minio/cmd/fs-v1-multipart.go

/*
 * 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 cmd

import (
	"crypto/md5"
	"encoding/hex"
	"fmt"
	"hash"
	"io"
	"os"
	pathutil "path"
	"runtime"
	"strings"
	"time"

	"github.com/minio/minio/pkg/lock"
	"github.com/minio/sha256-simd"
)

// Returns if the prefix is a multipart upload.
func (fs fsObjects) isMultipartUpload(bucket, prefix string) bool {
	uploadsIDPath := pathJoin(fs.fsPath, bucket, prefix, uploadsJSONFile)
	_, err := fsStatFile(uploadsIDPath)
	if err != nil {
		if err == errFileNotFound {
			return false
		}
		errorIf(err, "Unable to access uploads.json "+uploadsIDPath)
		return false
	}
	return true
}

// Delete uploads.json file wrapper handling a tricky case on windows.
func (fs fsObjects) deleteUploadsJSON(bucket, object, uploadID string) error {
	timeID := fmt.Sprintf("%X", time.Now().UTC().UnixNano())
	tmpPath := pathJoin(fs.fsPath, minioMetaTmpBucket, fs.fsUUID, uploadID+"+"+timeID)

	multipartBucketPath := pathJoin(fs.fsPath, minioMetaMultipartBucket)
	uploadPath := pathJoin(multipartBucketPath, bucket, object)
	uploadsMetaPath := pathJoin(uploadPath, uploadsJSONFile)

	// Special case for windows please read through.
	if runtime.GOOS == globalWindowsOSName {
		// Ordinarily windows does not permit deletion or renaming of files still
		// in use, but if all open handles to that file were opened with FILE_SHARE_DELETE
		// then it can permit renames and deletions of open files.
		//
		// There are however some gotchas with this, and it is worth listing them here.
		// Firstly, Windows never allows you to really delete an open file, rather it is
		// flagged as delete pending and its entry in its directory remains visible
		// (though no new file handles may be opened to it) and when the very last
		// open handle to the file in the system is closed, only then is it truly
		// deleted. Well, actually only sort of truly deleted, because Windows only
		// appears to remove the file entry from the directory, but in fact that
		// entry is merely hidden and actually still exists and attempting to create
		// a file with the same name will return an access denied error. How long it
		// silently exists for depends on a range of factors, but put it this way:
		// if your code loops creating and deleting the same file name as you might
		// when operating a lock file, you're going to see lots of random spurious
		// access denied errors and truly dismal lock file performance compared to POSIX.
		//
		// We work-around these un-POSIX file semantics by taking a dual step to
		// deleting files. Firstly, it renames the file to tmp location into multipartTmpBucket
		// We always open files with FILE_SHARE_DELETE permission enabled, with that
		// flag Windows permits renaming and deletion, and because the name was changed
		// to a very random name somewhere not in its origin directory before deletion,
		// you don't see those unexpected random errors when creating files with the
		// same name as a recently deleted file as you do anywhere else on Windows.
		// Because the file is probably not in its original containing directory any more,
		// deletions of that directory will not fail with "directory not empty" as they
		// otherwise normally would either.
		fsRenameFile(uploadsMetaPath, tmpPath)

		// Proceed to deleting the directory.
		if err := fsDeleteFile(multipartBucketPath, uploadPath); err != nil {
			return err
		}

		// Finally delete the renamed file.
		return fsDeleteFile(pathutil.Dir(tmpPath), tmpPath)
	}
	return fsDeleteFile(multipartBucketPath, uploadsMetaPath)
}

// Removes the uploadID, called either by CompleteMultipart of AbortMultipart. If the resuling uploads
// slice is empty then we remove/purge the file.
func (fs fsObjects) removeUploadID(bucket, object, uploadID string, rwlk *lock.LockedFile) error {
	uploadIDs := uploadsV1{}
	_, err := uploadIDs.ReadFrom(rwlk)
	if err != nil {
		return err
	}

	// Removes upload id from the uploads list.
	uploadIDs.RemoveUploadID(uploadID)

	// Check this is the last entry.
	if uploadIDs.IsEmpty() {
		// No more uploads left, so we delete `uploads.json` file.
		return fs.deleteUploadsJSON(bucket, object, uploadID)
	} // else not empty

	// Write update `uploads.json`.
	_, err = uploadIDs.WriteTo(rwlk)
	return err
}

// Adds a new uploadID if no previous `uploads.json` is
// found we initialize a new one.
func (fs fsObjects) addUploadID(bucket, object, uploadID string, initiated time.Time, rwlk *lock.LockedFile) error {
	uploadIDs := uploadsV1{}

