Github user oknet commented on the issue:
https://github.com/apache/trafficserver/pull/947
EVENTIO_ERROR means EPOLLHUP | EPOLLERR | EPOLLPRI.
EPOLLPRI means OOB or TCP URG is set. You will always receive EPOLLPRI with
EPOLLIN.
To EPOLLPRI, we need handle READ first and ignore EPOLLPRI, this is what
NetHandler does.
EPOLLHUP & EPOLLRDHUP
reference :
http://stackoverflow.com/questions/8707458/epoll-and-remote-1-way-shutdown
```
A socket listening for epoll events will typically receive an EPOLLRDHUP
(in addition to EPOLLIN) event flag upon the remote peer calling close or
shutdown(SHUT_WR). This does not neccessarily mean the socket is dead.
Subsequent calls to recv() will return any unread data on the socket and
eventually "0" will be returned to indicate EOF. It may even be possible to
send data back if the remote peer only did a half-close of its socket.
The one notable exception is if the remote peer is using the SO_LINGER
option enabled on its socket with a linger value of "0". The result of closing
such a socket may result in a TCP RST getting sent instead of a FIN. From what
I've read, a connection reset event will generate either a EPOLLHUP or
EPOLLERR. (I haven't had time to confirm, but it makes sense).
There is some documentation to suggest there are older Linux
implementations that don't support EPOLLRDHUP, as such EPOLLHUP gets generated
instead.
And for what it is worth, in my particular case, I found that it is not too
interesting to have code that special cases EPOLLHUP or EPOLLRDHUP events.
Instead, just treat these events the same as EPOLLIN/EPOLLOUT and call recv()
(or send() as appropriate). But pay close attention to return codes returned
back from recv() and send().
```
EPOLLERR means the possible non-fatal errors on socket fd such as EAGAIN,
EINTR, EWOULDBLOCK and fatal errors.
When you receive EPLLERR, it means an error of socketfd and also there may
be data before this error. Therefore we should call read() and write() to
figure out the actual meanning of this error
Currently, NetHandler try to perform read() & write() on the socket fd
first.
We will get non-fatal errors or fatal erros from read() or write().
if it is non-fatal error, just put socket fd into wait list.
if it is fatal error, signal SM to close socket fd.
e.g.
There is a Fatal ERROR if EPIPE is returned from write().
If "0" is returned from read() there is EOF.
So the currently implement of NetHandler is enough to handle all of this
and doesn't need to change.
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