application/x-www-form-urlencoded or multipart/form-data?

Question

In HTTP there are two ways to POST data: application/x-www-form-urlencoded and multipart/form-data. I understand that most browsers are only able t

Answer 1

I don't think HTTP is limited to POST in multipart or x-www-form-urlencoded. The Content-Type Header is orthogonal to the HTTP POST method (you can fill MIME type which suits you). This is also the case for typical HTML representation based webapps (e.g. json payload became very popular for transmitting payload for ajax requests).

Regarding Restful API over HTTP the most popular content-types I came in touch with are application/xml and application/json.

application/xml:

• data-size: XML very verbose, but usually not an issue when using compression and thinking that the write access case (e.g. through POST or PUT) is much more rare as read-access (in many cases it is <3% of all traffic). Rarely there where cases where I had to optimize the write performance
• existence of non-ascii chars: you can use utf-8 as encoding in XML
• existence of binary data: would need to use base64 encoding
• filename data: you can encapsulate this inside field in XML

application/json

• data-size: more compact less that XML, still text, but you can compress
• non-ascii chars: json is utf-8
• binary data: base64 (also see json-binary-question)
• filename data: encapsulate as own field-section inside json

binary data as own resource

I would try to represent binary data as own asset/resource. It adds another call but decouples stuff better. Example images:

POST /images
Content-type: multipart/mixed; boundary="xxxx" 
... multipart data

201 Created
Location: http://imageserver.org/../foo.jpg  

In later resources you could simply inline the binary resource as link: