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File 1292-Introduce-a-scheme-for-reusing-mandatory-distributio.patch of Package erlang (Revision 6154324f642e084a51ca65b7e728bede)

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From 318ed4605ccf4dc402623c6cd94ddb8547cb9875 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 10 Jun 2021 09:44:56 +0200
Subject: [PATCH 2/2] Introduce a scheme for reusing mandatory distribution
 flags

During distribution connect setup between two nodes, the nodes exchange
flags words encoding their capabilities. The connection setup is aborted
if one of the node lacks a capability that the other node requires.

In version 5 of the protocol (introduced in OTP R6), there are 32
possible capabilities (each encoded in a single bit). Since it seemed
that we would soon run out of capabilitiy bits, protocol version 6
(introduced in OTP 23) expanded the number of possible capability bits
to 64.

To avoid having to extend the number of capabilites yet again from 64
to 128 in some future release, this commit introduces a scheme to
allow reusing the bit numbers for capabilities that are now
mandatory. The scheme is described in lib/kernel/include/dist.hrl.

There are 10 mandatory capability bits as of OTP 25. This scheme will
allow reusing 9 of those capability bits as early as in OTP 27.
---
 erts/doc/src/erl_dist_protocol.xml            |   6 +
 erts/emulator/beam/dist.h                     |  85 ++++----
 lib/erl_interface/src/connect/ei_connect.c    |  11 +-
 .../src/connect/ei_connect_int.h              |  30 +--
 lib/erl_interface/test/ei_tmo_SUITE.erl       | 188 +++++++++++++-----
 .../otp/erlang/AbstractConnection.java        |   8 +
 .../com/ericsson/otp/erlang/AbstractNode.java |  13 +-
 lib/kernel/include/dist.hrl                   | 106 +++++++---
 lib/kernel/src/dist_util.erl                  |  20 +-
 lib/kernel/test/erl_distribution_wb_SUITE.erl |  74 +++++--
 10 files changed, 378 insertions(+), 163 deletions(-)

diff --git a/erts/doc/src/erl_dist_protocol.xml b/erts/doc/src/erl_dist_protocol.xml
index 0f3319d032..29027f0eeb 100644
--- a/erts/doc/src/erl_dist_protocol.xml
+++ b/erts/doc/src/erl_dist_protocol.xml
@@ -1115,6 +1115,12 @@ DiB == gen_digest(ChA, ICA)?
 	 <seeguide marker="#old_link_protocol">old link protocol</seeguide>
 	 will be used as a fallback.
 	</item>
+	<tag><c>-define(DFLAG_MANDATORY_25_DIGEST, (1 bsl 36)).</c></tag>
+ <item>
+	 The node supports all capabilities that are mandatory in OTP 25.
+ Introduced in OTP 25.
+ <note>This flag will become mandatory in OTP 27.</note>
+ </item>
 <tag><marker id="DFLAG_SPAWN"/><c>-define(DFLAG_SPAWN, (1 bsl 32)).</c></tag>
 <item>
 Set if the <seeguide marker="#SPAWN_REQUEST"><c>SPAWN_REQUEST</c></seeguide>,
diff --git a/erts/emulator/beam/dist.h b/erts/emulator/beam/dist.h
index 4db0cea1e6..b4f153f3bd 100644
--- a/erts/emulator/beam/dist.h
+++ b/erts/emulator/beam/dist.h
@@ -25,33 +25,35 @@
 #include "erl_node_tables.h"
 #include "zlib.h"
 
-#define DFLAG_PUBLISHED ((Uint64)0x01)
-#define DFLAG_ATOM_CACHE ((Uint64)0x02)
-#define DFLAG_EXTENDED_REFERENCES ((Uint64)0x04)
-#define DFLAG_DIST_MONITOR ((Uint64)0x08)
-#define DFLAG_FUN_TAGS ((Uint64)0x10)
-#define DFLAG_DIST_MONITOR_NAME ((Uint64)0x20)
-#define DFLAG_HIDDEN_ATOM_CACHE ((Uint64)0x40)
-#define DFLAG_NEW_FUN_TAGS ((Uint64)0x80)
-#define DFLAG_EXTENDED_PIDS_PORTS ((Uint64)0x100)
-#define DFLAG_EXPORT_PTR_TAG ((Uint64)0x200)
-#define DFLAG_BIT_BINARIES ((Uint64)0x400)
-#define DFLAG_NEW_FLOATS ((Uint64)0x800)
-#define DFLAG_UNICODE_IO ((Uint64)0x1000)
-#define DFLAG_DIST_HDR_ATOM_CACHE ((Uint64)0x2000)
-#define DFLAG_SMALL_ATOM_TAGS ((Uint64)0x4000)
-#define DFLAG_ETS_COMPRESSED ((Uint64)0x8000) /* internal */
-#define DFLAG_UTF8_ATOMS ((Uint64)0x10000)
-#define DFLAG_MAP_TAG ((Uint64)0x20000)
-#define DFLAG_BIG_CREATION ((Uint64)0x40000)
-#define DFLAG_SEND_SENDER ((Uint64)0x80000)
-#define DFLAG_BIG_SEQTRACE_LABELS ((Uint64)0x100000)
-#define DFLAG_PENDING_CONNECT ((Uint64)0x200000) /* internal */
-#define DFLAG_EXIT_PAYLOAD ((Uint64)0x400000)
-#define DFLAG_FRAGMENTS ((Uint64)0x800000)
-#define DFLAG_HANDSHAKE_23 ((Uint64)0x1000000)
-#define DFLAG_UNLINK_ID ((Uint64)0x2000000)
-#define DFLAG_RESERVED ((Uint64)0xfc000000)
+#define DFLAG_PUBLISHED ((Uint64)0x01)
+#define DFLAG_ATOM_CACHE ((Uint64)0x02)
+#define DFLAG_EXTENDED_REFERENCES ((Uint64)0x04)
+#define DFLAG_DIST_MONITOR ((Uint64)0x08)
+#define DFLAG_FUN_TAGS ((Uint64)0x10)
+#define DFLAG_DIST_MONITOR_NAME ((Uint64)0x20)
+#define DFLAG_HIDDEN_ATOM_CACHE ((Uint64)0x40)
+#define DFLAG_NEW_FUN_TAGS ((Uint64)0x80)
+#define DFLAG_EXTENDED_PIDS_PORTS ((Uint64)0x100)
+#define DFLAG_EXPORT_PTR_TAG ((Uint64)0x200)
+#define DFLAG_BIT_BINARIES ((Uint64)0x400)
+#define DFLAG_NEW_FLOATS ((Uint64)0x800)
+#define DFLAG_UNICODE_IO ((Uint64)0x1000)
+#define DFLAG_DIST_HDR_ATOM_CACHE ((Uint64)0x2000)
+#define DFLAG_SMALL_ATOM_TAGS ((Uint64)0x4000)
+#define DFLAG_ETS_COMPRESSED ((Uint64)0x8000) /* internal */
+#define DFLAG_UTF8_ATOMS ((Uint64)0x10000)
+#define DFLAG_MAP_TAG ((Uint64)0x20000)
+#define DFLAG_BIG_CREATION ((Uint64)0x40000)
+#define DFLAG_SEND_SENDER ((Uint64)0x80000)
+#define DFLAG_BIG_SEQTRACE_LABELS ((Uint64)0x100000)
+#define DFLAG_PENDING_CONNECT ((Uint64)0x200000) /* internal */
+#define DFLAG_EXIT_PAYLOAD ((Uint64)0x400000)
+#define DFLAG_FRAGMENTS ((Uint64)0x800000)
+#define DFLAG_HANDSHAKE_23 ((Uint64)0x1000000)
+#define DFLAG_UNLINK_ID ((Uint64)0x2000000)
+#define DFLAG_MANDATORY_25_DIGEST ((Uint64)0x4000000)
+#define DFLAG_RESERVED ((Uint64)0xf8000000)
+
 /*
 * As the old handshake only support 32 flag bits, we reserve the remaining
 * bits in the lower 32 for changes in the handshake protocol or potentially
@@ -62,17 +64,21 @@
 
