| // 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 |
| cacheControl 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 |
| } |
| |
| // CacheControl returns the cache control of the object. |
| func (r *Reader) CacheControl() string { |
| return r.cacheControl |
| } |