Unix套接字，SOCK_SEQPACKET VS SOCK_DGRAM [英] Unix socket, SOCK_SEQPACKET vs SOCK_DGRAM

问题描述

这似乎有ATLEAST 3个不同的地方/ Unix套接字类型（PF_UNIX），SOCK_STREAM，SOCK_DGRAM和SOCK_SEQPACKET。

It seems there's atleast 3 different local/unix socket types (PF_UNIX) , SOCK_STREAM, SOCK_DGRAM and SOCK_SEQPACKET.

虽然我知道，一个SOCK_STREAM给你一个双向字节流，如TCP或双向管道，和其他两个给你的messge /包API，什么是SOCK_DGRAM和SOCK_SEQPACKET的Unix套接字之间的区别？

While I know that a SOCK_STREAM gives you a bi-directional byte stream, like TCP or a bidirectional pipe, and the other two gives you a messge/packet API, what's the difference between a unix socket of SOCK_DGRAM and SOCK_SEQPACKET ?

由于这些仅是局部的，我想不出很好的理由有人可能重新排序的数据包的方式将实现SOCK_DGRAM一个的。

As these are local only, I can't think of a good reason someone would implement SOCK_DGRAM in a manner it could reorder packets.

此外，没有SOCK_DGRAM / SOCK_SEQPACKET聘请流量控制，也可以在邮件阅读速度慢的情况下，被丢弃？

Also, does SOCK_DGRAM/SOCK_SEQPACKET employ flow control, or can messages be dropped in case of slow readers ?

推荐答案

下面是 SOCK_SEQPACKET 的预期用途情况下的好文章，但事实上，它不是真正可用在IP协议族，以及如何可以得到同样的事情与现有的TCP语义：

Here is a good article on the intended use case for SOCK_SEQPACKET, the fact that it's not really available in the IP protocol families, and how you can get the same thing with existing TCP semantics:

<一个href=\"http://urchin.earth.li/~twic/Sequenced_Packets_Over_Ordinary_TCP.html\">http://urchin.earth.li/~twic/Sequenced_Packets_Over_Ordinary_TCP.html

注意 SOCK_SEQPACKET 是行为 SOCK_STREAM 比 SOCK_DGRAM 。

从引用的网站举例：

该SOCK_SEQPACKET套接字类型类似于SOCK_STREAM类型，也是面向连接的。这些之间的唯一区别
  类型是记录边界正在使用维护
  SOCK_SEQPACKET类型。 A记录可以使用一个或多个输出被发送
  操作和接收使用一个或多个输入操作，但一个
  单人操作从未传输多个记录的一部分。记录
  通过边界在该MSG_EOR标志是接收机可见
  收到邮件标志由recvmsg（）函数返回。它是
  协议特定的最大记录大小是否被强加的。

The SOCK_SEQPACKET socket type is similar to the SOCK_STREAM type, and is also connection-oriented. The only difference between these types is that record boundaries are maintained using the SOCK_SEQPACKET type. A record can be sent using one or more output operations and received using one or more input operations, but a single operation never transfers parts of more than one record. Record boundaries are visible to the receiver via the MSG_EOR flag in the received message flags returned by the recvmsg() function. It is protocol-specific whether a maximum record size is imposed.

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