August 2017
Intermediate to advanced
272 pages
5h 32m
Chinese
Content preview from Node.js物聯網裝置開發
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171
第十一章
飛向雲端
先前章節介紹的範例，能夠在區域網路上運作，現在，該是時候看看如何連接橫越網際
網路的各個裝置，但不會直接在裝置間傳遞訊息，而是由網路上的某個節點，擔任訊息
中介器的任務。藉由這台機器扮演中繼轉運站，進一步抽象化裝置所處的位置。
訊息中介器的使用案例通常如下：請想像在各個房屋裡、或是各個城市裡，有著許許多
多的感測器，如果這些感測器需使用
相同
的實體網路，那麼收集資料的工作將會顯得困
難（但因新型態的 LoRaWAN 網路現身，這點已經不再是大問題）。因此可行做法是採
用網路上任何地方都能存取得到的閘道器，或稱之為所謂的「訊息中介器」。
為了能在不同的區域網路間傳遞訊息，有項熱門的技術叫做 MQTT（Message Queue
Telemetry Transport，訊息佇列勘測傳輸）網路協定。藉由 MQTT，我們便能把「發佈 -
訂閱模式」套用到分散四處的多台裝置身上。MQTT 的用法有很多種，你可以設立一台
MQTT 伺服器，或是租用訊息傳輸服務。
發佈 - 訂閱模式為 MQTT 提供了基礎架構，即便自己動手以 JavaScript 語言實作此軟體
模式，也不是太困難。這麼一來，我們就能嘗試各種做法，在網路上散佈資訊狀態，以
及訂閱來自某台裝置的更新訊息。
發佈 - 訂閱模式
對於分散式系統來說，發佈 - 訂閱模式是個非常重要的軟體設計模式。簡言之，其運作
形式類似於報紙或 RSS 消息。許多人或許會對來自不同地方的新聞感到興趣，因此需
要所謂的新聞發報中心，擔任訊息發佈者的角色，讓讀者能夠訂閱。圖 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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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.