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// 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
}
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