sockets - socket.io-ipad最新的iOS xhr轮询

Question

我有一个使用最新的socket.io的应用程序。在使用最新iOS的iPad上，我注意到所选的传输方式为xhr-polling。我给人的印象是，websocket在移动浏览器中完全是supported。

出于好奇，我想知道为什么在该平台上支持websocket时选择了xhr-polling？

Answer 1

来自here的答案。

Socket.IO never assumes that WebSocket will just work, because in practice there’s a good chance that it won’t. Instead, it establishes a connection with XHR or JSONP right away, and then attempts to upgrade the connection to WebSocket. Compared to the fallback method which relies on timeouts, this means that none of your users will have a degraded experience.

同样，从Offical Socket.io GitHub页面上的README中:

Socket.IO is not a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the ack id when a message acknowledgement is needed.