Hi Rich,

Thanks for your time. The EADDRINUSE is in reality an EAGAIN, this is a
glitch in the Emscripten/WASI modification for musl (there are different
values for errnos per implementation):
__WASI_ERRNO_ADDRINUSE == -3 == EAI_AGAIN.

My question currently breaks down to: Is it common for this implementation
of getaddrinfo to return EAGAIN sometimes (I experience 1:100), even if
answers from DNS servers came in?
If not, I need to investigate much further. I really could not find issues
with my sockets implementation, although your thought is of course very
reasonable.

Regards
S.


Am Mi., 1. Juni 2022 um 16:14 Uhr schrieb Rich Felker <dalias@libc.org>:

> On Tue, May 31, 2022 at 12:24:19PM +0200, Sascha Braun wrote:
> > Hi everyone,
> >
> > I'm implementing a socket protocol with similar works to Emscripten - ok:
> >
> > Here's what I noticed
> >
> > - resolv.conf using multiple DNS servers
> > options timeout:22 attempts:5
> > nameserver 8.8.4.4
> > nameserver 208.67.222.222
> > nameserver 9.9.9.9
> > nameserver 1.1.1.1
> >
> > - getaddrinfo with no hints, so that IPV6 and IPV4 is resolved
> > void socketstest1_client_dnsonly(void) {
> >
> > struct addrinfo hints, * res;
> > memset(&hints, 0, sizeof(hints));
> > printf("begin lookup1...\n");
> > if (getaddrinfo("www.web.de", "80", &hints, &res) != 0) {
> > perror("getaddrinfo1");
> > }
> > printf("begin lookup2...\n");
> > if (getaddrinfo("www.google.de", "80", &hints, &res) != 0) {
> > perror("getaddrinfo2");
> > }
> > printf("begin lookup3...\n");
> > if (getaddrinfo("www.google.com", "80", &hints, &res) != 0) {
> > perror("getaddrinfo3");
> > }
> >
> > }
> >
> > When repeating socketstest1_client_dnsonly often, it appears that IPV6
> > answers for IPV4 requests to another server [or vice-versa] responses can
> > get mixed up and getaddrinfo reports sometimes only an error where none
> is.
> >
> > Below is a console dump of my test where you see the critical situation
> > (end)
> > 8.8.4.4:53 was queried, 9.9.9.9:53 responded for a (different IP Proto),
> > resulting in error getaddrinfo1: Address in use
> >
> > This happens in about 1/100 tests. When you specify IPV4 or IPV6 in
> hints,
> > this issue does NOT show up.
>
> Can you provide more information on how to interpret the console dump,
> and in particular, which of your syscalls is returning the EADDRINUSE
> error? I'm pretty sure this is just a bug in your socket
> stack/emulation. It looks like it's coming from recvfrom, and
> EADDRINUSE is not a valid error for recvfrom to produce.
>
> Rich
>