What is a MIME type?_问答_开发者_运维开发者技术经验分享

I have been reading about how to build plug-ins and this "MIME type" keeps getting discussed in it. I have tried to look 开发者_StackOverflow中文版into it and know that it is Multipurpose Internet Mail Extensions (MIME) but no suitable explanation of how it relates to browser plug-ins, as in what I need to know about it for building plug-ins, is provided, please explain in clear and simple words. What is it? Why do plug-ins have a MIME type?

A MIME type is a label used to identify a type of data. It is used so software can know how to handle the data. It serves the same purpose on the Internet that file extensions do on Microsoft Windows.

So if a server says "This is text/html" the client can go "Ah, this is an HTML document, I can render that internally", while if the server says "This is application/pdf" the client can go "Ah, I need to launch the FoxIt PDF Reader plugin that the user has installed and that has registered itself as the application/pdf handler."

You'll most commonly find them in the headers of HTTP messages (to describe the content that an HTTP server is responding with or the formatting of the data that is being POSTed in a request) and in email headers (to describe the message format and attachments).

MIME stands for Multi-purpose Internet Mail Extensions. MIME types form a standard way of classifying file types on the Internet. Internet programs such as Web servers and browsers all have a list of MIME types, so that they can transfer files of the same type in the same way, no matter what operating system they are working in.

A MIME type has two parts: a type and a subtype. They are separated by a slash (/). For example, the MIME type for Microsoft Word files is application and the subtype is msword. Together, the complete MIME type is application/msword.

Although there is a complete list of MIME types, it does not list the extensions associated with the files, nor a description of the file type. This means that if you want to find the MIME type for a certain kind of file, it can be difficult. Sometimes you have to look through the list and make a guess as to the MIME type of the file you are concerned with.

MIME stands for Multipurpose Internet Mail Extensions. It's a way of identifying files on the Internet according to their nature and format.

For example, using the Content-type header value defined in a HTTP response, the browser can open the file with the proper extension/plugin.

Internet Media Type (also Content-type) is the same as a MIME type. MIME types were originally created for emails sent using the SMTP protocol. Nowadays, this standard is used in a lot of other protocols, hence the new naming convention "Internet Media Type".

A MIME type is a string identifier composed of two parts: a type and a subtype.

The "type" refers to a logical grouping of many MIME types that are closely related to each other; it's no more than a high level category.
"subtypes" are specific to one file type within the "type".

The x- prefix of a MIME subtype simply means that it's non-standard.
The vnd prefix means that the MIME value is vendor specific.

Source

Explanation by analogy

Imagine that you wrote a letter to your pen pal but that you wrote it in different languages each time.

For example, you might have chosen to write your first letter in Tamil, and the second in German etc.

In order for your friend to translate those letters, your friend would need to:

(i) identify the language type, and
(ii) and then translate it accordingly. But identifying a language is not that easy - it's going to take a lot of computational energy. It would be much easier if you wrote the language you are sending across on the top of your letter - that would make life a lot easier for your friend.

So then, in order to highlight the language you are writing in, you simple annotate the language (e.g. "French") on the top of your letter.

What is a MIME type?

How would your friend know or be able to read or distinguish between the different language types you are specifying at the top of your letter? That's easy: you agree upon this beforehand.

Tying the analogy back in with HTML

Because there are different types of data formats which need to be sent over the internet, specifying the data type up front would allow the corresponding client to properly interpret and render the data accordingly to the user.

Why do we have different data formats?

Principally because they serve different purposes and have different abilities.

For example, a PDF format is very different from a picture format - which is also different from a sound format - both serve very different purposes and accordingly are written different prior to being sent over the internet.

I couldn't possibly explain it better than Wikipedia does in Media type:

In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format.

In other words, it helps the browser (or content consumer, because it may not just be a browser) determine what content they are about to consume; this means a browser may be able to make a decision on the correct plugin to use to display content, or a media player may be able to load up the correct codec or plugin.

It is useful to think of MIME in the context of the client-server model. Clients and servers communicate over what is known as the HTTP protocol. In an HTTP request or response, we can have a body. The Content-Type or MIME type specifies what is the type of the body, like text/javascript or something else like audio, video, etc.

However, MIME types are not limited just to HTTP.

As the name suggests, MIME stands for Multipurpose Internet Mail Extensions. Originally, SMTP only supported ASCII-encodings. However, there as a need for more. We could use MIME to slap a label on the content being transmitted or received.