Post a large file using io.Pipe() so that we don't need to read the whole file into memory

post_large_file.go

func (c *ClientImpl) PostLargeFile(reader io.ReadCloser, formParams map[string]string) (io.ReadCloser, error) {
	r, w := io.Pipe()
	writer := multipart.NewWriter(w)
	defer r.Close()

	go func() {
		defer w.Close()
		defer reader.Close()

		for key, val := range formParams {
			if key == util.SomeTag || key == util.SomeFileType {
				_ = writer.WriteField(key, val)
			}
		}

		part, err := writer.CreateFormFile(util.SomeTag, util.SomeFileType)
		if err != nil {
			logger.Error("error: %v", err)
			return
		}

		if _, err := io.Copy(part, reader); err != nil {
			logger.Error("error: %v", err)
			return
		}

		if err := writer.Close(); err != nil {
			logger.Error("error: %v", err)
			return
		}
	}()

	request, err := http.NewRequest(http.MethodPost, fmt.Sprintf("%s/%s", SomeURL, uploadPath), r)
	if err != nil {
		return nil, err
	}
	request.Header.Set(util.ContentType, writer.FormDataContentType())
	request.Header.Set(util.UserAgent, util.YourAppsVersion)
  
  // We can also create context and add it to the request
	resp, err := ac.doRequestWrapper(request)
	if err != nil {
		return nil, err
	}

	if resp.StatusCode != http.StatusOK {
		logger.Error("error: %v: ", "post request failed", resp.Status)
		return nil, errors.New(util.SomeError)
	}

	return resp.Body, nil
}