	_, err := uploadIDs.ReadFrom(rwlk)
	// For all unexpected errors, we return.
	if err != nil && errorCause(err) != io.EOF {
		return err
	}

	// If we couldn't read anything, we assume a default
	// (empty) upload info.
	if errorCause(err) == io.EOF {
		uploadIDs = newUploadsV1("fs")
	}

	// Adds new upload id to the list.
	uploadIDs.AddUploadID(uploadID, initiated)

	// Write update `uploads.json`.
	_, err = uploadIDs.WriteTo(rwlk)
	return err
}

// listMultipartUploadIDs - list all the upload ids from a marker up to 'count'.
func (fs fsObjects) listMultipartUploadIDs(bucketName, objectName, uploadIDMarker string, count int) ([]uploadMetadata, bool, error) {
	var uploads []uploadMetadata

	// Hold the lock so that two parallel complete-multipart-uploads
	// do not leave a stale uploads.json behind.
	objectMPartPathLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket, pathJoin(bucketName, objectName))
	objectMPartPathLock.RLock()
	defer objectMPartPathLock.RUnlock()

	uploadsPath := pathJoin(bucketName, objectName, uploadsJSONFile)
	rlk, err := fs.rwPool.Open(pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadsPath))
	if err != nil {
		if err == errFileNotFound || err == errFileAccessDenied {
			return nil, true, nil
		}
		return nil, false, traceError(err)
	}
	defer fs.rwPool.Close(pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadsPath))

	// Read `uploads.json`.
	uploadIDs := uploadsV1{}
	if _, err = uploadIDs.ReadFrom(rlk.LockedFile); err != nil {
		return nil, false, err
	}

	index := 0
	if uploadIDMarker != "" {
		for ; index < len(uploadIDs.Uploads); index++ {
			if uploadIDs.Uploads[index].UploadID == uploadIDMarker {
				// Skip the uploadID as it would already be listed in previous listing.
				index++
				break
			}
		}
	}

	for index < len(uploadIDs.Uploads) {
		uploads = append(uploads, uploadMetadata{
			Object:    objectName,
			UploadID:  uploadIDs.Uploads[index].UploadID,
			Initiated: uploadIDs.Uploads[index].Initiated,
		})
		count--
		index++
		if count == 0 {
			break
		}
	}

	end := (index == len(uploadIDs.Uploads))
	return uploads, end, nil
}

// listMultipartUploads - lists all multipart uploads.
func (fs fsObjects) listMultipartUploads(bucket, prefix, keyMarker, uploadIDMarker, delimiter string, maxUploads int) (ListMultipartsInfo, error) {
	result := ListMultipartsInfo{}
	recursive := true
	if delimiter == slashSeparator {
		recursive = false
	}

	result.IsTruncated = true
	result.MaxUploads = maxUploads
	result.KeyMarker = keyMarker
	result.Prefix = prefix
	result.Delimiter = delimiter

	// Not using path.Join() as it strips off the trailing '/'.
	multipartPrefixPath := pathJoin(bucket, prefix)
	if prefix == "" {
		// Should have a trailing "/" if prefix is ""
		// For ex. multipartPrefixPath should be "multipart/bucket/" if prefix is ""
		multipartPrefixPath += slashSeparator
	}
	multipartMarkerPath := ""
	if keyMarker != "" {
		multipartMarkerPath = pathJoin(bucket, keyMarker)
	}

	var uploads []uploadMetadata
	var err error
	var eof bool

	if uploadIDMarker != "" {
		uploads, _, err = fs.listMultipartUploadIDs(bucket, keyMarker, uploadIDMarker, maxUploads)
		if err != nil {
			return ListMultipartsInfo{}, err
		}
		maxUploads = maxUploads - len(uploads)
	}

	var walkResultCh chan treeWalkResult
	var endWalkCh chan struct{}

	// true only for xl.ListObjectsHeal(), set to false.
	heal := false

	// Proceed to list only if we have more uploads to be listed.
	if maxUploads > 0 {
		listPrms := listParams{minioMetaMultipartBucket, recursive, multipartMarkerPath, multipartPrefixPath, heal}

		// Pop out any previously waiting marker.
		walkResultCh, endWalkCh = fs.listPool.Release(listPrms)
		if walkResultCh == nil {
			endWalkCh = make(chan struct{})
			isLeaf := fs.isMultipartUpload
			listDir := fs.listDirFactory(isLeaf)
			walkResultCh = startTreeWalk(minioMetaMultipartBucket, multipartPrefixPath,
				multipartMarkerPath, recursive, listDir, isLeaf, endWalkCh)
		}

