99 lines
3 KiB
Go
99 lines
3 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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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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*/
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package main
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import "errors"
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// ReadFile - decoded erasure coded file.
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func (e erasure) ReadFile(volume, path string, bufferOffset int64, startOffset int64, buffer []byte) (int64, error) {
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// Calculate the current encoded block size.
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curEncBlockSize := getEncodedBlockLen(int64(len(buffer)), e.DataBlocks)
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offsetEncOffset := getEncodedBlockLen(startOffset, e.DataBlocks)
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// Allocate encoded blocks up to storage disks.
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enBlocks := make([][]byte, len(e.storageDisks))
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// Counter to keep success data blocks.
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var successDataBlocksCount = 0
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var noReconstruct bool // Set for no reconstruction.
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// Read from all the disks.
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for index, disk := range e.storageDisks {
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blockIndex := e.distribution[index] - 1
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// Initialize shard slice and fill the data from each parts.
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enBlocks[blockIndex] = make([]byte, curEncBlockSize)
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if disk == nil {
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enBlocks[blockIndex] = nil
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continue
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}
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// Read the necessary blocks.
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_, err := disk.ReadFile(volume, path, offsetEncOffset, enBlocks[blockIndex])
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if err != nil {
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enBlocks[blockIndex] = nil
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}
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// Verify if we have successfully read all the data blocks.
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if blockIndex < e.DataBlocks && enBlocks[blockIndex] != nil {
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successDataBlocksCount++
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// Set when we have all the data blocks and no
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// reconstruction is needed, so that we can avoid
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// erasure reconstruction.
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noReconstruct = successDataBlocksCount == e.DataBlocks
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if noReconstruct {
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// Break out we have read all the data blocks.
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break
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}
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}
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}
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// Check blocks if they are all zero in length, we have corruption return error.
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if checkBlockSize(enBlocks) == 0 {
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return 0, errDataCorrupt
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}
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// Verify if reconstruction is needed, proceed with reconstruction.
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if !noReconstruct {
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err := e.ReedSolomon.Reconstruct(enBlocks)
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if err != nil {
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return 0, err
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}
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// Verify reconstructed blocks (parity).
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ok, err := e.ReedSolomon.Verify(enBlocks)
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if err != nil {
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return 0, err
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}
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if !ok {
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// Blocks cannot be reconstructed, corrupted data.
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err = errors.New("Verification failed after reconstruction, data likely corrupted.")
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return 0, err
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}
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}
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// Get data blocks from encoded blocks.
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dataBlocks, err := getDataBlocks(enBlocks, e.DataBlocks, len(buffer))
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if err != nil {
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return 0, err
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}
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// Copy data blocks.
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copy(buffer, dataBlocks[bufferOffset:])
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// Relenquish memory.
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dataBlocks = nil
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return int64(len(buffer)), nil
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}
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