109 lines
3 KiB
Go
109 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 cmd
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import (
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"bytes"
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"io"
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"github.com/klauspost/reedsolomon"
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"github.com/minio/minio/pkg/errors"
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)
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// getDataBlockLen - get length of data blocks from encoded blocks.
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func getDataBlockLen(enBlocks [][]byte, dataBlocks int) int {
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size := 0
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// Figure out the data block length.
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for _, block := range enBlocks[:dataBlocks] {
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size += len(block)
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}
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return size
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}
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// Writes all the data blocks from encoded blocks until requested
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// outSize length. Provides a way to skip bytes until the offset.
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func writeDataBlocks(dst io.Writer, enBlocks [][]byte, dataBlocks int, offset int64, length int64) (int64, error) {
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// Offset and out size cannot be negative.
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if offset < 0 || length < 0 {
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return 0, errors.Trace(errUnexpected)
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}
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// Do we have enough blocks?
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if len(enBlocks) < dataBlocks {
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return 0, errors.Trace(reedsolomon.ErrTooFewShards)
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}
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// Do we have enough data?
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if int64(getDataBlockLen(enBlocks, dataBlocks)) < length {
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return 0, errors.Trace(reedsolomon.ErrShortData)
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}
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// Counter to decrement total left to write.
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write := length
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// Counter to increment total written.
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var totalWritten int64
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// Write all data blocks to dst.
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for _, block := range enBlocks[:dataBlocks] {
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// Skip blocks until we have reached our offset.
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if offset >= int64(len(block)) {
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// Decrement offset.
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offset -= int64(len(block))
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continue
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} else {
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// Skip until offset.
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block = block[offset:]
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// Reset the offset for next iteration to read everything
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// from subsequent blocks.
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offset = 0
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}
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// We have written all the blocks, write the last remaining block.
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if write < int64(len(block)) {
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n, err := io.Copy(dst, bytes.NewReader(block[:write]))
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if err != nil {
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return 0, errors.Trace(err)
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}
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totalWritten += n
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break
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}
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// Copy the block.
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n, err := io.Copy(dst, bytes.NewReader(block))
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if err != nil {
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return 0, errors.Trace(err)
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}
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// Decrement output size.
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write -= n
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// Increment written.
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totalWritten += n
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}
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// Success.
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return totalWritten, nil
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}
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// chunkSize is roughly BlockSize/DataBlocks.
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// chunkSize is calculated such that chunkSize*DataBlocks accommodates BlockSize bytes.
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// So chunkSize*DataBlocks can be slightly larger than BlockSize if BlockSize is not divisible by
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// DataBlocks. The extra space will have 0-padding.
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func getChunkSize(blockSize int64, dataBlocks int) int64 {
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return (blockSize + int64(dataBlocks) - 1) / int64(dataBlocks)
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}
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