multipart writer CreateFormFile stuck - http

Question

trying to post multipart/form-data image using go
image file receive from request client and already saved as multipart.File
here my code
func postImage(file multipart.File, url string, filename string) (*http.Response, error) {
r, w := io.Pipe()
defer w.Close()
m := multipart.NewWriter(w)
defer m.Close()
errchan := make(chan error)
defer close(errchan)
go func() {
part, err := m.CreateFormFile("file", filename)
log.Println(err)
if err != nil {
errchan <- err
return
}
if _, err := io.Copy(part, file); err != nil {
errchan <- err
return
}
}()
merr := <-errchan
if merr != nil {
return nil, merr
}
resp, err := http.Post(url, m.FormDataContentType(), r)
if err != nil {
return nil, err
}
defer resp.Body.Close()
return resp, err
}
when i try using it, it stuck at part, err := m.CreateFormFile("file", filename) never return anything
any solution?
Thanks

Answer 1

Use the pipe error to propagate the error back to the main goroutine. Close the write side of the pipe to prevent the client from blocking forever on read. Close the read side of the pipe to ensure that the goroutine exits.
func postImage(file multipart.File, url string, filename string) (*http.Response, error) {
r, w := io.Pipe()
// Close the read side of the pipe to ensure that
// the goroutine exits in the case where http.Post
// does not read all of the request body.
defer r.Close()
m := multipart.NewWriter(w)
go func() {
part, err := m.CreateFormFile("file", filename)
if err != nil {
// The error is returned from read on the pipe.
w.CloseWithError(err)
return
}
if _, err := io.Copy(part, file); err != nil {
// The error is returned from read on the pipe.
w.CloseWithError(err)
return
}
// The http.Post function reads the pipe until
// an error or EOF. Close to return an EOF to
// http.Post.
w.Close()
}()
resp, err := http.Post(url, m.FormDataContentType(), r)
if err != nil {
return nil, err
}
defer resp.Body.Close()
return resp, err
}