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/lifecycle.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"
+	"io"
+	"strings"
+)
+
+var (
+	errLifecycleTooManyRules      = errors.New("Lifecycle configuration allows a maximum of 1000 rules")
+	errLifecycleNoRule            = errors.New("Lifecycle configuration should have at least one rule")
+	errLifecycleOverlappingPrefix = errors.New("Lifecycle configuration has rules with overlapping prefix")
+)
+
+// Lifecycle - Configuration for bucket lifecycle.
+type Lifecycle struct {
+	XMLName xml.Name `xml:"LifecycleConfiguration"`
+	Rules   []Rule   `xml:"Rule"`
+}
+
+// IsEmpty - returns whether policy is empty or not.
+func (lc Lifecycle) IsEmpty() bool {
+	return len(lc.Rules) == 0
+}
+
+// ParseLifecycleConfig - parses data in given reader to Lifecycle.
+func ParseLifecycleConfig(reader io.Reader) (*Lifecycle, error) {
+	var lc Lifecycle
+	if err := xml.NewDecoder(reader).Decode(&lc); err != nil {
+		return nil, err
+	}
+	if err := lc.Validate(); err != nil {
+		return nil, err
+	}
+	return &lc, nil
+}
+
+// Validate - validates the lifecycle configuration
+func (lc Lifecycle) Validate() error {
+	// Lifecycle config can't have more than 1000 rules
+	if len(lc.Rules) > 1000 {
+		return errLifecycleTooManyRules
+	}
+	// Lifecycle config should have at least one rule
+	if len(lc.Rules) == 0 {
+		return errLifecycleNoRule
+	}
+	// Validate all the rules in the lifecycle config
+	for _, r := range lc.Rules {
+		if err := r.Validate(); err != nil {
+			return err
+		}
+	}
+	// Compare every rule's prefix with every other rule's prefix
+	for i := range lc.Rules {
+		if i == len(lc.Rules)-1 {
+			break
+		}
+		// N B Empty prefixes overlap with all prefixes
+		otherRules := lc.Rules[i+1:]
+		for _, otherRule := range otherRules {
+			if strings.HasPrefix(lc.Rules[i].Filter.Prefix, otherRule.Filter.Prefix) ||
+				strings.HasPrefix(otherRule.Filter.Prefix, lc.Rules[i].Filter.Prefix) {
+				return errLifecycleOverlappingPrefix
+			}
+		}
+	}
+	return nil
+}