s3store: Parallelize part uploads and information retrieval (#478)

* Add first draft of parallel upload queue

* s3store: Use queue for parallel uploads

* Revert "Add first draft of parallel upload queue"

This reverts commit 86a329cef2.

* Revert "s3store: Use queue for parallel uploads"

This reverts commit 29b59a2c90.

* s3store: Cache results from listing parts and checking incomplete object

* s3store: Remove debugging output`

* s3store: Make requests for fetching info concurrently

* s3store: Make parallel uploads work and tests pass

* s3store: Add semaphore package

* s3store: Add comments to semaphore package

* s3store: Encapsulate more logic into s3PartProducer

* s3store: Refactor WriteChunk

* s3store: Remove TODO

* s3store: Acquire lock before uploading

* cli: Add flag for setting concurrency limit

* s3store: One more comment

cmd/tusd/cli/flags.go

@@ -27,6 +27,7 @@ var Flags struct {
 	S3PartSize              int64
 	S3DisableContentHashes  bool
 	S3DisableSSL            bool
+	S3ConcurrentPartUploads int
 	GCSBucket               string
 	GCSObjectPrefix         string
 	EnabledHooksString      string
@@ -68,6 +69,7 @@ func ParseFlags() {
 	flag.Int64Var(&Flags.S3PartSize, "s3-part-size", 50*1024*1024, "Size in bytes of the individual upload requests made to the S3 API. Defaults to 50MiB (experimental and may be removed in the future)")
 	flag.BoolVar(&Flags.S3DisableContentHashes, "s3-disable-content-hashes", false, "Disable the calculation of MD5 and SHA256 hashes for the content that gets uploaded to S3 for minimized CPU usage (experimental and may be removed in the future)")
 	flag.BoolVar(&Flags.S3DisableSSL, "s3-disable-ssl", false, "Disable SSL and only use HTTP for communication with S3 (experimental and may be removed in the future)")
+	flag.IntVar(&Flags.S3ConcurrentPartUploads, "s3-concurrent-part-uploads", 10, "Number of concurrent part uploads to S3 (experimental and may be removed in the future)")
 	flag.StringVar(&Flags.GCSBucket, "gcs-bucket", "", "Use Google Cloud Storage with this bucket as storage backend (requires the GCS_SERVICE_ACCOUNT_FILE environment variable to be set)")
 	flag.StringVar(&Flags.GCSObjectPrefix, "gcs-object-prefix", "", "Prefix for GCS object names (can't contain underscore character)")
 	flag.StringVar(&Flags.EnabledHooksString, "hooks-enabled-events", "pre-create,post-create,post-receive,post-terminate,post-finish", "Comma separated list of enabled hook events (e.g. post-create,post-finish). Leave empty to enable default events")

internal/semaphore/semaphore.go

@@ -0,0 +1,20 @@
+// Package semaphore implements a basic semaphore for coordinating and limiting
+// non-exclusive, concurrent access.
+package semaphore
+
+type Semaphore chan struct{}
+
+// New creates a semaphore with the given concurrency limit.
+func New(concurrency int) Semaphore {
+	return make(chan struct{}, concurrency)
+}
+
+// Acquire will block until the semaphore can be acquired.
+func (s Semaphore) Acquire() {
+	s <- struct{}{}
+}
+
+// Release frees the acquired slot in the semaphore.
+func (s Semaphore) Release() {
+	<-s
+}

pkg/s3store/s3store.go

@@ -83,6 +83,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/tus/tusd/internal/semaphore"
 	"github.com/tus/tusd/internal/uid"
 	"github.com/tus/tusd/pkg/handler"
 
@@ -158,6 +159,9 @@ type S3Store struct {
 	// CPU, so it might be desirable to disable them.
 	// Note that this property is experimental and might be removed in the future!
 	DisableContentHashes bool
+
+	// uploadSemaphore limits the number of concurrent multipart part uploads to S3.
+	uploadSemaphore semaphore.Semaphore
 }
 
 type S3API interface {
@@ -165,6 +169,7 @@ type S3API interface {
 	ListPartsWithContext(ctx context.Context, input *s3.ListPartsInput, opt ...request.Option) (*s3.ListPartsOutput, error)
 	UploadPartWithContext(ctx context.Context, input *s3.UploadPartInput, opt ...request.Option) (*s3.UploadPartOutput, error)
 	GetObjectWithContext(ctx context.Context, input *s3.GetObjectInput, opt ...request.Option) (*s3.GetObjectOutput, error)
+	HeadObjectWithContext(ctx context.Context, input *s3.HeadObjectInput, opt ...request.Option) (*s3.HeadObjectOutput, error)
 	CreateMultipartUploadWithContext(ctx context.Context, input *s3.CreateMultipartUploadInput, opt ...request.Option) (*s3.CreateMultipartUploadOutput, error)
 	AbortMultipartUploadWithContext(ctx context.Context, input *s3.AbortMultipartUploadInput, opt ...request.Option) (*s3.AbortMultipartUploadOutput, error)
 	DeleteObjectWithContext(ctx context.Context, input *s3.DeleteObjectInput, opt ...request.Option) (*s3.DeleteObjectOutput, error)
@@ -189,9 +194,15 @@ func New(bucket string, service S3API) S3Store {
 		MaxObjectSize:      5 * 1024 * 1024 * 1024 * 1024,
 		MaxBufferedParts:   20,
 		TemporaryDirectory: "",
+		uploadSemaphore:    semaphore.New(10),
 	}
 }
 
+// S3ConcurrentPartUploads changes the limit on how many concurrent part uploads to S3 are allowed.
+func (store *S3Store) S3ConcurrentPartUploads(limit int) {
+	store.uploadSemaphore = semaphore.New(limit)
+}
+
 // UseIn sets this store as the core data store in the passed composer and adds
 // all possible extension to it.
 func (store S3Store) UseIn(composer *handler.StoreComposer) {
@@ -209,6 +220,18 @@ type s3Upload struct {
 	// been fetched yet from S3. Never read or write to it directly but instead use
 	// the GetInfo and writeInfo functions.
 	info *handler.FileInfo
+
+	// parts collects all parts for this upload. It will be nil if info is nil as well.
+	parts []*s3Part
+	// incompletePartSize is the size of an incomplete part object, if one exists. It will be 0 if info is nil as well.
+	incompletePartSize int64
+}
+
+// s3Part represents a single part of a S3 multipart upload.
+type s3Part struct {
+	number int64
+	size   int64
+	etag   string
 }
 
 func (store S3Store) NewUpload(ctx context.Context, info handler.FileInfo) (handler.Upload, error) {
@@ -253,7 +276,7 @@ func (store S3Store) NewUpload(ctx context.Context, info handler.FileInfo) (hand
 		"Key":    *store.keyWithPrefix(uploadId),
 	}
 
-	upload := &s3Upload{id, &store, nil}
+	upload := &s3Upload{id, &store, nil, []*s3Part{}, 0}
 	err = upload.writeInfo(ctx, info)
 	if err != nil {
 		return nil, fmt.Errorf("s3store: unable to create info file:\n%s", err)
@@ -263,7 +286,7 @@ func (store S3Store) NewUpload(ctx context.Context, info handler.FileInfo) (hand
 }
 
 func (store S3Store) GetUpload(ctx context.Context, id string) (handler.Upload, error) {
-	return &s3Upload{id, &store, nil}, nil
+	return &s3Upload{id, &store, nil, []*s3Part{}, 0}, nil
 }
 
 func (store S3Store) AsTerminatableUpload(upload handler.Upload) handler.TerminatableUpload {
@@ -302,14 +325,60 @@ func (upload *s3Upload) writeInfo(ctx context.Context, info handler.FileInfo) er
 	return err
 }
 