 #define DFLAG_DETERMINISTIC DFLAG_ATOM_CACHE
 
-/* Mandatory flags for distribution */
-#define DFLAG_DIST_MANDATORY (DFLAG_EXTENDED_REFERENCES \
- | DFLAG_FUN_TAGS \
- | DFLAG_EXTENDED_PIDS_PORTS \
-			 | DFLAG_UTF8_ATOMS \
-			 | DFLAG_NEW_FUN_TAGS \
- | DFLAG_BIG_CREATION \
- | DFLAG_NEW_FLOATS \
- | DFLAG_MAP_TAG \
- | DFLAG_EXPORT_PTR_TAG \
- | DFLAG_BIT_BINARIES)
+
+/* Mandatory flags for distribution in OTP 25. */
+#define DFLAG_DIST_MANDATORY_25 (DFLAG_EXTENDED_REFERENCES \
+ | DFLAG_FUN_TAGS \
+ | DFLAG_EXTENDED_PIDS_PORTS \
+ | DFLAG_UTF8_ATOMS \
+ | DFLAG_NEW_FUN_TAGS \
+ | DFLAG_BIG_CREATION \
+ | DFLAG_NEW_FLOATS \
+ | DFLAG_MAP_TAG \
+ | DFLAG_EXPORT_PTR_TAG \
+ | DFLAG_BIT_BINARIES)
+
+/* Mandatory flags for distribution. */
+#define DFLAG_DIST_MANDATORY DFLAG_DIST_MANDATORY_25
 
 /*
 * Additional optimistic flags when encoding toward pending connection.
@@ -98,7 +104,8 @@
 | DFLAG_SPAWN \
 | DFLAG_V4_NC		 \
 | DFLAG_ALIAS		 \
- | DFLAG_UNLINK_ID)
+ | DFLAG_UNLINK_ID \
+ | DFLAG_MANDATORY_25_DIGEST)
 
 /* Flags addable by local distr implementations */
 #define DFLAG_DIST_ADDABLE DFLAG_DIST_DEFAULT
diff --git a/lib/erl_interface/src/connect/ei_connect.c b/lib/erl_interface/src/connect/ei_connect.c
index 1d9f2eab8e..d15fed23b3 100644
--- a/lib/erl_interface/src/connect/ei_connect.c
+++ b/lib/erl_interface/src/connect/ei_connect.c
@@ -2264,7 +2264,8 @@ error:
 static DistFlags preferred_flags(void)
 {
 DistFlags flags =
- DFLAG_EXTENDED_REFERENCES
+ DFLAG_MANDATORY_25_DIGEST
+ | DFLAG_EXTENDED_REFERENCES
 | DFLAG_DIST_MONITOR
 | DFLAG_EXTENDED_PIDS_PORTS
 | DFLAG_FUN_TAGS
@@ -2508,6 +2509,10 @@ static int recv_challenge(ei_socket_callbacks *cbs, void *ctx,
 goto error;
 }
 
+ if (*flags & DFLAG_MANDATORY_25_DIGEST) {
+ *flags |= DFLAG_DIST_MANDATORY_25;
+ }
+
 if ((*flags & DFLAG_DIST_MANDATORY) != DFLAG_DIST_MANDATORY) {
 	EI_TRACE_ERR0("recv_challenge","<- RECV_CHALLENGE peer cannot "
 		 "handle all mandatory capabilities");
@@ -2901,6 +2906,10 @@ static int recv_name(ei_socket_callbacks *cbs, void *ctx,
 namelen = get16be(s);
 }
 
+ if (*flags & DFLAG_MANDATORY_25_DIGEST) {
+ *flags |= DFLAG_DIST_MANDATORY_25;
+ }
+
 if ((*flags & DFLAG_DIST_MANDATORY) != DFLAG_DIST_MANDATORY) {
 	EI_TRACE_ERR0("recv_name","<- RECV_NAME peer cannot "
 		 "handle all mandatory capabilities");
diff --git a/lib/erl_interface/src/connect/ei_connect_int.h b/lib/erl_interface/src/connect/ei_connect_int.h
index 9b121d6cc9..56cdb5811a 100644
--- a/lib/erl_interface/src/connect/ei_connect_int.h
+++ b/lib/erl_interface/src/connect/ei_connect_int.h
@@ -84,28 +84,34 @@ typedef EI_ULONGLONG DistFlags;
 #define DFLAG_BIG_CREATION 0x40000
 #define DFLAG_HANDSHAKE_23 0x1000000
 #define DFLAG_UNLINK_ID 0x2000000
-#define DFLAG_RESERVED 0xfc000000
-#define DFLAG_NAME_ME ((DistFlags)0x2 << 32)
+#define DFLAG_MANDATORY_25_DIGEST 0x4000000
+#define DFLAG_RESERVED 0xf8000000
+#define DFLAG_NAME_ME (((DistFlags)0x2) << 32)
 #define DFLAG_V4_NC (((DistFlags)0x4) << 32)
 
 /* Control message tags not exposed to user... */
 #define ERL_UNLINK_ID 35
 #define ERL_UNLINK_ID_ACK 36
 
