oracle: split broadcaster into parts

1. Generic parallel sending part can be reused by state service.
2. Specific oracle marshaling is implemented on top of (1).

pkg/services/helpers/rpcbroadcaster/client.go

@@ -0,0 +1,65 @@
+package rpcbroadcaster
+
+import (
+	"context"
+	"time"
+
+	"github.com/nspcc-dev/neo-go/pkg/rpc/client"
+	"github.com/nspcc-dev/neo-go/pkg/rpc/request"
+	"go.uber.org/zap"
+)
+
+// RPCClient represent rpc client for a single node.
+type RPCClient struct {
+	client      *client.Client
+	addr        string
+	close       chan struct{}
+	responses   chan request.RawParams
+	log         *zap.Logger
+	sendTimeout time.Duration
+	method      SendMethod
+}
+
+// SendMethod represents rpc method for sending data to other nodes.
+type SendMethod func(*client.Client, request.RawParams) error
+
+// NewRPCClient returns new rpc client for provided address and method.
+func (r *RPCBroadcaster) NewRPCClient(addr string, method SendMethod, timeout time.Duration, ch chan request.RawParams) *RPCClient {
+	return &RPCClient{
+		addr:        addr,
+		close:       r.close,
+		responses:   ch,
+		log:         r.Log.With(zap.String("address", addr)),
+		sendTimeout: timeout,
+		method:      method,
+	}
+}
+
+func (c *RPCClient) run() {
+	// We ignore error as not every node can be available on startup.
+	c.client, _ = client.New(context.Background(), "http://"+c.addr, client.Options{
+		DialTimeout:    c.sendTimeout,
+		RequestTimeout: c.sendTimeout,
+	})
+	for {
+		select {
+		case <-c.close:
+			return
+		case ps := <-c.responses:
+			if c.client == nil {
+				var err error
+				c.client, err = client.New(context.Background(), "http://"+c.addr, client.Options{
+					DialTimeout:    c.sendTimeout,
+					RequestTimeout: c.sendTimeout,
+				})
+				if err != nil {
+					continue
+				}
+			}
+			err := c.method(c.client, ps)
+			if err != nil {
+				c.log.Error("error while submitting oracle response", zap.Error(err))
+			}
+		}
+	}
+}