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minio/erasure-readfile.go

174 lines
4.7 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 (
"errors"
"io"
"sync"
)
// ReadFile - decoded erasure coded file.
func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int64) (io.ReadCloser, error) {
// Input validation.
if !isValidVolname(volume) {
return nil, errInvalidArgument
}
if !isValidPath(path) {
return nil, errInvalidArgument
}
var rwg = &sync.WaitGroup{}
readers := make([]io.ReadCloser, len(e.storageDisks))
for index, disk := range e.storageDisks {
rwg.Add(1)
go func(index int, disk StorageAPI) {
defer rwg.Done()
// If disk.ReadFile returns error and we don't have read
// quorum it will be taken care as ReedSolomon.Reconstruct()
// will fail later.
offset := int64(0)
if reader, err := disk.ReadFile(volume, path, offset); err == nil {
readers[index] = reader
}
}(index, disk)
}
// Wait for all readers.
rwg.Wait()
// Initialize pipe.
pipeReader, pipeWriter := io.Pipe()
go func() {
var totalLeft = totalSize
// Read until EOF.
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)
enBlocks := make([][]byte, len(e.storageDisks))
// Read all the readers.
for index, reader := range readers {
// Initialize shard slice and fill the data from each parts.
enBlocks[index] = make([]byte, curEncBlockSize)
if reader == nil {
continue
}
// Read the necessary blocks.
_, rErr := io.ReadFull(reader, enBlocks[index])
if rErr != nil && rErr != io.ErrUnexpectedEOF {
readers[index].Close()
readers[index] = nil
}
}
// Check blocks if they are all zero in length.
if checkBlockSize(enBlocks) == 0 {
pipeWriter.CloseWithError(errDataCorrupt)
return
}
// Verify the blocks.
ok, err := e.ReedSolomon.Verify(enBlocks)
if err != nil {
pipeWriter.CloseWithError(err)
return
}
// Verification failed, blocks require reconstruction.
if !ok {
for index, reader := range readers {
if reader == nil {
// Reconstruct expects missing blocks to be nil.
enBlocks[index] = nil
}
}
err = e.ReedSolomon.Reconstruct(enBlocks)
if err != nil {
pipeWriter.CloseWithError(err)
return
}
// Verify reconstructed blocks again.
ok, err = e.ReedSolomon.Verify(enBlocks)
if err != nil {
pipeWriter.CloseWithError(err)
return
}
if !ok {
// Blocks cannot be reconstructed, corrupted data.
err = errors.New("Verification failed after reconstruction, data likely corrupted.")
pipeWriter.CloseWithError(err)
return
}
}
// Get all the data 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))
}
// Write safely the necessary blocks.
_, err = pipeWriter.Write(dataBlocks[int(startOffset):])
if err != nil {
pipeWriter.CloseWithError(err)
return
}
// Reset dataBlocks to relenquish memory.
dataBlocks = nil
// Reset offset to '0' to read rest of the blocks.
startOffset = int64(0)
// Save what's left after reading erasureBlockSize.
totalLeft = totalLeft - erasureBlockSize
}
// Cleanly end the pipe after a successful decoding.
pipeWriter.Close()
// Cleanly close all the underlying data readers.
for _, reader := range readers {
if reader == nil {
continue
}
reader.Close()
}
}()
// Return the pipe for the top level caller to start reading.
return pipeReader, nil
}