Fix Faucet (#4624)

* fix faucet

* preston's review

tools/faucet/main.go

@@ -39,6 +39,7 @@ func main() {
 	)
 
 	reflection.Register(s)
+	go counterWatcher()
 
 	fmt.Printf("Serving gRPC requests on port %d\n", *port)
 	if err := s.Serve(lis); err != nil {

tools/faucet/server.go

@@ -22,12 +22,13 @@ import (
 	"google.golang.org/grpc/metadata"
 )
 
-const ipLimit = 3
+const ipLimit = 5
 
 var fundingAmount = big.NewInt(3.5 * params.Ether)
 var funded = make(map[string]bool)
 var ipCounter = make(map[string]int)
 var fundingLock sync.Mutex
+var pruneDuration = time.Hour * 4
 
 type faucetServer struct {
 	r        recaptcha.Recaptcha
@@ -178,3 +179,19 @@ func (s *faucetServer) getPeer(ctx context.Context) (string, error) {
 	peer := md.Get("x-forwarded-for")[0]
 	return peer, nil
 }
+
+// reduce the counter for each ip every few hours.
+func counterWatcher() {
+	ticker := time.NewTicker(pruneDuration)
+	for {
+		<-ticker.C
+		fundingLock.Lock()
+		for ip, ctr := range ipCounter {
+			if ctr == 0 {
+				continue
+			}
+			ipCounter[ip] = ctr - 1
+		}
+		fundingLock.Unlock()
+	}
+}