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75 lines
2.1 KiB
75 lines
2.1 KiB
8 years ago
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// Copyright 2016 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package storage
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import (
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"fmt"
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"hash/crc32"
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"io"
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)
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var crc32cTable = crc32.MakeTable(crc32.Castagnoli)
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// Reader reads a Cloud Storage object.
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// It implements io.Reader.
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type Reader struct {
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body io.ReadCloser
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remain, size int64
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contentType string
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checkCRC bool // should we check the CRC?
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wantCRC uint32 // the CRC32c value the server sent in the header
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gotCRC uint32 // running crc
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}
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// Close closes the Reader. It must be called when done reading.
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func (r *Reader) Close() error {
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return r.body.Close()
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}
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func (r *Reader) Read(p []byte) (int, error) {
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n, err := r.body.Read(p)
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if r.remain != -1 {
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r.remain -= int64(n)
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}
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if r.checkCRC {
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r.gotCRC = crc32.Update(r.gotCRC, crc32cTable, p[:n])
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// Check CRC here. It would be natural to check it in Close, but
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// everybody defers Close on the assumption that it doesn't return
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// anything worth looking at.
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if r.remain == 0 && r.gotCRC != r.wantCRC {
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return n, fmt.Errorf("storage: bad CRC on read: got %d, want %d",
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r.gotCRC, r.wantCRC)
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}
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}
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return n, err
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}
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// Size returns the size of the object in bytes.
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// The returned value is always the same and is not affected by
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// calls to Read or Close.
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func (r *Reader) Size() int64 {
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return r.size
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}
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// Remain returns the number of bytes left to read, or -1 if unknown.
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func (r *Reader) Remain() int64 {
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return r.remain
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}
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// ContentType returns the content type of the object.
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func (r *Reader) ContentType() string {
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return r.contentType
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}
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