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minio/cmd/xl-v1-object.go

741 lines
24 KiB

/*
* Minio Cloud Storage, (C) 2016, 2017 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 cmd
import (
"encoding/hex"
"io"
"path"
"strconv"
"strings"
"sync"
"github.com/minio/minio/pkg/errors"
"github.com/minio/minio/pkg/hash"
"github.com/minio/minio/pkg/mimedb"
"github.com/minio/minio/pkg/objcache"
)
// list all errors which can be ignored in object operations.
var objectOpIgnoredErrs = append(baseIgnoredErrs, errDiskAccessDenied)
// prepareFile hints the bottom layer to optimize the creation of a new object
func (xl xlObjects) prepareFile(bucket, object string, size int64, onlineDisks []StorageAPI, blockSize int64, dataBlocks, writeQuorum int) error {
pErrs := make([]error, len(onlineDisks))
// Calculate the real size of the part in one disk.
actualSize := xl.sizeOnDisk(size, blockSize, dataBlocks)
// Prepare object creation in a all disks
for index, disk := range onlineDisks {
if disk != nil {
if err := disk.PrepareFile(bucket, object, actualSize); err != nil {
// Save error to reduce it later
pErrs[index] = err
// Ignore later access to disk which generated the error
onlineDisks[index] = nil
}
}
}
return reduceWriteQuorumErrs(pErrs, objectOpIgnoredErrs, writeQuorum)
}
/// Object Operations
// CopyObject - copy object source object to destination object.
// if source object and destination object are same we only
// update metadata.
func (xl xlObjects) CopyObject(srcBucket, srcObject, dstBucket, dstObject string, metadata map[string]string) (oi ObjectInfo, e error) {
// Read metadata associated with the object from all disks.
metaArr, errs := readAllXLMetadata(xl.storageDisks, srcBucket, srcObject)
// get Quorum for this object
readQuorum, writeQuorum, err := objectQuorumFromMeta(xl, metaArr, errs)
if err != nil {
return oi, toObjectErr(err, srcBucket, srcObject)
}
if reducedErr := reduceReadQuorumErrs(errs, objectOpIgnoredErrs, readQuorum); reducedErr != nil {
return oi, toObjectErr(reducedErr, srcBucket, srcObject)
}
// List all online disks.
onlineDisks, modTime := listOnlineDisks(xl.storageDisks, metaArr, errs)
// Pick latest valid metadata.
xlMeta, err := pickValidXLMeta(metaArr, modTime)
if err != nil {
return oi, toObjectErr(err, srcBucket, srcObject)
}
// Reorder online disks based on erasure distribution order.
onlineDisks = shuffleDisks(onlineDisks, xlMeta.Erasure.Distribution)
// Length of the file to read.
length := xlMeta.Stat.Size
// Check if this request is only metadata update.
cpMetadataOnly := isStringEqual(pathJoin(srcBucket, srcObject), pathJoin(dstBucket, dstObject))
if cpMetadataOnly {
xlMeta.Meta = metadata
partsMetadata := make([]xlMetaV1, len(xl.storageDisks))
// Update `xl.json` content on each disks.
for index := range partsMetadata {
partsMetadata[index] = xlMeta
}
tempObj := mustGetUUID()
// Write unique `xl.json` for each disk.
if onlineDisks, err = writeUniqueXLMetadata(onlineDisks, minioMetaTmpBucket, tempObj, partsMetadata, writeQuorum); err != nil {
return oi, toObjectErr(err, srcBucket, srcObject)
}
// Rename atomically `xl.json` from tmp location to destination for each disk.
if _, err = renameXLMetadata(onlineDisks, minioMetaTmpBucket, tempObj, srcBucket, srcObject, writeQuorum); err != nil {
return oi, toObjectErr(err, srcBucket, srcObject)
}
return xlMeta.ToObjectInfo(srcBucket, srcObject), nil
}
// Initialize pipe.
pipeReader, pipeWriter := io.Pipe()
go func() {
var startOffset int64 // Read the whole file.
if gerr := xl.GetObject(srcBucket, srcObject, startOffset, length, pipeWriter); gerr != nil {
errorIf(gerr, "Unable to read %s of the object `%s/%s`.", srcBucket, srcObject)
pipeWriter.CloseWithError(toObjectErr(gerr, srcBucket, srcObject))
return
}
pipeWriter.Close() // Close writer explicitly signalling we wrote all data.
