From 210665e8a252faecf28ccebade999e734ab92582 Mon Sep 17 00:00:00 2001
From: Igor Slepchin <igor.slepchin@gmail.com>
Date: Mon, 24 Sep 2018 22:44:03 -0400
Subject: Add nopush TCP socket option

This translates to TCP_CORK on Linux and TCP_NOPUSH on
BSD.

In effect, this acts as super-Nagle: no partial TCP segments
are sent out until this option is turned off. Once turned off,
all accumulated unsent data is sent out immediately. The latter
is *not* the case on OSX, hence the implementation ignores
"nopush" on OSX to reduce confusion.
---
 lib/kernel/doc/src/inet.xml            | 12 ++++++++++++
 lib/kernel/src/inet_int.hrl            |  1 +
 lib/kernel/test/inet_sockopt_SUITE.erl |  9 +++++++--
 3 files changed, 20 insertions(+), 2 deletions(-)

(limited to 'lib')

diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index ed775d67eb..9fc361a234 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -1039,6 +1039,18 @@ setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp</code>
               is turned on for the socket, which means that also small
               amounts of data are sent immediately.</p>
           </item>
+          <tag><c>{nopush, Boolean}</c>(TCP/IP sockets)</tag>
+          <item>
+            <p>This translates to <c>TCP_NOPUSH</c> on BSD and
+              to <c>TCP_CORK</c> on Linux.</p>
+            <p>If <c>Boolean == true</c>, the corresponding option
+              is turned on for the socket, which means that small
+              amounts of data are accumulated until a full MSS-worth
+              of data is available or this option is turned off.</p>
+            <p>Note that while <c>TCP_NOPUSH</c> socket option is available on OSX, its semantics
+              is very different (e.g., unsetting it does not cause immediate send
+              of accumulated data). Hence, <c>nopush</c> option is intentionally ignored on OSX.</p>
+          </item>
           <tag><c>{packet, PacketType}</c>(TCP/IP sockets)</tag>
           <item>
             <p><marker id="packet"/>Defines the type of packets to use for a socket.
diff --git a/lib/kernel/src/inet_int.hrl b/lib/kernel/src/inet_int.hrl
index c8e09d18ad..f6525d7261 100644
--- a/lib/kernel/src/inet_int.hrl
+++ b/lib/kernel/src/inet_int.hrl
@@ -162,6 +162,7 @@
 -define(INET_OPT_PKTOPTIONS,      45).
 -define(INET_OPT_TTL,             46).
 -define(INET_OPT_RECVTTL,         47).
+-define(TCP_OPT_NOPUSH,           48).
 % Specific SCTP options: separate range:
 -define(SCTP_OPT_RTOINFO,	 	100).
 -define(SCTP_OPT_ASSOCINFO,	 	101).
diff --git a/lib/kernel/test/inet_sockopt_SUITE.erl b/lib/kernel/test/inet_sockopt_SUITE.erl
index ada9c2689c..27ff74e309 100644
--- a/lib/kernel/test/inet_sockopt_SUITE.erl
+++ b/lib/kernel/test/inet_sockopt_SUITE.erl
@@ -110,9 +110,14 @@ simple(Config) when is_list(Config) ->
     {S1,S2} = create_socketpair(Opt, Opt),
     {ok,Opt} = inet:getopts(S1,OptTags),
     {ok,Opt} = inet:getopts(S2,OptTags),
-    COpt = [{X,case X of nodelay -> false;_ -> Y end} || {X,Y} <- Opt],
+    NoPushOpt = case os:type() of
+                    {unix, Osname} when Osname =:= linux; Osname =:= freebsd -> {nopush, true};
+                    {_,_} -> {nopush, false}
+                end,
+    COpt = [{X,case X of nodelay -> false;_ -> Y end} || {X,Y} <- [NoPushOpt|Opt]],
+    COptTags = [X || {X,_} <- COpt],
     inet:setopts(S1,COpt),
-    {ok,COpt} = inet:getopts(S1,OptTags),
+    {ok,COpt} = inet:getopts(S1,COptTags),
     {ok,Opt} = inet:getopts(S2,OptTags),
     gen_tcp:close(S1),
     gen_tcp:close(S2),
-- 
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