-func (upload s3Upload) WriteChunk(ctx context.Context, offset int64, src io.Reader) (int64, error) {
+func (upload *s3Upload) WriteChunk(ctx context.Context, offset int64, src io.Reader) (int64, error) {
+	id := upload.id
+	store := upload.store
+
+	uploadId, _ := splitIds(id)
+
+	// Get the total size of the current upload, number of parts to generate next number and whether
+	// an incomplete part exists
+	_, _, incompletePartSize, err := upload.getInternalInfo(ctx)
+	if err != nil {
+		return 0, err
+	}
+
+	if incompletePartSize > 0 {
+		incompletePartFile, err := store.downloadIncompletePartForUpload(ctx, uploadId)
+		if err != nil {
+			return 0, err
+		}
+		if incompletePartFile == nil {
+			return 0, fmt.Errorf("s3store: Expected an incomplete part file but did not get any")
+		}
+		defer cleanUpTempFile(incompletePartFile)
+
+		if err := store.deleteIncompletePartForUpload(ctx, uploadId); err != nil {
+			return 0, err
+		}
+
+		// Prepend an incomplete part, if necessary and adapt the offset
+		src = io.MultiReader(incompletePartFile, src)
+		offset = offset - incompletePartSize
+	}
+
+	bytesUploaded, err := upload.uploadParts(ctx, offset, src)
+
+	// The size of the incomplete part should not be counted, because the
+	// process of the incomplete part should be fully transparent to the user.
+	bytesUploaded = bytesUploaded - incompletePartSize
+	if bytesUploaded < 0 {
+		bytesUploaded = 0
+	}
+
+	upload.info.Offset += bytesUploaded
+
+	return bytesUploaded, err
+}
+
+func (upload *s3Upload) uploadParts(ctx context.Context, offset int64, src io.Reader) (int64, error) {
 	id := upload.id
 	store := upload.store
 
 	uploadId, multipartId := splitIds(id)
 
-	// Get the total size of the current upload
+	// Get the total size of the current upload and number of parts to generate next number
-	info, err := upload.GetInfo(ctx)
+	info, parts, _, err := upload.getInternalInfo(ctx)
 	if err != nil {
 		return 0, err
 	}
@@ -321,83 +390,77 @@ func (upload s3Upload) WriteChunk(ctx context.Context, offset int64, src io.Read
 		return 0, err
 	}
 
-	// Get number of parts to generate next number
-	parts, err := store.listAllParts(ctx, id)
-	if err != nil {
-		return 0, err
-	}
-
 	numParts := len(parts)
 	nextPartNum := int64(numParts + 1)
 
-	incompletePartFile, incompletePartSize, err := store.downloadIncompletePartForUpload(ctx, uploadId)
+	partProducer, fileChan := newS3PartProducer(src, store.MaxBufferedParts, store.TemporaryDirectory)
-	if err != nil {
+	defer partProducer.stop()
-		return 0, err
-	}
-	if incompletePartFile != nil {
-		defer cleanUpTempFile(incompletePartFile)
-
-		if err := store.deleteIncompletePartForUpload(ctx, uploadId); err != nil {
-			return 0, err
-		}
-
-		src = io.MultiReader(incompletePartFile, src)
-	}
-
-	fileChan := make(chan *os.File, store.MaxBufferedParts)
-	doneChan := make(chan struct{})
-	defer close(doneChan)
-
-	// If we panic or return while there are still files in the channel, then
-	// we may leak file descriptors. Let's ensure that those are cleaned up.
-	defer func() {
-		for file := range fileChan {
-			cleanUpTempFile(file)
-		}
-	}()
-
-	partProducer := s3PartProducer{
-		store: store,
-		done:  doneChan,
-		files: fileChan,
-		r:     src,
-	}
 	go partProducer.produce(optimalPartSize)
 
-	for file := range fileChan {
+	var wg sync.WaitGroup
-		stat, err := file.Stat()
+	var uploadErr error
-		if err != nil {
+
-			return 0, err
+	for fileChunk := range fileChan {
-		}
+		partfile := fileChunk.file
-		n := stat.Size()
+		partsize := fileChunk.size
+
+		isFinalChunk := !info.SizeIsDeferred && (size == offset+bytesUploaded+partsize)
+		if partsize >= store.MinPartSize || isFinalChunk {
+			part := &s3Part{
+				etag:   "",
+				size:   partsize,
+				number: nextPartNum,
+			}
+			upload.parts = append(upload.parts, part)
+
+			wg.Add(1)
+			// We acquire the semaphore before starting the goroutine to avoid
+			// starting many goroutines, most of which are just waiting for the lock.
+			upload.store.uploadSemaphore.Acquire()
+			go func(file *os.File, part *s3Part) {
+				defer upload.store.uploadSemaphore.Release()
+				defer wg.Done()
 
-		isFinalChunk := !info.SizeIsDeferred && (size == (offset-incompletePartSize)+n)
-		if n >= store.MinPartSize || isFinalChunk {
 				uploadPartInput := &s3.UploadPartInput{
 					Bucket:     aws.String(store.Bucket),
 					Key:        store.keyWithPrefix(uploadId),
 					UploadId:   aws.String(multipartId),
-				PartNumber: aws.Int64(nextPartNum),
+					PartNumber: aws.Int64(part.number),
-			}
-			if err := upload.putPartForUpload(ctx, uploadPartInput, file, n); err != nil {
-				return bytesUploaded, err
 				}
+				etag, err := upload.putPartForUpload(ctx, uploadPartInput, file, part.size)
+				if err != nil {
+					uploadErr = err
 				} else {
+					part.etag = etag
+				}
+			}(partfile, part)
+		} else {
+			wg.Add(1)
+			// We acquire the semaphore before starting the goroutine to avoid
+			// starting many goroutines, most of which are just waiting for the lock.
+			upload.store.uploadSemaphore.Acquire()
+			go func(file *os.File) {
+				defer upload.store.uploadSemaphore.Release()
+				defer wg.Done()
+
 				if err := store.putIncompletePartForUpload(ctx, uploadId, file); err != nil {
-				return bytesUploaded, err
+					uploadErr = err
+				}
+				upload.incompletePartSize = partsize
+			}(partfile)
 		}
 
-			bytesUploaded += n
+		bytesUploaded += partsize
-
-			return (bytesUploaded - incompletePartSize), nil
-		}
-
-		offset += n
-		bytesUploaded += n
 		nextPartNum += 1
 	}
 
-	return bytesUploaded - incompletePartSize, partProducer.err
+	wg.Wait()
+
+	if uploadErr != nil {
+		return 0, uploadErr
+	}
+
+	return bytesUploaded, partProducer.err
 }
 
 func cleanUpTempFile(file *os.File) {
@@ -405,14 +468,17 @@ func cleanUpTempFile(file *os.File) {
 	os.Remove(file.Name())
 }
 
-func (upload *s3Upload) putPartForUpload(ctx context.Context, uploadPartInput *s3.UploadPartInput, file *os.File, size int64) error {
+func (upload *s3Upload) putPartForUpload(ctx context.Context, uploadPartInput *s3.UploadPartInput, file *os.File, size int64) (string, error) {
 	defer cleanUpTempFile(file)
 
 	if !upload.store.DisableContentHashes {
 		// By default, use the traditional approach to upload data
 		uploadPartInput.Body = file
-		_, err := upload.store.Service.UploadPartWithContext(ctx, uploadPartInput)
+		res, err := upload.store.Service.UploadPartWithContext(ctx, uploadPartInput)
-		return err
+		if err != nil {
+			return "", err
+		}
+		return *res.ETag, nil
 	} else {
 		// Experimental feature to prevent the AWS SDK from calculating the SHA256 hash
 		// for the parts we upload to S3.
@@ -420,19 +486,19 @@ func (upload *s3Upload) putPartForUpload(ctx context.Context, uploadPartInput *s
 		// on our own. This way, the body is not included in the SHA256 calculation.
 		s3api, ok := upload.store.Service.(s3APIForPresigning)
 		if !ok {
-			return fmt.Errorf("s3store: failed to cast S3 service for presigning")
+			return "", fmt.Errorf("s3store: failed to cast S3 service for presigning")
 		}
 
 		s3Req, _ := s3api.UploadPartRequest(uploadPartInput)
 
 		url, err := s3Req.Presign(15 * time.Minute)
 		if err != nil {
-			return err
+			return "", err
 		}
 
 		req, err := http.NewRequest("PUT", url, file)
 		if err != nil {
-			return err
+			return "", err
 		}
 