}()
hashReader, err := hash.NewReader(pipeReader, length, "", "")
if err != nil {
return oi, toObjectErr(errors.Trace(err), dstBucket, dstObject)
}
objInfo, err := xl.PutObject(dstBucket, dstObject, hashReader, metadata)
if err != nil {
return oi, toObjectErr(err, dstBucket, dstObject)
}
// Explicitly close the reader.
pipeReader.Close()
return objInfo, nil
}
// GetObject - reads an object erasured coded across multiple
// disks. Supports additional parameters like offset and length
// which are synonymous with HTTP Range requests.
//
// startOffset indicates the starting read location of the object.
// length indicates the total length of the object.
func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length int64, writer io.Writer) error {
if err := checkGetObjArgs(bucket, object); err != nil {
return err
}
// Start offset cannot be negative.
if startOffset < 0 {
return errors.Trace(errUnexpected)
}
// Writer cannot be nil.
if writer == nil {
return errors.Trace(errUnexpected)
}
// Read metadata associated with the object from all disks.
metaArr, errs := readAllXLMetadata(xl.storageDisks, bucket, object)
// get Quorum for this object
readQuorum, _, err := objectQuorumFromMeta(xl, metaArr, errs)
if err != nil {
return toObjectErr(err, bucket, object)
}
if reducedErr := reduceReadQuorumErrs(errs, objectOpIgnoredErrs, readQuorum); reducedErr != nil {
return toObjectErr(reducedErr, bucket, object)
}
// List all online disks.
onlineDisks, modTime := listOnlineDisks(xl.storageDisks, metaArr, errs)
// Pick latest valid metadata.
xlMeta, err := pickValidXLMeta(metaArr, modTime)
if err != nil {
return err
}
// Reorder online disks based on erasure distribution order.
onlineDisks = shuffleDisks(onlineDisks, xlMeta.Erasure.Distribution)
// Reorder parts metadata based on erasure distribution order.
metaArr = shufflePartsMetadata(metaArr, xlMeta.Erasure.Distribution)
// For negative length read everything.
if length < 0 {
length = xlMeta.Stat.Size - startOffset
}
// Reply back invalid range if the input offset and length fall out of range.
if startOffset > xlMeta.Stat.Size || startOffset+length > xlMeta.Stat.Size {
return errors.Trace(InvalidRange{startOffset, length, xlMeta.Stat.Size})
}
// Get start part index and offset.
partIndex, partOffset, err := xlMeta.ObjectToPartOffset(startOffset)
if err != nil {
return errors.Trace(InvalidRange{startOffset, length, xlMeta.Stat.Size})
}
// Calculate endOffset according to length
endOffset := startOffset
if length > 0 {
endOffset += length - 1
}
// Get last part index to read given length.
lastPartIndex, _, err := xlMeta.ObjectToPartOffset(endOffset)
if err != nil {
return errors.Trace(InvalidRange{startOffset, length, xlMeta.Stat.Size})
}
// Save the writer.
mw := writer
// Object cache enabled block.
if xlMeta.Stat.Size > 0 && xl.objCacheEnabled {
// Validate if we have previous cache.
var cachedBuffer io.ReaderAt
cachedBuffer, err = xl.objCache.Open(path.Join(bucket, object), modTime)
if err == nil { // Cache hit
// Create a new section reader, starting at an offset with length.
reader := io.NewSectionReader(cachedBuffer, startOffset, length)
// Copy the data out.
if _, err = io.Copy(writer, reader); err != nil {
return errors.Trace(err)
}
// Success.
return nil
} // Cache miss.
// For unknown error, return and error out.
if err != objcache.ErrKeyNotFoundInCache {
return errors.Trace(err)
} // Cache has not been found, fill the cache.
