Connection fails with "flush: Address family not supported by protocol"

[edubart]

Running the example simple.get I get the following error:

luajit: simple.get:47: cqueue: simple.get:18: socket:flush: Address family not supported by protocol
stack traceback:
	[C]: in function 'error'
	lala.lua:47: in main chunk
	[C]: at 0x00405b50

I am unable to connect to anything because of this.

My OS:

$ uname -a
Linux archlinux 4.11.3-1-ARCH #1 SMP PREEMPT Sun May 28 10:40:17 CEST 2017 x86_64 GNU/Linux
$ ldd --version
ldd (GNU libc) 2.25
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.

[edubart]

Running strace I've found:

recvfrom(3, "d\301\201\200\0\1\0\1\0\0\0\0\7example\3com\0\0\1\0\1\300\f\0"..., 768, 0, NULL, NULL) = 45
socket(AF_UNSPEC, SOCK_STREAM|SOCK_CLOEXEC, 0) = -1 EAFNOSUPPORT (Address family not supported by protocol)

The code line socket(AF_UNSPEC, SOCK_STREAM|SOCK_CLOEXEC, 0) does not work in my system, simple test case in C:

#include <sys/socket.h>
#include <stdio.h>
#include <string.h>

int main() {
    printf("%d", socket(AF_UNSPEC, SOCK_STREAM|SOCK_CLOEXEC, 0));
    perror("socket error");
    return 0;
}

Output:

$ gcc test.c -o test && ./test
socket error: Address family not supported by protocol
-1

[jdesgats]

Had the exact same issue with Arch, the most confusiong thing was that my debug build using my own fork of cqueues were still working.
I eventually tracked this down to the default compilation flags in Luarocsk: it copiles with -O2 by default, overriding this with -O0 produces a working binary.

$ LC_ALL=C gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc-multilib/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release
Thread model: posix
gcc version 7.1.1 20170528 (GCC) 

$ make clean && rm -fr /tmp/test && make install5.3 prefix=/tmp/test CFLAGS=-O2
...
$ LUA_PATH='/tmp/test/share/lua/5.3/?.lua;;' LUA_CPATH='/tmp/test/lib/lua/5.3/?.so' strace -e network lua -e 's=require("cqueues.socket"); print(s.listen("127.0.0.1", 4000):accept())'
socket(AF_UNSPEC, SOCK_STREAM|SOCK_CLOEXEC, 0) = -1 EAFNOSUPPORT (Address family not supported by protocol)
lua: (command line):1: socket:accept: Address family not supported by protocol
stack traceback:
	[C]: in function 'error'
	/tmp/test/share/lua/5.3/cqueues/socket.lua:90: in function </tmp/test/share/lua/5.3/cqueues/socket.lua:75>
	(...tail calls...)
	/tmp/test/share/lua/5.3/cqueues/socket.lua:231: in method 'accept'
	(command line):1: in main chunk
	[C]: in ?
+++ exited with 1 +++

$ make clean && rm -fr /tmp/test && make install5.3 prefix=/tmp/test CFLAGS=-O0
...
$ LUA_PATH='/tmp/test/share/lua/5.3/?.lua;;' LUA_CPATH='/tmp/test/lib/lua/5.3/?.so' strace -e network lua -e 's=require("cqueues.socket"); print(s.listen("127.0.0.1", 4000):accept())'
socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_IP) = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(3, SOL_SOCKET, SO_REUSEPORT, [0], 4) = 0
setsockopt(3, SOL_TCP, TCP_NODELAY, [0], 4) = 0
setsockopt(3, SOL_TCP, TCP_CORK, [0], 4) = 0
setsockopt(3, SOL_SOCKET, SO_OOBINLINE, [0], 4) = 0
getsockopt(3, SOL_SOCKET, SO_DOMAIN, [2], [4]) = 0
getsockopt(3, SOL_SOCKET, SO_TYPE, [1], [4]) = 0
getsockopt(3, SOL_SOCKET, SO_PROTOCOL, [6], [4]) = 0
getsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], [4]) = 0
getsockopt(3, SOL_SOCKET, SO_REUSEPORT, [0], [4]) = 0
getsockopt(3, SOL_SOCKET, SO_BROADCAST, [0], [4]) = 0
getsockopt(3, SOL_TCP, TCP_NODELAY, [0], [4]) = 0
getsockopt(3, SOL_TCP, TCP_CORK, [0], [4]) = 0
getsockopt(3, SOL_IPV6, IPV6_V6ONLY, 0x7ffd277da918, 0x7ffd277da91c) = -1 EOPNOTSUPP (Operation not supported)
getsockopt(3, SOL_SOCKET, SO_OOBINLINE, [0], [4]) = 0
bind(3, {sa_family=AF_INET, sin_port=htons(4000), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
listen(3, 128)                          = 0
accept4(3, NULL, NULL, SOCK_CLOEXEC)    = -1 EAGAIN (Resource temporarily unavailable)

Rolling back to gcc 6.3.1 (the only previous version in have in my package cache) or compiling with clang both produces a working binary. Not sure yet if it is a compiler bug or an undefined behaviour lying somewhere that GCC now optimizes differently.

[daurnimator]

@jdesgats ah ha! thankyou for discovering that. I've managed to replicate locally now.

The issue seems to be around dns_ai_setent and the aliasing via saddr. Using -fno-strict-aliasing doesn't seem to fix anything :(

[daurnimator]

This issue affects anyone using GCC 7, which is becoming more and more common @wahern could you please look at my proposed fix in #187?

[hoelzro]

I just ran into this myself - is the recommendation to install the code under #187 to get things working again until there's a release?

[daurnimator]

Yes. I've gotten permission (via email) from wahern to merge and make a release myself. Just haven't had time yet. I also wanted to fix compiling with luajit 2.1 beta, the best route to which was bringing in lua-compat-5.3, however I need @siffiejoe to cut a release there (as I need some of the code on their master) -> but I think that's blocked on lunarmodules/lua-compat-5.3#36