Handle tcp self connection issues

[jamesdillonharvey]

Issue

Fixes : #4588

If a zeromq socket attempts connection/reconnection to an ephemeral port on the same host that is not yet active (or recovering from being down), as it cycles through ephemeral ports (for src port) it may attempt reconnection to itself (src/dst ip/port match), the result is a failed connection protocol_error and no further connection attempts.

A good explanation of "tcp self connection" can be found here: https://totozhang.github.io/2016-01-11-tcp-self-connection/

Fix

When a protocol_error occurs, check to see if the src and dst clash. If they do allow the connection to FIN and carry on reconnecting on the next ephemeral port the OS picks.

Test

I cant think of a good way to add a automatic test as the issue is very random (OS randomizes port selection for src). To force the test locally I restrict the ephemeral range.

Manual tests

before change

09:57:53.937767 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40466: Flags [R.], seq 0, ack 108455980, win 0, length 0
09:57:54.127068 lo    In  IP 127.0.0.1.40470 > 127.0.0.1.40500: Flags [S], seq 2565083455, win 65495, options [mss 65495,sackOK,TS val 62504126 ecr 0,nop,wscale 7], length 0
09:57:54.127071 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40470: Flags [R.], seq 0, ack 231392135, win 0, length 0
09:57:54.324383 lo    In  IP 127.0.0.1.40474 > 127.0.0.1.40500: Flags [S], seq 3013252083, win 65495, options [mss 65495,sackOK,TS val 62504323 ecr 0,nop,wscale 7], length 0
09:57:54.324388 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40474: Flags [R.], seq 0, ack 3013252084, win 0, length 0
09:57:54.476636 lo    In  IP 127.0.0.1.40490 > 127.0.0.1.40500: Flags [S], seq 347750353, win 65495, options [mss 65495,sackOK,TS val 62504475 ecr 0,nop,wscale 7], length 0
09:57:54.476640 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40490: Flags [R.], seq 0, ack 347750354, win 0, length 0
09:57:54.667949 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [S], seq 326616065, win 65483, options [mss 65495,sackOK,TS val 62504667 ecr 62481315,nop,wscale 7], length 0
09:57:54.667958 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [S.], seq 326616065, ack 326616066, win 65483, options [mss 65495,sackOK,TS val 62504667 ecr 62504667,nop,wscale 7], length 0
09:57:54.667961 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 1, win 512, options [nop,nop,TS val 62504667 ecr 62504667], length 0
09:57:54.668047 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 1:11, ack 1, win 512, options [nop,nop,TS val 62504667 ecr 62504667], length 10
09:57:54.668051 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 11, win 512, options [nop,nop,TS val 62504667 ecr 62504667], length 0
09:57:54.668060 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 11:12, ack 11, win 512, options [nop,nop,TS val 62504667 ecr 62504667], length 1
09:57:54.668068 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 12:65, ack 12, win 512, options [nop,nop,TS val 62504667 ecr 62504667], length 53
09:57:54.668087 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 65:92, ack 65, win 512, options [nop,nop,TS val 62504667 ecr 62504667], length 27
09:57:54.708963 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 92, win 512, options [nop,nop,TS val 62504708 ecr 62504667], length 0
END - no more reconnects

