Hello ?????_????,
On Sat, Feb 8, 2014 at 5:32 PM, ?????_???? <[email protected]> wrote:
> It is my pleasure to write here for you.
> I have read 'Linux Programmer??s Manual RECV(2)'. The description of
> return value is like this: These calls return the number of bytes received,
> or -1 if an error occurred. The return value will be 0 when the peer has
> performed an orderly shutdown.
> Notice the bold text. It means that if the "recv" function return 0, the
> connection has already been broken gracefully. But in the fallowing code, it
> is not the case:
> char buf[256];
> ssize_t rc;
> size_t buflen = 0;
> rc = recv( sockfd, buf, buflen, 0 ); // the 'rc' will be 0, but
> the connection is still established
> If the value of 'buflen' is 0, the "recv" function also return 0. But the
> connection is still established. In another case, before the "recv" being
> called, the remote programe close the socket (it means that the connection
> has been broken), and the "recv" return 0 too.
> SERVER
> CLIENT
> char buf[256];
> ssize_t rc;
> size_t buflen = 0;
> ......
>
> close( sockfd );
> // before call recv, the connection has been broken gracefully
> ......
> rc = recv( sockfd, buf, buflen, 0 ); // the 'rc' will be 0, but
> the connection is broken
>
> So, when I call the "recv" function with the value 0 in the 3rd
> argument, I'm not sure whether the connection is still OK by the return
> value.
> I think there is a conflict between the definition of the 3rd argument
> and the return value.
Thanks for this report. Yes, there are several details missing there.
I've applied the patch below.
Cheers,
Michael
--- a/man2/recv.2
+++ b/man2/recv.2
@@ -403,8 +403,16 @@ if an error occurred.
In the event of an error,
.I errno
is set to indicate the error.
-The return value will be 0 when the
-peer has performed an orderly shutdown.
+
+When a stream socket peer has performed an orderly shutdown,
+the return value will be 0 (the traditional "end-of-file" return).
+
+Datagram sockets in various domains (e.g., the UNIX and Internet domains)
+permit zero-length datagrams.
+When such a datagram is received, the return value is 0.
+
+The value 0 may also be returned if the requested number of bytes
+to receive from a stream socket was 0.
.SH ERRORS
These are some standard errors generated by the socket layer.
Additional errors
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/