// Copyright (c) 2015-2021 MinIO, Inc.//// This file is part of MinIO Object Storage stack//// This program is free software: you can redistribute it and/or modify// it under the terms of the GNU Affero General Public License as published by// the Free Software Foundation, either version 3 of the License, or// (at your option) any later version.//// This program is distributed in the hope that it will be useful// but WITHOUT ANY WARRANTY; without even the implied warranty of// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the// GNU Affero General Public License for more details.//// You should have received a copy of the GNU Affero General Public License// along with this program.  If not, see <http://www.gnu.org/licenses/>. package cmd import (	"bytes"	"context"	"fmt"	"io" 	"github.com/klauspost/reedsolomon"	xioutil "github.com/minio/minio/internal/ioutil"	"github.com/minio/minio/internal/logger") // getDataBlockLen - get length of data blocks from encoded blocks.func getDataBlockLen(enBlocks [][]byte, dataBlocks int) int {	size := 0	// Figure out the data block length.	for _, block := range enBlocks[:dataBlocks] {		size += len(block)	}	return size} // Writes all the data blocks from encoded blocks until requested// outSize length. Provides a way to skip bytes until the offset.func writeDataBlocks(ctx context.Context, dst io.Writer, enBlocks [][]byte, dataBlocks int, offset int64, length int64) (int64, error) {	// Offset and out size cannot be negative.	if offset < 0 || length < 0 {		logger.LogIf(ctx, errUnexpected)		return 0, errUnexpected	} 	// Do we have enough blocks?	if len(enBlocks) < dataBlocks {		logger.LogIf(ctx, fmt.Errorf("diskBlocks(%d)/dataBlocks(%d) - %w", len(enBlocks), dataBlocks, reedsolomon.ErrTooFewShards))		return 0, reedsolomon.ErrTooFewShards	} 	// Do we have enough data?	if int64(getDataBlockLen(enBlocks, dataBlocks)) < length {		logger.LogIf(ctx, fmt.Errorf("getDataBlockLen(enBlocks, dataBlocks)(%d)/length(%d) - %w", getDataBlockLen(enBlocks, dataBlocks), length, reedsolomon.ErrShortData))		return 0, reedsolomon.ErrShortData	} 	// Counter to decrement total left to write.	write := length 	// Counter to increment total written.	var totalWritten int64 	// Write all data blocks to dst.	for _, block := range enBlocks[:dataBlocks] {		// Skip blocks until we have reached our offset.		if offset >= int64(len(block)) {			// Decrement offset.			offset -= int64(len(block))			continue		} else {			// Skip until offset.			block = block[offset:] 			// Reset the offset for next iteration to read everything			// from subsequent blocks.			offset = 0		} 		// We have written all the blocks, write the last remaining block.		if write < int64(len(block)) {			n, err := xioutil.Copy(dst, bytes.NewReader(block[:write]))			if err != nil {				// The writer will be closed incase of range queries, which will emit ErrClosedPipe.				// The reader pipe might be closed at ListObjects io.EOF ignore it.				if err != io.ErrClosedPipe && err != io.EOF {					logger.LogIf(ctx, err)				}				return 0, err			}			totalWritten += n			break		} 		// Copy the block.		n, err := xioutil.Copy(dst, bytes.NewReader(block))		if err != nil {			// The writer will be closed incase of range queries, which will emit ErrClosedPipe.			// The reader pipe might be closed at ListObjects io.EOF ignore it.			if err != io.ErrClosedPipe && err != io.EOF {				logger.LogIf(ctx, err)			}			return 0, err		} 		// Decrement output size.		write -= n 		// Increment written.		totalWritten += n	} 	// Success.	return totalWritten, nil}