// Cache is only set if whole object is being read.
if startOffset == 0 && length == xlMeta.Stat.Size {
// Proceed to set the cache.
var newBuffer io.WriteCloser
// Create a new entry in memory of length.
newBuffer, err = xl.objCache.Create(path.Join(bucket, object), length)
if err == nil {
// Create a multi writer to write to both memory and client response.
mw = io.MultiWriter(newBuffer, writer)
defer newBuffer.Close()
}
// Ignore error if cache is full, proceed to write the object.
if err != nil && err != objcache.ErrCacheFull {
// For any other error return here.
return toObjectErr(errors.Trace(err), bucket, object)
}
}
}
var totalBytesRead int64
storage, err := NewErasureStorage(onlineDisks, xlMeta.Erasure.DataBlocks, xlMeta.Erasure.ParityBlocks, xlMeta.Erasure.BlockSize)
if err != nil {
return toObjectErr(err, bucket, object)
}
checksums := make([][]byte, len(storage.disks))
for ; partIndex <= lastPartIndex; partIndex++ {
if length == totalBytesRead {
break
}
// Save the current part name and size.
partName := xlMeta.Parts[partIndex].Name
partSize := xlMeta.Parts[partIndex].Size
readSize := partSize - partOffset
// readSize should be adjusted so that we don't write more data than what was requested.
if readSize > (length - totalBytesRead) {
readSize = length - totalBytesRead
}
// Get the checksums of the current part.
var algorithm BitrotAlgorithm
for index, disk := range storage.disks {
if disk == OfflineDisk {
continue
}
checksumInfo := metaArr[index].Erasure.GetChecksumInfo(partName)
algorithm = checksumInfo.Algorithm
checksums[index] = checksumInfo.Hash
}
file, err := storage.ReadFile(mw, bucket, pathJoin(object, partName), partOffset, readSize, partSize, checksums, algorithm, xlMeta.Erasure.BlockSize)
if err != nil {
errorIf(err, "Unable to read %s of the object `%s/%s`.", partName, bucket, object)
return toObjectErr(err, bucket, object)
}
// Track total bytes read from disk and written to the client.
totalBytesRead += file.Size
// partOffset will be valid only for the first part, hence reset it to 0 for
// the remaining parts.
partOffset = 0
} // End of read all parts loop.
// Return success.
return nil
}
// GetObjectInfo - reads object metadata and replies back ObjectInfo.
func (xl xlObjects) GetObjectInfo(bucket, object string) (oi ObjectInfo, e error) {
if err := checkGetObjArgs(bucket, object); err != nil {
return oi, err
}
info, err := xl.getObjectInfo(bucket, object)
if err != nil {
return oi, toObjectErr(err, bucket, object)
}
return info, nil
}
// getObjectInfo - wrapper for reading object metadata and constructs ObjectInfo.
func (xl xlObjects) getObjectInfo(bucket, object string) (objInfo ObjectInfo, err error) {
// Extracts xlStat and xlMetaMap.
xlStat, xlMetaMap, err := xl.readXLMetaStat(bucket, object)
if err != nil {
return ObjectInfo{}, err
}
objInfo = ObjectInfo{
IsDir: false,
Bucket: bucket,
Name: object,
Size: xlStat.Size,
ModTime: xlStat.ModTime,
ContentType: xlMetaMap["content-type"],
ContentEncoding: xlMetaMap["content-encoding"],
}
// Extract etag.
objInfo.ETag = extractETag(xlMetaMap)
// etag/md5Sum has already been extracted. We need to
// remove to avoid it from appearing as part of
// response headers. e.g, X-Minio-* or X-Amz-*.
objInfo.UserDefined = cleanMetadata(xlMetaMap)
// Success.
return objInfo, nil
}
func undoRename(disks []StorageAPI, srcBucket, srcEntry, dstBucket, dstEntry string, isDir bool, errs []error) {
var wg = &sync.WaitGroup{}
// Undo rename object on disks where RenameFile succeeded.