+/* Mandatory flags for distribution in OTP 25. */
+#define DFLAG_DIST_MANDATORY_25 (DFLAG_EXTENDED_REFERENCES \
+ | DFLAG_FUN_TAGS \
+ | DFLAG_EXTENDED_PIDS_PORTS \
+ | DFLAG_UTF8_ATOMS \
+ | DFLAG_NEW_FUN_TAGS \
+ | DFLAG_BIG_CREATION \
+ | DFLAG_NEW_FLOATS \
+ | DFLAG_MAP_TAG \
+ | DFLAG_EXPORT_PTR_TAG \
+ | DFLAG_BIT_BINARIES)
+
+/* Mandatory flags for distribution. */
+
 /*
 * Mandatory flags for distribution. Keep them in sync with
 * erts/emulator/beam/dist.h.
 */
-#define DFLAG_DIST_MANDATORY (DFLAG_EXTENDED_REFERENCES \
- | DFLAG_FUN_TAGS \
- | DFLAG_EXTENDED_PIDS_PORTS \
- | DFLAG_UTF8_ATOMS \
- | DFLAG_NEW_FUN_TAGS \
- | DFLAG_BIG_CREATION \
- | DFLAG_NEW_FLOATS \
- | DFLAG_MAP_TAG \
- | DFLAG_EXPORT_PTR_TAG \
- | DFLAG_BIT_BINARIES)
+#define DFLAG_DIST_MANDATORY DFLAG_DIST_MANDATORY_25
 
 
 ei_cnode *ei_fd_to_cnode(int fd);
diff --git a/lib/erl_interface/test/ei_tmo_SUITE.erl b/lib/erl_interface/test/ei_tmo_SUITE.erl
index fe044fb34a..2db002b5f8 100644
--- a/lib/erl_interface/test/ei_tmo_SUITE.erl
+++ b/lib/erl_interface/test/ei_tmo_SUITE.erl
@@ -31,7 +31,8 @@
 ei_send_tmo/1,
 ei_send_failure_tmo/1,
 	 ei_connect_unreachable_tmo/0, ei_connect_unreachable_tmo/1,
- ei_recv_tmo/1]).
+ ei_recv_tmo/1,
+ ei_dflags/1]).
 
 suite() ->
 [{ct_hooks,[ts_install_cth]},
@@ -48,7 +49,8 @@ groups() ->
 Members = [ei_recv_tmo,
 ei_accept_tmo,
 ei_connect_tmo,
- ei_send_tmo],
+ ei_send_tmo,
+ ei_dflags],
 [{default, [], Members},
 {ussi, [], Members}].
 
@@ -61,6 +63,40 @@ init_per_testcase(Case, Config) ->
 end_per_testcase(_Case, _Config) ->
 ok.
 
+-define(DFLAG_PUBLISHED, 16#01).
+-define(DFLAG_ATOM_CACHE, 16#02).
+-define(DFLAG_EXTENDED_REFERENCES, 16#04).
+-define(DFLAG_DIST_MONITOR, 16#08).
+-define(DFLAG_FUN_TAGS, 16#10).
+-define(DFLAG_NEW_FUN_TAGS, 16#80).
+-define(DFLAG_EXTENDED_PIDS_PORTS, 16#100).
+-define(DFLAG_EXPORT_PTR_TAG, 16#200).
+-define(DFLAG_BIT_BINARIES, 16#400).
+-define(DFLAG_NEW_FLOATS, 16#800).
+-define(DFLAG_UTF8_ATOMS, 16#10000).
+-define(DFLAG_MAP_TAG, 16#20000).
+-define(DFLAG_BIG_CREATION, 16#40000).
+-define(DFLAG_HANDSHAKE_23, 16#1000000).
+-define(DFLAG_MANDATORY_25_DIGEST, 16#4000000).
+
+%% From OTP R9 extended references are compulsory.
+%% From OTP R10 extended pids and ports are compulsory.
+%% From OTP 20 UTF8 atoms are compulsory.
+%% From OTP 21 NEW_FUN_TAGS is compulsory (no more tuple fallback {fun, ...}).
+%% From OTP 23 BIG_CREATION is compulsory.
+%% From OTP 25 NEW_FLOATS, MAP_TAG, EXPORT_PTR_TAG, and BIT_BINARIES are compulsory.
+-define(COMPULSORY_DFLAGS,
+ (?DFLAG_EXTENDED_REFERENCES bor
+ ?DFLAG_FUN_TAGS bor
+ ?DFLAG_EXTENDED_PIDS_PORTS bor
+ ?DFLAG_UTF8_ATOMS bor
+ ?DFLAG_NEW_FUN_TAGS bor
+ ?DFLAG_BIG_CREATION bor
+ ?DFLAG_NEW_FLOATS bor
+ ?DFLAG_MAP_TAG bor
+ ?DFLAG_EXPORT_PTR_TAG bor
+ ?DFLAG_BIT_BINARIES)).
+
 %% Check the framework.
 framework_check(Config) when is_list(Config) ->
 %%dbg:tracer(),
@@ -221,14 +257,19 @@ ei_connect_unreachable_tmo(Config) when is_list(Config) ->
 
 ei_connect_tmo(Config) when is_list(Config) ->
 [begin
- io:format("Test dist version ~p published as ~p\n", [OurVer,OurEpmdVer]),
+ io:format("Test dist version ~p published as ~p\n",
+ [OurVer,OurEpmdVer]),
 do_ei_connect_tmo(Config, OurVer, OurEpmdVer)
 end
 || OurVer <- lists:seq(?EI_DIST_LOW, ?EI_DIST_HIGH),
 OurEpmdVer <- lists:seq(?EI_DIST_LOW, ?EI_DIST_HIGH),
- OurVer >= OurEpmdVer].
+ OurVer >= OurEpmdVer],
+
+ ok.
 
 do_ei_connect_tmo(Config, OurVer, OurEpmdVer) ->
+ Flags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+
 P2 = runner:start(Config, ?connect_tmo),
 runner:send_term(P2,{c_nod_connect_tmo_2,
 erlang:get_cookie(),
@@ -237,6 +278,7 @@ do_ei_connect_tmo(Config, OurVer, OurEpmdVer) ->
 {term, X} = runner:get_term(P2, 10000),
 runner:recv_eot(P2),
 true = is_integer(X),
+
 %% Aborted handshake test...
 {_,Host} = split(node()),
 OurName = join(cccc,Host),
@@ -263,7 +305,7 @@ do_ei_connect_tmo(Config, OurVer, OurEpmdVer) ->
 {hidden,Node} = recv_name(SocketB, OurEpmdVer), % See 1)
 send_status(SocketB, ok),
 MyChallengeB = gen_challenge(),
- send_challenge(SocketB, OurName, MyChallengeB, OurVer),
+ send_challenge(SocketB, OurName, MyChallengeB, OurVer, Flags),
 recv_complement(SocketB, OurVer, OurEpmdVer),
 _HisChallengeB = recv_challenge_reply(SocketB,
 MyChallengeB,
@@ -288,12 +330,15 @@ ei_accept_tmo(Config) when is_list(Config) ->
 ok.
 
