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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gensupport
import (
const (
// statusTooManyRequests is returned by the storage API if the
// per-project limits have been temporarily exceeded. The request
// should be retried.
statusTooManyRequests = 429
// ResumableUpload is used by the generated APIs to provide resumable uploads.
// It is not used by developers directly.
type ResumableUpload struct {
Client *http.Client
// URI is the resumable resource destination provided by the server after specifying "&uploadType=resumable".
URI string
UserAgent string // User-Agent for header of the request
// Media is the object being uploaded.
Media *MediaBuffer
// MediaType defines the media type, e.g. "image/jpeg".
MediaType string
mu sync.Mutex // guards progress
progress int64 // number of bytes uploaded so far
// Callback is an optional function that will be periodically called with the cumulative number of bytes uploaded.
Callback func(int64)
// If not specified, a default exponential backoff strategy will be used.
Backoff BackoffStrategy
// Progress returns the number of bytes uploaded at this point.
func (rx *ResumableUpload) Progress() int64 {
return rx.progress
// doUploadRequest performs a single HTTP request to upload data.
// off specifies the offset in rx.Media from which data is drawn.
// size is the number of bytes in data.
// final specifies whether data is the final chunk to be uploaded.
func (rx *ResumableUpload) doUploadRequest(ctx context.Context, data io.Reader, off, size int64, final bool) (*http.Response, error) {
req, err := http.NewRequest("POST", rx.URI, data)
if err != nil {
return nil, err
req.ContentLength = size
var contentRange string
if final {
if size == 0 {
contentRange = fmt.Sprintf("bytes */%v", off)
} else {
contentRange = fmt.Sprintf("bytes %v-%v/%v", off, off+size-1, off+size)
} else {
contentRange = fmt.Sprintf("bytes %v-%v/*", off, off+size-1)
req.Header.Set("Content-Range", contentRange)
req.Header.Set("Content-Type", rx.MediaType)
req.Header.Set("User-Agent", rx.UserAgent)
// Google's upload endpoint uses status code 308 for a
// different purpose than the "308 Permanent Redirect"
// since-standardized in RFC 7238. Because of the conflict in
// semantics, Google added this new request header which
// causes it to not use "308" and instead reply with 200 OK
// and sets the upload-specific "X-HTTP-Status-Code-Override:
// 308" response header.
req.Header.Set("X-GUploader-No-308", "yes")
return SendRequest(ctx, rx.Client, req)
func statusResumeIncomplete(resp *http.Response) bool {
// This is how the server signals "status resume incomplete"
// when X-GUploader-No-308 is set to "yes":
return resp != nil && resp.Header.Get("X-Http-Status-Code-Override") == "308"
// reportProgress calls a user-supplied callback to report upload progress.
// If old==updated, the callback is not called.
func (rx *ResumableUpload) reportProgress(old, updated int64) {
if updated-old == 0 {
rx.progress = updated
if rx.Callback != nil {
// transferChunk performs a single HTTP request to upload a single chunk from rx.Media.
func (rx *ResumableUpload) transferChunk(ctx context.Context) (*http.Response, error) {
chunk, off, size, err := rx.Media.Chunk()
done := err == io.EOF
if !done && err != nil {
return nil, err
res, err := rx.doUploadRequest(ctx, chunk, off, int64(size), done)
if err != nil {
return res, err
// We sent "X-GUploader-No-308: yes" (see comment elsewhere in
// this file), so we don't expect to get a 308.
if res.StatusCode == 308 {
return nil, errors.New("unexpected 308 response status code")
if res.StatusCode == http.StatusOK {
rx.reportProgress(off, off+int64(size))
if statusResumeIncomplete(res) {
return res, nil
func contextDone(ctx context.Context) bool {
select {
case <-ctx.Done():
return true
return false
// Upload starts the process of a resumable upload with a cancellable context.
// It retries using the provided back off strategy until cancelled or the
// strategy indicates to stop retrying.
// It is called from the auto-generated API code and is not visible to the user.
// Before sending an HTTP request, Upload calls any registered hook functions,
// and calls the returned functions after the request returns (see send.go).
// rx is private to the auto-generated API code.
// Exactly one of resp or err will be nil. If resp is non-nil, the caller must call resp.Body.Close.
func (rx *ResumableUpload) Upload(ctx context.Context) (resp *http.Response, err error) {
var pause time.Duration
backoff := rx.Backoff
if backoff == nil {
backoff = DefaultBackoffStrategy()
for {
// Ensure that we return in the case of cancelled context, even if pause is 0.
if contextDone(ctx) {
return nil, ctx.Err()
select {
case <-ctx.Done():
return nil, ctx.Err()
case <-time.After(pause):
resp, err = rx.transferChunk(ctx)
var status int
if resp != nil {
status = resp.StatusCode
// Check if we should retry the request.
if shouldRetry(status, err) {
var retry bool
pause, retry = backoff.Pause()
if retry {
if resp != nil && resp.Body != nil {
// If the chunk was uploaded successfully, but there's still
// more to go, upload the next chunk without any delay.
if statusResumeIncomplete(resp) {
pause = 0
// It's possible for err and resp to both be non-nil here, but we expose a simpler
// contract to our callers: exactly one of resp and err will be non-nil. This means
// that any response body must be closed here before returning a non-nil error.
if err != nil {
if resp != nil && resp.Body != nil {
return nil, err
return resp, nil