Added NewArnFromString to generalise the functionality of ARN parsing

pkg/notification/notification.go

@@ -21,6 +21,7 @@ import (
 	"encoding/xml"
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/minio/minio-go/v7/pkg/set"
 )
@@ -88,6 +89,27 @@ func NewArn(partition, service, region, accountID, resource string) Arn {
 	}
 }
 
+var (
+	// ErrInvalidArnPrefix is returned when ARN string format does not start with 'arn'
+	ErrInvalidArnPrefix = errors.New("invalid ARN format, must start with 'arn:'")
+	// ErrInvalidArnFormat is returned when ARN string format is not valid
+	ErrInvalidArnFormat = errors.New("invalid ARN format, must be 'arn:<partition>:<service>:<region>:<accountID>:<resource>'")
+)
+
+// NewArnFromString parses string representation of ARN into Arn object.
+// Returns an error if the string format is incorrect.
+func NewArnFromString(arn string) (Arn, error) {
+	parts := strings.Split(arn, ":")
+	if len(parts) != 6 {
+		return Arn{}, ErrInvalidArnFormat
+	}
+	if parts[0] != "arn" {
+		return Arn{}, ErrInvalidArnPrefix
+	}
+
+	return NewArn(parts[1], parts[2], parts[3], parts[4], parts[5]), nil
+}
+
 // String returns the string format of the ARN
 func (arn Arn) String() string {
 	return "arn:" + arn.Partition + ":" + arn.Service + ":" + arn.Region + ":" + arn.AccountID + ":" + arn.Resource

pkg/notification/notification_test.go

@@ -1405,3 +1405,31 @@ func TestConfigEqual(t *testing.T) {
 		})
 	}
 }
+
+func TestNewArnFromString(t *testing.T) {
+	t.Run("valid ARN", func(t *testing.T) {
+		arn := NewArn("partition", "service", "region", "accountID", "resource")
+		arnString := arn.String()
+		arnFromString, err := NewArnFromString(arnString)
+		if err != nil {
+			t.Fatalf("did not exect an error, but got %v", err)
+		}
+		if arnFromString.String() != arnString {
+			t.Errorf("expected ARNs to be equal, but they are not: arnFromString = %s, arn = %s", arnFromString.String(), arnString)
+		}
+	})
+
+	t.Run("invalid ARN format", func(t *testing.T) {
+		_, err := NewArnFromString("arn:only:four:parts")
+		if err != ErrInvalidArnFormat {
+			t.Errorf("expected an error %v, but got %v", ErrInvalidArnFormat, err)
+		}
+	})
+
+	t.Run("invalid ARN prefix", func(t *testing.T) {
+		_, err := NewArnFromString("non-arn:partition:service:region:accountID:resource")
+		if err != ErrInvalidArnPrefix {
+			t.Errorf("expected an error %v, but got %v", ErrInvalidArnPrefix, err)
+		}
+	})
+}