		// List until maxUploads requested.
		for maxUploads > 0 {
			walkResult, ok := <-walkResultCh
			if !ok {
				// Closed channel.
				eof = true
				break
			}

			// For any walk error return right away.
			if walkResult.err != nil {
				// File not found or Disk not found is a valid case.
				if isErrIgnored(walkResult.err, fsTreeWalkIgnoredErrs...) {
					eof = true
					break
				}
				return ListMultipartsInfo{}, walkResult.err
			}

			entry := strings.TrimPrefix(walkResult.entry, retainSlash(bucket))
			if strings.HasSuffix(walkResult.entry, slashSeparator) {
				uploads = append(uploads, uploadMetadata{
					Object: entry,
				})
				maxUploads--
				if maxUploads == 0 {
					if walkResult.end {
						eof = true
						break
					}
				}
				continue
			}

			var tmpUploads []uploadMetadata
			var end bool
			uploadIDMarker = ""

			tmpUploads, end, err = fs.listMultipartUploadIDs(bucket, entry, uploadIDMarker, maxUploads)
			if err != nil {
				return ListMultipartsInfo{}, err
			}

			uploads = append(uploads, tmpUploads...)
			maxUploads -= len(tmpUploads)
			if walkResult.end && end {
				eof = true
				break
			}
		}
	}

	// Loop through all the received uploads fill in the multiparts result.
	for _, upload := range uploads {
		var objectName string
		var uploadID string
		if strings.HasSuffix(upload.Object, slashSeparator) {
			// All directory entries are common prefixes.
			uploadID = "" // Upload ids are empty for CommonPrefixes.
			objectName = upload.Object
			result.CommonPrefixes = append(result.CommonPrefixes, objectName)
		} else {
			uploadID = upload.UploadID
			objectName = upload.Object
			result.Uploads = append(result.Uploads, upload)
		}
		result.NextKeyMarker = objectName
		result.NextUploadIDMarker = uploadID
	}

	if !eof {
		// Save the go-routine state in the pool so that it can continue from where it left off on
		// the next request.
		fs.listPool.Set(listParams{bucket, recursive, result.NextKeyMarker, prefix, heal}, walkResultCh, endWalkCh)
	}

	result.IsTruncated = !eof
	if !result.IsTruncated {
		result.NextKeyMarker = ""
		result.NextUploadIDMarker = ""
	}

	// Success.
	return result, nil
}

// ListMultipartUploads - lists all the pending multipart uploads on a
// bucket. Additionally takes 'prefix, keyMarker, uploadIDmarker and a
// delimiter' which allows us to list uploads match a particular
// prefix or lexically starting from 'keyMarker' or delimiting the
// output to get a directory like listing.
//
// Implements S3 compatible ListMultipartUploads API. The resulting
// ListMultipartsInfo structure is unmarshalled directly into XML and
// replied back to the client.
func (fs fsObjects) ListMultipartUploads(bucket, prefix, keyMarker, uploadIDMarker, delimiter string, maxUploads int) (ListMultipartsInfo, error) {
	if err := checkListMultipartArgs(bucket, prefix, keyMarker, uploadIDMarker, delimiter, fs); err != nil {
		return ListMultipartsInfo{}, err
	}

	if _, err := fs.statBucketDir(bucket); err != nil {
		return ListMultipartsInfo{}, toObjectErr(err, bucket)
	}

	return fs.listMultipartUploads(bucket, prefix, keyMarker, uploadIDMarker, delimiter, maxUploads)
}

// newMultipartUpload - wrapper for initializing a new multipart
// request, returns back a unique upload id.
//
// Internally this function creates 'uploads.json' associated for the
// incoming object at '.minio.sys/multipart/bucket/object/uploads.json' on
// all the disks. `uploads.json` carries metadata regarding on going
// multipart operation on the object.
func (fs fsObjects) newMultipartUpload(bucket string, object string, meta map[string]string) (uploadID string, err error) {
	// Initialize `fs.json` values.
	fsMeta := newFSMetaV1()

	// Save additional metadata.
	fsMeta.Meta = meta

	uploadID = mustGetUUID()
	initiated := time.Now().UTC()

	// Add upload ID to uploads.json
	uploadsPath := pathJoin(bucket, object, uploadsJSONFile)
	rwlk, err := fs.rwPool.Create(pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadsPath))
	if err != nil {
		return "", toObjectErr(traceError(err), bucket, object)
	}
	defer rwlk.Close()

	uploadIDPath := pathJoin(bucket, object, uploadID)
	fsMetaPath := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, fsMetaJSONFile)
	metaFile, err := fs.rwPool.Create(fsMetaPath)
	if err != nil {
		return "", toObjectErr(traceError(err), bucket, object)
	}
	defer metaFile.Close()

