limit number of /subscribe clients and queries per client (#3269)

* limit number of /subscribe clients and queries per client

Add the following config variables (under [rpc] section):
  * max_subscription_clients
  * max_subscriptions_per_client
  * timeout_broadcast_tx_commit

Fixes #2826

new HTTPClient interface for subscriptions

finalize HTTPClient events interface

remove EventSubscriber

fix data race

```
WARNING: DATA RACE
Read at 0x00c000a36060 by goroutine 129:
  github.com/tendermint/tendermint/rpc/client.(*Local).Subscribe.func1()
      /go/src/github.com/tendermint/tendermint/rpc/client/localclient.go:168 +0x1f0

Previous write at 0x00c000a36060 by goroutine 132:
  github.com/tendermint/tendermint/rpc/client.(*Local).Subscribe()
      /go/src/github.com/tendermint/tendermint/rpc/client/localclient.go:191 +0x4e0
  github.com/tendermint/tendermint/rpc/client.WaitForOneEvent()
      /go/src/github.com/tendermint/tendermint/rpc/client/helpers.go:64 +0x178
  github.com/tendermint/tendermint/rpc/client_test.TestTxEventsSentWithBroadcastTxSync.func1()
      /go/src/github.com/tendermint/tendermint/rpc/client/event_test.go:139 +0x298
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162

Goroutine 129 (running) created at:
  github.com/tendermint/tendermint/rpc/client.(*Local).Subscribe()
      /go/src/github.com/tendermint/tendermint/rpc/client/localclient.go:164 +0x4b7
  github.com/tendermint/tendermint/rpc/client.WaitForOneEvent()
      /go/src/github.com/tendermint/tendermint/rpc/client/helpers.go:64 +0x178
  github.com/tendermint/tendermint/rpc/client_test.TestTxEventsSentWithBroadcastTxSync.func1()
      /go/src/github.com/tendermint/tendermint/rpc/client/event_test.go:139 +0x298
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162

Goroutine 132 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:878 +0x659
  github.com/tendermint/tendermint/rpc/client_test.TestTxEventsSentWithBroadcastTxSync()
      /go/src/github.com/tendermint/tendermint/rpc/client/event_test.go:119 +0x186
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162
==================
```

lite client works (tested manually)

godoc comments

httpclient: do not close the out channel

use TimeoutBroadcastTxCommit

no timeout for unsubscribe

but 1s Local (5s HTTP) timeout for resubscribe

format code

change Subscribe#out cap to 1

and replace config vars with RPCConfig

TimeoutBroadcastTxCommit can't be greater than rpcserver.WriteTimeout

rpc: Context as first parameter to all functions

reformat code

fixes after my own review

fixes after Ethan's review

add test stubs

fix config.toml

* fixes after manual testing

- rpc: do not recommend to use BroadcastTxCommit because it's slow and wastes
Tendermint resources (pubsub)
- rpc: better error in Subscribe and BroadcastTxCommit
- HTTPClient: do not resubscribe if err = ErrAlreadySubscribed

* fixes after Ismail's review

* Update rpc/grpc/grpc_test.go

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

lite/proxy/wrapper.go

@@ -1,12 +1,16 @@
 package proxy
 
 import (
+	"context"
+	"fmt"
+
 	cmn "github.com/tendermint/tendermint/libs/common"
 
 	"github.com/tendermint/tendermint/crypto/merkle"
 	"github.com/tendermint/tendermint/lite"
 	rpcclient "github.com/tendermint/tendermint/rpc/client"
 	ctypes "github.com/tendermint/tendermint/rpc/core/types"
+	rpctypes "github.com/tendermint/tendermint/rpc/lib/types"
 )
 
 var _ rpcclient.Client = Wrapper{}
@@ -149,6 +153,55 @@ func (w Wrapper) RegisterOpDecoder(typ string, dec merkle.OpDecoder) {
 	w.prt.RegisterOpDecoder(typ, dec)
 }
 
+// SubscribeWS subscribes for events using the given query and remote address as
+// a subscriber, but does not verify responses (UNSAFE)!
+func (w Wrapper) SubscribeWS(ctx *rpctypes.Context, query string) (*ctypes.ResultSubscribe, error) {
+	out, err := w.Client.Subscribe(context.Background(), ctx.RemoteAddr(), query)
+	if err != nil {
+		return nil, err
+	}
+
+	go func() {
+		for {
+			select {
+			case resultEvent := <-out:
+				// XXX(melekes) We should have a switch here that performs a validation
+				// depending on the event's type.
+				ctx.WSConn.TryWriteRPCResponse(
+					rpctypes.NewRPCSuccessResponse(
+						ctx.WSConn.Codec(),
+						rpctypes.JSONRPCStringID(fmt.Sprintf("%v#event", ctx.JSONReq.ID)),
+						resultEvent,
+					))
+			case <-w.Client.Quit():
+				return
+			}
+		}
+	}()
+
+	return &ctypes.ResultSubscribe{}, nil
+}
+
+// UnsubscribeWS calls original client's Unsubscribe using remote address as a
+// subscriber.
+func (w Wrapper) UnsubscribeWS(ctx *rpctypes.Context, query string) (*ctypes.ResultUnsubscribe, error) {
+	err := w.Client.Unsubscribe(context.Background(), ctx.RemoteAddr(), query)
+	if err != nil {
+		return nil, err
+	}
+	return &ctypes.ResultUnsubscribe{}, nil
+}
+
+// UnsubscribeAllWS calls original client's UnsubscribeAll using remote address
+// as a subscriber.
+func (w Wrapper) UnsubscribeAllWS(ctx *rpctypes.Context) (*ctypes.ResultUnsubscribe, error) {
+	err := w.Client.UnsubscribeAll(context.Background(), ctx.RemoteAddr())
+	if err != nil {
+		return nil, err
+	}
+	return &ctypes.ResultUnsubscribe{}, nil
+}
+
 // // WrappedSwitch creates a websocket connection that auto-verifies any info
 // // coming through before passing it along.
 // //