gateway: Use default params when no args provided (#4315)

For S3 & Azure, use default parameters when no arguments (endpoint) are
provided. This also avoids a crash.

cmd/gateway-s3.go

@@ -17,13 +17,15 @@
 package cmd
 
 import (
-	"encoding/hex"
 	"errors"
 	"io"
 	"net/http"
 	"os"
 	"path"
 
+	"encoding/hex"
+
+	"github.com/minio/cli"
 	minio "github.com/minio/minio-go"
 	"github.com/minio/minio-go/pkg/policy"
 )
@@ -99,15 +101,21 @@ type s3Objects struct {
 }
 
 // newS3Gateway returns s3 gatewaylayer
-func newS3Gateway(args []string) (GatewayLayer, error) {
-	endpoint, secure, err := parseGatewayEndpoint(args[0])
-	if err != nil {
-		return nil, err
-	}
+func newS3Gateway(args cli.Args) (GatewayLayer, error) {
 
-	if endpoint == "" {
-		endpoint = "s3.amazonaws.com"
-		secure = true
+	var err error
+
+	// Default endpoint parameters
+	endpoint := "s3.amazonaws.com"
+	secure := true
+
+	// Check if user provided some parameters
+	if len(args) > 0 {
+		// Override default params if the endpoint is provided
+		endpoint, secure, err = parseGatewayEndpoint(args.First())
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	accessKey := os.Getenv("MINIO_ACCESS_KEY")