谈谈TCP socket和Web socket之间通信的区别 - 转

WebSocket大家也许都熟悉,他其实和Tcp Socket一样,都属于Socket通信,那么其中两个之间有哪些区别,来说一说

首先看一下Websocket的百科介绍:


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其中有个国外的类似知乎的技术社区stackoverflow上有人提出过这个问题,也有大牛进行解答过,我们来看看

地址是:https://stackoverflow.com/questions/16945345/differences-between-tcp-sockets-and-web-sockets-one-more-time


这个讨论有超过8万的阅读量。

首先我们来阅读这段有166个赞的回答:

When you send bytes from a buffer with a normal TCP socket, the send function returns the number of bytes of the buffer that were sent. 
当我们向一个通常的TCP套接字发送一段来自内存buffer中的字节数据时,send系统调用返回的是实际发送的字节数。
If it is a non-blocking socket or a non-blocking send then the number of bytes sent may be less than the size of the buffer.

如果发送数据的目的方套接字是一个非阻塞套接字或者是对写操作非阻塞的套接字,那么send返回的已发送字节数可能小于buffer中待发送字节数。

If it is a blocking socket or blocking send, then the number returned will match the size of the buffer but the call may block. 
如果是阻塞套接字,两者会相等,因为顾名思义,如果send系统调用没有把所有待发送数据全部发送,则API调用不会返回。

With WebSockets, the data that is passed to the send method is always either sent as a whole "message" or not at all. Also, browser WebSocket implementations do not block on the send call.

而Web socket和TCP socket的区别,从发送的数据来看,不再是一系列字节,而是按照一个完整的"消息体"发送出去的,这个"消息体"无法进一步再分割,要么全部发送成功,要么压根就不发送,不存在像TCP套接字非阻塞操作那样出现部分发送的情况。换言之,Web Socket里对套接字的操作是非阻塞操作。

这个区别在维基百科上也有清晰阐述:
Websocket differs from TCP in that it enables a stream of messages instead of a stream of bytes

再来看接收方的区别。
原文:
But there are more important differences on the receiving side of things. When the receiver does a recv (or read) on a TCP socket, there is no guarantee that the number of bytes returned correspond to a single send (or write) on the sender side. It might be the same, it may be less (or zero) and it might even be more (in which case bytes from multiple send/writes are received). With WebSockets, the receipt of a message is event driven (you generally register a message handler routine), and the data in the event is always the entire message that the other side sent.

同理,在TCP套接字的场景下,接收方从TCP套接字读取的字节数,并不一定等于发送方调用send所发送的字节数。而WebSocket呢?WebSocket的接收方从套接字读取数据,根本不是像TCP 套接字那样直接用recv/read来读取, 而是采取事件驱动机制。即应用程序注册一个事件处理函数,当web socket的发送方发送的数据在接收方应用从内核缓冲区拷贝到应用程序层已经处于可用状态时 ,应用程序注册的事件处理函数以回调(callback)的方式被调用。


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