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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 sniffBuffSize = 512
func newContentSniffer(r io.Reader) *contentSniffer {
return &contentSniffer{r: r}
// contentSniffer wraps a Reader, and reports the content type determined by sniffing up to 512 bytes from the Reader.
type contentSniffer struct {
r io.Reader
start []byte // buffer for the sniffed bytes.
err error // set to any error encountered while reading bytes to be sniffed.
ctype string // set on first sniff.
sniffed bool // set to true on first sniff.
func (cs *contentSniffer) Read(p []byte) (n int, err error) {
// Ensure that the content type is sniffed before any data is consumed from Reader.
_, _ = cs.ContentType()
if len(cs.start) > 0 {
n := copy(p, cs.start)
cs.start = cs.start[n:]
return n, nil
// We may have read some bytes into start while sniffing, even if the read ended in an error.
// We should first return those bytes, then the error.
if cs.err != nil {
return 0, cs.err
// Now we have handled all bytes that were buffered while sniffing. Now just delegate to the underlying reader.
return cs.r.Read(p)
// ContentType returns the sniffed content type, and whether the content type was succesfully sniffed.
func (cs *contentSniffer) ContentType() (string, bool) {
if cs.sniffed {
return cs.ctype, cs.ctype != ""
cs.sniffed = true
// If ReadAll hits EOF, it returns err==nil.
cs.start, cs.err = ioutil.ReadAll(io.LimitReader(cs.r, sniffBuffSize))
// Don't try to detect the content type based on possibly incomplete data.
if cs.err != nil {
return "", false
cs.ctype = http.DetectContentType(cs.start)
return cs.ctype, true
// DetermineContentType determines the content type of the supplied reader.
// If the content type is already known, it can be specified via ctype.
// Otherwise, the content of media will be sniffed to determine the content type.
// If media implements googleapi.ContentTyper (deprecated), this will be used
// instead of sniffing the content.
// After calling DetectContentType the caller must not perform further reads on
// media, but rather read from the Reader that is returned.
func DetermineContentType(media io.Reader, ctype string) (io.Reader, string) {
// Note: callers could avoid calling DetectContentType if ctype != "",
// but doing the check inside this function reduces the amount of
// generated code.
if ctype != "" {
return media, ctype
// For backwards compatability, allow clients to set content
// type by providing a ContentTyper for media.
if typer, ok := media.(googleapi.ContentTyper); ok {
return media, typer.ContentType()
sniffer := newContentSniffer(media)
if ctype, ok := sniffer.ContentType(); ok {
return sniffer, ctype
// If content type could not be sniffed, reads from sniffer will eventually fail with an error.
return sniffer, ""
type typeReader struct {
typ string
// multipartReader combines the contents of multiple readers to creat a multipart/related HTTP body.
// Close must be called if reads from the multipartReader are abandoned before reaching EOF.
type multipartReader struct {
pr *io.PipeReader
pipeOpen bool
ctype string
func newMultipartReader(parts []typeReader) *multipartReader {
mp := &multipartReader{pipeOpen: true}
var pw *io.PipeWriter, pw = io.Pipe()
mpw := multipart.NewWriter(pw)
mp.ctype = "multipart/related; boundary=" + mpw.Boundary()
go func() {
for _, part := range parts {
w, err := mpw.CreatePart(typeHeader(part.typ))
if err != nil {
pw.CloseWithError(fmt.Errorf("googleapi: CreatePart failed: %v", err))
_, err = io.Copy(w, part.Reader)
if err != nil {
pw.CloseWithError(fmt.Errorf("googleapi: Copy failed: %v", err))
return mp
func (mp *multipartReader) Read(data []byte) (n int, err error) {
func (mp *multipartReader) Close() error {
if !mp.pipeOpen {
return nil
mp.pipeOpen = false
// CombineBodyMedia combines a json body with media content to create a multipart/related HTTP body.
// It returns a ReadCloser containing the combined body, and the overall "multipart/related" content type, with random boundary.
// The caller must call Close on the returned ReadCloser if reads are abandoned before reaching EOF.
func CombineBodyMedia(body io.Reader, bodyContentType string, media io.Reader, mediaContentType string) (io.ReadCloser, string) {
mp := newMultipartReader([]typeReader{
{body, bodyContentType},
{media, mediaContentType},
return mp, mp.ctype
func typeHeader(contentType string) textproto.MIMEHeader {
h := make(textproto.MIMEHeader)
if contentType != "" {
h.Set("Content-Type", contentType)
return h
// PrepareUpload determines whether the data in the supplied reader should be
// uploaded in a single request, or in sequential chunks.
