Chunk upload

Uploading files in chunks

For large documents it's better using files Chunk API which allows splitting upload into separate REST API requests reducing memory consumption and providing a more manageable upload mechanism.

Files Chunk API appeared in SharePoint 2016 and should not be expected to work in the previous version.

Chunk upload can't be used in SharePoint 2013

Basic chunk upload example

file, err := os.Open("/path/to/large/")
if err != nil {
log.Fatalf("unable to read a file: %v\n", err)
defer file.Close()
fileAddResp, err := foler.Files().AddChunked("My", file, nil)
if err != nil {
fmt.Printf("New file URL: %s\n", fileAddResp.Data().ServerRelativeURL)

Upload flow

Fluent API abstracts some aspects of the chunked upload. Internally, /StartUpload, /ContinueUpload, /CancelUpload, and /FinishUpload endpoints are used. However, these are not exposed for the simplicity. Nonetheless, there is a way for canceling upload with the help of api.AddChunkedOptions.

Add chunked options

There are a few options which are optional. The third method parameter is a configuration structure.

type AddChunkedOptions struct {
Overwrite bool // should overwrite existing file
// on progress callback, execute custom logic on each chunk
// if the Progress is used it should return "true" to continue upload
// otherwise upload is canceled
Progress func(data *FileUploadProgressData) bool
ChunkSize int // chunk size in bytes

Defaults are: Overwrite is true and ChunkSize equals to 10485760 bytes.

Progress callback allows not only trigger a progress logic, for example upload percentage update, but also to cancel an upload. To cancel an upload the progress callback should return false.

filePath := "/path/to/large/"
file, err := os.Open(filePath)
if err != nil {
log.Fatalf("unable to read a file: %v\n", err)
defer file.Close()
info, _ := os.Stat(filePath)
options := &api.AddChunkedOptions{
Overwrite: false,
ChunkSize: 5 * 1024 * 1024,
Progress: func(data *api.FileUploadProgressData) bool {
"Block %d, sent %d%%\n",
return true // to cancel an upload on some external condition, return "false"
if _, err := foler.Files().AddChunked("My", file, options); err != nil {