors"
"fmt"
@@ -35,16 +36,31 @@ import (
)
var (
- ErrClientQuit = errors.New("client is closed")
- ErrNoResult = errors.New("no result in JSON-RPC response")
+ ErrClientQuit = errors.New("client is closed")
+ ErrNoResult = errors.New("no result in JSON-RPC response")
+ ErrSubscriptionQueueOverflow = errors.New("subscription queue overflow")
)
const (
- clientSubscriptionBuffer = 100 // if exceeded, the client stops reading
- tcpKeepAliveInterval = 30 * time.Second
- defaultDialTimeout = 10 * time.Second // used when dialing if the context has no deadline
- defaultWriteTimeout = 10 * time.Second // used for calls if the context has no deadline
- subscribeTimeout = 5 * time.Second // overall timeout eth_subscribe, rpc_modules calls
+ // Timeouts
+ tcpKeepAliveInterval = 30 * time.Second
+ defaultDialTimeout = 10 * time.Second // used when dialing if the context has no deadline
+ defaultWriteTimeout = 10 * time.Second // used for calls if the context has no deadline
+ subscribeTimeout = 5 * time.Second // overall timeout eth_subscribe, rpc_modules calls
+)
+
+const (
+ // Subscriptions are removed when the subscriber cannot keep up.
+ //
+ // This can be worked around by supplying a channel with sufficiently sized buffer,
+ // but this can be inconvenient and hard to explain in the docs. Another issue with
+ // buffered channels is that the buffer is static even though it might not be needed
+ // most of the time.
+ //
+ // The approach taken here is to maintain a per-subscription linked list buffer
+ // shrinks on demand. If the buffer reaches the size below, the subscription is
+ // dropped.
+ maxClientSubscriptionBuffer = 8000
)
// BatchElem is an element in a batch request.
@@ -276,9 +292,9 @@ func (c *Client) BatchCall(b []BatchElem) error {
// to return a response for all of them. The wait duration is bounded by the
// context's deadline.
//
-// In contrast to CallContext, BatchCallContext only returns I/O errors. Any
-// error specific to a request is reported through the Error field of the
-// corresponding BatchElem.
+// In contrast to CallContext, BatchCallContext only returns errors that have occurred
+// while sending the request. Any error specific to a request is reported through the
+// Error field of the corresponding BatchElem.
//
// Note that batch calls may not be executed atomically on the server side.
func (c *Client) BatchCallContext(ctx context.Context, b []BatchElem) error {
@@ -338,11 +354,11 @@ func (c *Client) BatchCallContext(ctx context.Context, b []BatchElem) error {
// sent to the given channel. The element type of the channel must match the
// expected type of content returned by the subscription.
//
-// Callers should not use the same channel for multiple calls to EthSubscribe.
-// The channel is closed when the notification is unsubscribed or an error
-// occurs. The error can be retrieved via the Err method of the subscription.
//
-// Slow subscribers will block the clients ingress path eventually.
+// Slow subscribers will be dropped eventually. Client buffers up to 8000 notifications
+// before considering the subscriber dead. The subscription Err channel will receive
+// ErrSubscriptionQueueOverflow. Use a sufficiently large buffer on the channel or ensure
+// that the channel usually has at least one reader to prevent this issue.
func (c *Client) EthSubscribe(channel interface{}, args ...interface{}) (*ClientSubscription, error) {
// Check type of channel first.
chanVal := reflect.ValueOf(channel)
@@ -657,8 +673,7 @@ func newClientSubscription(c *Client, channel reflect.Value) *ClientSubscription
channel: channel,
quit: make(chan struct{}),
err: make(chan error, 1),
- // in is buffered so dispatch can continue even if the subscriber is slow.
- in: make(chan json.RawMessage, clientSubscriptionBuffer),
+ in: make(chan json.RawMessage),
}
return sub
}
@@ -684,13 +699,16 @@ func (sub *ClientSubscription) Unsubscribe() {
func (sub *ClientSubscription) quitWithError(err error, unsubscribeServer bool) {
sub.quitOnce.Do(func() {
+ // The dispatch loop won't be able to execute the unsubscribe call
+ // if it is blocked on deliver. Close sub.quit first because it
+ // unblocks deliver.
+ close(sub.quit)
if unsubscribeServer {
sub.requestUnsubscribe()
}
if err != nil {
sub.err <- err
}
- close(sub.quit)
})
}
@@ -710,32 +728,46 @@ func (sub *ClientSubscription) start() {
func (sub *ClientSubscription) forward() (err error, unsubscribeServer bool) {
cases := []reflect.SelectCase{
{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(sub.quit)},
+ {Dir: reflect.SelectRecv, Chan: reflect.ValueOf(sub.in)},
{Dir: reflect.SelectSend, Chan: sub.channel},
}
+ buffer := list.New()
+ defer buffer.Init()
for {
- select {
- case result := <-sub.in:
- val, err := sub.unmarshal(result)
+ var chosen int
+ var recv reflect.Value
+ if buffer.Len() == 0 {
+ // Idle, omit send case.
