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/expiration.go

@@ -0,0 +1,119 @@
+/*
+ * 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"
+	"time"
+)
+
+var (
+	errLifecycleInvalidDate       = errors.New("Date must be provided in ISO 8601 format")
+	errLifecycleInvalidDays       = errors.New("Days must be positive integer when used with Expiration")
+	errLifecycleInvalidExpiration = errors.New("At least one of Days or Date should be present inside Expiration")
+	errLifecycleDateNotMidnight   = errors.New(" 'Date' must be at midnight GMT")
+)
+
+// ExpirationDays is a type alias to unmarshal Days in Expiration
+type ExpirationDays int
+
+// UnmarshalXML parses number of days from Expiration and validates if
+// greater than zero
+func (eDays *ExpirationDays) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
+	var numDays int
+	err := d.DecodeElement(&numDays, &startElement)
+	if err != nil {
+		return err
+	}
+	if numDays <= 0 {
+		return errLifecycleInvalidDays
+	}
+	*eDays = ExpirationDays(numDays)
+	return nil
+}
+
+// MarshalXML encodes number of days to expire if it is non-zero and
+// encodes empty string otherwise
+func (eDays *ExpirationDays) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
+	if *eDays == ExpirationDays(0) {
+		return nil
+	}
+	return e.EncodeElement(int(*eDays), startElement)
+}
+
+// ExpirationDate is a embedded type containing time.Time to unmarshal
+// Date in Expiration
+type ExpirationDate struct {
+	time.Time
+}
+
+// UnmarshalXML parses date from Expiration and validates date format
+func (eDate *ExpirationDate) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
+	var dateStr string
+	err := d.DecodeElement(&dateStr, &startElement)
+	if err != nil {
+		return err
+	}
+	// While AWS documentation mentions that the date specified
+	// must be present in ISO 8601 format, in reality they allow
+	// users to provide RFC 3339 compliant dates.
+	expDate, err := time.Parse(time.RFC3339, dateStr)
+	if err != nil {
+		return errLifecycleInvalidDate
+	}
+	// Allow only date timestamp specifying midnight GMT
+	hr, min, sec := expDate.Clock()
+	nsec := expDate.Nanosecond()
+	loc := expDate.Location()
+	if !(hr == 0 && min == 0 && sec == 0 && nsec == 0 && loc.String() == time.UTC.String()) {
+		return errLifecycleDateNotMidnight
+	}
+
+	*eDate = ExpirationDate{expDate}
+	return nil
+}
+
+// MarshalXML encodes expiration date if it is non-zero and encodes
+// empty string otherwise
+func (eDate *ExpirationDate) MarshalXML(e *xml.Encoder, startElement xml.StartElement) error {
+	if *eDate == (ExpirationDate{time.Time{}}) {
+		return nil
+	}
+	return e.EncodeElement(eDate.Format(time.RFC3339), startElement)
+}
+
+// Expiration - expiration actions for a rule in lifecycle configuration.
+type Expiration struct {
+	XMLName xml.Name       `xml:"Expiration"`
+	Days    ExpirationDays `xml:"Days,omitempty"`
+	Date    ExpirationDate `xml:"Date,omitempty"`
+}
+
+// Validate - validates the "Expiration" element
+func (e Expiration) Validate() error {
+	// Neither expiration days or date is specified
+	if e.Days == ExpirationDays(0) && e.Date == (ExpirationDate{time.Time{}}) {
+		return errLifecycleInvalidExpiration
+	}
+
+	// Both expiration days and date are specified
+	if e.Days != ExpirationDays(0) && e.Date != (ExpirationDate{time.Time{}}) {
+		return errLifecycleInvalidExpiration
+	}
+	return nil
+}