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minio/erasure-readfile.go

130 lines
3.8 KiB

/*
* Minio Cloud Storage, (C) 2016 Minio, Inc.
*
* 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 main
import (
"bytes"
"errors"
"io"
)
// ReadFile - decoded erasure coded file.
func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int64) (io.Reader, error) {
var totalLeft = totalSize
var bufWriter = new(bytes.Buffer)
for totalLeft > 0 {
// Figure out the right blockSize as it was encoded before.
var curBlockSize int64
if erasureBlockSize < totalLeft {
curBlockSize = erasureBlockSize
} else {
curBlockSize = totalLeft
}
// Calculate the current encoded block size.
curEncBlockSize := getEncodedBlockLen(curBlockSize, e.DataBlocks)
// Allocate encoded blocks up to storage disks.
enBlocks := make([][]byte, len(e.storageDisks))
// Counter to keep success data blocks.
var successDataBlocksCount = 0
var noReconstruct bool // Set for no reconstruction.
// Read from all the disks.
for index, disk := range e.storageDisks {
blockIndex := e.distribution[index] - 1
// Initialize shard slice and fill the data from each parts.
enBlocks[blockIndex] = make([]byte, curEncBlockSize)
if disk == nil {
enBlocks[blockIndex] = nil
} else {
var offset = int64(0)
// Read the necessary blocks.
_, err := disk.ReadFile(volume, path, offset, enBlocks[blockIndex])
if err != nil {
enBlocks[blockIndex] = nil
}
}
// Verify if we have successfully read all the data blocks.
if blockIndex < e.DataBlocks && enBlocks[blockIndex] != nil {
successDataBlocksCount++
// Set when we have all the data blocks and no
// reconstruction is needed, so that we can avoid
// erasure reconstruction.
noReconstruct = successDataBlocksCount == e.DataBlocks
if noReconstruct {
// Break out we have read all the data blocks.
break
}
}
}
// Check blocks if they are all zero in length, we have corruption return error.
if checkBlockSize(enBlocks) == 0 {
return nil, errDataCorrupt
}
// Verify if reconstruction is needed, proceed with reconstruction.
if !noReconstruct {
err := e.ReedSolomon.Reconstruct(enBlocks)
if err != nil {
return nil, err
}
// Verify reconstructed blocks (parity).
ok, err := e.ReedSolomon.Verify(enBlocks)
if err != nil {
return nil, err
}
if !ok {
// Blocks cannot be reconstructed, corrupted data.
err = errors.New("Verification failed after reconstruction, data likely corrupted.")
return nil, err
}
}
// Get data blocks from encoded blocks.
dataBlocks := getDataBlocks(enBlocks, e.DataBlocks, int(curBlockSize))
// Verify if the offset is right for the block, if not move to
// the next block.
if startOffset > 0 {
startOffset = startOffset - int64(len(dataBlocks))
// Start offset is greater than or equal to zero, skip the dataBlocks.
if startOffset >= 0 {
totalLeft = totalLeft - erasureBlockSize
continue
}
// Now get back the remaining offset if startOffset is negative.
startOffset = startOffset + int64(len(dataBlocks))
}
// Copy data blocks.
_, err := bufWriter.Write(dataBlocks[startOffset:])
if err != nil {
return nil, err
}
// Reset dataBlocks to relenquish memory.
dataBlocks = nil
// Save what's left after reading erasureBlockSize.
totalLeft = totalLeft - erasureBlockSize
}
return bufWriter, nil
}