 		// Set the Content-Length manually to prevent the usage of Transfer-Encoding: chunked,
@@ -441,89 +507,122 @@ func (upload *s3Upload) putPartForUpload(ctx context.Context, uploadPartInput *s
 
 		res, err := http.DefaultClient.Do(req)
 		if err != nil {
-			return err
+			return "", err
 		}
 		defer res.Body.Close()
 
 		if res.StatusCode != 200 {
 			buf := new(strings.Builder)
 			io.Copy(buf, res.Body)
-			return fmt.Errorf("s3store: unexpected response code %d for presigned upload: %s", res.StatusCode, buf.String())
+			return "", fmt.Errorf("s3store: unexpected response code %d for presigned upload: %s", res.StatusCode, buf.String())
 		}
 
-		return nil
+		return res.Header.Get("ETag"), nil
 	}
 }
 
 func (upload *s3Upload) GetInfo(ctx context.Context) (info handler.FileInfo, err error) {
-	if upload.info != nil {
+	info, _, _, err = upload.getInternalInfo(ctx)
-		return *upload.info, nil
-	}
-
-	info, err = upload.fetchInfo(ctx)
-	if err != nil {
 	return info, err
 }
 
-	upload.info = &info
+func (upload *s3Upload) getInternalInfo(ctx context.Context) (info handler.FileInfo, parts []*s3Part, incompletePartSize int64, err error) {
-	return info, nil
+	if upload.info != nil {
+		return *upload.info, upload.parts, upload.incompletePartSize, nil
 	}
 
-func (upload s3Upload) fetchInfo(ctx context.Context) (info handler.FileInfo, err error) {
+	info, parts, incompletePartSize, err = upload.fetchInfo(ctx)
+	if err != nil {
+		return info, parts, incompletePartSize, err
+	}
+
+	upload.info = &info
+	upload.parts = parts
+	upload.incompletePartSize = incompletePartSize
+	return info, parts, incompletePartSize, nil
+}
+
+func (upload s3Upload) fetchInfo(ctx context.Context) (info handler.FileInfo, parts []*s3Part, incompletePartSize int64, err error) {
 	id := upload.id
 	store := upload.store
 	uploadId, _ := splitIds(id)
 
+	var wg sync.WaitGroup
+	wg.Add(3)
+
+	// We store all errors in here and handle them all together once the wait
+	// group is done.
+	var infoErr error
+	var partsErr error
+	var incompletePartSizeErr error
+
+	go func() {
+		defer wg.Done()
+
 		// Get file info stored in separate object
-	res, err := store.Service.GetObjectWithContext(ctx, &s3.GetObjectInput{
+		var res *s3.GetObjectOutput
+		res, infoErr = store.Service.GetObjectWithContext(ctx, &s3.GetObjectInput{
 			Bucket: aws.String(store.Bucket),
 			Key:    store.metadataKeyWithPrefix(uploadId + ".info"),
 		})
-	if err != nil {
+		if infoErr == nil {
-		if isAwsError(err, "NoSuchKey") {
+			infoErr = json.NewDecoder(res.Body).Decode(&info)
-			return info, handler.ErrNotFound
 		}
+	}()
 
-		return info, err
+	go func() {
-	}
+		defer wg.Done()
-
-	if err := json.NewDecoder(res.Body).Decode(&info); err != nil {
-		return info, err
-	}
 
 		// Get uploaded parts and their offset
-	parts, err := store.listAllParts(ctx, id)
+		parts, partsErr = store.listAllParts(ctx, id)
-	if err != nil {
+	}()
-		// Check if the error is caused by the upload not being found. This happens
+
+	go func() {
+		defer wg.Done()
+
+		// Get size of optional incomplete part file.
+		incompletePartSize, incompletePartSizeErr = store.headIncompletePartForUpload(ctx, uploadId)
+	}()
+
+	wg.Wait()
+
+	// Finally, after all requests are complete, let's handle the errors
+	if infoErr != nil {
+		err = infoErr
+		// If the info file is not found, we consider the upload to be non-existant
+		if isAwsError(err, "NoSuchKey") {
+			err = handler.ErrNotFound
+		}
+		return
+	}
+
+	if partsErr != nil {
+		err = partsErr
+		// Check if the error is caused by the multipart upload not being found. This happens
 		// when the multipart upload has already been completed or aborted. Since
 		// we already found the info object, we know that the upload has been
 		// completed and therefore can ensure the the offset is the size.
 		if isAwsError(err, "NoSuchUpload") {
 			info.Offset = info.Size
-			return info, nil
+			err = nil
-		} else {
-			return info, err
 		}
+		return
 	}
 
-	offset := int64(0)
+	if incompletePartSizeErr != nil {
+		err = incompletePartSizeErr
+		return
+	}
 
+	// The offset is the sum of all part sizes and the size of the incomplete part file.
+	offset := incompletePartSize
 	for _, part := range parts {
-		offset += *part.Size
+		offset += part.size
-	}
-
-	incompletePartObject, err := store.getIncompletePartForUpload(ctx, uploadId)
-	if err != nil {
-		return info, err
-	}
-	if incompletePartObject != nil {
-		defer incompletePartObject.Body.Close()
-		offset += *incompletePartObject.ContentLength
 	}
 
 	info.Offset = offset
 
-	return
+	return info, parts, incompletePartSize, nil
 }
 
 func (upload s3Upload) GetReader(ctx context.Context) (io.Reader, error) {
@@ -640,7 +739,7 @@ func (upload s3Upload) FinishUpload(ctx context.Context) error {
 	uploadId, multipartId := splitIds(id)
 
 	// Get uploaded parts
-	parts, err := store.listAllParts(ctx, id)
+	_, parts, _, err := upload.getInternalInfo(ctx)
 	if err != nil {
 		return err
 	}
@@ -660,10 +759,11 @@ func (upload s3Upload) FinishUpload(ctx context.Context) error {
 			return err
 		}
 
-		parts = []*s3.Part{
+		parts = []*s3Part{
-			&s3.Part{
+			&s3Part{
-				ETag:       res.ETag,
+				etag:   *res.ETag,
-				PartNumber: aws.Int64(1),
+				number: 1,
+				size:   0,
 			},
 		}
 
@@ -675,8 +775,8 @@ func (upload s3Upload) FinishUpload(ctx context.Context) error {
 
 	for index, part := range parts {
 		completedParts[index] = &s3.CompletedPart{
-			ETag:       part.ETag,
+			ETag:       aws.String(part.etag),
-			PartNumber: part.PartNumber,
+			PartNumber: aws.Int64(part.number),
 		}
 	}
 
@@ -790,10 +890,16 @@ func (upload *s3Upload) concatUsingMultipart(ctx context.Context, partialUploads
 		partialS3Upload := partialUpload.(*s3Upload)
 		partialId, _ := splitIds(partialS3Upload.id)
 
+		upload.parts = append(upload.parts, &s3Part{
+			number: int64(i + 1),
+			size:   -1,
+			etag:   "",
+		})
+
 		go func(i int, partialId string) {
 			defer wg.Done()
 
-			_, err := store.Service.UploadPartCopyWithContext(ctx, &s3.UploadPartCopyInput{
+			res, err := store.Service.UploadPartCopyWithContext(ctx, &s3.UploadPartCopyInput{
 				Bucket:   aws.String(store.Bucket),
 				Key:      store.keyWithPrefix(uploadId),
 				UploadId: aws.String(multipartId),
@@ -806,6 +912,8 @@ func (upload *s3Upload) concatUsingMultipart(ctx context.Context, partialUploads
 				errs = append(errs, err)
 				return
 			}
+
+			upload.parts[i].etag = *res.CopyPartResult.ETag
 		}(i, partialId)
 	}
 
@@ -829,7 +937,7 @@ func (upload *s3Upload) DeclareLength(ctx context.Context, length int64) error {
 	return upload.writeInfo(ctx, info)
 }
 
