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Content-Type or MIME type in Post

The Content-Type representation header is used to indicate the original media type of the resource (prior to any content encoding applied for sending).

Syntax

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

Most used

The most commonly used Content-Type (or MIME type) for POST HTTP requests depends on the type of data being sent. Here are a few of the most frequently used Content-Type headers:

  1. application/json: Used for sending JSON data.

Examples

Content-Type in HTML forms

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="/foo" 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):

HTTP
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--

MIME types

A MIME type (now properly called "media type", but also sometimes "content type") is a string sent along with a file indicating the type of the file (describing the content format, for example, a sound file might be labeled audio/ogg, or an image file image/png).

Multipart types

There are two multipart types:

  1. message
  2. multipart

Important MIME types for Web developers

  1. application/octet-stream

    This is the default for binary files. As it means unknown binary file, browsers usually don't execute it, or even ask if it should be executed. They treat it as if the Content-Disposition header was set to attachment, and propose a "Save As" dialog.

  2. text/plain

    This is the default for textual files. Even if it really means "unknown textual file," browsers assume they can display it.

Example 
Text

text/html: HTML documents.
Content-Type: text/html

text/css: Cascading Style Sheets.
Content-Type: text/css

text/javascript or application/javascript: JavaScript files.
Content-Type: text/javascript

Application

application/json: JSON data.
Content-Type: application/json

application/xml: XML data.
Content-Type: application/xml

application/octet-stream: Arbitrary binary data. Often used for file downloads.
Content-Type: application/octet-stream

application/pdf: PDF documents.
Content-Type: application/pdf

application/x-www-form-urlencoded: Form data in URL-encoded format.
Content-Type: application/x-www-form-urlencoded

multipart/form-data: Form data that includes files or binary data.
Content-Type: multipart/form-data; boundary=---boundary

Images

image/jpeg: JPEG images.
Content-Type: image/jpeg

image/png: PNG images.
Content-Type: image/png

image/gif: GIF images.
Content-Type: image/gif

image/svg+xml: SVG vector images.
Content-Type: image/svg+xml

Audio/Video

audio/mpeg: MP3 audio files.
Content-Type: audio/mpeg

audio/ogg: OGG audio files.
Content-Type: audio/ogg

audio/wav: WAV audio files.
Content-Type: audio/wav

video/mp4: MP4 video files.
Content-Type: video/mp4

video/ogg: OGG video files.
Content-Type: video/ogg

Fonts

font/woff: Web Open Font Format (WOFF).
Content-Type: font/woff

font/woff2: Web Open Font Format (WOFF2).
Content-Type: font/woff2

Understanding these MIME types is crucial for web development as they help ensure that the server and browser correctly interpret and handle various types of content. Using the correct MIME type ensures proper rendering and functionality of web pages and applications.

MIME-Type & Content-Type Realtionship

MIME Type

  • What it is: A way to describe the type of content.
  • Format: type/subtype (e.g., application/json, text/html).
  • Example: application/json means the content is JSON.

Content-Type

  • What it is: An HTTP header that tells the server what type of content is being sent.
  • What it contains: A MIME type.
  • Example: Content-Type: application/json means the content being sent is JSON.

Relationship

  • The Content-Type header uses MIME types to specify the format of the data.
  • In other words: MIME type is the value, and Content-Type is the header that holds that value.

Example in a POST Request

When sending JSON data in a POST request:

POST /api/resource HTTP/1.1
Host: example.com
Content-Type: application/json
Content-Length: 27

{
  "name": "John",
  "age": 30
}
  • Content-Type header: Content-Type: application/json
  • MIME type used: application/json

Summary

  • MIME Type: Describes the type of content (e.g., application/json).
  • Content-Type: The HTTP header that includes the MIME type to tell the server what kind of data you're sending.

So, MIME type and Content-Type are closely related, with MIME type being the description of the content and Content-Type being the header that communicates this description in HTTP requests.

Reference