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/*
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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 (
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"encoding/hex"
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"errors"
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"github.com/klauspost/reedsolomon"
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)
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// PartObjectChecksum - returns the checksum for the part name from the checksum slice.
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func (e erasureInfo) PartObjectChecksum(partName string) checkSumInfo {
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for _, checksum := range e.Checksum {
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if checksum.Name == partName {
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return checksum
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}
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}
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return checkSumInfo{}
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}
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// xlMetaPartBlockChecksums - get block checksums for a given part.
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func metaPartBlockChecksums(disks []StorageAPI, eInfos []erasureInfo, partName string) (blockCheckSums []checkSumInfo) {
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for index := range disks {
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// Save the read checksums for a given part.
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blockCheckSums = append(blockCheckSums, eInfos[index].PartObjectChecksum(partName))
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}
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return blockCheckSums
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}
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// Takes block index and block distribution to get the disk index.
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func toDiskIndex(blockIdx int, distribution []int) (diskIndex int) {
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diskIndex = -1
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// Find out the right disk index for the input block index.
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for index, blockIndex := range distribution {
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if blockIndex == blockIdx {
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diskIndex = index
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}
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}
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return diskIndex
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}
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// isValidBlock - calculates the checksum hash for the block and
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// validates if its correct returns true for valid cases, false otherwise.
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func isValidBlock(disks []StorageAPI, volume, path string, diskIndex int, blockCheckSums []checkSumInfo) bool {
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// Unknown block index requested, treat it as error.
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if diskIndex == -1 {
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return false
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}
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// Disk is not present, treat entire block to be non existent.
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if disks[diskIndex] == nil {
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return false
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}
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// Read everything for a given block and calculate hash.
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hashWriter := newHash(blockCheckSums[diskIndex].Algorithm)
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hashBytes, err := hashSum(disks[diskIndex], volume, path, hashWriter)
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if err != nil {
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return false
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}
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return hex.EncodeToString(hashBytes) == blockCheckSums[diskIndex].Hash
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}
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// decodeData - decode encoded blocks.
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func decodeData(enBlocks [][]byte, dataBlocks, parityBlocks int) error {
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rs, err := reedsolomon.New(dataBlocks, parityBlocks)
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if err != nil {
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return err
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}
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err = rs.Reconstruct(enBlocks)
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if err != nil {
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return err
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}
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// Verify reconstructed blocks (parity).
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ok, err := rs.Verify(enBlocks)
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if err != nil {
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return 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 err
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}
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return nil
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}
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// ReadFile - decoded erasure coded file.
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func erasureReadFile(disks []StorageAPI, volume string, path string, partName string, size int64, eInfos []erasureInfo) ([]byte, error) {
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// Return data buffer.
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var buffer []byte
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// Total size left
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totalSizeLeft := size
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// Starting offset for reading.
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startOffset := int64(0)
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// Gather previously calculated block checksums.
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blockCheckSums := metaPartBlockChecksums(disks, eInfos, partName)
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// Pick one erasure info.
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eInfo := eInfos[0]
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// Write until each parts are read and exhausted.
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for totalSizeLeft > 0 {
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// Calculate the proper block size.
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var curBlockSize int64
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if eInfo.BlockSize < totalSizeLeft {
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curBlockSize = eInfo.BlockSize
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} else {
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curBlockSize = totalSizeLeft
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}
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// Calculate the current encoded block size.
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curEncBlockSize := getEncodedBlockLen(curBlockSize, eInfo.DataBlocks)
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offsetEncOffset := getEncodedBlockLen(startOffset, eInfo.DataBlocks)
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// Allocate encoded blocks up to storage disks.
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enBlocks := make([][]byte, len(disks))
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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 disks {
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blockIndex := eInfo.Distribution[index] - 1
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if !isValidBlock(disks, volume, path, toDiskIndex(blockIndex, eInfo.Distribution), blockCheckSums) {
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continue
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}
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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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// 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 < eInfo.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 == eInfo.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 nil, 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 := decodeData(enBlocks, eInfo.DataBlocks, eInfo.ParityBlocks)
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if err != nil {
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return nil, 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, eInfo.DataBlocks, int(curBlockSize))
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if err != nil {
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return nil, err
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}
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// Copy data blocks.
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buffer = append(buffer, dataBlocks...)
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// Negate the 'n' size written to client.
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totalSizeLeft -= int64(len(dataBlocks))
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// Increase the offset to move forward.
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startOffset += int64(len(dataBlocks))
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// Relenquish memory.
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dataBlocks = nil
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}
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return buffer, nil
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}
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