-func (store S3Store) listAllParts(ctx context.Context, id string) (parts []*s3.Part, err error) {
+func (store S3Store) listAllParts(ctx context.Context, id string) (parts []*s3Part, err error) {
 	uploadId, multipartId := splitIds(id)
 
 	partMarker := int64(0)
@@ -845,7 +953,14 @@ func (store S3Store) listAllParts(ctx context.Context, id string) (parts []*s3.P
 			return nil, err
 		}
 
-		parts = append(parts, (*listPtr).Parts...)
+		// TODO: Find more efficient way when appending many elements
+		for _, part := range (*listPtr).Parts {
+			parts = append(parts, &s3Part{
+				number: *part.PartNumber,
+				size:   *part.Size,
+				etag:   *part.ETag,
+			})
+		}
 
 		if listPtr.IsTruncated != nil && *listPtr.IsTruncated {
 			partMarker = *listPtr.NextPartNumberMarker
@@ -856,36 +971,36 @@ func (store S3Store) listAllParts(ctx context.Context, id string) (parts []*s3.P
 	return parts, nil
 }
 
-func (store S3Store) downloadIncompletePartForUpload(ctx context.Context, uploadId string) (*os.File, int64, error) {
+func (store S3Store) downloadIncompletePartForUpload(ctx context.Context, uploadId string) (*os.File, error) {
 	incompleteUploadObject, err := store.getIncompletePartForUpload(ctx, uploadId)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 	if incompleteUploadObject == nil {
 		// We did not find an incomplete upload
-		return nil, 0, nil
+		return nil, nil
 	}
 	defer incompleteUploadObject.Body.Close()
 
 	partFile, err := ioutil.TempFile(store.TemporaryDirectory, "tusd-s3-tmp-")
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 
 	n, err := io.Copy(partFile, incompleteUploadObject.Body)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 	if n < *incompleteUploadObject.ContentLength {
-		return nil, 0, errors.New("short read of incomplete upload")
+		return nil, errors.New("short read of incomplete upload")
 	}
 
 	_, err = partFile.Seek(0, 0)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 
-	return partFile, n, nil
+	return partFile, nil
 }
 
 func (store S3Store) getIncompletePartForUpload(ctx context.Context, uploadId string) (*s3.GetObjectOutput, error) {
@@ -901,6 +1016,22 @@ func (store S3Store) getIncompletePartForUpload(ctx context.Context, uploadId st
 	return obj, err
 }
 
+func (store S3Store) headIncompletePartForUpload(ctx context.Context, uploadId string) (int64, error) {
+	obj, err := store.Service.HeadObjectWithContext(ctx, &s3.HeadObjectInput{
+		Bucket: aws.String(store.Bucket),
+		Key:    store.metadataKeyWithPrefix(uploadId + ".part"),
+	})
+
+	if err != nil {
+		if isAwsError(err, s3.ErrCodeNoSuchKey) || isAwsError(err, "NotFound") || isAwsError(err, "AccessDenied") {
+			err = nil
+		}
+		return 0, err
+	}
+
+	return *obj.ContentLength, nil
+}
+
 func (store S3Store) putIncompletePartForUpload(ctx context.Context, uploadId string, file *os.File) error {
 	defer cleanUpTempFile(file)
 

pkg/s3store/s3store_mock_test.go

@@ -6,10 +6,11 @@ package s3store
 
 import (
 	context "context"
+	reflect "reflect"
+
 	request "github.com/aws/aws-sdk-go/aws/request"
 	s3 "github.com/aws/aws-sdk-go/service/s3"
 	gomock "github.com/golang/mock/gomock"
-	reflect "reflect"
 )
 
 // MockS3API is a mock of S3API interface
@@ -155,6 +156,26 @@ func (mr *MockS3APIMockRecorder) GetObjectWithContext(arg0, arg1 interface{}, ar
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GetObjectWithContext", reflect.TypeOf((*MockS3API)(nil).GetObjectWithContext), varargs...)
 }
 
+// HeadObjectWithContext mocks base method
+func (m *MockS3API) HeadObjectWithContext(arg0 context.Context, arg1 *s3.HeadObjectInput, arg2 ...request.Option) (*s3.HeadObjectOutput, error) {
+	m.ctrl.T.Helper()
+	varargs := []interface{}{arg0, arg1}
+	for _, a := range arg2 {
+		varargs = append(varargs, a)
+	}
+	ret := m.ctrl.Call(m, "HeadObjectWithContext", varargs...)
+	ret0, _ := ret[0].(*s3.HeadObjectOutput)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// HeadObjectWithContext indicates an expected call of HeadObjectWithContext
+func (mr *MockS3APIMockRecorder) HeadObjectWithContext(arg0, arg1 interface{}, arg2 ...interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	varargs := append([]interface{}{arg0, arg1}, arg2...)
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "HeadObjectWithContext", reflect.TypeOf((*MockS3API)(nil).HeadObjectWithContext), varargs...)
+}
+
 // ListPartsWithContext mocks base method
 func (m *MockS3API) ListPartsWithContext(arg0 context.Context, arg1 *s3.ListPartsInput, arg2 ...request.Option) (*s3.ListPartsOutput, error) {
 	m.ctrl.T.Helper()

pkg/s3store/s3store_part_producer.go

@@ -8,45 +8,79 @@ import (
 
 // s3PartProducer converts a stream of bytes from the reader into a stream of files on disk
 type s3PartProducer struct {
-	store *S3Store
+	tmpDir string
-	files chan<- *os.File
+	files  chan fileChunk
 	done   chan struct{}
 	err    error
 	r      io.Reader
 }
 
-func (spp *s3PartProducer) produce(partSize int64) {
+type fileChunk struct {
-	for {
+	file *os.File
-		file, err := spp.nextPart(partSize)
+	size int64
-		if err != nil {
-			spp.err = err
-			close(spp.files)
-			return
 }
-		if file == nil {
+
-			close(spp.files)
+func newS3PartProducer(source io.Reader, backlog int64, tmpDir string) (s3PartProducer, <-chan fileChunk) {
-			return
+	fileChan := make(chan fileChunk, backlog)
+	doneChan := make(chan struct{})
+
+	partProducer := s3PartProducer{
+		tmpDir: tmpDir,
+		done:   doneChan,
+		files:  fileChan,
+		r:      source,
+	}
+
+	return partProducer, fileChan
+}
+
+// stop should always be called by the consumer to ensure that the channels
+// are properly closed and emptied.
+func (spp *s3PartProducer) stop() {
+	close(spp.done)
+
+	// If we return while there are still files in the channel, then
+	// we may leak file descriptors. Let's ensure that those are cleaned up.
+	for fileChunk := range spp.files {
+		cleanUpTempFile(fileChunk.file)
+	}
+}
+
+func (spp *s3PartProducer) produce(partSize int64) {
+outerloop:
+	for {
+		file, ok, err := spp.nextPart(partSize)
+		if err != nil {
+			// An error occured. Stop producing.
+			spp.err = err
+			break
+		}
+		if !ok {
+			// The source was fully read. Stop producing.
+			break
 		}
 		select {
 		case spp.files <- file:
 		case <-spp.done:
-			close(spp.files)
+			// We are told to stop producing. Stop producing.
-			return
+			break outerloop
-		}
 		}
 	}
 
-func (spp *s3PartProducer) nextPart(size int64) (*os.File, error) {
+	close(spp.files)
+}
+
+func (spp *s3PartProducer) nextPart(size int64) (fileChunk, bool, error) {
 	// Create a temporary file to store the part
-	file, err := ioutil.TempFile(spp.store.TemporaryDirectory, "tusd-s3-tmp-")
+	file, err := ioutil.TempFile(spp.tmpDir, "tusd-s3-tmp-")
 	if err != nil {
-		return nil, err
+		return fileChunk{}, false, err
 	}
 
 	limitedReader := io.LimitReader(spp.r, size)
 	n, err := io.Copy(file, limitedReader)
 	if err != nil {
-		return nil, err
+		return fileChunk{}, false, err
 	}
 
 	// If the entire request body is read and no more data is available,
@@ -54,11 +88,14 @@ func (spp *s3PartProducer) nextPart(size int64) (*os.File, error) {
 	// case, we can close the s3PartProducer.
 	if n == 0 {
 		cleanUpTempFile(file)
-		return nil, nil
+		return fileChunk{}, false, nil
 	}
 
