REST API for uploading file inside JSON

I am designing an REST API to upload a largish (100MB) file together with some information. So it's natural to think of json encoding.

So something like this:

{
   file: content of the file or URL?
   name: string
   description: string
}

The name and description are easy to do with json but I'm not sure how the file content can be added to it.

Also I'm thinking I should use http PUT method. Is this correct?

Incidentally, golang is used to implement this API if it matters.

For a JSON encoding, use a []byte value to hold the file contents. The standard encoding/json package encodes []byte values as base64 strings.

Here's a sketch of how to implement the JSON encoding. Declare a type representing the payload:

type Upload struct {
    Name string
    Description string
    Content []byte
}

To encode the file to a request body:

v := Upload{Name: fileName, Description: description, Content: content}
var buf bytes.Buffer
if err := json.NewEncoder(&buf).Encode(v); err != nil {
    // handle error
}
req, err := http.NewRequest("PUT", url, &buf)
if err != nil {
   // handle error
}
resp, err := http.DefaultClient.Do(req)

To decode the from a request body on the server:

var v Upload
if err := json.NewDecoder(req.Body).Decode(&v); err != nil {
  // handle error
}

Another option is to use the mime/multipart package. The multipart encoding will be more efficient than JSON encoding because no base64 or other text encoding of the file is required for multipart.

To me, the most clear-cut way to do it would be to encode the file bytes somehow. base64 seems like a good choice, and golang has built-in support for it with "encoding/base64".