Check to see if OpenFile has the O_EXCL flag and return the appropriate error if it does.

Author: jawr

memfs/memory.go

@@ -51,6 +51,10 @@ func (fs *Memory) OpenFile(filename string, flag int, perm os.FileMode) (billy.F
 			return nil, err
 		}
 	} else {
+		if isExclusive(flag) {
+			return nil, os.ErrExist
+		}
+
 		if target, isLink := fs.resolveLink(filename, f); isLink {
 			return fs.OpenFile(target, flag, perm)
 		}
@@ -368,6 +372,10 @@ func isCreate(flag int) bool {
 	return flag&os.O_CREATE != 0
 }
 
+func isExclusive(flag int) bool {
+	return flag&os.O_EXCL != 0
+}
+
 func isAppend(flag int) bool {
 	return flag&os.O_APPEND != 0
 }

memfs/memory_test.go

@@ -1,7 +1,9 @@
 package memfs
 
 import (
+	"fmt"
 	"io"
+	"os"
 	"testing"
 
 	"github.com/go-git/go-billy/v5"
@@ -44,3 +46,16 @@ func (s *MemorySuite) TestNegativeOffsets(c *C) {
 	_, err = f.Write(buf)
 	c.Assert(err, ErrorMatches, "writeat negative: negative offset")
 }
+
+func (s *MemorySuite) TestExclusive(c *C) {
+	f, err := s.FS.OpenFile("exclusive", os.O_CREATE|os.O_EXCL|os.O_RDWR, 0666)
+	c.Assert(err, IsNil)
+
+	fmt.Fprint(f, "mememememe")
+
+	err = f.Close()
+	c.Assert(err, IsNil)
+
+	_, err = s.FS.OpenFile("exclusive", os.O_CREATE|os.O_EXCL|os.O_RDWR, 0666)
+	c.Assert(err, ErrorMatches, os.ErrExist.Error())
+}