 	// Seek to the beginning of the file
 	file.Seek(0, 0)
 
-	return file, nil
+	return fileChunk{
+		file: file,
+		size: n,
+	}, true, nil
 }

pkg/s3store/s3store_part_producer_test.go

@@ -22,32 +22,28 @@ func (ErrorReader) Read(b []byte) (int, error) {
 }
 
 func TestPartProducerConsumesEntireReaderWithoutError(t *testing.T) {
-	fileChan := make(chan *os.File)
-	doneChan := make(chan struct{})
 	expectedStr := "test"
 	r := strings.NewReader(expectedStr)
-	pp := s3PartProducer{
+	pp, fileChan := newS3PartProducer(r, 0, "")
-		store: &S3Store{},
-		done:  doneChan,
-		files: fileChan,
-		r:     r,
-	}
 	go pp.produce(1)
 
 	actualStr := ""
 	b := make([]byte, 1)
-	for f := range fileChan {
+	for chunk := range fileChan {
-		n, err := f.Read(b)
+		n, err := chunk.file.Read(b)
 		if err != nil {
 			t.Fatalf("unexpected error: %s", err)
 		}
 		if n != 1 {
 			t.Fatalf("incorrect number of bytes read: wanted %d, got %d", 1, n)
 		}
+		if chunk.size != 1 {
+			t.Fatalf("incorrect number of bytes in struct: wanted %d, got %d", 1, chunk.size)
+		}
 		actualStr += string(b)
 
-		os.Remove(f.Name())
+		os.Remove(chunk.file.Name())
-		f.Close()
+		chunk.file.Close()
 	}
 
 	if actualStr != expectedStr {
@@ -59,15 +55,8 @@ func TestPartProducerConsumesEntireReaderWithoutError(t *testing.T) {
 	}
 }
 
-func TestPartProducerExitsWhenDoneChannelIsClosed(t *testing.T) {
+func TestPartProducerExitsWhenProducerIsStopped(t *testing.T) {
-	fileChan := make(chan *os.File)
+	pp, fileChan := newS3PartProducer(InfiniteZeroReader{}, 0, "")
-	doneChan := make(chan struct{})
-	pp := s3PartProducer{
-		store: &S3Store{},
-		done:  doneChan,
-		files: fileChan,
-		r:     InfiniteZeroReader{},
-	}
 
 	completedChan := make(chan struct{})
 	go func() {
@@ -75,35 +64,7 @@ func TestPartProducerExitsWhenDoneChannelIsClosed(t *testing.T) {
 		completedChan <- struct{}{}
 	}()
 
-	close(doneChan)
+	pp.stop()
-
-	select {
-	case <-completedChan:
-		// producer exited cleanly
-	case <-time.After(2 * time.Second):
-		t.Error("timed out waiting for producer to exit")
-	}
-
-	safelyDrainChannelOrFail(fileChan, t)
-}
-
-func TestPartProducerExitsWhenDoneChannelIsClosedBeforeAnyPartIsSent(t *testing.T) {
-	fileChan := make(chan *os.File)
-	doneChan := make(chan struct{})
-	pp := s3PartProducer{
-		store: &S3Store{},
-		done:  doneChan,
-		files: fileChan,
-		r:     InfiniteZeroReader{},
-	}
-
-	close(doneChan)
-
-	completedChan := make(chan struct{})
-	go func() {
-		pp.produce(10)
-		completedChan <- struct{}{}
-	}()
 
 	select {
 	case <-completedChan:
@@ -116,14 +77,7 @@ func TestPartProducerExitsWhenDoneChannelIsClosedBeforeAnyPartIsSent(t *testing.
 }
 
 func TestPartProducerExitsWhenUnableToReadFromFile(t *testing.T) {
-	fileChan := make(chan *os.File)
+	pp, fileChan := newS3PartProducer(ErrorReader{}, 0, "")
-	doneChan := make(chan struct{})
-	pp := s3PartProducer{
-		store: &S3Store{},
-		done:  doneChan,
-		files: fileChan,
-		r:     ErrorReader{},
-	}
 
 	completedChan := make(chan struct{})
 	go func() {
@@ -145,12 +99,12 @@ func TestPartProducerExitsWhenUnableToReadFromFile(t *testing.T) {
 	}
 }
 
-func safelyDrainChannelOrFail(c chan *os.File, t *testing.T) {
+func safelyDrainChannelOrFail(c <-chan fileChunk, t *testing.T) {
 	// At this point, we've signaled that the producer should exit, but it may write a few files
 	// into the channel before closing it and exiting. Make sure that we get a nil value
 	// eventually.
 	for i := 0; i < 100; i++ {
-		if f := <-c; f == nil {
+		if _, more := <-c; !more {
 			return
 		}
 	}

pkg/s3store/s3store_test.go

@@ -171,6 +171,9 @@ func TestNewUploadWithMetadataObjectPrefix(t *testing.T) {
 	assert.NotNil(upload)
 }
 
+// This test ensures that an newly created upload without any chunks can be
+// directly finished. There are no calls to ListPart or HeadObject because
+// the upload is not fetched from S3 first.
 func TestEmptyUpload(t *testing.T) {
 	mockCtrl := gomock.NewController(t)
 	defer mockCtrl.Finish()
@@ -193,14 +196,6 @@ func TestEmptyUpload(t *testing.T) {
 			Body:          bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":0,"SizeIsDeferred":false,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":{"Bucket":"bucket","Key":"uploadId","Type":"s3store"}}`)),
 			ContentLength: aws.Int64(int64(208)),
 		}),
-		s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
-			Bucket:           aws.String("bucket"),
-			Key:              aws.String("uploadId"),
-			UploadId:         aws.String("multipartId"),
-			PartNumberMarker: aws.Int64(0),
-		}).Return(&s3.ListPartsOutput{
-			Parts: []*s3.Part{},
-		}, nil),
 		s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 			Bucket:     aws.String("bucket"),
 			Key:        aws.String("uploadId"),
@@ -272,6 +267,17 @@ func TestGetInfoNotFound(t *testing.T) {
 		Key:    aws.String("uploadId.info"),
 	}).Return(nil, awserr.New("NoSuchKey", "The specified key does not exist.", nil))
 
+	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
+		Bucket:           aws.String("bucket"),
+		Key:              aws.String("uploadId"),
+		UploadId:         aws.String("multipartId"),
+		PartNumberMarker: aws.Int64(0),
+	}).Return(nil, awserr.New("NoSuchUpload", "Not found", nil))
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
+		Bucket: aws.String("bucket"),
+		Key:    aws.String("uploadId.part"),
+	}).Return(nil, awserr.New("NoSuchKey", "Not found", nil))
+
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
 
@@ -287,13 +293,12 @@ func TestGetInfo(t *testing.T) {
 	s3obj := NewMockS3API(mockCtrl)
 	store := New("bucket", s3obj)
 
-	gomock.InOrder(
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.info"),
 	}).Return(&s3.GetObjectOutput{
 		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":500,"Offset":0,"MetaData":{"bar":"menü","foo":"hello"},"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":{"Bucket":"bucket","Key":"my/uploaded/files/uploadId","Type":"s3store"}}`))),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -302,15 +307,20 @@ func TestGetInfo(t *testing.T) {
 	}).Return(&s3.ListPartsOutput{
 		Parts: []*s3.Part{
 			{
+				PartNumber: aws.Int64(1),
 				Size:       aws.Int64(100),
+				ETag:       aws.String("etag-1"),
 			},
 			{
+				PartNumber: aws.Int64(2),
 				Size:       aws.Int64(200),
+				ETag:       aws.String("etag-2"),
 			},
 		},
 		NextPartNumberMarker: aws.Int64(2),
+		// Simulate a truncated response, so s3store should send a second request
 		IsTruncated: aws.Bool(true),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -319,15 +329,16 @@ func TestGetInfo(t *testing.T) {
 	}).Return(&s3.ListPartsOutput{
 		Parts: []*s3.Part{
 			{
+				PartNumber: aws.Int64(3),
 				Size:       aws.Int64(100),
+				ETag:       aws.String("etag-3"),
 			},
 		},
-		}, nil),
+	}, nil)
-		s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-		}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "Not found", nil)),
+	}).Return(nil, awserr.New("NoSuchKey", "Not found", nil))
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -353,13 +364,12 @@ func TestGetInfoWithMetadataObjectPrefix(t *testing.T) {
 	store := New("bucket", s3obj)
 	store.MetadataObjectPrefix = "my/metadata"
 
