Generic Realtime Intermediary Protocol
转自:https://pushpin.org/docs/protocols/grip/
Introduction
The Generic Realtime Intermediary Protocol (“GRIP”) makes it possible for a web service to delegate realtime push behavior to a proxy component. Listening entities, such as long-lived HTTP or WebSocket connections, are managed by the proxy. The web service backend can instruct the proxy to associate listeners with publish-subscribe channels. The web service backend may publish data to channels, and the proxy will relay the data to all associated listeners. When data is published, the entirety of the transmission is specified, allowing complete control over the application protocol exposed to listeners.
There are many advantages to this approach:
Reusability. The primary goal of GRIP is to isolate the common aspects of realtime push functionality into a reusable proxy component. A GRIP proxy should be able to power any kind of web service, with any kind of API contract, for any kind of application, running at any organization. Adding new endpoints, changing protocol flows, or using different data formats should be possible without modifying the proxy.
Simplified routing. Knowing if or where a listening entity may be connected in a cluster makes for a tricky routing problem. It’s simpler for data sources to publish data to channels rather than to individual listeners. With GRIP, data can be sent to a sole proxy, or to each proxy instance in a cluster (either directly or optionally via a message queue), without having to know whether or not any listeners are present.
High scalability. Many listeners may be associated with a single channel. This means data can be sent to the proxy once and multicasted to a set of listeners. Proxies can be chained to message brokers to form a multi-tiered architecture capable of massive output (e.g. publishing to a million connections at the same time across a set of proxies).
Stateless development. In the case of long-lived HTTP connections such as long-polling or streaming, a GRIP proxy communicates to a backend server using short-lived HTTP requests. This means the backend doesn’t have to maintain long-lived connections and it can generally operate statelessly; it can handle incoming requests statelessly and publish data to the proxy statelessly. In the case of WebSockets, a proxy and backend may optionally choose to communicate statelessly on the backend side (e.g. via HTTP).
Transports
There are two main transports defined: HTTP and WebSocket.
HTTP
The HTTP GRIP transport allows a proxy to hold open HTTP requests on behalf of a backend web service, facilitating realtime data push over those held requests. There are two hold modes: response
and stream
.
When a request is made to the proxy, the proxy forwards it to a backend server. The proxy may include special headers. The following request headers are defined:
Grip-Sig
: A JSON Web Token signed with a key known between the proxy and the backend server. The backend can look for this header if it needs to know whether or not a request came from a known GRIP proxy. The JWT claim SHOULD contain aniss
field as a hint for which key is being used (in case there are multiple possible keys). The JWT claim MUST contain anexp
field. If the token cannot be fully verified for any reason, including expiration, then the backend should behave as if the header wasn’t present.
When the backend responds to the request, it MAY specify instructions to the proxy about how to behave, such as the hold mode to use and any channels that should be associated with the request. Once the backend has responded, the transaction between the proxy and the backend is complete. However, the request between the client and the proxy remains open according to the instructions provided.
Instructions are provided via headers. The following response headers are defined:
Grip-Hold
: The hold mode, eitherresponse
orstream
. This header MUST be present in order for the proxy to take GRIP-related action, otherwise it should behave normally (e.g. by relaying the response back to the client).Grip-Channel
: A channel to subscribe the request to. MultipleGrip-Channel
headers may be specified in the response, to subscribe multiple channels to the request. At least oneGrip-Channel
header MUST be present ifGrip-Hold
is present. This header type may include parameters. The only defined parameter isprev-id
, which specifies the ID of data that was last published to the specified channel (used to avoid a race condition). Theprev-id
parameter is OPTIONAL and only applies to theresponse
mode.Grip-Timeout
: The length of time the request should be held open before timing out. This header is OPTIONAL and only applies to theresponse
mode. If omitted, the proxy SHOULD use a default of 55 seconds.Grip-Keep-Alive
: Data to be sent to the client after a certain amount of activity passes. This header is OPTIONAL and only applies to thestream
mode. This header type may include optional parameters. Defined parameters aretimeout
andformat
. Thetimeout
parameter specifies the length of time a request must be idle before the keep alive data is sent. If omitted, the proxy SHOULD use a default of 55 seconds. Theformat
parameter specifies the format of the keep alive data. Allowed values areraw
,cstring
, andbase64
. If omitted,raw
is assumed. For example, if a newline character should be sent to the client after 20 seconds of inactivity, the following header could be used:Grip-Keep-Alive: \n; format=cstring; timeout=20
.