// If srcEntry/dstEntry are objects then add a trailing slash to copy
// over all the parts inside the object directory
if isDir {
srcEntry = retainSlash(srcEntry)
dstEntry = retainSlash(dstEntry)
}
for index, disk := range disks {
if disk == nil {
continue
}
// Undo rename object in parallel.
wg.Add(1)
go func(index int, disk StorageAPI) {
defer wg.Done()
if errs[index] != nil {
return
}
_ = disk.RenameFile(dstBucket, dstEntry, srcBucket, srcEntry)
}(index, disk)
}
wg.Wait()
}
// rename - common function that renamePart and renameObject use to rename
// the respective underlying storage layer representations.
func rename(disks []StorageAPI, srcBucket, srcEntry, dstBucket, dstEntry string, isDir bool, writeQuorum int) ([]StorageAPI, error) {
// Initialize sync waitgroup.
var wg = &sync.WaitGroup{}
// Initialize list of errors.
var errs = make([]error, len(disks))
if isDir {
dstEntry = retainSlash(dstEntry)
srcEntry = retainSlash(srcEntry)
}
// Rename file on all underlying storage disks.
for index, disk := range disks {
if disk == nil {
errs[index] = errDiskNotFound
continue
}
wg.Add(1)
go func(index int, disk StorageAPI) {
defer wg.Done()
err := disk.RenameFile(srcBucket, srcEntry, dstBucket, dstEntry)
if err != nil && err != errFileNotFound {
errs[index] = errors.Trace(err)
}
}(index, disk)
}
// Wait for all renames to finish.
wg.Wait()
// We can safely allow RenameFile errors up to len(xl.storageDisks) - writeQuorum
// otherwise return failure. Cleanup successful renames.
err := reduceWriteQuorumErrs(errs, objectOpIgnoredErrs, writeQuorum)
if errors.Cause(err) == errXLWriteQuorum {
// Undo all the partial rename operations.
undoRename(disks, srcBucket, srcEntry, dstBucket, dstEntry, isDir, errs)
}
return evalDisks(disks, errs), err
}
// renamePart - renames a part of the source object to the destination
// across all disks in parallel. Additionally if we have errors and do
// not have a readQuorum partially renamed files are renamed back to
// its proper location.
func renamePart(disks []StorageAPI, srcBucket, srcPart, dstBucket, dstPart string, quorum int) ([]StorageAPI, error) {
isDir := false
return rename(disks, srcBucket, srcPart, dstBucket, dstPart, isDir, quorum)
}
// renameObject - renames all source objects to destination object
// across all disks in parallel. Additionally if we have errors and do
// not have a readQuorum partially renamed files are renamed back to
// its proper location.
func renameObject(disks []StorageAPI, srcBucket, srcObject, dstBucket, dstObject string, quorum int) ([]StorageAPI, error) {
isDir := true
return rename(disks, srcBucket, srcObject, dstBucket, dstObject, isDir, quorum)
}
// PutObject - creates an object upon reading from the input stream
// until EOF, erasure codes the data across all disk and additionally
// writes `xl.json` which carries the necessary metadata for future
// object operations.
func (xl xlObjects) PutObject(bucket string, object string, data *hash.Reader, metadata map[string]string) (objInfo ObjectInfo, err error) {
// This is a special case with size as '0' and object ends with
// a slash separator, we treat it like a valid operation and
// return success.
if isObjectDir(object, data.Size()) {
// Check if an object is present as one of the parent dir.
// -- FIXME. (needs a new kind of lock).
// -- FIXME (this also causes performance issue when disks are down).
if xl.parentDirIsObject(bucket, path.Dir(object)) {
return ObjectInfo{}, toObjectErr(errors.Trace(errFileAccessDenied), bucket, object)
}
return dirObjectInfo(bucket, object, data.Size(), metadata), nil
}
// Validate put object input args.
if err = checkPutObjectArgs(bucket, object, xl); err != nil {
return ObjectInfo{}, err
}
// Validate input data size and it can never be less than zero.
if data.Size() < 0 {
return ObjectInfo{}, toObjectErr(errors.Trace(errInvalidArgument))
}
// Check if an object is present as one of the parent dir.
// -- FIXME. (needs a new kind of lock).
// -- FIXME (this also causes performance issue when disks are down).
if xl.parentDirIsObject(bucket, path.Dir(object)) {
return ObjectInfo{}, toObjectErr(errors.Trace(errFileAccessDenied), bucket, object)
}
// No metadata is set, allocate a new one.
if metadata == nil {
metadata = make(map[string]string)
}
uniqueID := mustGetUUID()
tempObj := uniqueID
// Limit the reader to its provided size if specified.
var reader io.Reader = data
// Proceed to set the cache.
var newBuffer io.WriteCloser
// If caching is enabled, proceed to set the cache.
if data.Size() > 0 && xl.objCacheEnabled {
// PutObject invalidates any previously cached object in memory.
