Cleanup and fixes (#3273)

* newRequestID() (previously generateUploadID()) returns string than byte array.
* Remove unclear comments and added appropriate comments.
* SHA-256, MD5 Hash functions return Hex/Base64 encoded string than byte array.
* Remove duplicate MD5 hasher functions.
* Rename listObjectsValidateArgs() into validateListObjectsArgs()
* Remove repeated auth check code in all bucket request handlers.
* Remove abbreviated names in bucket-metadata
* Avoid nested if in bucketPolicyMatchStatement()
* Use ioutil.ReadFile() instead of os.Open() and ioutil.ReadAll()
* Set crossDomainXML as constant.

cmd/hasher.go

@@ -0,0 +1,48 @@
+/*
+ * Minio Cloud Storage, (C) 2016 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 cmd
+
+import (
+	"crypto/md5"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+)
+
+// getSHA256Hash returns SHA-256 hash of given data.
+func getSHA256Hash(data []byte) string {
+	hash := sha256.New()
+	hash.Write(data)
+	return hex.EncodeToString(hash.Sum(nil))
+}
+
+// getMD5Sum returns MD5 sum of given data.
+func getMD5Sum(data []byte) []byte {
+	hash := md5.New()
+	hash.Write(data)
+	return hash.Sum(nil)
+}
+
+// getMD5Hash returns MD5 hash of given data.
+func getMD5Hash(data []byte) string {
+	return hex.EncodeToString(getMD5Sum(data))
+}
+
+// getMD5HashBase64 returns MD5 hash in base64 encoding of given data.
+func getMD5HashBase64(data []byte) string {
+	return base64.StdEncoding.EncodeToString(getMD5Sum(data))
+}