Implement gateway support Google Cloud Storage

vendor/cloud.google.com/go/storage/reader.go

@@ -0,0 +1,74 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// 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 storage
+
+import (
+	"fmt"
+	"hash/crc32"
+	"io"
+)
+
+var crc32cTable = crc32.MakeTable(crc32.Castagnoli)
+
+// Reader reads a Cloud Storage object.
+// It implements io.Reader.
+type Reader struct {
+	body         io.ReadCloser
+	remain, size int64
+	contentType  string
+	checkCRC     bool   // should we check the CRC?
+	wantCRC      uint32 // the CRC32c value the server sent in the header
+	gotCRC       uint32 // running crc
+}
+
+// Close closes the Reader. It must be called when done reading.
+func (r *Reader) Close() error {
+	return r.body.Close()
+}
+
+func (r *Reader) Read(p []byte) (int, error) {
+	n, err := r.body.Read(p)
+	if r.remain != -1 {
+		r.remain -= int64(n)
+	}
+	if r.checkCRC {
+		r.gotCRC = crc32.Update(r.gotCRC, crc32cTable, p[:n])
+		// Check CRC here. It would be natural to check it in Close, but
+		// everybody defers Close on the assumption that it doesn't return
+		// anything worth looking at.
+		if r.remain == 0 && r.gotCRC != r.wantCRC {
+			return n, fmt.Errorf("storage: bad CRC on read: got %d, want %d",
+				r.gotCRC, r.wantCRC)
+		}
+	}
+	return n, err
+}
+
+// Size returns the size of the object in bytes.
+// The returned value is always the same and is not affected by
+// calls to Read or Close.
+func (r *Reader) Size() int64 {
+	return r.size
+}
+
+// Remain returns the number of bytes left to read, or -1 if unknown.
+func (r *Reader) Remain() int64 {
+	return r.remain
+}
+
+// ContentType returns the content type of the object.
+func (r *Reader) ContentType() string {
+	return r.contentType
+}