-	gomock.InOrder(
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("my/metadata/uploadId.info"),
 	}).Return(&s3.GetObjectOutput{
 		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":500,"Offset":0,"MetaData":{"bar":"menü","foo":"hello"},"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":{"Bucket":"bucket","Key":"my/uploaded/files/uploadId","Type":"s3store"}}`))),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -368,15 +378,20 @@ func TestGetInfoWithMetadataObjectPrefix(t *testing.T) {
 	}).Return(&s3.ListPartsOutput{
 		Parts: []*s3.Part{
 			{
+				PartNumber: aws.Int64(1),
 				Size:       aws.Int64(100),
+				ETag:       aws.String("etag-1"),
 			},
 			{
+				PartNumber: aws.Int64(2),
 				Size:       aws.Int64(200),
+				ETag:       aws.String("etag-2"),
 			},
 		},
 		NextPartNumberMarker: aws.Int64(2),
+		// Simulate a truncated response, so s3store should send a second request
 		IsTruncated: aws.Bool(true),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -385,15 +400,16 @@ func TestGetInfoWithMetadataObjectPrefix(t *testing.T) {
 	}).Return(&s3.ListPartsOutput{
 		Parts: []*s3.Part{
 			{
+				PartNumber: aws.Int64(3),
 				Size:       aws.Int64(100),
+				ETag:       aws.String("etag-3"),
 			},
 		},
-		}, nil),
+	}, nil)
-		s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("my/metadata/uploadId.part"),
-		}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "Not found", nil)),
+	}).Return(nil, awserr.New("NoSuchKey", "Not found", nil))
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -418,27 +434,24 @@ func TestGetInfoWithIncompletePart(t *testing.T) {
 	s3obj := NewMockS3API(mockCtrl)
 	store := New("bucket", s3obj)
 
-	gomock.InOrder(
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.info"),
 	}).Return(&s3.GetObjectOutput{
 		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":500,"Offset":0,"MetaData":{},"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":null}`))),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
 		UploadId:         aws.String("multipartId"),
 		PartNumberMarker: aws.Int64(0),
-		}).Return(&s3.ListPartsOutput{Parts: []*s3.Part{}}, nil),
+	}).Return(&s3.ListPartsOutput{Parts: []*s3.Part{}}, nil)
-		s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-		}).Return(&s3.GetObjectOutput{
+	}).Return(&s3.HeadObjectOutput{
 		ContentLength: aws.Int64(10),
-			Body:          ioutil.NopCloser(bytes.NewReader([]byte("0123456789"))),
+	}, nil)
-		}, nil),
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -457,20 +470,22 @@ func TestGetInfoFinished(t *testing.T) {
 	s3obj := NewMockS3API(mockCtrl)
 	store := New("bucket", s3obj)
 
-	gomock.InOrder(
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.info"),
 	}).Return(&s3.GetObjectOutput{
 		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId","Size":500,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":null}`))),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
 		UploadId:         aws.String("multipartId"),
 		PartNumberMarker: aws.Int64(0),
-		}).Return(nil, awserr.New("NoSuchUpload", "The specified upload does not exist.", nil)),
+	}).Return(nil, awserr.New("NoSuchUpload", "The specified upload does not exist.", nil))
-	)
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
+		Bucket: aws.String("bucket"),
+		Key:    aws.String("uploadId.part"),
+	}).Return(nil, awserr.New("NoSuchKey", "Not found", nil))
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -572,13 +587,12 @@ func TestDeclareLength(t *testing.T) {
 	s3obj := NewMockS3API(mockCtrl)
 	store := New("bucket", s3obj)
 
-	gomock.InOrder(
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.info"),
 	}).Return(&s3.GetObjectOutput{
 		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":0,"SizeIsDeferred":true,"Offset":0,"MetaData":{},"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":{"Bucket":"bucket","Key":"uploadId","Type":"s3store"}}`))),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -586,18 +600,17 @@ func TestDeclareLength(t *testing.T) {
 		PartNumberMarker: aws.Int64(0),
 	}).Return(&s3.ListPartsOutput{
 		Parts: []*s3.Part{},
-		}, nil),
+	}, nil)
-		s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-		}).Return(nil, awserr.New("NotFound", "Not Found", nil)),
+	}).Return(nil, awserr.New("NotFound", "Not Found", nil))
 	s3obj.EXPECT().PutObjectWithContext(context.Background(), &s3.PutObjectInput{
 		Bucket:        aws.String("bucket"),
 		Key:           aws.String("uploadId.info"),
 		Body:          bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":500,"SizeIsDeferred":false,"Offset":0,"MetaData":{},"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":{"Bucket":"bucket","Key":"uploadId","Type":"s3store"}}`)),
 		ContentLength: aws.Int64(int64(208)),
-		}),
+	})
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -617,7 +630,12 @@ func TestFinishUpload(t *testing.T) {
 	s3obj := NewMockS3API(mockCtrl)
 	store := New("bucket", s3obj)
 
-	gomock.InOrder(
+	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+		Bucket: aws.String("bucket"),
+		Key:    aws.String("uploadId.info"),
+	}).Return(&s3.GetObjectOutput{
+		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId","Size":400,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":null}`))),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -627,18 +645,18 @@ func TestFinishUpload(t *testing.T) {
 		Parts: []*s3.Part{
 			{
 				Size:       aws.Int64(100),
-					ETag:       aws.String("foo"),
+				ETag:       aws.String("etag-1"),
 				PartNumber: aws.Int64(1),
 			},
 			{
 				Size:       aws.Int64(200),
-					ETag:       aws.String("bar"),
+				ETag:       aws.String("etag-2"),
 				PartNumber: aws.Int64(2),
 			},
 		},
 		NextPartNumberMarker: aws.Int64(2),
 		IsTruncated:          aws.Bool(true),
-		}, nil),
+	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
 		Key:              aws.String("uploadId"),
@@ -648,11 +666,15 @@ func TestFinishUpload(t *testing.T) {
 		Parts: []*s3.Part{
 			{
 				Size:       aws.Int64(100),
-					ETag:       aws.String("foobar"),
+				ETag:       aws.String("etag-3"),
 				PartNumber: aws.Int64(3),
 			},
 		},
-		}, nil),
+	}, nil)
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
+		Bucket: aws.String("bucket"),
+		Key:    aws.String("uploadId.part"),
+	}).Return(nil, awserr.New("NotFound", "Not Found", nil))
 	s3obj.EXPECT().CompleteMultipartUploadWithContext(context.Background(), &s3.CompleteMultipartUploadInput{
 		Bucket:   aws.String("bucket"),
 		Key:      aws.String("uploadId"),
@@ -660,21 +682,20 @@ func TestFinishUpload(t *testing.T) {
 		MultipartUpload: &s3.CompletedMultipartUpload{
 			Parts: []*s3.CompletedPart{
 				{
-						ETag:       aws.String("foo"),
+					ETag:       aws.String("etag-1"),
 					PartNumber: aws.Int64(1),
 				},
 				{
-						ETag:       aws.String("bar"),
+					ETag:       aws.String("etag-2"),
 					PartNumber: aws.Int64(2),
 				},
 				{
-						ETag:       aws.String("foobar"),
+					ETag:       aws.String("etag-3"),
 					PartNumber: aws.Int64(3),
 				},
 			},
 		},
-		}).Return(nil, nil),
+	}).Return(nil, nil)
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -696,6 +717,7 @@ func TestWriteChunk(t *testing.T) {
 	store.MaxMultipartParts = 10000
 	store.MaxObjectSize = 5 * 1024 * 1024 * 1024 * 1024
 
