Body

data-type-headers

Data type and Encoding

Http Body uses MIME type as data type.

MIME is Multipurpose Internet Mail Extensions.

There are some categories.

  • text: text/html, text/css, text/plain, ...

  • image: image/gif, image/jpeg, image/png, ...

  • audio/video: audio/mpeg, video/mp4, ...

  • application: application/json, application/javascript, application/pdf

    If we don't know the type of "application", we use application/octet-stream

What's more, we need to know Encoding type.

There are 3 kinds.

  • gzip: it's the most popular one.

  • deflate

  • br

Data type headers

Once a http message has MIME type and Encoding type, we can seed it.

At client side, we need to add Accept to tell the server what kind of data is accepted.

Accept: text/html,application/xml,image/webp,image/png
Accept-Encoding: gzip, deflate, br

At server side, the server will add the data type to the headers.

Content-Type: text/html
Content-Encoding: gzip

If Encoding is not added, the message won't be compressed at server side, or compressed message won't be accepted.

Language encoding

The Unicode character set that follows the UTF-8 character encoding is the standard character set on the Internet.

We set Accept-Charset or Content-Type in the headers.

// client side

Accept-Language: zh-CN, zh, en
Accept-Charset: gbk, utf-8

// server side

Content-Language: zh-CN
Content-Type: text/html; charset=utf-8

However, language and charactor set can be detected by both browser and server. Therefore, Only Accept-Language will be set at client side, and Content-Type is set by the server.

Priority

Since a browser can accept multiple types of data, we can set the priority by q

Accept: text/html,application/xml;q=0.9,*/*;q=0.8

That means text/html (q = 1.0) > application/xml (q = 0.9) > */* (q = 0.8).

Vary

Vary: Accept-Encoding,User-Agent,Accept

That means the server sent the response according to Accept-Encoding, User-Agent and Accept in the resquest headers.

Large body

To transfer the large body, there are several ways.

Compress

Using Accept-Encoding and Content-Encoding, we can compress the data. It works fine with text, but doesn't good for images or videos.

Chunk

We can chunk the body and sent them multiple responses.

In the response header, we set:

Transfer-Encoding: chunked

Since the body is chunked, the body length is unknown. Therefore, Content-Length is NOT set.

Range request

Range request allows the client requests a part of the body.

However, range request isn't supported by all the server. The server need to tell the client whether it can accept it.

Accept-Ranges: bytes

If Accept-Ranges is missing, it means range request isn't supported.

Then, the client ask for the partial body.

Range: bytes=0-31

The server receives the request.

  • If it's out of range, return 416 Range Not Satisfiable.

  • If it's ok, return 206 Partial Content

    The server need to add Content-Range to tell the range and the length of the body.

Content-Length: 32
Accept-Ranges: bytes
Content-Range: bytes 0-31/96

We can asks for multiple ranges, too.

Range: bytes=0-9, 20-29

The body will be split by boundary.

HTTP/1.1 206 Partial Content
Content-Type: multipart/byteranges; boundary=00000000001
Content-Length: 189
Connection: keep-alive
Accept-Ranges: bytes


--00000000001
Content-Type: text/plain
Content-Range: bytes 0-9/96

// this is
--00000000001
Content-Type: text/plain
Content-Range: bytes 20-29/96

ext json d
--00000000001--

--00000000001 is the separator.

--00000000001-- is the end point.