Add rate-limiter (#7)

* Add rate limiter

* Refuse to update state without new inclusion

* Address comments

* Address comment

go.mod

@@ -6,4 +6,5 @@ require (
 	github.com/INFURA/go-ethlibs v0.0.0-20190906161005-7045fb26c40c
 	github.com/jessevdk/go-flags v0.0.0-20141203071132-1679536dcc89
 	github.com/umbracle/go-web3 v0.0.0-20200107141429-b044b1dc2479
+	golang.org/x/time v0.0.0-20191024005414-555d28b269f0
 )

go.sum

@@ -108,6 +108,8 @@ golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
+golang.org/x/time v0.0.0-20191024005414-555d28b269f0 h1:/5xXl8Y5W96D+TtHSlonuFqGHIWVuyCkGJLwGh9JJFs=
+golang.org/x/time v0.0.0-20191024005414-555d28b269f0/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 google.golang.org/appengine v1.6.5/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 gopkg.in/airbrake/gobrake.v2 v2.0.9/go.mod h1:/h5ZAUhDkGaJfjzjKLSjv6zCL6O0LLBxU4K+aSYdM/U=

main.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/INFURA/go-ethlibs/node"
 	flags "github.com/jessevdk/go-flags"
+	"golang.org/x/time/rate"
 )
 
 // Version of the binary, assigned during build.
@@ -21,6 +22,7 @@ var Version = "dev"
 type Options struct {
 	Methods      map[string]int64 `short:"m" long:"method" description:"A map from json rpc methods to their weight" default:"eth_getCode:100" default:"eth_getLogs:250" default:"eth_getTransactionByHash:250" default:"eth_blockNumber:350" default:"eth_getTransactionCount:400" default:"eth_getBlockByNumber:400" default:"eth_getBalance:550" default:"eth_getTransactionReceipt:600" default:"eth_call:2000"`
 	Web3Endpoint string           `long:"rpc" description:"Ethereum JSONRPC provider, such as Infura or Cloudflare" default:"https://mainnet.infura.io/v3/af500e495f2d4e7cbcae36d0bfa66bcb"` // Versus API key on Infura
+	RateLimit    float64          `short:"r" long:"ratelimit" description:"rate limit for generating jsonrpc calls"`
 
 	Version bool `long:"version" description:"Print version and exit."`
 }
@@ -75,6 +77,17 @@ func main() {
 		for {
 			newState, err := mkState.Refresh(&state)
 			if err != nil {
+				// It can happen in some testnets that most of the blocks
+				// are empty(no transaction included), don't refresh the
+				// generator state without new inclusion.
+				if err == errEmptyBlock {
+					select {
+					case <-time.After(5 * time.Second):
+					case <-ctx.Done():
+						return
+					}
+					continue
+				}
 				exit(2, "failed to refresh state")
 			}
 			select {
@@ -90,6 +103,10 @@ func main() {
 		}
 	}()
 
+	var rlimit *rate.Limiter
+	if options.RateLimit != 0 {
+		rlimit = rate.NewLimiter(rate.Limit(options.RateLimit), 10)
+	}
 	state := <-stateChannel
 	for {
 		// Update state when a new one is emitted
@@ -99,6 +116,9 @@ func main() {
 			return
 		default:
 		}
+		if rlimit != nil {
+			rlimit.Wait(context.Background())
+		}
 		if err := gen.Query(os.Stdout, state); err == io.EOF {
 			// Done
 			return

state.go

@@ -10,6 +10,8 @@ import (
 	"github.com/INFURA/go-ethlibs/node"
 )
 
+var errEmptyBlock = errors.New("the sampled block is empty")
+
 type State interface {
 	RandInt64() int64
 	ID() int64
@@ -130,7 +132,10 @@ func (p *stateProducer) Refresh(oldState *liveState) (*liveState, error) {
 	if err != nil {
 		return nil, err
 	}
-
+	// Short circuit if the sampled block is empty
+	if len(b.Transactions) == 0 {
+		return nil, errEmptyBlock
+	}
 	// txs will grow to the maximum contract transaction list size we'll see in a block, and the higher-indexed ones will stick around longer
 	txs := oldState.transactions
 	for i, tx := range b.Transactions {