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/bucket_policy.go

@@ -0,0 +1,194 @@
+/*
+ * 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 (
+	"encoding/json"
+	"io"
+	"strings"
+)
+
+// User - canonical
+type User struct {
+	AWS string
+}
+
+// Statement - minio policy statement
+type Statement struct {
+	Sid       string
+	Effect    string
+	Principal User
+	Action    []string
+	Resource  []string
+	// add Condition struct/var TODO - fix it in future if necessary
+}
+
+// BucketPolicy - minio policy collection
+type BucketPolicy struct {
+	Version   string // date in 0000-00-00 format
+	Statement []Statement
+}
+
+// Resource delimiter
+const (
+	MinioResource = "minio:::"
+)
+
+// TODO support canonical user
+// Principal delimiter
+const (
+	MinioPrincipal = "minio::"
+)
+
+// Action map
+var SupportedActionMap = map[string]bool{
+	"*":                        true,
+	"minio:GetObject":          true,
+	"minio:ListBucket":         true,
+	"minio:PutObject":          true,
+	"minio:CreateBucket":       true,
+	"minio:GetBucketPolicy":    true,
+	"minio:DeleteBucketPolicy": true,
+	"minio:ListAllMyBuckets":   true,
+	"minio:PutBucketPolicy":    true,
+}
+
+// Effect map
+var SupportedEffectMap = map[string]bool{
+	"Allow": true,
+	"Deny":  true,
+}
+
+func isValidAction(action []string) bool {
+	for _, a := range action {
+		if !SupportedActionMap[a] {
+			return false
+		}
+	}
+	return true
+}
+
+func isValidEffect(effect string) bool {
+	if SupportedEffectMap[effect] {
+		return true
+	}
+	return false
+}
+
+func isValidResource(resources []string) bool {
+	var ok bool
+	for _, resource := range resources {
+		switch true {
+		case strings.HasPrefix(resource, AwsResource):
+			bucket := strings.SplitAfter(resource, AwsResource)[1]
+			ok = true
+			if len(bucket) == 0 {
+				ok = false
+			}
+		case strings.HasPrefix(resource, MinioResource):
+			bucket := strings.SplitAfter(resource, MinioResource)[1]
+			ok = true
+			if len(bucket) == 0 {
+				ok = false
+			}
+		default:
+			ok = false
+		}
+	}
+	return ok
+}
+
+func isValidPrincipal(principal string) bool {
+	var ok bool
+	if principal == "*" {
+		return true
+	}
+	switch true {
+	case strings.HasPrefix(principal, AwsPrincipal):
+		username := strings.SplitAfter(principal, AwsPrincipal)[1]
+		ok = true
+		if len(username) == 0 {
+			ok = false
+		}
+
+	case strings.HasPrefix(principal, MinioPrincipal):
+		username := strings.SplitAfter(principal, MinioPrincipal)[1]
+		ok = true
+		if len(username) == 0 {
+			ok = false
+		}
+	default:
+		ok = false
+	}
+	return ok
+}
+
+// Parsepolicy - validate request body is proper JSON and in accordance with policy standards
+func Parsepolicy(data io.Reader) (BucketPolicy, bool) {
+	var policy BucketPolicy
+	decoder := json.NewDecoder(data)
+	err := decoder.Decode(&policy)
+	if err != nil {
+		goto error
+	}
+	if len(policy.Version) == 0 {
+		goto error
+	}
+	_, err = parseDate(policy.Version)
+	if err != nil {
+		goto error
+	}
+	if len(policy.Statement) == 0 {
+		goto error
+	}
+
+	for _, statement := range policy.Statement {
+		if len(statement.Sid) == 0 {
+			goto error
+		}
+		if len(statement.Effect) == 0 {
+			goto error
+		}
+		if !isValidEffect(statement.Effect) {
+			goto error
+		}
+
+		if len(statement.Principal.AWS) == 0 {
+			goto error
+		}
+		if !isValidPrincipal(statement.Principal.AWS) {
+			goto error
+		}
+		if len(statement.Action) == 0 {
+			goto error
+		}
+		if !isValidAction(statement.Action) && !isValidActionS3(statement.Action) {
+			goto error
+		}
+		if len(statement.Resource) == 0 {
+			goto error
+		}
+
+		if !isValidResource(statement.Resource) {
+			goto error
+		}
+	}
+	return policy, true
+
+error:
+	return BucketPolicy{}, false
+}