// chunkSize is the size of the chunk that media should be split into.
// If chunkSize is zero, media is returned as the first value, and the other
// two return values are nil, true.
// Otherwise, a MediaBuffer is returned, along with a bool indicating whether the
// contents of media fit in a single chunk.
// After PrepareUpload has been called, media should no longer be used: the
// media content should be accessed via one of the return values.
func PrepareUpload(media io.Reader, chunkSize int) (r io.Reader, mb *MediaBuffer, singleChunk bool) {
if chunkSize == 0 { // do not chunk
return media, nil, true
mb = NewMediaBuffer(media, chunkSize)
_, _, _, err := mb.Chunk()
// If err is io.EOF, we can upload this in a single request. Otherwise, err is
// either nil or a non-EOF error. If it is the latter, then the next call to
// mb.Chunk will return the same error. Returning a MediaBuffer ensures that this
// error will be handled at some point.
return nil, mb, err == io.EOF
// MediaInfo holds information for media uploads. It is intended for use by generated
// code only.
type MediaInfo struct {
// At most one of Media and MediaBuffer will be set.
media io.Reader
buffer *MediaBuffer
singleChunk bool
mType string
size int64 // mediaSize, if known. Used only for calls to progressUpdater_.
progressUpdater googleapi.ProgressUpdater
// NewInfoFromMedia should be invoked from the Media method of a call. It returns a
// MediaInfo populated with chunk size and content type, and a reader or MediaBuffer
// if needed.
func NewInfoFromMedia(r io.Reader, options []googleapi.MediaOption) *MediaInfo {
mi := &MediaInfo{}
opts := googleapi.ProcessMediaOptions(options)
if !opts.ForceEmptyContentType {
r, mi.mType = DetermineContentType(r, opts.ContentType)
}, mi.buffer, mi.singleChunk = PrepareUpload(r, opts.ChunkSize)
return mi
// NewInfoFromResumableMedia should be invoked from the ResumableMedia method of a
// call. It returns a MediaInfo using the given reader, size and media type.
func NewInfoFromResumableMedia(r io.ReaderAt, size int64, mediaType string) *MediaInfo {
rdr := ReaderAtToReader(r, size)
rdr, mType := DetermineContentType(rdr, mediaType)
return &MediaInfo{
size: size,
mType: mType,
buffer: NewMediaBuffer(rdr, googleapi.DefaultUploadChunkSize),
media: nil,
singleChunk: false,
func (mi *MediaInfo) SetProgressUpdater(pu googleapi.ProgressUpdater) {
if mi != nil {
mi.progressUpdater = pu
// UploadType determines the type of upload: a single request, or a resumable
// series of requests.
func (mi *MediaInfo) UploadType() string {
if mi.singleChunk {
return "multipart"
return "resumable"
// UploadRequest sets up an HTTP request for media upload. It adds headers
// as necessary, and returns a replacement for the body.
func (mi *MediaInfo) UploadRequest(reqHeaders http.Header, body io.Reader) (newBody io.Reader, cleanup func()) {
cleanup = func() {}
if mi == nil {
return body, cleanup
var media io.Reader
if != nil {
// This only happens when the caller has turned off chunking. In that
// case, we write all of media in a single non-retryable request.
media =
} else if mi.singleChunk {
// The data fits in a single chunk, which has now been read into the MediaBuffer.
// We obtain that chunk so we can write it in a single request. The request can
// be retried because the data is stored in the MediaBuffer.
media, _, _, _ = mi.buffer.Chunk()
if media != nil {
combined, ctype := CombineBodyMedia(body, "application/json", media, mi.mType)
cleanup = func() { combined.Close() }
reqHeaders.Set("Content-Type", ctype)
body = combined
if mi.buffer != nil && mi.mType != "" && !mi.singleChunk {
reqHeaders.Set("X-Upload-Content-Type", mi.mType)
return body, cleanup
// ResumableUpload returns an appropriately configured ResumableUpload value if the
// upload is resumable, or nil otherwise.
func (mi *MediaInfo) ResumableUpload(locURI string) *ResumableUpload {
if mi == nil || mi.singleChunk {
return nil
return &ResumableUpload{
URI: locURI,
Media: mi.buffer,
MediaType: mi.mType,
Callback: func(curr int64) {
if mi.progressUpdater != nil {
mi.progressUpdater(curr, mi.size)