xl.objCache.Delete(path.Join(bucket, object))
// Create a new entry in memory of size.
newBuffer, err = xl.objCache.Create(path.Join(bucket, object), data.Size())
if err == nil {
// Cache incoming data into a buffer
reader = io.TeeReader(data, newBuffer)
} else {
// Return errors other than ErrCacheFull
if err != objcache.ErrCacheFull {
return ObjectInfo{}, toObjectErr(errors.Trace(err), bucket, object)
}
}
}
// Get parity and data drive count based on storage class metadata
dataDrives, parityDrives := getRedundancyCount(metadata[amzStorageClass], len(xl.storageDisks))
// we now know the number of blocks this object needs for data and parity.
// writeQuorum is dataBlocks + 1
writeQuorum := dataDrives + 1
// Initialize parts metadata
partsMetadata := make([]xlMetaV1, len(xl.storageDisks))
xlMeta := newXLMetaV1(object, dataDrives, parityDrives)
// Initialize xl meta.
for index := range partsMetadata {
partsMetadata[index] = xlMeta
}
// Order disks according to erasure distribution
onlineDisks := shuffleDisks(xl.storageDisks, partsMetadata[0].Erasure.Distribution)
// Delete temporary object in the event of failure.
// If PutObject succeeded there would be no temporary
// object to delete.
defer xl.deleteObject(minioMetaTmpBucket, tempObj)
// Total size of the written object
var sizeWritten int64
storage, err := NewErasureStorage(onlineDisks, xlMeta.Erasure.DataBlocks, xlMeta.Erasure.ParityBlocks, xlMeta.Erasure.BlockSize)
if err != nil {
return ObjectInfo{}, toObjectErr(err, bucket, object)
}
// Alloc additional space for parity blocks created while erasure coding
buffer := make([]byte, xlMeta.Erasure.BlockSize, 2*xlMeta.Erasure.BlockSize)
// Read data and split into parts - similar to multipart mechanism
for partIdx := 1; ; partIdx++ {
// Compute part name
partName := "part." + strconv.Itoa(partIdx)
// Compute the path of current part
tempErasureObj := pathJoin(uniqueID, partName)
// Calculate the size of the current part.
var curPartSize int64
curPartSize, err = calculatePartSizeFromIdx(data.Size(), globalPutPartSize, partIdx)
if err != nil {
return ObjectInfo{}, toObjectErr(err, bucket, object)
}
// Hint the filesystem to pre-allocate one continuous large block.
// This is only an optimization.
var curPartReader io.Reader
if curPartSize > 0 {
pErr := xl.prepareFile(minioMetaTmpBucket, tempErasureObj, curPartSize, storage.disks, xlMeta.Erasure.BlockSize, xlMeta.Erasure.DataBlocks, writeQuorum)
if pErr != nil {
return ObjectInfo{}, toObjectErr(pErr, bucket, object)
}
}
if curPartSize < data.Size() {
curPartReader = io.LimitReader(reader, curPartSize)
} else {
curPartReader = reader
}
file, erasureErr := storage.CreateFile(curPartReader, minioMetaTmpBucket,
tempErasureObj, buffer, DefaultBitrotAlgorithm, writeQuorum)
if erasureErr != nil {
return ObjectInfo{}, toObjectErr(erasureErr, minioMetaTmpBucket, tempErasureObj)
}
// Should return IncompleteBody{} error when reader has fewer bytes
// than specified in request header.
if file.Size < curPartSize {
return ObjectInfo{}, errors.Trace(IncompleteBody{})
}
// Update the total written size
sizeWritten += file.Size
for i := range partsMetadata {
partsMetadata[i].AddObjectPart(partIdx, partName, "", file.Size)
partsMetadata[i].Erasure.AddChecksumInfo(ChecksumInfo{partName, file.Algorithm, file.Checksums[i]})
}
// We wrote everything, break out.
if sizeWritten == data.Size() {
break
}
}
// Save additional erasureMetadata.
modTime := UTCNow()
metadata["etag"] = hex.EncodeToString(data.MD5Current())
// Guess content-type from the extension if possible.
if metadata["content-type"] == "" {
if objectExt := path.Ext(object); objectExt != "" {
if content, ok := mimedb.DB[strings.ToLower(strings.TrimPrefix(objectExt, "."))]; ok {
metadata["content-type"] = content.ContentType
}
}
}
if xl.isObject(bucket, object) {
// Rename if an object already exists to temporary location.
newUniqueID := mustGetUUID()
// Delete successfully renamed object.
defer xl.deleteObject(minioMetaTmpBucket, newUniqueID)
// NOTE: Do not use online disks slice here.