+	// From GetInfo
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.info"),
@@ -711,49 +733,54 @@ func TestWriteChunk(t *testing.T) {
 		Parts: []*s3.Part{
 			{
 				Size:       aws.Int64(100),
+				ETag:       aws.String("etag-1"),
+				PartNumber: aws.Int64(1),
 			},
 			{
 				Size:       aws.Int64(200),
+				ETag:       aws.String("etag-2"),
+				PartNumber: aws.Int64(2),
 			},
 		},
-	}, nil).Times(2)
+	}, nil)
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "Not found", nil))
+	}).Return(nil, awserr.New("NoSuchKey", "Not found", nil))
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
-		Bucket: aws.String("bucket"),
-		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "The specified key does not exist.", nil))
 
-	gomock.InOrder(
+	// From WriteChunk
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(3),
 		Body:       bytes.NewReader([]byte("1234")),
-		})).Return(nil, nil),
+	})).Return(&s3.UploadPartOutput{
+		ETag: aws.String("etag-3"),
+	}, nil)
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(4),
 		Body:       bytes.NewReader([]byte("5678")),
-		})).Return(nil, nil),
+	})).Return(&s3.UploadPartOutput{
+		ETag: aws.String("etag-4"),
+	}, nil)
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(5),
 		Body:       bytes.NewReader([]byte("90AB")),
-		})).Return(nil, nil),
+	})).Return(&s3.UploadPartOutput{
+		ETag: aws.String("etag-5"),
+	}, nil)
 	s3obj.EXPECT().PutObjectWithContext(context.Background(), NewPutObjectInputMatcher(&s3.PutObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
 		Body:   bytes.NewReader([]byte("CD")),
-		})).Return(nil, nil),
+	})).Return(nil, nil)
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -786,28 +813,26 @@ func TestWriteChunkWriteIncompletePartBecauseTooSmall(t *testing.T) {
 		Parts: []*s3.Part{
 			{
 				Size:       aws.Int64(100),
+				ETag:       aws.String("etag-1"),
+				PartNumber: aws.Int64(1),
 			},
 			{
 				Size:       aws.Int64(200),
+				ETag:       aws.String("etag-2"),
+				PartNumber: aws.Int64(2),
 			},
 		},
-	}, nil).Times(2)
+	}, nil)
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "The specified key does not exist", nil))
+	}).Return(nil, awserr.New("NoSuchKey", "The specified key does not exist", nil))
 
-	gomock.InOrder(
-		s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
-			Bucket: aws.String("bucket"),
-			Key:    aws.String("uploadId.part"),
-		}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "The specified key does not exist.", nil)),
 	s3obj.EXPECT().PutObjectWithContext(context.Background(), NewPutObjectInputMatcher(&s3.PutObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
 		Body:   bytes.NewReader([]byte("1234567890")),
-		})).Return(nil, nil),
+	})).Return(nil, nil)
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -836,12 +861,19 @@ func TestWriteChunkPrependsIncompletePart(t *testing.T) {
 	}).Return(&s3.GetObjectOutput{
 		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId","Size":5,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":null}`))),
 	}, nil)
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
+		Bucket:           aws.String("bucket"),
+		Key:              aws.String("uploadId"),
+		UploadId:         aws.String("multipartId"),
+		PartNumberMarker: aws.Int64(0),
+	}).Return(&s3.ListPartsOutput{
+		Parts: []*s3.Part{},
+	}, nil)
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{
+	}).Return(&s3.HeadObjectOutput{
 		ContentLength: aws.Int64(3),
-		Body:          ioutil.NopCloser(bytes.NewReader([]byte("123"))),
 	}, nil)
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
@@ -854,29 +886,25 @@ func TestWriteChunkPrependsIncompletePart(t *testing.T) {
 		Bucket: aws.String(store.Bucket),
 		Key:    aws.String("uploadId.part"),
 	}).Return(&s3.DeleteObjectOutput{}, nil)
-	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
-		Bucket:           aws.String("bucket"),
-		Key:              aws.String("uploadId"),
-		UploadId:         aws.String("multipartId"),
-		PartNumberMarker: aws.Int64(0),
-	}).Return(&s3.ListPartsOutput{Parts: []*s3.Part{}}, nil).Times(2)
 
-	gomock.InOrder(
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(1),
 		Body:       bytes.NewReader([]byte("1234")),
-		})).Return(nil, nil),
+	})).Return(&s3.UploadPartOutput{
+		ETag: aws.String("etag-1"),
+	}, nil)
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(2),
 		Body:       bytes.NewReader([]byte("5")),
-		})).Return(nil, nil),
+	})).Return(&s3.UploadPartOutput{
-	)
+		ETag: aws.String("etag-2"),
+	}, nil)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -910,33 +938,39 @@ func TestWriteChunkPrependsIncompletePartAndWritesANewIncompletePart(t *testing.
 		Key:              aws.String("uploadId"),
 		UploadId:         aws.String("multipartId"),
 		PartNumberMarker: aws.Int64(0),
-	}).Return(&s3.ListPartsOutput{Parts: []*s3.Part{}}, nil).Times(2)
+	}).Return(&s3.ListPartsOutput{Parts: []*s3.Part{}}, nil)
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
+		Bucket: aws.String("bucket"),
+		Key:    aws.String("uploadId.part"),
+	}).Return(&s3.HeadObjectOutput{
+		ContentLength: aws.Int64(3),
+	}, nil)
 	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
 	}).Return(&s3.GetObjectOutput{
 		ContentLength: aws.Int64(3),
 		Body:          ioutil.NopCloser(bytes.NewReader([]byte("123"))),
-	}, nil).Times(2)
+	}, nil)
 	s3obj.EXPECT().DeleteObjectWithContext(context.Background(), &s3.DeleteObjectInput{
 		Bucket: aws.String(store.Bucket),
 		Key:    aws.String("uploadId.part"),
 	}).Return(&s3.DeleteObjectOutput{}, nil)
 
-	gomock.InOrder(
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(1),
 		Body:       bytes.NewReader([]byte("1234")),
-		})).Return(nil, nil),
+	})).Return(&s3.UploadPartOutput{
+		ETag: aws.String("etag-1"),
+	}, nil)
 	s3obj.EXPECT().PutObjectWithContext(context.Background(), NewPutObjectInputMatcher(&s3.PutObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
 		Body:   bytes.NewReader([]byte("5")),
-		})).Return(nil, nil),
+	})).Return(nil, nil)
-	)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -969,28 +1003,30 @@ func TestWriteChunkAllowTooSmallLast(t *testing.T) {
 	}).Return(&s3.ListPartsOutput{
 		Parts: []*s3.Part{
 			{
+				PartNumber: aws.Int64(1),
 				Size:       aws.Int64(400),
+				ETag:       aws.String("etag-1"),
 			},
 			{
+				PartNumber: aws.Int64(2),
 				Size:       aws.Int64(90),
+				ETag:       aws.String("etag-2"),
 			},
 		},
-	}, nil).Times(2)
+	}, nil)
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("AccessDenied", "Access Denied.", nil))
+	}).Return(nil, awserr.New("AccessDenied", "Access Denied.", nil))
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
-		Bucket: aws.String("bucket"),
-		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "The specified key does not exist.", nil))
 	s3obj.EXPECT().UploadPartWithContext(context.Background(), NewUploadPartInputMatcher(&s3.UploadPartInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		PartNumber: aws.Int64(3),
 		Body:       bytes.NewReader([]byte("1234567890")),
-	})).Return(nil, nil)
+	})).Return(&s3.UploadPartOutput{
+		ETag: aws.String("etag-3"),
+	}, nil)
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
@@ -1101,13 +1137,33 @@ func TestConcatUploadsUsingMultipart(t *testing.T) {
 	store := New("bucket", s3obj)
 	store.MinPartSize = 100
 
