Content-Type

The Content-Type entity header is used to indicate the media type of the resource.

In responses, a Content-Type header tells the client what the content type of the returned content actually is. Browsers will do MIME sniffing in some cases and will not necessarily follow the value of this header; to prevent this behavior, the header X-Content-Type-Options can be set to nosniff.

In requests, (such as POST or PUT), the client tells the server what type of data is actually sent.

Content-Type: text/html; charset=UTF-8
Content-Type: multipart/form-data; boundary=something

media-type

The MIME type of the resource or the data.

charset

The character encoding standard.

boundary

For multipart entities the boundary directive is required, which consists of 1 to 70 characters from a set of characters known to be very robust through email gateways, and not ending with white space. It is used to encapsulate the boundaries of the multiple parts of the message. Often, the header boundary is prepended with two dashes and the final boundary has two dashes appended at the end.

In a POST request, resulting from an HTML form submission, the Content-Type of the request is specified by the enctype attribute on the <form> element.

<form action="/" method="post" enctype="multipart/form-data">
  <input type="text" name="description" value="some text">
  <input type="file" name="myFile">
  <button type="submit">Submit</button>
</form>

The request looks something like this (less interesting headers are omitted here):

POST /foo HTTP/1.1
Content-Length: 68137
Content-Type: multipart/form-data; boundary=---------------------------974767299852498929531610575

-----------------------------974767299852498929531610575
Content-Disposition: form-data; name="description"

some text
-----------------------------974767299852498929531610575
Content-Disposition: form-data; name="myFile"; filename="foo.txt"
Content-Type: text/plain

(content of the uploaded file foo.txt)
-----------------------------974767299852498929531610575--

• Accept and Accept-Charset
• Content-Disposition
• 206 Partial Content
• X-Content-Type-Options