To publish data to any held open connections, http-response
and/or http-stream
payloads must be transmitted to the proxy using the Control Service. Examples:
"http-response": {
"code": int,
"status", str,
"headers": {
name: str,
...
},
"body": str,
"body-bin": base64 str
}
"http-stream": {
"content": str,
"content-bin": base64 str
}
WebSocket
The WebSocket GRIP transport allows a proxy to associate channels with WebSocket connections, so that data may be published to these connections.
When a client makes a WebSocket connection to the proxy, the proxy makes a WebSocket connection to the backend server. In this connection request, the proxy includes the grip
extension in the Sec-WebSocket-Extensions
header. The proxy SHOULD also include a Grip-Sig
header as described in the HTTP section:
GET /websocket/path/ HTTP/1.1
Host: example.com
Upgrade: websocket
Connection: Upgrade
Grip-Sig: [... JWT ...]
Sec-WebSocket-Version: 13
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ=
Sec-WebSocket-Extensions: grip
...
The backend server then accepts the connection with the proxy by responding with status code 101. In order to enable GRIP functionality, the backend must include the grip
extension in its response. If the backend does not include this extension, then the proxy MUST assume that the backend server is not GRIP capable and treat the session as a passthrough.
If the backend server provides the grip
extension, then the proxy will know that the backend is GRIP capable and the backend may send special control messages to the proxy. In order to disambiguate control messages from normal messages, the backend denotes the type of message by including a prefix in the payload of the message. If the message spans multiple frames, then the prefix would be included in the first frame only. By default, the prefix for normal messages is m:
and the prefix for control messages is c:
. The proxy MUST strip off the prefix before relaying or processing.
The grip
extension has an optional parameter called message-prefix
that the backend server can use to override the prefix for normal messages. The backend can even specify a blank string for this value, to indicate that there should be no prefix at all. This can be useful if the backend speaks entirely in JSON, in which case there is no chance of conflict with control messages (a JSON payload would never begin with c:
). For example:
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Extensions: grip; message-prefix=""
...
Control messages are JSON format, encoded as an object with a type
field indicating the type of control message. All other fields in the object are specific to the control message type. The following control messages are defined:
{ "type": "subscribe", "channel": "{channel}" }
{ "type": "unsubscribe", "channel": "{channel}" }
{ "type": "detach" }
Note that control messages are only ever sent by the backend server to the proxy. The proxy does not send control messages to the backend, and the client has no awareness of GRIP. The backend uses the subscribe
and unsubscribe
messages to control the GRIP channels that the client’s WebSocket connection is subscribed to.
The detach
message is used to disconnect the backend from the proxy without the proxy disconnecting from the client. Once a connection is detached, any further messages the proxy receives from the client are dropped. Detached mode only makes sense if the connection has been subscribed to at least one channel and the client is not expected to send anything further. This is useful if the connection is used only for one-way transmission.
The backend server may publish data to the proxy using the ws-message
format, transmitted to the proxy using the Control Service. Example:
"ws-message": {
"content": str,
"content-bin": base64 str
}
This format contains just one child field, content
or content-bin
, containing an entire message to be relayed to all clients subscribed to the channel being published to. The content
field is a string containing a text message. The content-bin
field is a string containing a binary message encoded in Base64.
Control Service
A GRIP proxy may be controlled via the Extensible Pubsub Control Protocol (EPCP). GRIP requires support for the publish endpoint, which is used to send items over HTTP or WebSocket connections that have been bound to channels.
EPCP defines a generalized and extensible way of publishing data through a publish-subscribe service using HTTP. A pubsub service offering an EPCP interface must make a REST API available at a known base URI. For example, if the base URI of the EPCP service is http://localhost:9000/epcp
, then method endpoints would be appended onto that. For example, the publish
endpoint would be available at http://localhost:9000/epcp/publish/
.
Publishing
For example, a publish request may look like this:
POST /publish/ HTTP/1.1
Host: localhost:5561
Content-Type: application/json
{
"items": [
{
"channel": str,
"id": str,
"prev-id": str,
format_1: {},
format_2: {},
...
},
...
