在 golang 中解析 javascript Blob

Question

In Go, you can read a form sent using Ajax and FormData using r.ParseMultipartForm() , which populates the Form map with form request data.

func form(w http.ResponseWriter, r *http.Request) {
    r.ParseMultipartForm(500) //
    fmt.Fprintf(w, "This is the value of %+v", r.Form)
}

However, I haven't found a method to parse Blobs. The above code returns an empty map whenever instead of sending a form, I send a Blob. That is, when I send this:

var blob = new Blob([JSON.stringify(someJavascriptObj)]);
//XHR initialization, etc. etc.
xhr.send(blob);

the Go code above doesn't work. Now, when I send this:

var form = new FormData(document.querySelector("form"));
//...
xhr.send(form);

I can read form data without problems.

Answer 1

r.ParseMultipartForm(500)

Perhaps an error is being returned here? Try capturing the error:

if err := r.ParseMultipartForm(500); err != nil {
    http.Error(w, err.Error(), http.StatusInternalServerError)
}

Also, consider raising the 500 byte memory limit as larger blobs will be written to temporary files.

Answer 2

I think javascript treats blob as file, so your can look it in r.MultipartForm.File , get file header, open it, read, decode and parse. Try for example

r.ParseMultipartForm(500) 
fmt.Fprintf(w, "This is the value of %+v", *r.MultipartForm.File)
}

Answer 3

I presume Javascript's Blob is a hex string which can eventually be converted to []byte , which is a standard type for JSON in Go.

// Once you get the blob
blobString := `7b22666f6f223a205b22626172222c202262617a222c2039395d7d`

b, _ := hex.DecodeString(blobString)
json := string(b)
fmt.Println(json) // prints out {"foo": ["bar", "baz", 99]}

You might want to look into encoding/hex and encoding/binary packages to decode your blob acquired from Javascript to type []byte in Go, if it's not already.