Method="Post" Enctype="Text/Plain" Are Not Compatible

method=post enctype=text/plain are not compatible?

[Revised]

The answer is, because PHP doesn't handle it (and it is not a bug):

https://bugs.php.net/bug.php?id=33741

Valid values for enctype in <form> tag are:

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

The first is the default, the second one you need only when you upload files.

@Alohci provided explanation why PHP doesn't populate $_POST array, but store the value inside a variable $HTTP_RAW_POST_DATA.

Example of what can go wrong with text/plain enctype:

file1.php:

<form method="post" enctype="text/plain" action="file2.php">
<textarea name="input1">abc
input2=def</textarea>
<input name="input2" value="ghi" />
<input type="submit">
</form>

file2.php:

<?php
print($HTTP_RAW_POST_DATA);
?>

Result:

input1=abc
input2=def
input2=ghi

No way to distinguish what is the value of input1 and input2 variables. It can be

• input1=abc\r\ninput2=def, input2=ghi, as well as
• input1=abc, input2=def\r\ninput2=ghi

No such problem when using the other two encodings mentioned before.

The difference between GET and POST:

• in GET, the variables are part of URL and are present in URL as query string, therefore they must be URL-encoded (and they are, even if you write enctype="text/plain" - it just gets ignored by the browser; you can test it using Wireshark to sniff the request packets),
• when sending POST, the variables are not part of URL, but are sent as the last header in HTTP request (POSTDATA), and you can choose whether you want to send them as text/plain or application/x-www-form-urlencoded, but the second one is the only non-ambiguous solution.

What does enctype='multipart/form-data' mean?

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)
• multipart/form-data
• text/plain

Work was being done on adding application/json, but that has been abandoned.

(Other encodings are possible with HTTP requests generated using other means than an HTML form submission. JSON is a common format for use with web services and some still use SOAP.)

The specifics of the formats don't matter to most developers. The important points are:

• Never use text/plain.

When you are writing client-side code:

• use multipart/form-data when your form includes any <input type="file"> elements
• otherwise you can use multipart/form-data or application/x-www-form-urlencoded but application/x-www-form-urlencoded will be more efficient

When you are writing server-side code:

• Use a prewritten form handling library

Most (such as Perl's CGI->param or the one exposed by PHP's $_POST superglobal) will take care of the differences for you. Don't bother trying to parse the raw input received by the server.

Sometimes you will find a library that can't handle both formats. Node.js's most popular library for handling form data is body-parser which cannot handle multipart requests (but has documentation that recommends some alternatives which can).

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 Network Panel in the developer tools of most browsers) are better for that).

Form not working with Mailto correctly

You forgot to set the name attribute! The subject you can set as a parameter (subject) on the email address. Try the following code:

<form action="mailto:example@example.com?subject=Test" method="post" enctype="text/plain" class="form-horizontal">  <div class="form-group">    <label for="name" class="col-sm-2 control-label">Name</label>    <div class="col-sm-10">      <input type="text" class="form-control" name="name" id="name" placeholder="Name">    </div>  </div>  <div class="form-group">    <label for="company" class="col-sm-2 control-label">Company</label>    <div class="col-sm-10">      <input type="text" class="form-control" name="company" id="company" placeholder="Company">    </div>  </div>  <div class="form-group">    <label for="email" class="col-sm-2 control-label">Email</label>    <div class="col-sm-10">      <input type="email" class="form-control" name="email" id="email" placeholder="Email">    </div>  </div>  <div class="form-group">    <label for="message" class="col-sm-2 control-label">Message</label>    <div class="col-sm-10">      <textarea class="form-control" rows="3" name="message" placeholder="Your Message"></textarea>    </div>  </div>  <div class="form-group">    <div class="col-sm-offset-2 col-sm-10">      <button type="submit" class="btn btn-default">Submit</button>    </div>  </div></form>

async function sendData(url, data) {
  const formData  = new FormData();

  for(const name in data) {
    formData.append(name, data[name]);
  }

  const response = await fetch(url, {
    method: 'POST',
    body: formData
  });

  // ...
}

@WebServlet("/Relay")
@MultipartConfig
public class Relay extends HttpServlet {   
    // ...
}