 do_ei_accept_tmo(Config, OurVer, AssumedVer) ->
+ Flags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+
 P = runner:start(Config, ?accept_tmo),
 runner:send_term(P,{c_nod_som_ingen_kontaktar_1,
 kaksmula_som_ingen_bryr_sig_om,
 get_group(Config)}),
 {term,{-1,ETimedout,ETimedout}} = runner:get_term(P, 10000),
 runner:recv_eot(P),
+
 P2 = runner:start(Config, ?accept_tmo),
 runner:send_term(P2,{c_nod_som_vi_kontaktar_1,
 erlang:get_cookie(),
@@ -304,8 +349,14 @@ do_ei_accept_tmo(Config, OurVer, AssumedVer) ->
 {term, X} = runner:get_term(P2, 10000),
 runner:recv_eot(P2),
 true = is_integer(X),
- P3 = runner:start(Config, ?accept_tmo),
- runner:send_term(P3,{c_nod_som_vi_kontaktar_2,
+
+ normal_accept(Config, OurVer, AssumedVer, Flags),
+
+ ok.
+
+normal_accept(Config, OurVer, AssumedVer, Flags) ->
+ P = runner:start(Config, ?accept_tmo),
+ runner:send_term(P,{c_nod_som_vi_kontaktar_2,
 erlang:get_cookie(),
 get_group(Config)}),
 receive after 1000 -> ok end,
@@ -317,7 +368,7 @@ do_ei_accept_tmo(Config, OurVer, AssumedVer) ->
 {ok, SocketA} = gen_tcp:connect(atom_to_list(NB),PortNo,
 [{active,false},
 {packet,2}]),
- send_name(SocketA,OurName,OurVer,AssumedVer),
+ send_name(SocketA, OurName, OurVer, AssumedVer, Flags),
 ok = recv_status(SocketA),
 {hidden,_Node,HisChallengeA} = recv_challenge(SocketA,OurVer), % See 1)
 _OurChallengeA = gen_challenge(),
@@ -325,9 +376,40 @@ do_ei_accept_tmo(Config, OurVer, AssumedVer) ->
 %% Dont do the last two steps of the connection setup...
 %% send_challenge_reply(SocketA, OurChallengeA, OurDigestA),
 %% ok = recv_challenge_ack(SocketA, OurChallengeA, erlang:get_cookie()),
- {term, {-1,ETimedout,ETimedout}} = runner:get_term(P3, 10000),
- runner:recv_eot(P3),
- gen_tcp:close(SocketA),
+ {term, {-1,ETimedout,ETimedout}} = runner:get_term(P, 10000),
+ runner:recv_eot(P),
+ gen_tcp:close(SocketA).
+
+normal_connect(Config, OurVer, Flags) ->
+ {_,Host} = split(node()),
+ OurName = join(cccc,Host),
+ Node = join(c_nod_connect_tmo_3,Host),
+ LSocket = case gen_tcp:listen(0, [{active, false}, {packet,2}]) of
+ {ok, Socket} ->
+ Socket;
+ Else ->
+ exit(Else)
+ end,
+ EpmdSocket = epmd_register(OurName, LSocket, OurVer),
+ P3 = runner:start(Config, ?connect_tmo),
+ Cookie = kaksmula_som_ingen_bryr_sig_om,
+ runner:send_term(P3, {c_nod_connect_tmo_3,
+ Cookie,
+ OurName,
+ get_group(Config)}),
+ SocketB = case gen_tcp:accept(LSocket) of
+ {ok, Socket1} ->
+ Socket1;
+ Else2 ->
+ exit(Else2)
+ end,
+ {hidden,Node} = recv_name(SocketB, OurVer),
+ send_status(SocketB, ok),
+ MyChallengeB = gen_challenge(),
+ send_challenge(SocketB, OurName, MyChallengeB, OurVer, Flags),
+ recv_complement(SocketB, OurVer, OurVer),
+ gen_tcp:close(SocketB),
+ gen_tcp:close(EpmdSocket),
 ok.
 
 make_node(X) ->
@@ -345,6 +427,25 @@ make_and_check_dummy() ->
 
 list_to_atom("dummy@"++HostNotReachable).
 
+%% Test that erl_interface sets the appropriate distributions flags.
+ei_dflags(Config) ->
+ AssumedVer = 5,
+ OurVer = 6,
+
+ %% Test compatibility with OTP 24 and earlier.
+ normal_connect(Config, AssumedVer, ?COMPULSORY_DFLAGS),
+ normal_connect(Config, OurVer, ?COMPULSORY_DFLAGS),
+ normal_accept(Config, OurVer, AssumedVer, ?COMPULSORY_DFLAGS),
+ normal_accept(Config, OurVer, OurVer, ?COMPULSORY_DFLAGS),
+
+ %% Test compatibility with future versions.
+ normal_connect(Config, AssumedVer, ?DFLAG_MANDATORY_25_DIGEST),
+ normal_connect(Config, OurVer, ?DFLAG_MANDATORY_25_DIGEST),
+ normal_accept(Config, OurVer, AssumedVer, ?DFLAG_MANDATORY_25_DIGEST),
+ normal_accept(Config, OurVer, OurVer, ?DFLAG_MANDATORY_25_DIGEST),
+
+ ok.
+
 %%
 %% Stolen from the erl_distribution_wb_test in kernel
 %% To be able to do partial handshakes...
@@ -359,39 +460,6 @@ make_and_check_dummy() ->
 R
 end).
 
