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Merge pull request #2891 from fjl/rpc-client-fixes

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rpc: client bug fixes
This commit is contained in:
Péter Szilágyi 2016-08-09 11:51:01 +03:00 committed by GitHub
commit d6625ac34d
4 changed files with 159 additions and 63 deletions
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102
rpc/client.go
View File

@ -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 {
@ -338,12 +354,14 @@ 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.
// The context argument cancels the RPC request that sets up the subscription but has no
// effect on the subscription after EthSubscribe has returned.
//
// Slow subscribers will block the clients ingress path eventually.
func (c *Client) EthSubscribe(channel interface{}, args ...interface{}) (*ClientSubscription, error) {
// 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(ctx context.Context, channel interface{}, args ...interface{}) (*ClientSubscription, error) {
// Check type of channel first.
chanVal := reflect.ValueOf(channel)
if chanVal.Kind() != reflect.Chan || chanVal.Type().ChanDir()&reflect.SendDir == 0 {
@ -365,8 +383,6 @@ func (c *Client) EthSubscribe(channel interface{}, args ...interface{}) (*Client
resp: make(chan *jsonrpcMessage),
sub: newClientSubscription(c, chanVal),
}
ctx, cancel := context.WithTimeout(context.Background(), subscribeTimeout)
defer cancel()
// Send the subscription request.
// The arrival and validity of the response is signaled on sub.quit.
@ -398,6 +414,10 @@ func (c *Client) send(ctx context.Context, op *requestOp, msg interface{}) error
err := c.write(ctx, msg)
c.sendDone <- err
return err
case <-ctx.Done():
// This can happen if the client is overloaded or unable to keep up with
// subscription notifications.
return ctx.Err()
case <-c.didQuit:
return ErrClientQuit
}
@ -653,8 +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
}
@ -680,13 +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)
})
}
@ -706,32 +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 {

59
rpc/client_example_test.go
View File

@ -22,6 +22,7 @@ import (
"time"
"github.com/ethereum/go-ethereum/rpc"
"golang.org/x/net/context"
)
// In this example, our client whishes to track the latest 'block number'
@ -41,7 +42,16 @@ func ExampleClientSubscription() {
// Connect the client.
client, _ := rpc.Dial("ws://127.0.0.1:8485")
subch := make(chan Block)
go subscribeBlocks(client, subch)
// Ensure that subch receives the latest block.
go func() {
for i := 0; ; i++ {
if i > 0 {
time.Sleep(2 * time.Second)
}
subscribeBlocks(client, subch)
}
}()
// Print events from the subscription as they arrive.
for block := range subch {
@ -52,32 +62,27 @@ func ExampleClientSubscription() {
// subscribeBlocks runs in its own goroutine and maintains
// a subscription for new blocks.
func subscribeBlocks(client *rpc.Client, subch chan Block) {
for i := 0; ; i++ {
if i > 0 {
time.Sleep(2 * time.Second)
}
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
// Subscribe to new blocks.
sub, err := client.EthSubscribe(subch, "newBlocks")
if err == rpc.ErrClientQuit {
return // Stop reconnecting if the client was closed.
} else if err != nil {
fmt.Println("subscribe error:", err)
continue
}
// The connection is established now.
// Update the channel with the current block.
var lastBlock Block
if err := client.Call(&lastBlock, "eth_getBlockByNumber", "latest"); err != nil {
fmt.Println("can't get latest block:", err)
continue
}
subch <- lastBlock
// The subscription will deliver events to the channel. Wait for the
// subscription to end for any reason, then loop around to re-establish
// the connection.
fmt.Println("connection lost: ", <-sub.Err())
// Subscribe to new blocks.
sub, err := client.EthSubscribe(ctx, subch, "newBlocks")
if err != nil {
fmt.Println("subscribe error:", err)
return
}
// The connection is established now.
// Update the channel with the current block.
var lastBlock Block
if err := client.CallContext(ctx, &lastBlock, "eth_getBlockByNumber", "latest"); err != nil {
fmt.Println("can't get latest block:", err)
return
}
subch <- lastBlock
// The subscription will deliver events to the channel. Wait for the
// subscription to end for any reason, then loop around to re-establish
// the connection.
fmt.Println("connection lost: ", <-sub.Err())
}

57
rpc/client_test.go
View File

@ -215,7 +215,7 @@ func TestClientSubscribeInvalidArg(t *testing.T) {
t.Error(string(buf))
}
}()
client.EthSubscribe(arg, "foo_bar")
client.EthSubscribe(context.Background(), arg, "foo_bar")
}
check(true, nil)
check(true, 1)
@ -233,7 +233,7 @@ func TestClientSubscribe(t *testing.T) {
nc := make(chan int)
count := 10
sub, err := client.EthSubscribe(nc, "someSubscription", count, 0)
sub, err := client.EthSubscribe(context.Background(), nc, "someSubscription", count, 0)
if err != nil {
t.Fatal("can't subscribe:", err)
}
@ -275,7 +275,7 @@ func TestClientSubscribeClose(t *testing.T) {
err error
)
go func() {
sub, err = client.EthSubscribe(nc, "hangSubscription", 999)
sub, err = client.EthSubscribe(context.Background(), nc, "hangSubscription", 999)
errc <- err
}()
@ -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(ctx, 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()

4
rpc/notification_test.go
View File

@ -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()