如何将图像写入请求正文

I have a jpeg image.Image and I want to decode to a request body. Simplified below, it doesn't seem to finish the request ever. The program hangs.

  r, w := io.Pipe()
  jpeg.Encode(w, img, &jpeg.Options{ 80 })

  req, e := http.NewRequest("PUT", myUrl, r)
  if e != nil {
    return nil, e
  }
  http.DefaultClient.Do(req)

How can I write an image to the request body?

Just use a buffer

var w bytes.Buffer

jpeg.Encode(&w, img, &jpeg.Options{80})

req, e := http.NewRequest("PUT", myUrl, &w)
if e != nil {
    log.Fatal(e)
}
http.DefaultClient.Do(req)

jpeg.Encode can't procede, because it's blocked writing to the pipe (pipes don't buffer).

You either need to buffer the encoded image, or run the Encode and http request concurrently.

// make sure to buffer this channel, so the goroutine can exit if we return early
errChan := make(chan error, 1)

r, w := io.Pipe()
go func() {
    errChan <- jpeg.Encode(w, img, &jpeg.Options{80})
}()

req, err := http.NewRequest("PUT", myUrl, r)
if err != nil {
    return nil, err
}
err := http.DefaultClient.Do(req)
if err != nil {
    return nil, err
}

// check for an encoding error
err := <-errChan
if err != nil {
    return nil, err
}