	// Add a new upload id.
	if err = fs.addUploadID(bucket, object, uploadID, initiated, rwlk); err != nil {
		return "", toObjectErr(err, bucket, object)
	}

	// Write all the set metadata.
	if _, err = fsMeta.WriteTo(metaFile); err != nil {
		return "", toObjectErr(err, bucket, object)
	}

	// Return success.
	return uploadID, nil
}

// NewMultipartUpload - initialize a new multipart upload, returns a
// unique id. The unique id returned here is of UUID form, for each
// subsequent request each UUID is unique.
//
// Implements S3 compatible initiate multipart API.
func (fs fsObjects) NewMultipartUpload(bucket, object string, meta map[string]string) (string, error) {
	if err := checkNewMultipartArgs(bucket, object, fs); err != nil {
		return "", err
	}

	if _, err := fs.statBucketDir(bucket); err != nil {
		return "", toObjectErr(err, bucket)
	}

	// Hold the lock so that two parallel complete-multipart-uploads
	// do not leave a stale uploads.json behind.
	objectMPartPathLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket, pathJoin(bucket, object))
	objectMPartPathLock.Lock()
	defer objectMPartPathLock.Unlock()

	return fs.newMultipartUpload(bucket, object, meta)
}

// Returns if a new part can be appended to fsAppendDataFile.
func partToAppend(fsMeta fsMetaV1, fsAppendMeta fsMetaV1) (part objectPartInfo, appendNeeded bool) {
	if len(fsMeta.Parts) == 0 {
		return
	}

	// As fsAppendMeta.Parts will be sorted len(fsAppendMeta.Parts) will naturally be the next part number
	nextPartNum := len(fsAppendMeta.Parts) + 1
	nextPartIndex := fsMeta.ObjectPartIndex(nextPartNum)
	if nextPartIndex == -1 {
		return
	}

	return fsMeta.Parts[nextPartIndex], true
}

// PutObjectPart - reads incoming data until EOF for the part file on
// an ongoing multipart transaction. Internally incoming data is
// written to '.minio.sys/tmp' location and safely renamed to
// '.minio.sys/multipart' for reach parts.
func (fs fsObjects) PutObjectPart(bucket, object, uploadID string, partID int, size int64, data io.Reader, md5Hex string, sha256sum string) (string, error) {
	if err := checkPutObjectPartArgs(bucket, object, fs); err != nil {
		return "", err
	}

	if _, err := fs.statBucketDir(bucket); err != nil {
		return "", toObjectErr(err, bucket)
	}

	// Hold the lock so that two parallel complete-multipart-uploads
	// do not leave a stale uploads.json behind.
	objectMPartPathLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket, pathJoin(bucket, object))
	objectMPartPathLock.Lock()
	defer objectMPartPathLock.Unlock()

	// Disallow any parallel abort or complete multipart operations.
	uploadsPath := pathJoin(fs.fsPath, minioMetaMultipartBucket, bucket, object, uploadsJSONFile)
	if _, err := fs.rwPool.Open(uploadsPath); err != nil {
		if err == errFileNotFound || err == errFileAccessDenied {
			return "", traceError(InvalidUploadID{UploadID: uploadID})
		}
		return "", toObjectErr(traceError(err), bucket, object)
	}
	defer fs.rwPool.Close(uploadsPath)

	uploadIDPath := pathJoin(bucket, object, uploadID)

	// Just check if the uploadID exists to avoid copy if it doesn't.
	fsMetaPath := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, fsMetaJSONFile)
	rwlk, err := fs.rwPool.Write(fsMetaPath)
	if err != nil {
		if err == errFileNotFound || err == errFileAccessDenied {
			return "", traceError(InvalidUploadID{UploadID: uploadID})
		}
		return "", toObjectErr(traceError(err), bucket, object)
	}
	defer rwlk.Close()

	fsMeta := fsMetaV1{}
	_, err = fsMeta.ReadFrom(rwlk)
	if err != nil {
		return "", toObjectErr(err, minioMetaMultipartBucket, fsMetaPath)
	}

	partSuffix := fmt.Sprintf("object%d", partID)
	tmpPartPath := uploadID + "." + mustGetUUID() + "." + partSuffix

	// Initialize md5 writer.
	md5Writer := md5.New()
	hashWriters := []io.Writer{md5Writer}

	var sha256Writer hash.Hash
	if sha256sum != "" {
		sha256Writer = sha256.New()
		hashWriters = append(hashWriters, sha256Writer)
	}
	multiWriter := io.MultiWriter(hashWriters...)

