Golang通过多部分处理图像并流式传输到Azure

Question

In the process of learning golang, I'm trying to write a web app with multiple image upload functionality.

I'm using Azure Blob Storage to store images, but I am having trouble streaming the images from the multipart request to Blob Storage.

Here's the handler I've written so far:

func (imgc *ImageController) UploadInstanceImageHandler(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
reader, err := r.MultipartReader()

if err != nil {
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return
}

for {
    part, partErr := reader.NextPart()

    // No more parts to process
    if partErr == io.EOF {
        break
    }

    // if part.FileName() is empty, skip this iteration.
    if part.FileName() == "" {
        continue
    }

    // Check file type
    if part.Header["Content-Type"][0] != "image/jpeg" {
        fmt.Printf("
Not image/jpeg!")
        break
    }

    var read uint64
    fileName := uuid.NewV4().String() + ".jpg"
    buffer := make([]byte, 100000000)

    // Get Size
    for {
        cBytes, err := part.Read(buffer)

        if err == io.EOF {
            fmt.Printf("
Last buffer read!")
            break
        }

        read = read + uint64(cBytes)
    }

    stream := bytes.NewReader(buffer[0:read])
    err = imgc.blobClient.CreateBlockBlobFromReader(imgc.imageContainer, fileName, read, stream, nil)

    if err != nil {
        fmt.Println(err)
        break
    }
}

w.WriteHeader(http.StatusOK)

}

In the process of my research, I've read through using r.FormFile, ParseMultipartForm, but decided on trying to learn how to use MultiPartReader.

I was able to upload an image to the golang backend and save the file to my machine using MultiPartReader.

At the moment, I'm able to upload files to Azure but they end up being corrupted. The file sizes seem on point but clearly something is not working.

Am I misunderstanding how to create a io.Reader for CreateBlockBlobFromReader?

Any help is much appreciated!

Answer 1

A Reader can return both an io.EOF and a valid final bytes read, it looks like the final bytes (cBytes) is not added to read total bytes. Also, careful: if an error is returned by part.Read(buffer) other than io.EOF, the read loop might not exit. Consider ioutil.ReadAll instead.

CreateBlockBlobFromReader takes a Reader, and part is a Reader, so you may be able to pass the part in directly.

You may also want to consider Azure block size limits might be smaller than the image, see Asure blobs.