shutdown() and SHUT_RD on TCP sockets - anomalous behaviour?

Hello,

I did an archive search and found a post that indicated that what I describe below is known behaviour. The question is: why does this occur on Linux?

According to SUSv3, if we perform a shutdown(fd, SHUT_RD) on a socket, then further reads on that socket should be disabled. In the AF_UNIX domain, all is fine - things operate as expected. However, for stream sockets, things are different (tested on 2.2.14, and 2.4.19):

1. If we perform a read() on the socket and there is no data, then 0 (EOF) is (immediately) returned. (This is expected.)

2. However, the peer can still write() to the socket, and afterwards we can read() that data from the socket, even though the reading half of the socket should be shutdown. Instead of this behaviour, I expected the data to be discarded, and the read() to return 0 as in point 1.

I've read the relevant source code to confirm the anomalous behaviour in point 2. The question is: why do things happen in this way on Linux?

Thansk

Michael