Failure to connect on mDNS hostnames which resolve to an IPv6 link local address

[bartelsielski]

I did this

This issue, which was previously reported in #21669, is still present. The commit which "fixes" the issue contains the following note:

     * NOTE: On multi-homed hosts with several interfaces having
     * link-local addresses, this picks the first one found, which
     * may not be the correct outgoing interface. */

This is the issue I see now when I run curl -v .... The scope_id which curl uses is not the correct one.

I expected the following

No response

curl/libcurl version

curl 8.21.0 (upstream Arch Linux package version 8.21.0-1)

operating system

Arch Linux

[bagder]

Duplicate? Doesn't the fix in #21728 (present in git) work for you?

[bagder]

Or perhaps: how can we figure out the correct one?

[bartelsielski]

No, the current solution doesn't work in all cases, as noted in the comment in the code. The scope_id is set incorrectly on my machine because I use multiple network interfaces.

Regarding to how this should be fixed? Don't split the DNS resolution into a separate A and AAAA query but to just keep them as a single call to getaddrinfo. Or do the call to glibc's getaddrinfo with the hints.ai_family field set to AF_UNSPEC when trying to resolve an IPv6 address and then filter out the IPv4 addresses it returns.

This has been a known issue in glibc since 2012 BTW (https://sourceware.org/bugzilla/show_bug.cgi?id=14413).

[bagder]

Don't split the DNS resolution into a separate A and AAAA query but to just keep them as a single call to getaddrinfo.

What a strange limitation.

That's a rather high price to pay to work around a glibc bug for just a few users. We do the resolves separately so that we don't need to wait for the slowest of those results...

[icing]

@bartelsielski could you check if #22368 solves the issue for you? Thanks.

[bartelsielski]

That works. Thanks.