Add 'show_econnreset' TCP socket option

An ECONNRESET is a socket error which tells us that a TCP peer has sent
an RST. The RST indicates that they have aborted the connection and
that the payload we have received should not be considered complete. Up
until now, the implementation of TCP in inet_drv.c has hidden the
receipt of the RST from the user, treating it as though it was just
a FIN terminating the read side of the socket.

There are many cases where user code needs to be able to distinguish
between a socket that was closed normally and one that was aborted.
Setting the option {show_econnreset, true} enables the user to receive
ECONNRESET errors on both active and passive sockets.

A connected socket returned from gen_tcp:accept/1 will inherit the
show_econnreset setting of the listening socket.

By default this option is set to {show_econnreset, false}.

Note that this patch only enables the reporting of ECONNRESET when
the socket is being read from. It does not report ECONNRESET (or
EPIPE) when the user tries to write to a connection when an RST
has already been received. Currently the TCP implementation in
inet_drv.c hides all such send errors from the user in favour
of returning {error, close}. A separate patch will be needed to
enable the reporting of such errors.

1 files changed, 27 insertions, 0 deletions

diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index 77a8caaaf6..a364f9e0c9 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -1037,6 +1037,33 @@ setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp
 			<marker id="option-sndbuf"></marker>
           </item>
 
+          <tag><c>{show_econnreset, Boolean}</c>(TCP/IP sockets)</tag>
+          <item>
+            <p>When this option is set to <c>false</c>, as it is by
+              default, an RST that is received from the TCP peer is treated
+              as a normal close (as though a FIN was sent). A caller
+              to <seealso marker="gen_tcp#recv/2">gen_tcp:recv/2</seealso>
+              will get <c>{error, closed}</c>. In active
+              mode the controlling process will receive a
+              <c>{tcp_close, Socket}</c> message, indicating that the
+              peer has closed the connection.</p>
+            <p>Setting this option to <c>true</c> will allow you to
+              distinguish between a connection that was closed normally,
+              and one which was aborted (intentionally or unintentionally)
+              by the TCP peer. A call to
+              <seealso marker="gen_tcp#recv/2">gen_tcp:recv/2</seealso>
+              will return <c>{error, econnreset}</c>. In
+              active mode, the controlling process will receive a
+              <c>{tcp_error, Socket, econnreset}</c> message
+              before the usual <c>{tcp_closed, Socket}</c>, as is
+              the case for any other socket error.</p>
+            <p>A connected socket returned from
+              <seealso marker="gen_tcp#accept/1">gen_tcp:accept/1</seealso>
+              will inherit the <c>show_econnreset</c> setting from the
+              listening socket.</p>
+			<marker id="option-show_econnreset"></marker>
+          </item>
+
           <tag><c>{sndbuf, Size}</c></tag>
           <item>
             <p>The minimum size of the send buffer to use for the socket.