Code restructuring, assigning proper subsystems to each

- Drivers contain
    * donut/*
    * file/*
    * memory/*

 - Storage format contains
    * donut/*
      - GetObject() --> renamed to GetObjectReader()
      - Deleted stale objectwriter.go, renamed donutwriter.go to object_writer.go

Simplifying, and documenting codebase further

pkg/drivers/driver.go

@@ -0,0 +1,150 @@
+/*
+ * Minimalist Object Storage, (C) 2015 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 drivers
+
+import (
+	"io"
+	"regexp"
+	"time"
+	"unicode/utf8"
+)
+
+// Driver - generic API interface for various drivers - donut, file, memory
+type Driver interface {
+	// Bucket Operations
+	ListBuckets() ([]BucketMetadata, error)
+	CreateBucket(bucket string) error
+	CreateBucketPolicy(bucket string, p BucketPolicy) error
+	GetBucketPolicy(bucket string) (BucketPolicy, error)
+
+	// Object Operations
+	GetObject(w io.Writer, bucket, object string) (int64, error)
+	GetPartialObject(w io.Writer, bucket, object string, start, length int64) (int64, error)
+	GetObjectMetadata(bucket string, object string, prefix string) (ObjectMetadata, error)
+	ListObjects(bucket string, resources BucketResourcesMetadata) ([]ObjectMetadata, BucketResourcesMetadata, error)
+	CreateObject(bucket string, key string, contentType string, md5sum string, data io.Reader) error
+}
+
+// BucketMetadata - name and create date
+type BucketMetadata struct {
+	Name    string
+	Created time.Time
+}
+
+// ObjectMetadata - object key and its relevant metadata
+type ObjectMetadata struct {
+	Bucket string
+	Key    string
+
+	ContentType string
+	Created     time.Time
+	Md5         string
+	Size        int64
+}
+
+// FilterMode type
+type FilterMode int
+
+// FilterMode list
+const (
+	DelimiterPrefixMode FilterMode = iota
+	DelimiterMode
+	PrefixMode
+	DefaultMode
+)
+
+// BucketResourcesMetadata - various types of bucket resources
+type BucketResourcesMetadata struct {
+	Prefix         string
+	Marker         string
+	Maxkeys        int
+	Delimiter      string
+	IsTruncated    bool
+	CommonPrefixes []string
+	Mode           FilterMode
+
+	Policy bool
+	// TODO
+	Logging      string
+	Notification string
+}
+
+// GetMode - Populate filter mode
+func GetMode(resources BucketResourcesMetadata) FilterMode {
+	var f FilterMode
+	switch true {
+	case resources.Delimiter != "" && resources.Prefix != "":
+		f = DelimiterPrefixMode
+	case resources.Delimiter != "" && resources.Prefix == "":
+		f = DelimiterMode
+	case resources.Delimiter == "" && resources.Prefix != "":
+		f = PrefixMode
+	case resources.Delimiter == "" && resources.Prefix == "":
+		f = DefaultMode
+	}
+
+	return f
+}
+
+// IsDelimiterPrefixSet Delimiter and Prefix set
+func (b BucketResourcesMetadata) IsDelimiterPrefixSet() bool {
+	return b.Mode == DelimiterPrefixMode
+}
+
+// IsDelimiterSet Delimiter set
+func (b BucketResourcesMetadata) IsDelimiterSet() bool {
+	return b.Mode == DelimiterMode
+}
+
+// IsPrefixSet Prefix set
+func (b BucketResourcesMetadata) IsPrefixSet() bool {
+	return b.Mode == PrefixMode
+}
+
+// IsDefault No query values
+func (b BucketResourcesMetadata) IsDefault() bool {
+	return b.Mode == DefaultMode
+}
+
+// IsValidBucket - verify bucket name in accordance with
+//  - http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingBucket.html
+func IsValidBucket(bucket string) bool {
+	if len(bucket) < 3 || len(bucket) > 63 {
+		return false
+	}
+	if bucket[0] == '.' || bucket[len(bucket)-1] == '.' {
+		return false
+	}
+	if match, _ := regexp.MatchString("\\.\\.", bucket); match == true {
+		return false
+	}
+	// We don't support buckets with '.' in them
+	match, _ := regexp.MatchString("^[a-zA-Z][a-zA-Z0-9\\-]+[a-zA-Z0-9]$", bucket)
+	return match
+}
+
+// IsValidObject - verify object name in accordance with
+//   - http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingMetadata.html
+func IsValidObject(object string) bool {
+	if len(object) > 1024 || len(object) == 0 {
+		return false
+	}
+	if !utf8.ValidString(object) {
+		return false
+	}
+	return true
+}