--define(DFLAG_PUBLISHED, 1).
--define(DFLAG_ATOM_CACHE, 2).
--define(DFLAG_EXTENDED_REFERENCES, 4).
--define(DFLAG_DIST_MONITOR, 8).
--define(DFLAG_FUN_TAGS, 16#10).
--define(DFLAG_NEW_FUN_TAGS, 16#80).
--define(DFLAG_EXTENDED_PIDS_PORTS, 16#100).
--define(DFLAG_EXPORT_PTR_TAG, 16#200).
--define(DFLAG_BIT_BINARIES, 16#400).
--define(DFLAG_NEW_FLOATS, 16#800).
--define(DFLAG_UTF8_ATOMS, 16#10000).
--define(DFLAG_MAP_TAG, 16#20000).
--define(DFLAG_BIG_CREATION, 16#40000).
--define(DFLAG_HANDSHAKE_23, 16#1000000).
-
-%% From OTP R9 extended references are compulsory.
-%% From OTP R10 extended pids and ports are compulsory.
-%% From OTP 20 UTF8 atoms are compulsory.
-%% From OTP 21 NEW_FUN_TAGS is compulsory (no more tuple fallback {fun, ...}).
-%% From OTP 23 BIG_CREATION is compulsory.
-%% From OTP 25 NEW_FLOATS, MAP_TAG, EXPORT_PTR_TAG, and BIT_BINARIES are compulsory.
--define(COMPULSORY_DFLAGS,
- (?DFLAG_EXTENDED_REFERENCES bor
- ?DFLAG_FUN_TAGS bor
- ?DFLAG_EXTENDED_PIDS_PORTS bor
- ?DFLAG_UTF8_ATOMS bor
- ?DFLAG_NEW_FUN_TAGS bor
- ?DFLAG_BIG_CREATION bor
- ?DFLAG_NEW_FLOATS bor
- ?DFLAG_MAP_TAG bor
- ?DFLAG_EXPORT_PTR_TAG bor
- ?DFLAG_BIT_BINARIES)).
-
 -define(shutdown(X), exit(X)).
 -define(int16(X), [((X) bsr 8) band 16#ff, (X) band 16#ff]).
 
@@ -451,7 +519,8 @@ recv_status(Socket) ->
 end.
 
 send_challenge(Socket, Node, Challenge, OurVer) ->
- send_challenge(Socket, Node, Challenge, OurVer, ?COMPULSORY_DFLAGS).
+ DefaultFlags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+ send_challenge(Socket, Node, Challenge, OurVer, DefaultFlags).
 
 send_challenge(Socket, Node, Challenge, OurVer, Flags) ->
 if OurVer =:= 5 ->
@@ -484,6 +553,7 @@ recv_challenge(Socket, OurVer) ->
 _Cr3,_Cr2,_Cr1,_Cr0, NL1,NL0 | Rest]} ->
 true = (OurVer >= 6),
 <<Flags:64>> = <<F7,F6,F5,F4,F3,F2,F1,F0>>,
+ verify_flags(Flags),
 Type = flags_to_type(Flags),
 NameLen = ?u16(NL1,NL0),
 {NodeName,_} = lists:split(NameLen, Rest),
@@ -538,14 +608,11 @@ send_challenge_ack(Socket, Digest) ->
 % ?shutdown(bad_challenge_ack)
 % end.
 
-send_name(Socket, MyNode, OurVer, AssumedVer) ->
- Flags = ?COMPULSORY_DFLAGS bor (case OurVer of
- 5 -> 0;
- 6 -> ?DFLAG_HANDSHAKE_23
- end),
- send_name(Socket, MyNode, OurVer, AssumedVer, Flags).
-
-send_name(Socket, MyNode, OurVer, AssumedVer, Flags) ->
+send_name(Socket, MyNode, OurVer, AssumedVer, Flags0) ->
+ Flags = Flags0 bor case OurVer of
+ 5 -> 0;
+ 6 -> ?DFLAG_HANDSHAKE_23
+ end,
 NodeName = atom_to_binary(MyNode, latin1),
 if AssumedVer =:= 5 ->
 ?to_port(Socket, [$n,?int16(OurVer),?int32(Flags),NodeName]);
@@ -563,12 +630,15 @@ recv_name(Socket, OurEpmdVer) ->
 {ok,[$n, V1,V0, F3,F2,F1,F0 | OtherNode]} ->
 5 = OurEpmdVer,
 5 = ?u16(V1,V0),
- Type = flags_to_type(?u32(F3,F2,F1,F0)),
+ Flags = ?u32(F3, F2, F1, F0),
+ verify_flags(Flags),
+ Type = flags_to_type(Flags),
 {Type, list_to_atom(OtherNode)};
 {ok,[$N, F7,F6,F5,F4,F3,F2,F1,F0, _Cr3,_Cr2,_Cr1,_Cr0, NL1, NL0 | Rest]} ->
 true = (OurEpmdVer >= 6),
 {OtherNode, _Residue} = lists:split(?u16(NL1,NL0), Rest),
 <<Flags:64>> = <<F7,F6,F5,F4,F3,F2,F1,F0>>,
+ verify_flags(Flags),
 Type = flags_to_type(Flags),
 {Type, list_to_atom(OtherNode)};
 Res ->
@@ -655,6 +725,16 @@ epmd_register(NodeName, ListenSocket, OurVer) ->
 exit(Other)
 end.
 
+verify_flags(Flags) ->
+ RequiredFlags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+ if
+ Flags band RequiredFlags =:= RequiredFlags ->
+ ok;
+ true ->
+ io:format("Given flags: ~.16.0B\n", [Flags]),
+ io:format("Required flags: ~.16.0B\n", [RequiredFlags]),
+ ct:fail(missing_dflags)
+ end.
 
 %%
 %% Utilities
diff --git a/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractConnection.java b/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractConnection.java
index 6e58794b43..db56478667 100644
--- a/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractConnection.java
+++ b/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractConnection.java
@@ -1283,6 +1283,10 @@ public abstract class AbstractConnection extends Thread {
 throw new IOException("Unknown remote node type");
 }
 
+ if ((apeer.flags & AbstractNode.dFlagMandatory25Digest) != 0) {
+ apeer.flags |= AbstractNode.mandatoryFlags25;
+ }
+
 if ((apeer.flags & AbstractNode.mandatoryFlags) != AbstractNode.mandatoryFlags) {
 throw new IOException(
 "Handshake failed - peer cannot handle all mandatory capabilities");
@@ -1344,6 +1348,10 @@ public abstract class AbstractConnection extends Thread {
 "Handshake failed - peer has wrong name: " + hisname);
 }
 
+ if ((peer.flags & AbstractNode.dFlagMandatory25Digest) != 0) {
+ peer.flags |= AbstractNode.mandatoryFlags25;
+ }
+
 if ((peer.flags & AbstractNode.mandatoryFlags) != AbstractNode.mandatoryFlags) {
 throw new IOException(
 "Handshake failed - peer cannot handle all mandatory capabilities");
diff --git a/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractNode.java b/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractNode.java
index 08bb63db73..13ee63cb42 100644
--- a/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractNode.java
+++ b/lib/jinterface/java_src/com/ericsson/otp/erlang/AbstractNode.java
@@ -95,11 +95,11 @@ public class AbstractNode implements OtpTransportFactory {
 static final int dFlagBigCreation = 0x40000;
 static final int dFlagHandshake23 = 0x1000000;
 static final int dFlagUnlinkId = 0x2000000;
+ static final int dFlagMandatory25Digest = 0x4000000;
 static final long dFlagV4PidsRefs = 0x4L << 32;
 
