Golang将多个文件添加到HTTP多部分请求

Question

Currently i am streaming 2 multipart requests separately.

1. Contains the file as a blob
2. contains a json file as a description of the blob

How can i upload them at the same time with multipart?

this is the request that runs 2 times. I want to add the 2 files in this 1 request

 func(c *Client) Upload(h *UploadHandle) (*PutResult, error) {
        bodyReader, bodySize, err := h.Read()
        if err != nil {
            return nil, fmt.Errorf("Failed to peek the body size %v", err)
        }

        if bodySize > constants.MaxDropSize {
            return nil, errors.New("The size of the body is to big")
        }

        pipeReader, pipeWriter := io.Pipe()
        writer := multipart.NewWriter(pipeWriter)

        errChan := make(chan error, 1)
        go func() {
            defer pipeWriter.Close()
            part, err := writer.CreateFormFile(h.DropRef, h.DropRef)
            if err != nil {
                errChan <- err
                return
            }
            _, err = io.Copy(part, bodyReader)
            if err == nil {
                err = writer.Close()
            }
            errChan <- err
        }()

        uploadUrl := fmt.Sprintf("%s/drops/upload", c.Server)
        req, err := http.NewRequest("POST", uploadUrl, pipeReader)
        if err != nil {
            return nil, err
        }
        req.Header.Add("Content-Type", writer.FormDataContentType())
        req.Body = ioutil.NopCloser(pipeReader)

        resp, err := c.Do(req)
        if err != nil {
            return nil, fmt.Errorf("Failed doing request: %v", err)
        }
        defer resp.Body.Close()

        // Handling the error the routine may caused
        if err := <-errChan; err != nil {
            return nil, err
        }
        if resp.StatusCode != 200 {
            return nil, fmt.Errorf("The server responded with a status %d", resp.StatusCode)
        }
    return &PutResult{h.DropRef, bodySize}, nil
}

Answer 1

You simply call CreateFormFile again (or CreateFormField) and write your json to the writer returned.

j, err := writer.CreateFormFile("meta", h.DropRef + ".json")
enc := json.NewEncoder(j)
enc.Encode(some-struct-you-want-to-write-as-json)

Just make sure you finish writing your first file before creating a new one, because according to the docs:

After calling CreatePart, any previous part may no longer be written to.