]
}
More than one item may be published in a single request. Each item may contain one or more formats by providing field names for each format along with their values. Item formats may be specified in further specifications. EPCP alone does not define any item formats. GRIP defines the following item formats: http-response
(see HTTP), http-stream
(see HTTP, and ws-message
(see WebSocket).
Generic Realtime Intermediary Protocol的更多相关文章
- WebSocket-Over-HTTP Protocol
转自:https://pushpin.org/docs/protocols/websocket-over-http/ WebSocket-Over-HTTP Protocol The WebSocke ...
- RFC 2616
Network Working Group R. Fielding Request for Comments: 2616 UC Irvine Obsoletes: 2068 J. Gettys Cat ...
- RFC3261--sip
本文转载自 http://www.ietf.org/rfc/rfc3261.txt 中文翻译可参考 http://wenku.baidu.com/view/3e59517b1711cc7931b716 ...
- RFC-RTSP
Network Working Group H. Schulzrinne Request for Comments: 2326 Columbia U. Category: Standards Trac ...
- RTSP Spectification
Refer: https://www.ietf.org/rfc/rfc2326.txt Network Working Group H. SchulzrinneRequest for Comments ...
- wifi display代码 分析
转自:http://blog.csdn.net/lilian0118/article/details/23168531 这一章中我们来看Wifi Display连接过程的建立,包含P2P的部分和RTS ...
- A Study of WebRTC Security
转自:http://webrtc-security.github.io/ A Study of WebRTC Security Abstract Web Real-Time Communication ...
- Cisco IOS Debug Command Reference I through L
debug iapp through debug ip ftp debug iapp : to begin debugging of IAPP operations(in privileged EXE ...
- H.264视频的RTP荷载格式
Status of This Memo This document specifies an Internet standards track protocol for the Internet ...
随机推荐
- dns资源记录类型
资源记录的定义格式: 语法:name [TTL] IN RR_TYPE value SOA: name:当前区域的名字,例如"magedu.com.",或者"2.168. ...
- C++基础知识:STL简介
1.标准模板库STL ― STL , 即 : Standard Template Library , 是 C++的一部分― STL是常用数据结构和算法的集合― STL的目标是标准化组件 , 提高开发效 ...
- SQL-25 获取员工其当前的薪水比其manager当前薪水还高的相关信息
题目描述 获取员工其当前的薪水比其manager当前薪水还高的相关信息,当前表示to_date='9999-01-01',结果第一列给出员工的emp_no,第二列给出其manager的manager_ ...
- windows消息传送(自定义消息和WM_COPYDATA)
通过SendMessge实现的进程间通信. 0x01 自定义消息 1,WINDOWS中自定义消息的定义和使用: (1)在WNDOWS中消息分系统消息和自定义消息.系统消息定义从0到0x3FF,使用0x ...
- DevExpress v18.1新版亮点——Analytics Dashboard篇(一)
用户界面套包DevExpress v18.1日前正式发布,本站将以连载的形式为大家介绍各版本新增内容.本文将介绍了DevExpress Analytics Dashboard v18.1 的新功能,快 ...
- 关于 global nonlocal 用法
# 1 关于 globals() locals() nolocl 还有内置函数的引用## 概念的解释# 命名空间# 1 局部命名空间:每一个函数都有自己的命名空间# 2 全局命名空间:写在函数外的变量 ...
- js 自执行匿名函数(转载)
自执行匿名函数: 常见格式:(function() { /* code */ })(); 解释:包围函数(function(){})的第一对括号向脚本返回未命名的函数,随后一对空括号立即执行返回的未命 ...
- jetty安装、配置、优化
)Jetty: 作用:Jetty 是一个开源的servlet容器,它为基于Java的web内容,例如JSP和servlet提供运行环境. 特性:易用性,可扩展性,易嵌入性 2) Jetty安装: t ...
- 2019-03-20-day015-序列化存储
昨日回顾 序列化模块: json -- load dump dumps loads pickle -- load dump dumps loads shelve -- 文件 + 字典 f = shel ...
- C++---String类小结
本随笔是我自己在敲代码的时候一些感受,可能有的地方简略了,还有部分是融合了一点其他资料上的知识点,如有错误欢迎指出,谢谢_(:°з」∠)_ string类是C++中常用的字符串类型,比之普通的字符串要 ...