+	// Calls from NewUpload
+	s3obj.EXPECT().CreateMultipartUploadWithContext(context.Background(), &s3.CreateMultipartUploadInput{
+		Bucket:   aws.String("bucket"),
+		Key:      aws.String("uploadId"),
+		Metadata: map[string]*string{},
+	}).Return(&s3.CreateMultipartUploadOutput{
+		UploadId: aws.String("multipartId"),
+	}, nil)
+	s3obj.EXPECT().PutObjectWithContext(context.Background(), &s3.PutObjectInput{
+		Bucket:        aws.String("bucket"),
+		Key:           aws.String("uploadId.info"),
+		Body:          bytes.NewReader([]byte(`{"ID":"uploadId+multipartId","Size":0,"SizeIsDeferred":false,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":true,"PartialUploads":["aaa+AAA","bbb+BBB","ccc+CCC"],"Storage":{"Bucket":"bucket","Key":"uploadId","Type":"s3store"}}`)),
+		ContentLength: aws.Int64(int64(234)),
+	})
+
+	// Calls from ConcatUploads
 	s3obj.EXPECT().UploadPartCopyWithContext(context.Background(), &s3.UploadPartCopyInput{
 		Bucket:     aws.String("bucket"),
 		Key:        aws.String("uploadId"),
 		UploadId:   aws.String("multipartId"),
 		CopySource: aws.String("bucket/aaa"),
 		PartNumber: aws.Int64(1),
-	}).Return(nil, nil)
+	}).Return(&s3.UploadPartCopyOutput{
+		CopyPartResult: &s3.CopyPartResult{
+			ETag: aws.String("etag-1"),
+		},
+	}, nil)
 
 	s3obj.EXPECT().UploadPartCopyWithContext(context.Background(), &s3.UploadPartCopyInput{
 		Bucket:     aws.String("bucket"),
@@ -1115,7 +1171,11 @@ func TestConcatUploadsUsingMultipart(t *testing.T) {
 		UploadId:   aws.String("multipartId"),
 		CopySource: aws.String("bucket/bbb"),
 		PartNumber: aws.Int64(2),
-	}).Return(nil, nil)
+	}).Return(&s3.UploadPartCopyOutput{
+		CopyPartResult: &s3.CopyPartResult{
+			ETag: aws.String("etag-2"),
+		},
+	}, nil)
 
 	s3obj.EXPECT().UploadPartCopyWithContext(context.Background(), &s3.UploadPartCopyInput{
 		Bucket:     aws.String("bucket"),
@@ -1123,31 +1183,13 @@ func TestConcatUploadsUsingMultipart(t *testing.T) {
 		UploadId:   aws.String("multipartId"),
 		CopySource: aws.String("bucket/ccc"),
 		PartNumber: aws.Int64(3),
-	}).Return(nil, nil)
+	}).Return(&s3.UploadPartCopyOutput{
+		CopyPartResult: &s3.CopyPartResult{
+			ETag: aws.String("etag-3"),
+		},
+	}, nil)
 
-	// Output from s3Store.FinishUpload
+	// Calls from FinishUpload
-	gomock.InOrder(
-		s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
-			Bucket:           aws.String("bucket"),
-			Key:              aws.String("uploadId"),
-			UploadId:         aws.String("multipartId"),
-			PartNumberMarker: aws.Int64(0),
-		}).Return(&s3.ListPartsOutput{
-			Parts: []*s3.Part{
-				{
-					ETag:       aws.String("foo"),
-					PartNumber: aws.Int64(1),
-				},
-				{
-					ETag:       aws.String("bar"),
-					PartNumber: aws.Int64(2),
-				},
-				{
-					ETag:       aws.String("baz"),
-					PartNumber: aws.Int64(3),
-				},
-			},
-		}, nil),
 	s3obj.EXPECT().CompleteMultipartUploadWithContext(context.Background(), &s3.CompleteMultipartUploadInput{
 		Bucket:   aws.String("bucket"),
 		Key:      aws.String("uploadId"),
@@ -1155,23 +1197,31 @@ func TestConcatUploadsUsingMultipart(t *testing.T) {
 		MultipartUpload: &s3.CompletedMultipartUpload{
 			Parts: []*s3.CompletedPart{
 				{
-						ETag:       aws.String("foo"),
+					ETag:       aws.String("etag-1"),
 					PartNumber: aws.Int64(1),
 				},
 				{
-						ETag:       aws.String("bar"),
+					ETag:       aws.String("etag-2"),
 					PartNumber: aws.Int64(2),
 				},
 				{
-						ETag:       aws.String("baz"),
+					ETag:       aws.String("etag-3"),
 					PartNumber: aws.Int64(3),
 				},
 			},
 		},
-		}).Return(nil, nil),
+	}).Return(nil, nil)
-	)
 
-	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
+	info := handler.FileInfo{
+		ID:      "uploadId",
+		IsFinal: true,
+		PartialUploads: []string{
+			"aaa+AAA",
+			"bbb+BBB",
+			"ccc+CCC",
+		},
+	}
+	upload, err := store.NewUpload(context.Background(), info)
 	assert.Nil(err)
 
 	uploadA, err := store.GetUpload(context.Background(), "aaa+AAA")
@@ -1269,13 +1319,13 @@ type s3APIWithTempFileAssertion struct {
 func (s s3APIWithTempFileAssertion) UploadPartWithContext(context.Context, *s3.UploadPartInput, ...request.Option) (*s3.UploadPartOutput, error) {
 	assert := s.assert
 
-	// Make sure that only the two temporary files from tusd are in here.
+	// Make sure that there are temporary files from tusd in here.
 	files, err := ioutil.ReadDir(s.tempDir)
 	assert.Nil(err)
 	for _, file := range files {
 		assert.True(strings.HasPrefix(file.Name(), "tusd-s3-tmp-"))
 	}
-	assert.Equal(len(files), 2)
+	assert.True(len(files) > 0)
 
 	return nil, fmt.Errorf("not now")
 }
@@ -1316,7 +1366,7 @@ func TestWriteChunkCleansUpTempFiles(t *testing.T) {
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.info"),
 	}).Return(&s3.GetObjectOutput{
-		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId","Size":500,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":null}`))),
+		Body: ioutil.NopCloser(bytes.NewReader([]byte(`{"ID":"uploadId","Size":14,"Offset":0,"MetaData":null,"IsPartial":false,"IsFinal":false,"PartialUploads":null,"Storage":null}`))),
 	}, nil)
 	s3obj.EXPECT().ListPartsWithContext(context.Background(), &s3.ListPartsInput{
 		Bucket:           aws.String("bucket"),
@@ -1324,30 +1374,19 @@ func TestWriteChunkCleansUpTempFiles(t *testing.T) {
 		UploadId:         aws.String("multipartId"),
 		PartNumberMarker: aws.Int64(0),
 	}).Return(&s3.ListPartsOutput{
-		Parts: []*s3.Part{
+		Parts: []*s3.Part{},
-			{
+	}, nil)
-				Size: aws.Int64(100),
+	s3obj.EXPECT().HeadObjectWithContext(context.Background(), &s3.HeadObjectInput{
-			},
-			{
-				Size: aws.Int64(200),
-			},
-		},
-	}, nil).Times(2)
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
 		Bucket: aws.String("bucket"),
 		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "Not found", nil))
+	}).Return(nil, awserr.New("NoSuchKey", "Not found", nil))
-	s3obj.EXPECT().GetObjectWithContext(context.Background(), &s3.GetObjectInput{
-		Bucket: aws.String("bucket"),
-		Key:    aws.String("uploadId.part"),
-	}).Return(&s3.GetObjectOutput{}, awserr.New("NoSuchKey", "The specified key does not exist.", nil))
 
 	// No calls to s3obj.EXPECT().UploadPartWithContext since that is handled by s3APIWithTempFileAssertion
 
 	upload, err := store.GetUpload(context.Background(), "uploadId+multipartId")
 	assert.Nil(err)
 
-	bytesRead, err := upload.WriteChunk(context.Background(), 300, bytes.NewReader([]byte("1234567890ABCD")))
+	bytesRead, err := upload.WriteChunk(context.Background(), 0, bytes.NewReader([]byte("1234567890ABCD")))
 	assert.NotNil(err)
 	assert.Equal(err.Error(), "not now")
 	assert.Equal(int64(0), bytesRead)