	// Limit the reader to its provided size if specified.
	var limitDataReader io.Reader
	if size > 0 {
		// This is done so that we can avoid erroneous clients sending more data than the set content size.
		limitDataReader = io.LimitReader(data, size)
	} else {
		// else we read till EOF.
		limitDataReader = data
	}

	teeReader := io.TeeReader(limitDataReader, multiWriter)
	bufSize := int64(readSizeV1)
	if size > 0 && bufSize > size {
		bufSize = size
	}
	buf := make([]byte, int(bufSize))

	fsPartPath := pathJoin(fs.fsPath, minioMetaTmpBucket, fs.fsUUID, tmpPartPath)
	bytesWritten, cErr := fsCreateFile(fsPartPath, teeReader, buf, size)
	if cErr != nil {
		fsRemoveFile(fsPartPath)
		return "", toObjectErr(cErr, minioMetaTmpBucket, tmpPartPath)
	}

	// Should return IncompleteBody{} error when reader has fewer
	// bytes than specified in request header.
	if bytesWritten < size {
		fsRemoveFile(fsPartPath)
		return "", traceError(IncompleteBody{})
	}

	// Delete temporary part in case of failure. If
	// PutObjectPart succeeds then there would be nothing to
	// delete.
	defer fsRemoveFile(fsPartPath)

	newMD5Hex := hex.EncodeToString(md5Writer.Sum(nil))
	if md5Hex != "" {
		if newMD5Hex != md5Hex {
			return "", traceError(BadDigest{md5Hex, newMD5Hex})
		}
	}

	if sha256sum != "" {
		newSHA256sum := hex.EncodeToString(sha256Writer.Sum(nil))
		if newSHA256sum != sha256sum {
			return "", traceError(SHA256Mismatch{})
		}
	}

	partPath := pathJoin(bucket, object, uploadID, partSuffix)
	// Lock the part so that another part upload with same part-number gets blocked
	// while the part is getting appended in the background.
	partLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket, partPath)
	partLock.Lock()

	fsNSPartPath := pathJoin(fs.fsPath, minioMetaMultipartBucket, partPath)
	if err = fsRenameFile(fsPartPath, fsNSPartPath); err != nil {
		partLock.Unlock()
		return "", toObjectErr(err, minioMetaMultipartBucket, partPath)
	}

	// Save the object part info in `fs.json`.
	fsMeta.AddObjectPart(partID, partSuffix, newMD5Hex, size)
	if _, err = fsMeta.WriteTo(rwlk); err != nil {
		partLock.Unlock()
		return "", toObjectErr(err, minioMetaMultipartBucket, uploadIDPath)
	}

	// Append the part in background.
	errCh := fs.append(bucket, object, uploadID, fsMeta)
	go func() {
		// Also receive the error so that the appendParts go-routine
		// does not block on send. But the error received is ignored
		// as fs.PutObjectPart() would have already returned success
		// to the client.
		<-errCh
		partLock.Unlock()
	}()

	return newMD5Hex, nil
}

// listObjectParts - wrapper scanning through
// '.minio.sys/multipart/bucket/object/UPLOADID'. Lists all the parts
// saved inside '.minio.sys/multipart/bucket/object/UPLOADID'.
func (fs fsObjects) listObjectParts(bucket, object, uploadID string, partNumberMarker, maxParts int) (ListPartsInfo, error) {
	result := ListPartsInfo{}

	uploadIDPath := pathJoin(bucket, object, uploadID)
	fsMetaPath := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, fsMetaJSONFile)
	metaFile, err := fs.rwPool.Open(fsMetaPath)
	if err != nil {
		if err == errFileNotFound || err == errFileAccessDenied {
			// On windows oddly this is returned.
			return ListPartsInfo{}, traceError(InvalidUploadID{UploadID: uploadID})
		}
		return ListPartsInfo{}, toObjectErr(traceError(err), bucket, object)
	}
	defer fs.rwPool.Close(fsMetaPath)

	fsMeta := fsMetaV1{}
	_, err = fsMeta.ReadFrom(metaFile.LockedFile)
	if err != nil {
		return ListPartsInfo{}, toObjectErr(err, minioMetaBucket, fsMetaPath)
	}