- /* Mandatory flags for distribution. Keep them in sync with
- DFLAG_DIST_MANDATORY in erts/emulator/beam/dist.h. */
- static final long mandatoryFlags = dFlagExtendedReferences
+ /* Mandatory flags in OTP 25. */
+ static final long mandatoryFlags25 = dFlagExtendedReferences
 | dFlagFunTags
 | dFlagExtendedPidsPorts
 | dFlagUtf8Atoms
@@ -110,6 +110,10 @@ public class AbstractNode implements OtpTransportFactory {
 | dFlagExportPtrTag
 | dFlagBitBinaries;
 
+ /* Mandatory flags for distribution. Keep them in sync with
+ DFLAG_DIST_MANDATORY in erts/emulator/beam/dist.h. */
+ static final long mandatoryFlags = mandatoryFlags25;
+
 int ntype = NTYPE_R6;
 int proto = 0; // tcp/ip
 int distHigh = 6;
@@ -118,7 +122,8 @@ public class AbstractNode implements OtpTransportFactory {
 long flags = mandatoryFlags
 | dFlagHandshake23
 | dFlagUnlinkId
- | dFlagV4PidsRefs;
+ | dFlagV4PidsRefs
+ | dFlagMandatory25Digest;
 
 /* initialize hostname and default cookie */
 static {
diff --git a/lib/kernel/include/dist.hrl b/lib/kernel/include/dist.hrl
index 05beaf9a48..7080b60f2e 100644
--- a/lib/kernel/include/dist.hrl
+++ b/lib/kernel/include/dist.hrl
@@ -22,35 +22,54 @@
 %% Distribution capabilities flags (corresponds with dist.h).
 %%
 
--define(DFLAG_PUBLISHED,1).
--define(DFLAG_ATOM_CACHE,2).
--define(DFLAG_EXTENDED_REFERENCES,4).
--define(DFLAG_DIST_MONITOR,8).
--define(DFLAG_FUN_TAGS,16#10).
--define(DFLAG_DIST_MONITOR_NAME,16#20).
--define(DFLAG_HIDDEN_ATOM_CACHE,16#40).
--define(DFLAG_NEW_FUN_TAGS,16#80).
--define(DFLAG_EXTENDED_PIDS_PORTS,16#100).
--define(DFLAG_EXPORT_PTR_TAG,16#200).
--define(DFLAG_BIT_BINARIES,16#400).
--define(DFLAG_NEW_FLOATS,16#800).
--define(DFLAG_UNICODE_IO,16#1000).
--define(DFLAG_DIST_HDR_ATOM_CACHE,16#2000).
--define(DFLAG_SMALL_ATOM_TAGS, 16#4000).
--define(DFLAG_UTF8_ATOMS, 16#10000).
--define(DFLAG_MAP_TAG, 16#20000).
--define(DFLAG_BIG_CREATION, 16#40000).
--define(DFLAG_SEND_SENDER, 16#80000).
--define(DFLAG_BIG_SEQTRACE_LABELS, 16#100000).
-%% -define(DFLAG_NO_MAGIC, 16#200000). %% Used internally only
--define(DFLAG_EXIT_PAYLOAD, 16#400000).
--define(DFLAG_FRAGMENTS, 16#00800000).
--define(DFLAG_HANDSHAKE_23, 16#01000000).
--define(DFLAG_RESERVED, 16#fe000000).
--define(DFLAG_SPAWN, 16#100000000).
--define(DFLAG_NAME_ME, 16#200000000).
--define(DFLAG_V4_NC, 16#400000000).
--define(DFLAG_ALIAS, 16#800000000).
+-define(DFLAG_PUBLISHED, 16#01).
+-define(DFLAG_ATOM_CACHE, 16#02).
+-define(DFLAG_EXTENDED_REFERENCES, 16#04).
+-define(DFLAG_DIST_MONITOR, 16#08).
+-define(DFLAG_FUN_TAGS, 16#10).
+-define(DFLAG_DIST_MONITOR_NAME, 16#20).
+-define(DFLAG_HIDDEN_ATOM_CACHE, 16#40).
+-define(DFLAG_NEW_FUN_TAGS, 16#80).
+-define(DFLAG_EXTENDED_PIDS_PORTS, 16#100).
+-define(DFLAG_EXPORT_PTR_TAG, 16#200).
+-define(DFLAG_BIT_BINARIES, 16#400).
+-define(DFLAG_NEW_FLOATS, 16#800).
+-define(DFLAG_UNICODE_IO, 16#1000).
+-define(DFLAG_DIST_HDR_ATOM_CACHE, 16#2000).
+-define(DFLAG_SMALL_ATOM_TAGS, 16#4000).
+-define(DFLAG_UTF8_ATOMS, 16#10000).
+-define(DFLAG_MAP_TAG, 16#20000).
+-define(DFLAG_BIG_CREATION, 16#40000).
+-define(DFLAG_SEND_SENDER, 16#80000).
+-define(DFLAG_BIG_SEQTRACE_LABELS, 16#100000).
+%% -define(DFLAG_NO_MAGIC, 16#200000). %% Used internally only
+-define(DFLAG_EXIT_PAYLOAD, 16#400000).
+-define(DFLAG_FRAGMENTS, 16#00800000).
+-define(DFLAG_HANDSHAKE_23, 16#01000000).
+-define(DFLAG_UNLINK_ID, 16#02000000).
+-define(DFLAG_MANDATORY_25_DIGEST, 16#04000000).
+-define(DFLAG_RESERVED, 16#f8000000).
+
+%% Second 32-bit flag word.
+-define(DFLAG_SPAWN, (16#01 bsl 32)).
+-define(DFLAG_NAME_ME, (16#02 bsl 32)).
+-define(DFLAG_V4_NC, (16#04 bsl 32)).
+-define(DFLAG_ALIAS, (16#08 bsl 32)).
+
+%% The following flags are mandatory in OTP 25. OTP 25 and higher
+%% will accept ?DFLAG_MANDATORY_25_DIGEST as a shorthand for all those
+%% flags.
+-define(MANDATORY_DFLAGS_25,
+ (?DFLAG_EXTENDED_REFERENCES bor
+ ?DFLAG_FUN_TAGS bor
+ ?DFLAG_EXTENDED_PIDS_PORTS bor
+ ?DFLAG_NEW_FUN_TAGS bor
+ ?DFLAG_EXPORT_PTR_TAG bor
+ ?DFLAG_BIT_BINARIES bor
+ ?DFLAG_NEW_FLOATS bor
+ ?DFLAG_UTF8_ATOMS bor
+ ?DFLAG_MAP_TAG bor
+ ?DFLAG_BIG_CREATION)).
 
