make SFTP extensions configurable

sftp.go

@@ -85,10 +85,14 @@ const (
 	sshFxfExcl   = 0x00000020
 )
 
-var sftpExtensions = []sshExtensionPair{
+var (
-	{"hardlink@openssh.com", "1"},
+	// supportedSFTPExtensions defines the supported extensions
-	{"posix-rename@openssh.com", "1"},
+	supportedSFTPExtensions = []sshExtensionPair{
-}
+		{"hardlink@openssh.com", "1"},
+		{"posix-rename@openssh.com", "1"},
+	}
+	sftpExtensions = supportedSFTPExtensions
+)
 
 type fxp uint8
 
@@ -227,3 +231,29 @@ func (s *StatusError) Error() string {
 func (s *StatusError) FxCode() fxerr {
 	return fxerr(s.Code)
 }
+
+func getSupportedExtensionByName(extensionName string) (sshExtensionPair, error) {
+	for _, supportedExtension := range supportedSFTPExtensions {
+		if supportedExtension.Name == extensionName {
+			return supportedExtension, nil
+		}
+	}
+	return sshExtensionPair{}, fmt.Errorf("Unsupported extension: %v", extensionName)
+}
+
+// SetSFTPExtensions allows to customize the supported server extensions.
+// See the variable supportedSFTPExtensions for supported extensions.
+// This method accepts a slice of sshExtensionPair names for example 'hardlink@openssh.com'.
+// If an invalid extension is given an error will be returned and nothing will be changed
+func SetSFTPExtensions(extensions ...string) error {
+	tempExtensions := []sshExtensionPair{}
+	for _, extension := range extensions {
+		sftpExtension, err := getSupportedExtensionByName(extension)
+		if err != nil {
+			return err
+		}
+		tempExtensions = append(tempExtensions, sftpExtension)
+	}
+	sftpExtensions = tempExtensions
+	return nil
+}

sftp_test.go

@@ -26,3 +26,50 @@ func TestErrFxCode(t *testing.T) {
 		assert.Equal(t, statusErr.FxCode(), tt.fx)
 	}
 }
+
+func TestSupportedExtensions(t *testing.T) {
+	for _, supportedExtension := range supportedSFTPExtensions {
+		_, err := getSupportedExtensionByName(supportedExtension.Name)
+		assert.NoError(t, err)
+	}
+	_, err := getSupportedExtensionByName("invalid@example.com")
+	assert.Error(t, err)
+}
+
+func TestExtensions(t *testing.T) {
+	var supportedExtensions []string
+	for _, supportedExtension := range supportedSFTPExtensions {
+		supportedExtensions = append(supportedExtensions, supportedExtension.Name)
+	}
+
+	testSFTPExtensions := []string{"hardlink@openssh.com"}
+	expectedSFTPExtensions := []sshExtensionPair{
+		{"hardlink@openssh.com", "1"},
+	}
+	err := SetSFTPExtensions(testSFTPExtensions...)
+	assert.NoError(t, err)
+	assert.Equal(t, expectedSFTPExtensions, sftpExtensions)
+
+	invalidSFTPExtensions := []string{"invalid@example.com"}
+	err = SetSFTPExtensions(invalidSFTPExtensions...)
+	assert.Error(t, err)
+	assert.Equal(t, expectedSFTPExtensions, sftpExtensions)
+
+	emptySFTPExtensions := []string{}
+	expectedSFTPExtensions = []sshExtensionPair{}
+	err = SetSFTPExtensions(emptySFTPExtensions...)
+	assert.NoError(t, err)
+	assert.Equal(t, expectedSFTPExtensions, sftpExtensions)
+
+	// if we only have an invalid extension nothing will be modified.
+	invalidSFTPExtensions = []string{
+		"hardlink@openssh.com",
+		"invalid@example.com",
+	}
+	err = SetSFTPExtensions(invalidSFTPExtensions...)
+	assert.Error(t, err)
+	assert.Equal(t, expectedSFTPExtensions, sftpExtensions)
+
+	err = SetSFTPExtensions(supportedExtensions...)
+	assert.Equal(t, supportedSFTPExtensions, sftpExtensions)
+}