November 2022
Intermediate to advanced
276 pages
3h 51m
Chinese
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112 ｜
第
4
章
4.2.2 HTTP
和
WebSocket
最后介绍的这两个
IoT
协议是超文本传输协议
(Hypertext Transfer Protocol
，
HTTP)
和
WebSocket
，它们在
IoT
开发人员中的采用率实际上比
MQTT
略高。
注
1
HTTP
本质上是一个请求
–
应答协议（不是发布
–
订阅协议，如
MQTT
），
因此不支持连接方之间的任意双向对话。但是，它可以作为具有
HTTP/2
中
的一些功能的流式解决方案，这是当今大多数客户端（如
Web
浏览器）和服
务器使用的
HTTP
版本。
另一方面，
WebSocket
是一种通信协议，旨在允许在
TCP
连接上进行双向对话。
它与
HTTP
不同，但被设计成可以与
HTTP
无缝衔接。如今，许多分布式系
统使用
WebSocket
作为核心连接协议，这些分布式系统必须来回发送信息以
完成任务。
HTTP
和
WebSocket
中的信息交换比
MQTT
更加“点对点”。这两种协议都
没有发布
–
订阅语义。没有用于连接和接收特定数据的“主题”概念。消费
者只需通过一个标准的
HTTP
或
WebSocket
请求消息向生产者发出一个请求，
然后服务器就会打开并维持一个不确定时间的连接。在
HTTP
的情况下，将
优化连接以供生产者流式传输到消费者。另一方面，
WebSocket
将很容易支
持双向流式传输。
基于
HTTP
和基于
WebSocket
的事件连接如图
4-5
所示。
生产者
HTTP请求
流数据（一种方式）
WebSocket请求
流数据（两种方式，如果需要）
消费者A
消费者B
图
4
-
5
：HTTP 和 WebSocket ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.