Posting a File and Associated Data to a RESTful WebService preferably as JSON

I asked a similar question here:

How do I upload a file with metadata using a REST web service?

You basically have three choices:

1. Base64 encode the file, at the expense of increasing the data size by around 33%, and add processing overhead in both the server and the client for encoding/decoding.
2. Send the file first in a multipart/form-data POST, and return an ID to the client. The client then sends the metadata with the ID, and the server re-associates the file and the metadata.
3. Send the metadata first, and return an ID to the client. The client then sends the file with the ID, and the server re-associates the file and the metadata.

You can send the file and data over in one request using the multipart/form-data content type:

In many applications, it is possible for a user to be presented witha form. The user will fill out the form, including information thatis typed, generated by user input, or included from files that theuser has selected. When the form is filled out, the data from theform is sent from the user to the receiving application.

The definition of MultiPart/Form-Data is derived from one of thoseapplications...

From http://www.faqs.org/rfcs/rfc2388.html:

"multipart/form-data" contains a series of parts. Each part isexpected to contain a content-disposition header [RFC 2183] where thedisposition type is "form-data", and where the disposition containsan (additional) parameter of "name", where the value of thatparameter is the original field name in the form. For example, a partmight contain a header:

Content-Disposition: form-data; name="user"

with the value corresponding to the entry of the "user" field.

You can include file information or field information within each section between boundaries. I've successfully implemented a RESTful service that required the user to submit both data and a form, and multipart/form-data worked perfectly. The service was built using Java/Spring, and the client was using C#, so unfortunately I don't have any Grails examples to give you concerning how to set up the service. You don't need to use JSON in this case since each "form-data" section provides you a place to specify the name of the parameter and its value.

The good thing about using multipart/form-data is that you're using HTTP-defined headers, so you're sticking with the REST philosophy of using existing HTTP tools to create your service.

I know that this thread is quite old, however, I am missing here one option. If you have metadata (in any format) that you want to send along with the data to upload, you can make a single multipart/related request.

The Multipart/Related media type is intended for compound objects consisting of several inter-related body parts.

You can check RFC 2387 specification for more in-depth details.

Basically each part of such a request can have content with different type and all parts are somehow related (e.g. an image and it metadata). The parts are identified by a boundary string, and the final boundary string is followed by two hyphens.

Example:

POST /upload HTTP/1.1Host: www.hostname.comContent-Type: multipart/related; boundary=xyzContent-Length: [actual-content-length]--xyzContent-Type: application/json; charset=UTF-8{    "name": "Sample image",    "desc": "...",    ...}--xyzContent-Type: image/jpeg[image data][image data][image data]...--foo_bar_baz--