Issue 1017 taken port (#1108)

* add git ignore to avoid intellij bazel plugin files.

* check if port for p2p is available

* add unit test for port taken

.gitignore

@@ -6,6 +6,7 @@ bazel-*
 
 # IntelliJ
 .idea
+.ijwb
 
 # delve debugger output (not sure how to get rid of these)
 **/debug.test

shared/p2p/service.go

@@ -3,6 +3,8 @@ package p2p
 import (
 	"context"
 	"fmt"
+	"github.com/prysmaticlabs/prysm/shared/iputils"
+	"net"
 	"reflect"
 	"sync"
 
@@ -53,6 +55,10 @@ func NewServer(cfg *ServerConfig) (*Server, error) {
 	if cfg.RelayNodeAddr != "" {
 		opts = append(opts, libp2p.AddrsFactory(relayAddrsOnly(cfg.RelayNodeAddr)))
 	}
+	if !checkAvailablePort(cfg.Port) {
+		cancel()
+		return nil, fmt.Errorf("error listening on p2p, port %d already taken", cfg.Port)
+	}
 	h, err := libp2p.New(ctx, opts...)
 	if err != nil {
 		cancel()
@@ -84,6 +90,22 @@ func NewServer(cfg *ServerConfig) (*Server, error) {
 	}, nil
 }
 
+func checkAvailablePort(port int) bool {
+	ip, err := iputils.ExternalIPv4()
+	if err != nil {
+		log.Errorf("Could not get IPv4 address: %v", err)
+	}
+
+	ln, err := net.Listen("tcp", fmt.Sprintf("%s:%d", ip, port))
+	if err != nil {
+		return false
+	}
+
+	ln.Close()
+
+	return true
+}
+
 // Start the main routine for an p2p server.
 func (s *Server) Start() {
 	ctx, span := trace.StartSpan(s.ctx, "p2p_server_start")

shared/p2p/service_test.go

@@ -50,6 +50,25 @@ func TestStartDialRelayNodeFails(t *testing.T) {
 	logContains(t, hook, "Could not dial relay node: invalid multiaddr, must begin with /", logrus.ErrorLevel)
 }
 
+func TestP2pPortTakenError(t *testing.T) {
+	thePort := 10000
+	_, err := NewServer(&ServerConfig{
+		Port: thePort,
+	})
+
+	if err != nil {
+		t.Fatalf("unable to create server: %s", err)
+	}
+
+	_, err = NewServer(&ServerConfig{
+		Port: thePort,
+	})
+
+	if !strings.Contains(err.Error(), fmt.Sprintf("port %d already taken", thePort)) {
+		t.Fatalf("expected fail when setting another server with same p2p port")
+	}
+}
+
 func TestBroadcast(t *testing.T) {
 	s, err := NewServer(&ServerConfig{})
 	if err != nil {