	// Only parts with higher part numbers will be listed.
	partIdx := fsMeta.ObjectPartIndex(partNumberMarker)
	parts := fsMeta.Parts
	if partIdx != -1 {
		parts = fsMeta.Parts[partIdx+1:]
	}

	count := maxParts
	for _, part := range parts {
		var fi os.FileInfo
		partNamePath := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, part.Name)
		fi, err = fsStatFile(partNamePath)
		if err != nil {
			return ListPartsInfo{}, toObjectErr(err, minioMetaMultipartBucket, partNamePath)
		}
		result.Parts = append(result.Parts, partInfo{
			PartNumber:   part.Number,
			ETag:         part.ETag,
			LastModified: fi.ModTime(),
			Size:         fi.Size(),
		})
		count--
		if count == 0 {
			break
		}
	}

	// If listed entries are more than maxParts, we set IsTruncated as true.
	if len(parts) > len(result.Parts) {
		result.IsTruncated = true
		// Make sure to fill next part number marker if IsTruncated is
		// true for subsequent listing.
		nextPartNumberMarker := result.Parts[len(result.Parts)-1].PartNumber
		result.NextPartNumberMarker = nextPartNumberMarker
	}
	result.Bucket = bucket
	result.Object = object
	result.UploadID = uploadID
	result.MaxParts = maxParts

	// Success.
	return result, nil
}

// ListObjectParts - lists all previously uploaded parts for a given
// object and uploadID.  Takes additional input of part-number-marker
// to indicate where the listing should begin from.
//
// Implements S3 compatible ListObjectParts API. The resulting
// ListPartsInfo structure is unmarshalled directly into XML and
// replied back to the client.
func (fs fsObjects) ListObjectParts(bucket, object, uploadID string, partNumberMarker, maxParts int) (ListPartsInfo, error) {
	if err := checkListPartsArgs(bucket, object, fs); err != nil {
		return ListPartsInfo{}, err
	}

	if _, err := fs.statBucketDir(bucket); err != nil {
		return ListPartsInfo{}, toObjectErr(err, bucket)
	}

	// Hold the lock so that two parallel complete-multipart-uploads
	// do not leave a stale uploads.json behind.
	objectMPartPathLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket, pathJoin(bucket, object))
	objectMPartPathLock.RLock()
	defer objectMPartPathLock.RUnlock()

	listPartsInfo, err := fs.listObjectParts(bucket, object, uploadID, partNumberMarker, maxParts)
	if err != nil {
		return ListPartsInfo{}, toObjectErr(err, bucket, object)
	}

	// Success.
	return listPartsInfo, nil
}

// CompleteMultipartUpload - completes an ongoing multipart
// transaction after receiving all the parts indicated by the client.
// Returns an md5sum calculated by concatenating all the individual
// md5sums of all the parts.
//
// Implements S3 compatible Complete multipart API.
func (fs fsObjects) CompleteMultipartUpload(bucket string, object string, uploadID string, parts []completePart) (ObjectInfo, error) {
	if err := checkCompleteMultipartArgs(bucket, object, fs); err != nil {
		return ObjectInfo{}, err
	}

	if _, err := fs.statBucketDir(bucket); err != nil {
		return ObjectInfo{}, toObjectErr(err, bucket)
	}

	// Calculate s3 compatible md5sum for complete multipart.
	s3MD5, err := getCompleteMultipartMD5(parts)
	if err != nil {
		return ObjectInfo{}, err
	}

	uploadIDPath := pathJoin(bucket, object, uploadID)

	// Hold the lock so that two parallel complete-multipart-uploads
	// do not leave a stale uploads.json behind.
	objectMPartPathLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket, pathJoin(bucket, object))
	objectMPartPathLock.Lock()
	defer objectMPartPathLock.Unlock()

	fsMetaPathMultipart := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, fsMetaJSONFile)
	rlk, err := fs.rwPool.Open(fsMetaPathMultipart)
	if err != nil {
		if err == errFileNotFound || err == errFileAccessDenied {
			return ObjectInfo{}, traceError(InvalidUploadID{UploadID: uploadID})
		}
		return ObjectInfo{}, toObjectErr(traceError(err), bucket, object)
	}

	// Disallow any parallel abort or complete multipart operations.
	rwlk, err := fs.rwPool.Write(pathJoin(fs.fsPath, minioMetaMultipartBucket, bucket, object, uploadsJSONFile))
	if err != nil {
		fs.rwPool.Close(fsMetaPathMultipart)
		if err == errFileNotFound || err == errFileAccessDenied {
			return ObjectInfo{}, traceError(InvalidUploadID{UploadID: uploadID})
		}
		return ObjectInfo{}, toObjectErr(traceError(err), bucket, object)
	}
	defer rwlk.Close()

	fsMeta := fsMetaV1{}
	// Read saved fs metadata for ongoing multipart.
	_, err = fsMeta.ReadFrom(rlk.LockedFile)
	if err != nil {
		fs.rwPool.Close(fsMetaPathMultipart)
		return ObjectInfo{}, toObjectErr(err, minioMetaMultipartBucket, fsMetaPathMultipart)
	}