// The reason is that existing object should be purged
// regardless of `xl.json` status and rolled back in case of errors.
_, err = renameObject(xl.storageDisks, bucket, object, minioMetaTmpBucket, newUniqueID, writeQuorum)
if err != nil {
return ObjectInfo{}, toObjectErr(err, bucket, object)
}
}
// Fill all the necessary metadata.
// Update `xl.json` content on each disks.
for index := range partsMetadata {
partsMetadata[index].Meta = metadata
partsMetadata[index].Stat.Size = sizeWritten
partsMetadata[index].Stat.ModTime = modTime
}
// Write unique `xl.json` for each disk.
if onlineDisks, err = writeUniqueXLMetadata(onlineDisks, minioMetaTmpBucket, tempObj, partsMetadata, writeQuorum); err != nil {
return ObjectInfo{}, toObjectErr(err, bucket, object)
}
// Rename the successfully written temporary object to final location.
if _, err = renameObject(onlineDisks, minioMetaTmpBucket, tempObj, bucket, object, writeQuorum); err != nil {
return ObjectInfo{}, toObjectErr(err, bucket, object)
}
// Once we have successfully renamed the object, Close the buffer which would
// save the object on cache.
if sizeWritten > 0 && xl.objCacheEnabled && newBuffer != nil {
newBuffer.Close()
}
// Object info is the same in all disks, so we can pick the first meta
// of the first disk
xlMeta = partsMetadata[0]
objInfo = ObjectInfo{
IsDir: false,
Bucket: bucket,
Name: object,
Size: xlMeta.Stat.Size,
ModTime: xlMeta.Stat.ModTime,
ETag: xlMeta.Meta["etag"],
ContentType: xlMeta.Meta["content-type"],
ContentEncoding: xlMeta.Meta["content-encoding"],
UserDefined: xlMeta.Meta,
}
// Success, return object info.
return objInfo, nil
}
// deleteObject - wrapper for delete object, deletes an object from
// all the disks in parallel, including `xl.json` associated with the
// object.
func (xl xlObjects) deleteObject(bucket, object string) error {
// Initialize sync waitgroup.
var wg = &sync.WaitGroup{}
// Read metadata associated with the object from all disks.
metaArr, errs := readAllXLMetadata(xl.storageDisks, bucket, object)
// get Quorum for this object
_, writeQuorum, err := objectQuorumFromMeta(xl, metaArr, errs)
if err != nil {
return err
}
// Initialize list of errors.
var dErrs = make([]error, len(xl.storageDisks))
for index, disk := range xl.storageDisks {
if disk == nil {
dErrs[index] = errors.Trace(errDiskNotFound)
continue
}
wg.Add(1)
go func(index int, disk StorageAPI) {
defer wg.Done()
err := cleanupDir(disk, bucket, object)
if err != nil && errors.Cause(err) != errVolumeNotFound {
dErrs[index] = err
}
}(index, disk)
}
// Wait for all routines to finish.
wg.Wait()
return reduceWriteQuorumErrs(dErrs, objectOpIgnoredErrs, writeQuorum)
}
// DeleteObject - deletes an object, this call doesn't necessary reply
// any error as it is not necessary for the handler to reply back a
// response to the client request.
func (xl xlObjects) DeleteObject(bucket, object string) (err error) {
if err = checkDelObjArgs(bucket, object); err != nil {
return err
}
// Validate object exists.
if !xl.isObject(bucket, object) {
return errors.Trace(ObjectNotFound{bucket, object})
} // else proceed to delete the object.
// Delete the object on all disks.
err = xl.deleteObject(bucket, object)
if err != nil {
return toObjectErr(err, bucket, object)
}
if xl.objCacheEnabled {
// Delete from the cache.
xl.objCache.Delete(pathJoin(bucket, object))
}
// Success.
return nil
}