When you make a POST request, you have to encode the data that forms the body of the request in some way.
HTML forms provide three methods of encoding.
application/x-www-form-urlencoded (the default)
Work was being done on adding but that has been abandoned.
The specifics of the formats don't matter to most developers. The important points are:
When you are writing client-side code, all you need to know is use
multipart/form-data when your form includes any elements.
When you are writing server-side code: Use a prewritten form handling library (e.g. Perl's
CGI->param or the one exposed by PHP's
$_POST superglobal) and it will take care of the differences for you. Don't bother trying to parse the raw input received by the server.
If you are writing (or debugging) a library for parsing or generating the raw data, then you need to start worrying about the format. You might also want to know about it for interest's sake.
application/x-www-form-urlencoded is more or less the same as a query string on the end of the URL.
multipart/form-data is significantly more complicated but it allows entire files to be included in the data. An example of the result can be found in the HTML 4 specification.
text/plain is introduced by HTML 5 and is useful only for debugging — from the spec: They are not reliably interpretable by computer — and I'd argue that the others combined with tools (like the Net tab in the developer tools of most browsers) are better for that).
- answered 4 years ago
- G John