	// Wait for any competing PutObject() operation on bucket/object, since same namespace
	// would be acquired for `fs.json`.
	fsMetaPath := pathJoin(fs.fsPath, minioMetaBucket, bucketMetaPrefix, bucket, object, fsMetaJSONFile)
	metaFile, err := fs.rwPool.Create(fsMetaPath)
	if err != nil {
		fs.rwPool.Close(fsMetaPathMultipart)
		return ObjectInfo{}, toObjectErr(traceError(err), bucket, object)
	}
	defer metaFile.Close()

	fsNSObjPath := pathJoin(fs.fsPath, bucket, object)

	// This lock is held during rename of the appended tmp file to the actual
	// location so that any competing GetObject/PutObject/DeleteObject do not race.
	appendFallback := true // In case background-append did not append the required parts.

	if isPartsSame(fsMeta.Parts, parts) {
		err = fs.complete(bucket, object, uploadID, fsMeta)
		if err == nil {
			appendFallback = false
			fsTmpObjPath := pathJoin(fs.fsPath, minioMetaTmpBucket, fs.fsUUID, uploadID)
			if err = fsRenameFile(fsTmpObjPath, fsNSObjPath); err != nil {
				fs.rwPool.Close(fsMetaPathMultipart)
				return ObjectInfo{}, toObjectErr(err, minioMetaTmpBucket, uploadID)
			}
		}
	}

	if appendFallback {
		// background append could not do append all the required parts, hence we do it here.
		tempObj := uploadID + "-" + "part.1"

		fsTmpObjPath := pathJoin(fs.fsPath, minioMetaTmpBucket, fs.fsUUID, tempObj)
		// Delete the temporary object in the case of a
		// failure. If PutObject succeeds, then there would be
		// nothing to delete.
		defer fsRemoveFile(fsTmpObjPath)

		// Allocate staging buffer.
		var buf = make([]byte, readSizeV1)

		// Validate all parts and then commit to disk.
		for i, part := range parts {
			partIdx := fsMeta.ObjectPartIndex(part.PartNumber)
			if partIdx == -1 {
				fs.rwPool.Close(fsMetaPathMultipart)
				return ObjectInfo{}, traceError(InvalidPart{})
			}

			if fsMeta.Parts[partIdx].ETag != part.ETag {
				fs.rwPool.Close(fsMetaPathMultipart)
				return ObjectInfo{}, traceError(BadDigest{})
			}

			// All parts except the last part has to be atleast 5MB.
			if (i < len(parts)-1) && !isMinAllowedPartSize(fsMeta.Parts[partIdx].Size) {
				fs.rwPool.Close(fsMetaPathMultipart)
				return ObjectInfo{}, traceError(PartTooSmall{
					PartNumber: part.PartNumber,
					PartSize:   fsMeta.Parts[partIdx].Size,
					PartETag:   part.ETag,
				})
			}

			// Construct part suffix.
			partSuffix := fmt.Sprintf("object%d", part.PartNumber)
			multipartPartFile := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, partSuffix)

			var reader io.ReadCloser
			offset := int64(0)
			reader, _, err = fsOpenFile(multipartPartFile, offset)
			if err != nil {
				fs.rwPool.Close(fsMetaPathMultipart)
				if err == errFileNotFound {
					return ObjectInfo{}, traceError(InvalidPart{})
				}
				return ObjectInfo{}, toObjectErr(traceError(err), minioMetaMultipartBucket, partSuffix)
			}

			// No need to hold a lock, this is a unique file and will be only written
			// to one one process per uploadID per minio process.
			var wfile *os.File
			wfile, err = os.OpenFile(preparePath(fsTmpObjPath), os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0666)
			if err != nil {
				reader.Close()
				fs.rwPool.Close(fsMetaPathMultipart)
				return ObjectInfo{}, toObjectErr(traceError(err), bucket, object)
			}

			_, err = io.CopyBuffer(wfile, reader, buf)
			if err != nil {
				wfile.Close()
				reader.Close()
				fs.rwPool.Close(fsMetaPathMultipart)
				return ObjectInfo{}, toObjectErr(traceError(err), bucket, object)
			}

			wfile.Close()
			reader.Close()
		}

		if err = fsRenameFile(fsTmpObjPath, fsNSObjPath); err != nil {
			fs.rwPool.Close(fsMetaPathMultipart)
			return ObjectInfo{}, toObjectErr(err, minioMetaTmpBucket, uploadID)
		}
	}

	// No need to save part info, since we have concatenated all parts.
	fsMeta.Parts = nil

	// Save additional metadata.
	if len(fsMeta.Meta) == 0 {
		fsMeta.Meta = make(map[string]string)
	}
	fsMeta.Meta["md5Sum"] = s3MD5

	// Write all the set metadata.
	if _, err = fsMeta.WriteTo(metaFile); err != nil {
		fs.rwPool.Close(fsMetaPathMultipart)
		return ObjectInfo{}, toObjectErr(err, bucket, object)
	}

	// Close lock held on bucket/object/uploadid/fs.json,
	// this needs to be done for windows so that we can happily
	// delete the bucket/object/uploadid
	fs.rwPool.Close(fsMetaPathMultipart)

	// Cleanup all the parts if everything else has been safely committed.
	multipartObjectDir := pathJoin(fs.fsPath, minioMetaMultipartBucket, bucket, object)
	multipartUploadIDDir := pathJoin(multipartObjectDir, uploadID)
	if err = fsRemoveUploadIDPath(multipartObjectDir, multipartUploadIDDir); err != nil {
		return ObjectInfo{}, toObjectErr(err, bucket, object)
	}

	// Remove entry from `uploads.json`.
	if err = fs.removeUploadID(bucket, object, uploadID, rwlk); err != nil {
		return ObjectInfo{}, toObjectErr(err, minioMetaMultipartBucket, pathutil.Join(bucket, object))
	}

	fi, err := fsStatFile(fsNSObjPath)
	if err != nil {
		return ObjectInfo{}, toObjectErr(err, bucket, object)
	}

	// Return object info.
	return fsMeta.ToObjectInfo(bucket, object, fi), nil
}

// AbortMultipartUpload - aborts an ongoing multipart operation
// signified by the input uploadID. This is an atomic operation
// doesn't require clients to initiate multiple such requests.
//
// All parts are purged from all disks and reference to the uploadID
// would be removed from the system, rollback is not possible on this
// operation.
//
// Implements S3 compatible Abort multipart API, slight difference is
// that this is an atomic idempotent operation. Subsequent calls have
// no affect and further requests to the same uploadID would not be
// honored.
func (fs fsObjects) AbortMultipartUpload(bucket, object, uploadID string) error {
	if err := checkAbortMultipartArgs(bucket, object, fs); err != nil {
		return err
	}

	if _, err := fs.statBucketDir(bucket); err != nil {
		return toObjectErr(err, bucket)
	}

	uploadIDPath := pathJoin(bucket, object, uploadID)

	// Hold the lock so that two parallel complete-multipart-uploads
	// do not leave a stale uploads.json behind.
	objectMPartPathLock := globalNSMutex.NewNSLock(minioMetaMultipartBucket,
		pathJoin(bucket, object))
	objectMPartPathLock.Lock()
	defer objectMPartPathLock.Unlock()

	fsMetaPath := pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadIDPath, fsMetaJSONFile)
	if _, err := fs.rwPool.Open(fsMetaPath); err != nil {
		if err == errFileNotFound || err == errFileAccessDenied {
			return traceError(InvalidUploadID{UploadID: uploadID})
		}
		return toObjectErr(traceError(err), bucket, object)
	}

	uploadsPath := pathJoin(bucket, object, uploadsJSONFile)
	rwlk, err := fs.rwPool.Write(pathJoin(fs.fsPath, minioMetaMultipartBucket, uploadsPath))
	if err != nil {
		fs.rwPool.Close(fsMetaPath)
		if err == errFileNotFound || err == errFileAccessDenied {
			return traceError(InvalidUploadID{UploadID: uploadID})
		}
		return toObjectErr(traceError(err), bucket, object)
	}
	defer rwlk.Close()

	// Signal appendParts routine to stop waiting for new parts to arrive.
	fs.abort(uploadID)

	// Close lock held on bucket/object/uploadid/fs.json,
	// this needs to be done for windows so that we can happily
	// delete the bucket/object/uploadid
	fs.rwPool.Close(fsMetaPath)

	// Cleanup all uploaded parts and abort the upload.
	multipartObjectDir := pathJoin(fs.fsPath, minioMetaMultipartBucket, bucket, object)
	multipartUploadIDDir := pathJoin(multipartObjectDir, uploadID)
	if err = fsRemoveUploadIDPath(multipartObjectDir, multipartUploadIDDir); err != nil {
		return toObjectErr(err, bucket, object)
	}

	// Remove entry from `uploads.json`.
	if err = fs.removeUploadID(bucket, object, uploadID, rwlk); err != nil {
		return toObjectErr(err, bucket, object)
	}

	return nil
}