after change

10:13:57.698649 lo    In  IP 127.0.0.1.40468 > 127.0.0.1.40500: Flags [S], seq 2285633953, win 65495, options [mss 65495,sackOK,TS val 63467697 ecr 0,nop,wscale 7], length 0
10:13:57.698654 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40468: Flags [R.], seq 0, ack 2285633954, win 0, length 0
10:13:57.835886 lo    In  IP 127.0.0.1.40472 > 127.0.0.1.40500: Flags [S], seq 3740063029, win 65495, options [mss 65495,sackOK,TS val 63467835 ecr 0,nop,wscale 7], length 0
10:13:57.835892 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40472: Flags [R.], seq 0, ack 1078652377, win 0, length 0
10:13:57.966115 lo    In  IP 127.0.0.1.40482 > 127.0.0.1.40500: Flags [S], seq 1019657631, win 65495, options [mss 65495,sackOK,TS val 63467965 ecr 0,nop,wscale 7], length 0
10:13:57.966121 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40482: Flags [R.], seq 0, ack 1068807057, win 0, length 0
10:13:58.124384 lo    In  IP 127.0.0.1.40498 > 127.0.0.1.40500: Flags [S], seq 3452255652, win 65495, options [mss 65495,sackOK,TS val 63468123 ecr 0,nop,wscale 7], length 0
10:13:58.124389 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40498: Flags [R.], seq 0, ack 1069119880, win 0, length 0
10:13:58.260628 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [S], seq 3386550211, win 65495, options [mss 65495,sackOK,TS val 63468259 ecr 0,nop,wscale 7], length 0
10:13:58.260636 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [S.], seq 3386550211, ack 3386550212, win 65495, options [mss 65495,sackOK,TS val 63468259 ecr 63468259,nop,wscale 7], length 0
10:13:58.260639 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 1, win 512, options [nop,nop,TS val 63468259 ecr 63468259], length 0
10:13:58.260812 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 1:11, ack 1, win 512, options [nop,nop,TS val 63468259 ecr 63468259], length 10
10:13:58.260815 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 11, win 512, options [nop,nop,TS val 63468259 ecr 63468259], length 0
10:13:58.260827 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 11:12, ack 11, win 512, options [nop,nop,TS val 63468259 ecr 63468259], length 1
10:13:58.260835 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 12:65, ack 12, win 512, options [nop,nop,TS val 63468259 ecr 63468259], length 53
10:13:58.260885 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [P.], seq 65:92, ack 65, win 512, options [nop,nop,TS val 63468260 ecr 63468259], length 27
10:13:58.300970 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 92, win 512, options [nop,nop,TS val 63468300 ecr 63468260], length 0
10:14:28.291074 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [F.], seq 92, ack 92, win 512, options [nop,nop,TS val 63498290 ecr 63468300], length 0
10:14:28.291085 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40500: Flags [.], ack 93, win 512, options [nop,nop,TS val 63498290 ecr 63498290], length 0
10:14:28.406352 lo    In  IP 127.0.0.1.40558 > 127.0.0.1.40500: Flags [S], seq 1355520654, win 65495, options [mss 65495,sackOK,TS val 63498405 ecr 0,nop,wscale 7], length 0
10:14:28.406359 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40558: Flags [R.], seq 0, ack 688771957, win 0, length 0
10:14:28.591664 lo    In  IP 127.0.0.1.40568 > 127.0.0.1.40500: Flags [S], seq 325944154, win 65495, options [mss 65495,sackOK,TS val 63498590 ecr 0,nop,wscale 7], length 0
10:14:28.591670 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40568: Flags [R.], seq 0, ack 1029202136, win 0, length 0
10:14:28.699875 lo    In  IP 127.0.0.1.40570 > 127.0.0.1.40500: Flags [S], seq 230932052, win 65495, options [mss 65495,sackOK,TS val 63498698 ecr 0,nop,wscale 7], length 0
10:14:28.699880 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40570: Flags [R.], seq 0, ack 1238378028, win 0, length 0
10:14:28.883186 lo    In  IP 127.0.0.1.40582 > 127.0.0.1.40500: Flags [S], seq 1648067009, win 65495, options [mss 65495,sackOK,TS val 63498882 ecr 0,nop,wscale 7], length 0
10:14:28.883191 lo    In  IP 127.0.0.1.40500 > 127.0.0.1.40582: Flags [R.], seq 0, ack 1648067010, win 0, length 0
10:14:28.988414 lo    In  IP 127.0.0.1.40586 > 127.0.0.1.40500: Flags [S], seq 1410782548, win 65495, options [mss 65495,sackOK,TS val 63498987 ecr 0,nop,wscale 7], length 0

[bluca]

This needs to be fixed: https://github.com/zeromq/libzmq/actions/runs/6468544183/job/17560783020?pr=4599

[jamesdillonharvey]

This needs to be fixed: https://github.com/zeromq/libzmq/actions/runs/6468544183/job/17560783020?pr=4599

I fixed the clang-format issue but the fuzzers are failing with
clang-15: error: no such file or directory: './external/unity/libunity.a'