+ chosen, recv, _ = reflect.Select(cases[:2])
+ } else {
+ // Non-empty buffer, send the first queued item.
+ cases[2].Send = reflect.ValueOf(buffer.Front().Value)
+ chosen, recv, _ = reflect.Select(cases)
+ }
+
+ switch chosen {
+ case 0: // <-sub.quit
+ return nil, false
+ case 1: // <-sub.in
+ val, err := sub.unmarshal(recv.Interface().(json.RawMessage))
if err != nil {
return err, true
}
- cases[1].Send = val
- switch chosen, _, _ := reflect.Select(cases); chosen {
- case 0: // <-sub.quit
- return nil, false
- case 1: // sub.channel<-
- continue
+ if buffer.Len() == maxClientSubscriptionBuffer {
+ return ErrSubscriptionQueueOverflow, true
}
- case <-sub.quit:
- return nil, false
+ buffer.PushBack(val)
+ case 2: // sub.channel<-
+ cases[2].Send = reflect.Value{} // Don't hold onto the value.
+ buffer.Remove(buffer.Front())
}
}
}
-func (sub *ClientSubscription) unmarshal(result json.RawMessage) (reflect.Value, error) {
+func (sub *ClientSubscription) unmarshal(result json.RawMessage) (interface{}, error) {
val := reflect.New(sub.etype)
err := json.Unmarshal(result, val.Interface())
- return val.Elem(), err
+ return val.Elem().Interface(), err
}
func (sub *ClientSubscription) requestUnsubscribe() error {
diff --git a/rpc/client_test.go b/rpc/client_test.go
index 58dceada066834a56242cb492819bc01b720491c..424d7f5bc0a0aa81725a94c9fdfe54b645aa4bd7 100644
--- a/rpc/client_test.go
+++ b/rpc/client_test.go
@@ -296,6 +296,57 @@ func TestClientSubscribeClose(t *testing.T) {
}
}
+// This test checks that Client doesn't lock up when a single subscriber
+// doesn't read subscription events.
+func TestClientNotificationStorm(t *testing.T) {
+ server := newTestServer("eth", new(NotificationTestService))
+ defer server.Stop()
+
+ doTest := func(count int, wantError bool) {
+ client := DialInProc(server)
+ defer client.Close()
+ ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+ defer cancel()
+
+ // Subscribe on the server. It will start sending many notifications
+ // very quickly.
+ nc := make(chan int)
+ sub, err := client.EthSubscribe(nc, "someSubscription", count, 0)
+ if err != nil {
+ t.Fatal("can't subscribe:", err)
+ }
+ defer sub.Unsubscribe()
+
+ // Process each notification, try to run a call in between each of them.
+ for i := 0; i < count; i++ {
+ select {
+ case val := <-nc:
+ if val != i {
+ t.Fatalf("(%d/%d) unexpected value %d", i, count, val)
+ }
+ case err := <-sub.Err():
+ if wantError && err != ErrSubscriptionQueueOverflow {
+ t.Fatalf("(%d/%d) got error %q, want %q", i, count, err, ErrSubscriptionQueueOverflow)
+ } else if !wantError {
+ t.Fatalf("(%d/%d) got unexpected error %q", i, count, err)
+ }
+ return
+ }
+ var r int
+ err := client.CallContext(ctx, &r, "eth_echo", i)
+ if err != nil {
+ if !wantError {
+ t.Fatalf("(%d/%d) call error: %v", i, count, err)
+ }
+ return
+ }
+ }
+ }
+
+ doTest(8000, false)
+ doTest(10000, true)
+}
+
func TestClientHTTP(t *testing.T) {
server := newTestServer("service", new(Service))
defer server.Stop()
diff --git a/rpc/notification_test.go b/rpc/notification_test.go
index 28050322252265ea3b075e90356c2fdfeb206c85..52352848c4af915f388515da19b1e7857a17d46b 100644
--- a/rpc/notification_test.go
+++ b/rpc/notification_test.go
@@ -34,6 +34,10 @@ type NotificationTestService struct {
unblockHangSubscription chan struct{}
}
+func (s *NotificationTestService) Echo(i int) int {
+ return i
+}
+
func (s *NotificationTestService) wasUnsubCallbackCalled() bool {
s.mu.Lock()
defer s.mu.Unlock()