http2

朴灿烈づ我的快乐病毒、 2021-11-05 09:58 295阅读 0赞

http2:

链接地址：http://http2.github.io/http2-spec/index.html

http1.1:采用文本协议,虽然支持连接复用，但是在返回的时候仍然是顺序串行话的，导致很多网站采用多个域名同时建立多个链接来提升性能，

造成冗长和重复，导致不必要的网络io及tcp消耗

http2:由于上一个版本存在的问题，采用了spdy的思想，使用binary 协议，加上frame、stream的概念

1、header压缩

2、connection共用

3、使用二进制frame作为单元传输

4、push promise 服务器端的预推送

5、增加优先级概念及flow control

http2有两个版本通过h2、h2c来标识，h2标识通过TLS传输、h2c标识cleartext明文传输

在查询server是否使用http2时可以使用如下头

GET / HTTP/1.1
    Host: server.example.com
    Connection: Upgrade, HTTP2-Settings
    Upgrade: h2c
    HTTP2-Settings: <base64url encoding of HTTP/2 SETTINGS payload>

A server 如果不支持那么upgrade头不会出现如下：

HTTP/1.1 200 OK
    Content-Length: 243
    Content-Type: text/html

支持的话如下:

HTTP/1.1 101 Switching Protocols
    Connection: Upgrade
    Upgrade: h2c
    
    [ HTTP/2 connection ...

如果一个请求升级到http2的头必须包含一个HTTP2-Settings header field. The HTTP2-Settings header field is a connection-specific header field that includes parameters that govern the HTTP/2 connection, provided in anticipation of the server accepting the request to upgrade.

HTTP2-Settings    = token68

## Frame的格式 ##

All frames begin with a fixed 9-octet header followed by a variable-length payload.

+-----------------------------------------------+
     |                 Length (24)                   |
     +---------------+---------------+---------------+
     |   Type (8)    |   Flags (8)   |
     +-+-------------+---------------+-------------------------------+
     |R|                 Stream Identifier (31)                      |
     +=+=============================================================+
     |                   Frame Payload (0...)                      ...
     +---------------------------------------------------------------+

Figure 1: Frame Layout

The fields of the frame header are defined as:

Length:

The length of the frame payload expressed as an unsigned 24-bit integer. Values greater than 214(16,384) MUST NOT be sent unless the receiver has set a larger value for[SETTINGS\_MAX\_FRAME\_SIZE][SETTINGS_MAX_FRAME_SIZE].

The 9 octets of the frame header are not included in this value.

Type:

The 8-bit type of the frame. The frame type determines the format and semantics of the frame. Implementations MUST ignore and discard any frame that has a type that is unknown.

Flags:

An 8-bit field reserved for boolean flags specific to the frame type.

Flags are assigned semantics specific to the indicated frame type. Flags that have no defined semantics for a particular frame type MUST be ignored and MUST be left unset (0x0) when sending.

A reserved 1-bit field. The semantics of this bit are undefined, and the bit MUST remain unset (0x0) when sending and MUST be ignored when receiving.

Stream Identifier:

A stream identifier (see [Section 5.1.1][Section_5.1.1]) expressed as an unsigned 31-bit integer. The value 0x0 is reserved for frames that are associated with the connection as a whole as opposed to an individual stream.

The structure and content of the frame payload is dependent entirely on the frame type.

frame的大小由[SETTINGS\_MAX\_FRAME\_SIZE][SETTINGS_MAX_FRAME_SIZE] settings 决定

HEADER传输采用由一系列不中断的header blocks，最后一个headers或者[CONTINUATION][]包含end\_headers 标识，如下组成

+---------------+
     |Pad Length? (8)|
     +-+-------------+-----------------------------------------------+
     |E|                 Stream Dependency? (31)                     |
     +-+-------------+-----------------------------------------------+
     |  Weight? (8)  |
     +-+-------------+-----------------------------------------------+
     |                   Header Block Fragment (*)                 ...
     +---------------------------------------------------------------+
     |                           Padding (*)                       ...
     +---------------------------------------------------------------+

DATA:如下组成

+---------------+
     |Pad Length? (8)|
     +---------------+-----------------------------------------------+
     |                            Data (*)                         ...
     +---------------------------------------------------------------+
     |                           Padding (*)                       ...
     +---------------------------------------------------------------+

http2还包含各种frame如SETTINGS(包含全局设置如flow control大小，也包含stream设置)、RST\_STREAM(取消或重置当前的stream)、PUSH\_PROMISE(预推送)、PING(侦测链接是否可用)、GOAWAY(关闭链接一般包含一个比当前链接的stream都要大的id，可以优雅的结束当前的小于id的stream)、WINDOW\_UPDATE(窗口大小用于flow control)

http1.1与http2例子对比：

request:
    GET /resource HTTP/1.1           HEADERS
      Host: example.org          ==>     + END_STREAM
      Accept: image/jpeg                 + END_HEADERS
                                           :method = GET
                                           :scheme = https
                                           :path = /resource
                                           host = example.org
                                           accept = image/jpeg
    reponse:

HTTP/1.1 304 Not Modified        HEADERS
      ETag: "xyzzy"              ==>     + END_STREAM
      Expires: Thu, 23 Jan ...           + END_HEADERS
                                           :status = 304
                                           etag = "xyzzy"
                                           expires = Thu, 23 Jan ...

request:
    POST /resource HTTP/1.1          HEADERS
      Host: example.org          ==>     - END_STREAM
      Content-Type: image/jpeg           - END_HEADERS
      Content-Length: 123                  :method = POST
                                           :path = /resource
      {binary data}                        :scheme = https
    
                                       CONTINUATION
                                         + END_HEADERS
                                           content-type = image/jpeg
                                           host = example.org
                                           content-length = 123
    
                                       DATA
                                         + END_STREAM
                                       {binary data}
    reponse:

HTTP/1.1 200 OK                  HEADERS
      Content-Type: image/jpeg   ==>     - END_STREAM
      Content-Length: 123                + END_HEADERS
                                           :status = 200
      {binary data}                        content-type = image/jpeg
                                           content-length = 123
    
                                       DATA
                                         + END_STREAM
                                       {binary data}

HTTP/1.1 100 Continue            HEADERS
      Extension-Field: bar       ==>     - END_STREAM
                                         + END_HEADERS
                                           :status = 100
                                           extension-field = bar
    
      HTTP/1.1 200 OK                  HEADERS
      Content-Type: image/jpeg   ==>     - END_STREAM
      Transfer-Encoding: chunked         + END_HEADERS
      Trailer: Foo                         :status = 200
                                           content-length = 123
      123                                  content-type = image/jpeg
      {binary data}                        trailer = Foo
      0
      Foo: bar                         DATA
                                         - END_STREAM
                                       {binary data}
    
                                       HEADERS
                                         + END_STREAM
                                         + END_HEADERS
                                           foo = bar

转载于:https://www.cnblogs.com/hike2008/p/4549304.html

[SETTINGS_MAX_FRAME_SIZE]: http://http2.github.io/http2-spec/index.html#SETTINGS_MAX_FRAME_SIZE
[Section_5.1.1]: http://http2.github.io/http2-spec/index.html#StreamIdentifiers
[CONTINUATION]: http://http2.github.io/http2-spec/index.html#CONTINUATION