 %% Also update dflag2str() in ../src/dist_util.erl
 %% when adding flags...
@@ -62,3 +81,32 @@
 -define(ERL_DIST_VER_LOW, ?ERL_DIST_VER_5).
 -define(ERL_DIST_VER_HIGH, ?ERL_DIST_VER_6).
 
+%%%
+%%% To avoid having to extend the number of distribution flags from 64
+%%% to 128, a scheme for garbage collection of the flags was
+%%% introduced in OTP 25.
+%%%
+%%% In OTP 25, ?DFLAG_MANDATORY_25_DIGEST was introduced as a synonym
+%%% for the flags defined by ?MANDATORY_DFLAGS_25. OTP 25/26 will
+%%% accept the old flags to support communication with 24 and earlier,
+%%% as well as ?DFLAG_MANDATORY_25_DIGEST.
+%%%
+%%% OTP 27 will make ?DFLAG_MANDATORY_25_DIGEST mandatory, meaning that an
+%%% OTP 27 node can only communicate with OTP 25 and higher.
+%%%
+%%% An OTP 27 node will also introduce the new flag
+%%% ?DFLAG_MANDATORY_27_DIGEST:
+%%%
+%%% * If ?DFLAG_MANDATORY_27_DIGEST is set, it means that all bit
+%%% numbers defined by ?MANDATORY_DFLAGS_25, as well as the bit
+%%% number defined by ?DFLAG_MANDATORY_25_DIGEST and any other bits
+%%% made mandatory in OTP 26/27, lose their previous meanings. New
+%%% meanings can then be assigned to those bit numbers as
+%%% needed. (This is for communication between nodes from OTP 27 and
+%%% up.)
+%%%
+%%% * If ?DFLAG_MANDATORY_27_DIGEST is not set, then
+%%% ?DFLAG_MANDATORY_25_DIGEST must be set and all bit numbers
+%%% defined by ?MANDATORY_DFLAGS_25 are ignored. (This is for
+%%% communication between an OTP 27 node and an OTP 25/26 node.)
+%%%
diff --git a/lib/kernel/src/dist_util.erl b/lib/kernel/src/dist_util.erl
index d8a6371d9c..9d58bf52c6 100644
--- a/lib/kernel/src/dist_util.erl
+++ b/lib/kernel/src/dist_util.erl
@@ -124,6 +124,10 @@ dflag2str(?DFLAG_FRAGMENTS) ->
 "FRAGMENTS";
 dflag2str(?DFLAG_HANDSHAKE_23) ->
 "HANDSHAKE_23";
+dflag2str(?DFLAG_UNLINK_ID) ->
+ "UNLINK_ID";
+dflag2str(?DFLAG_MANDATORY_25_DIGEST) ->
+ "MANDATORY_25_DIGEST";
 dflag2str(?DFLAG_SPAWN) ->
 "SPAWN";
 dflag2str(?DFLAG_NAME_ME) ->
@@ -132,8 +136,8 @@ dflag2str(?DFLAG_V4_NC) ->
 "V4_NC";
 dflag2str(?DFLAG_ALIAS) ->
 "ALIAS";
-dflag2str(_) ->
- "UNKNOWN".
+dflag2str(Other) ->
+ lists:flatten(io_lib:format("UNKNOWN<~.16.0B>", [Other])).
 
 
 adjust_flags(ThisFlags, OtherFlags) ->
@@ -200,7 +204,8 @@ handshake_other_started(#hs_data{request_type=ReqType,
 AddFlgs = convert_flags(AddFlgs0),
 RejFlgs = convert_flags(RejFlgs0),
 ReqFlgs = convert_flags(ReqFlgs0),
- {PreOtherFlags,NodeOrHost,Creation,SendNameVersion} = recv_name(HSData0),
+ {PreOtherFlags0,NodeOrHost,Creation,SendNameVersion} = recv_name(HSData0),
+ PreOtherFlags = expand_mandatory_25_flag(PreOtherFlags0),
 EDF = erts_internal:get_dflags(),
 PreThisFlags = make_this_flags(ReqType, AddFlgs, RejFlgs, NodeOrHost, EDF,
 PreOtherFlags),
@@ -235,6 +240,15 @@ handshake_other_started(#hs_data{request_type=ReqType,
 handshake_other_started(OldHsData) when element(1,OldHsData) =:= hs_data ->
 handshake_other_started(convert_old_hsdata(OldHsData)).
 
+expand_mandatory_25_flag(Flags) ->
+ if
+ Flags band ?DFLAG_MANDATORY_25_DIGEST =/= 0 ->
+ %% From OTP 25, the single flag ?DFLAG_MANDATORY_25_DIGEST can
+ %% replace all the flags in ?MANDATORY_DFLAGS_25.
+ Flags bor ?MANDATORY_DFLAGS_25;
+ true ->
+ Flags
+ end.
 
 %%
 %% Check mandatory flags...
diff --git a/lib/kernel/test/erl_distribution_wb_SUITE.erl b/lib/kernel/test/erl_distribution_wb_SUITE.erl
index ae4794107e..12c8d0afef 100644
--- a/lib/kernel/test/erl_distribution_wb_SUITE.erl
+++ b/lib/kernel/test/erl_distribution_wb_SUITE.erl
@@ -26,7 +26,8 @@
 	 init_per_group/2,end_per_group/2]).
 
 -export([init_per_testcase/2, end_per_testcase/2, whitebox/1, 
-	 switch_options/1, missing_compulsory_dflags/1]).
+	 switch_options/1, missing_compulsory_dflags/1,
+ dflag_mandatory_25/1]).
 
 
 -define(to_port(Socket, Data),
@@ -41,20 +42,21 @@
 -define(DIST_VER_HIGH, 6).
 -define(DIST_VER_LOW, 5).
 
