possible libuv issue with macos 10.15: empty udp message not registering

Version:
v12.12.0
Platform:
macos catalina/10.15 (19A602)
Subsystem:
n/a

When sending an empty udp message, the message will not be received until another non-empty udp message is received.

Example/Reproduce: (may only affect macos 10.15?)

file server.js

var PORT = 33333;
var HOST = '127.0.0.1';

var dgram = require('dgram');
var server = dgram.createSocket('udp4');

server.on('listening', function() {
  var address = server.address();
 console.log('UDP Server listening on ' + address.address + ':' + address.port);
});

server.on('message', function(message, remote) {
 console.log(remote.address + ':' + remote.port +' - ' + message);
});

server.bind(PORT, HOST);

file client_test.js

var PORT = 33333;
var HOST = '127.0.0.1';

var dgram = require('dgram');


var client = dgram.createSocket('udp4');
var message = Buffer.from('abc');

client.send(message, 0, message.length, PORT, HOST, function(err, bytes) {
  if (err) throw err;
  console.log('UDP message sent to ' + HOST +':'+ PORT);
  client.close();
});

file client_0.js

var PORT = 33333;
var HOST = '127.0.0.1';

var dgram = require('dgram');


var client = dgram.createSocket('udp4');
var message = Buffer.from('');

client.send(message, 0, message.length, PORT, HOST, function(err, bytes) {
  if (err) throw err;
  console.log('UDP message sent to ' + HOST +':'+ PORT);
  client.close();
});

run the server code, then run the client_0.js: no response in server.
followed by running client_test.js: server got empty and the "abc" message.

Does this also happen with Node 12.11.1?

@addaleax

@addaleax Yes, just tried with the binary using https://nodejs.org/dist/v12.11.1/

@daviehh

/cc @nodejs/platform-macos

@daviehh Have you tried recreating this with e.g. Python? I’m not on a mac but I have the suspicion that this may actually be just a platform quirk of macOS that we can’t do anything about.

@addaleax

@addaleax I have actually tried Python, empty udp message works there:

receiving:

import socket

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(("127.0.0.1", 6000))

while True:
    data, addr = sock.recvfrom(1024)
    print("received message:", data)

sending:

import socket

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(b"", ("127.0.0.1", 6000))

It seems our test suite also fails due to this on macOS Catalina.

=== release test-dgram-connect-send-empty-buffer ===                          
Path: parallel/test-dgram-connect-send-empty-buffer
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-dgram-connect-send-empty-buffer.js
--- TIMEOUT ---
=== release test-dgram-connect-send-empty-array ===        
Path: parallel/test-dgram-connect-send-empty-array
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-dgram-connect-send-empty-array.js
--- TIMEOUT ---
=== release test-dgram-connect-send-empty-packet ===       
Path: parallel/test-dgram-connect-send-empty-packet
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-dgram-connect-send-empty-packet.js
--- TIMEOUT ---
=== release test-dgram-send-empty-array ===                
Path: parallel/test-dgram-send-empty-array
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-dgram-send-empty-array.js
--- TIMEOUT ---
=== release test-dgram-send-empty-buffer ===               
Path: parallel/test-dgram-send-empty-buffer
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-dgram-send-empty-buffer.js
--- TIMEOUT ---
=== release test-dgram-send-empty-packet ===
Path: parallel/test-dgram-send-empty-packet
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-dgram-send-empty-packet.js
--- TIMEOUT ---
[03:46|% 100|+ 2791|-   6]: Done

Thanks! I first noticed this issue with a beta version of another language that uses libuv (julia), so it's likely that it's a libuv bug; is it good for the bug report to be here or is it better to report to libuv? Not sure how to write a simple c code that directly uses libuv to reproduce the issue though.

Yeah, I've reproduced the issue in libuv. Apparently the message is actually sent (I've checked it with tcpdump) but not received.

It looks like a problem with kqueue not reporting the event. The python example does not seem to apply to our case as it's waiting on recvfrom syscall.

@nodejs/libuv Has anybody reported this to Apple yet? I’m assuming that that’s the thing to do here, no?

Yes... except sending a bug report to Apple is like throwing matter into a black hole: it disappears and is never seen again.

I have a channel to get some additional information from Apple given the bug report number. Has anyone reported it?

Oh... I just realized that I might have reported this in 2014 and provided a fix. Here is a repo (by other person) that reproduces the issue using outdated libuv version: https://github.com/misterdjules/udp-empty-dgram-repro

Apple has told me that they have identified a fix and will ship it in a future OS update, but have not provided any further details than that.

@Keno

@Keno At least that something, thanks for letting us know!

#22546 (Can only find the PR to remove the skip)

The skip is very old and was added in the old repository (see #30030 (comment)).

test: mark empty udp tests flaky on OS X

I'm seeing multiple instances of our test suite not respecting the mark of flaky in these tests, any idea what's up?

https://ci.nodejs.org/job/node-test-commit-osx/32536/#showFailuresLink

nvm failure is due to test-timers-blocking-callback

test: mark empty udp tests flaky on OS X

The issue seems to be fixed in macOS 10.15.4

Other discussion: nodejs/node#30030

Add UDP test using sending empty data

Add UDP test sending empty data

Closing as based on the comments this is fixed, and the tests are no longer skipped in CI on macOS.

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possible libuv issue with macos 10.15: empty udp message not registering #30030

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possible libuv issue with macos 10.15: empty udp message not registering #30030

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addaleax commented on Oct 18, 2019

daviehh commented on Oct 18, 2019

addaleax commented on Oct 18, 2019

daviehh commented on Oct 18, 2019

lpinca commented on Oct 20, 2019

daviehh commented on Oct 20, 2019

santigimeno commented on Oct 20, 2019

santigimeno commented on Oct 20, 2019

addaleax commented on Dec 15, 2019

bnoordhuis commented on Dec 16, 2019

indutny commented on Dec 17, 2019

indutny commented on Dec 17, 2019

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Keno commented on Mar 4, 2020

AshCripps commented on Mar 4, 2020

richardlau commented on Mar 4, 2020

MylesBorins commented on Mar 11, 2020

lpinca commented on Mar 25, 2020

BethGriggs commented on Nov 17, 2021

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