Add initial support for bucket lifecycle (#7563)

This PR is based off @sinhaashish's PR for object lifecycle
management, which includes support only for,
- Expiration of object
- Filter using object prefix (_not_ object tags)

N B the code for actual expiration of objects will be included in a
subsequent PR.

pkg/lifecycle/rule.go

@@ -0,0 +1,86 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package lifecycle
+
+import (
+	"encoding/xml"
+	"errors"
+)
+
+// Rule - a rule for lifecycle configuration.
+type Rule struct {
+	XMLName    xml.Name   `xml:"Rule"`
+	ID         string     `xml:"ID,omitempty"`
+	Status     string     `xml:"Status"`
+	Filter     Filter     `xml:"Filter"`
+	Expiration Expiration `xml:"Expiration,omitempty"`
+	Transition Transition `xml:"Transition,omitempty"`
+	// FIXME: add a type to catch unsupported AbortIncompleteMultipartUpload AbortIncompleteMultipartUpload `xml:"AbortIncompleteMultipartUpload,omitempty"`
+	NoncurrentVersionExpiration NoncurrentVersionExpiration `xml:"NoncurrentVersionExpiration,omitempty"`
+	NoncurrentVersionTransition NoncurrentVersionTransition `xml:"NoncurrentVersionTransition,omitempty"`
+}
+
+var (
+	errInvalidRuleID           = errors.New("ID must be less than 255 characters")
+	errEmptyRuleStatus         = errors.New("Status should not be empty")
+	errInvalidRuleStatus       = errors.New("Status must be set to either Enabled or Disabled")
+	errMissingExpirationAction = errors.New("No expiration action found")
+)
+
+// isIDValid - checks if ID is valid or not.
+func (r Rule) validateID() error {
+	// cannot be longer than 255 characters
+	if len(string(r.ID)) > 255 {
+		return errInvalidRuleID
+	}
+	return nil
+}
+
+// isStatusValid - checks if status is valid or not.
+func (r Rule) validateStatus() error {
+	// Status can't be empty
+	if len(r.Status) == 0 {
+		return errEmptyRuleStatus
+	}
+
+	// Status must be one of Enabled or Disabled
+	if r.Status != "Enabled" && r.Status != "Disabled" {
+		return errInvalidRuleStatus
+	}
+	return nil
+}
+
+func (r Rule) validateAction() error {
+	if r.Expiration == (Expiration{}) {
+		return errMissingExpirationAction
+	}
+	return nil
+}
+
+// Validate - validates the rule element
+func (r Rule) Validate() error {
+	if err := r.validateID(); err != nil {
+		return err
+	}
+	if err := r.validateStatus(); err != nil {
+		return err
+	}
+	if err := r.validateAction(); err != nil {
+		return err
+	}
+	return nil
+}