--define(DFLAG_PUBLISHED, 1).
--define(DFLAG_ATOM_CACHE, 2).
--define(DFLAG_EXTENDED_REFERENCES, 4).
--define(DFLAG_DIST_MONITOR, 8).
--define(DFLAG_FUN_TAGS, 16#10).
--define(DFLAG_NEW_FUN_TAGS, 16#80).
--define(DFLAG_EXTENDED_PIDS_PORTS, 16#100).
--define(DFLAG_EXPORT_PTR_TAG, 16#200).
--define(DFLAG_BIT_BINARIES, 16#400).
--define(DFLAG_NEW_FLOATS, 16#800).
--define(DFLAG_UTF8_ATOMS, 16#10000).
--define(DFLAG_MAP_TAG, 16#20000).
--define(DFLAG_BIG_CREATION, 16#40000).
--define(DFLAG_HANDSHAKE_23, 16#1000000).
+-define(DFLAG_PUBLISHED, 16#01).
+-define(DFLAG_ATOM_CACHE, 16#02).
+-define(DFLAG_EXTENDED_REFERENCES, 16#04).
+-define(DFLAG_DIST_MONITOR, 16#08).
+-define(DFLAG_FUN_TAGS, 16#10).
+-define(DFLAG_NEW_FUN_TAGS, 16#80).
+-define(DFLAG_EXTENDED_PIDS_PORTS, 16#100).
+-define(DFLAG_EXPORT_PTR_TAG, 16#200).
+-define(DFLAG_BIT_BINARIES, 16#400).
+-define(DFLAG_NEW_FLOATS, 16#800).
+-define(DFLAG_UTF8_ATOMS, 16#10000).
+-define(DFLAG_MAP_TAG, 16#20000).
+-define(DFLAG_BIG_CREATION, 16#40000).
+-define(DFLAG_HANDSHAKE_23, 16#1000000).
+-define(DFLAG_MANDATORY_25_DIGEST, 16#4000000).
 
 %% From OTP R9 extended references are compulsory.
 %% From OTP R10 extended pids and ports are compulsory.
@@ -98,7 +100,7 @@ suite() ->
 {timetrap,{minutes,1}}].
 
 all() -> 
- [whitebox, switch_options, missing_compulsory_dflags].
+ [whitebox, switch_options, missing_compulsory_dflags, dflag_mandatory_25].
 
 groups() -> 
 [].
@@ -417,6 +419,23 @@ missing_compulsory_dflags(Config) when is_list(Config) ->
 stop_node(Node),
 ok.
 
+%% Test that instead of passing all compulsory flags, we can instead
+%% pass only ?DFLAG_MANDATORY_25_DIGEST to ensure that we will be able to communicate
+%% with a future release where ?DFLAG_MANDATORY_25_DIGEST is mandatory.
+dflag_mandatory_25(_Config) ->
+ [Name1, Name2] = get_nodenames(2, ?FUNCTION_NAME),
+ {ok, Node} = start_node(Name1, ""),
+ {NA,NB} = split(Node),
+ {port,PortNo,_} = erl_epmd:port_please(NA, NB),
+ {ok, SocketA} = gen_tcp:connect(atom_to_list(NB),
+ PortNo,
+ [{active,false},{packet,2}]),
+ OtherNode = list_to_atom(atom_to_list(Name2)++"@"++atom_to_list(NB)),
+ send_name(SocketA, OtherNode, ?DIST_VER_HIGH, ?DIST_VER_HIGH, ?DFLAG_MANDATORY_25_DIGEST),
+ ok = recv_status(SocketA),
+ gen_tcp:close(SocketA),
+ ok.
+
 %%
 %% Here comes the utilities
 %%
@@ -526,7 +545,8 @@ recv_status(Socket) ->
 end.
 
 send_challenge(Socket, Node, Challenge, Version, GotFlags) ->
- send_challenge(Socket, Node, Challenge, Version, GotFlags, ?COMPULSORY_DFLAGS).
+ Flags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+ send_challenge(Socket, Node, Challenge, Version, GotFlags, Flags).
 
 send_challenge(Socket, Node, Challenge, ?DIST_VER_LOW, _GotFlags, Flags) ->
 {ok, {{_Ip1,_Ip2,_Ip3,_Ip4}, _}} = inet:sockname(Socket),
@@ -550,8 +570,8 @@ recv_challenge(Socket, OurVersion) ->
 	{?DIST_VER_LOW,
 [$n,V1,V0,Fl1,Fl2,Fl3,Fl4,CA3,CA2,CA1,CA0 | Ns]} ->
 	 Flags = ?u32(Fl1,Fl2,Fl3,Fl4),
- true = (Flags band ?COMPULSORY_DFLAGS) =:= ?COMPULSORY_DFLAGS,
-	 Node =list_to_atom(Ns),
+ verify_flags(Flags),
+ Node = list_to_atom(Ns),
 	 ?DIST_VER_LOW = ?u16(V1,V0),
 	 Challenge = ?u32(CA3,CA2,CA1,CA0),
 	 {Node,$n,Challenge};
@@ -560,7 +580,7 @@ recv_challenge(Socket, OurVersion) ->
 [$N, F7,F6,F5,F4,F3,F2,F1,F0, CA3,CA2,CA1,CA0,
 Cr3,Cr2,Cr1,Cr0, NL1,NL0 | Ns]} ->
 	 <<Flags:64>> = <<F7,F6,F5,F4,F3,F2,F1,F0>>,
- true = (Flags band ?COMPULSORY_DFLAGS) =:= ?COMPULSORY_DFLAGS,
+ verify_flags(Flags),
 <<Creation:32>> = <<Cr3,Cr2,Cr1,Cr0>>,
 true = (Creation =/= 0),
 <<NameLen:16>> = <<NL1,NL0>>,
@@ -573,6 +593,17 @@ recv_challenge(Socket, OurVersion) ->
 	 ?shutdown(no_node)	 
 end.
 
+verify_flags(Flags) ->
+ RequiredFlags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+ if
+ Flags band RequiredFlags =:= RequiredFlags ->
+ ok;
+ true ->
+ io:format("Given flags: ~.16.0B\n", [Flags]),
+ io:format("Required flags: ~.16.0B\n", [RequiredFlags]),
+ ct:fail(missing_dflags)
+ end.
+
 send_complement(Socket, SentNameMsg, ChallengeMsg, OurVersion) ->
 case {SentNameMsg,ChallengeMsg} of
 {$n,$N} ->
@@ -627,7 +658,8 @@ recv_challenge_ack(Socket, ChallengeB, CookieA) ->
 end.
 
 send_name(Socket, MyNode0, OurVersion, AssumedVersion) ->
- send_name(Socket, MyNode0, OurVersion, AssumedVersion, ?COMPULSORY_DFLAGS).
+ Flags = ?COMPULSORY_DFLAGS bor ?DFLAG_MANDATORY_25_DIGEST,
+ send_name(Socket, MyNode0, OurVersion, AssumedVersion, Flags).
 
 send_name(Socket, MyNode0, OurVersion, AssumedVersion, Flags) ->
 MyNode = atom_to_list(MyNode0),
-- 
2.26.2

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File 1292-Introduce-a-scheme-for-reusing-mandatory-distributio.patch of Package erlang (Revision 6154324f642e084a51ca65b7e728bede)

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