net: DNS resolver use both A and AAAA queries if only tcp4 network use

[VovkoO]

Go version

go1.23.4

Output of go env in your module/workspace:

GO111MODULE='on'
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/vladimir/Library/Caches/go-build'
GOENV='/Users/vladimir/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/vladimir/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/vladimir/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/vladimir/go/go1.23.4'
GOSUMDB='off'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/vladimir/go/go1.23.4/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.4'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/vladimir/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/vladimir/go/src/tests/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/81/t0n_z8cd16q83h4w7fg9ml9r0000gp/T/go-build2923957466=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Hello, I'm trying to get dns resolver in grpc to use only A queries, instead of using both A and AAAA. It use method LookupHost from dns resolver:
https://github.com/golang/go/blob/master/src/net/lookup_unix.go#L55
Which uses either "cgoLookupHost" or "goLookupHostOrder" method, depending on the chosen resolver. But in both of them, the use of "ip" in the network argument is hardcoded, which leads to the use of both ipv4 and ip6 as I understand it.
So, Is this behavior correct and can it be used only "A" dns queries?

What did you see happen?

Both A and AAAA dns queries use.

What did you expect to see?

Only A dns queries use if tcp4 usage is explicitly specified

[mateusz834]

You can try Resolver.LookupNetIP, there you can pass the network as a parameter. Not sure whether there is anything that we can do here.

[seankhliao]

I think it's up to the caller to provide an appropriate Dial function to Resolver.

[ianlancetaylor]

I'm not sure that's right. See #45024.

[mateusz834]

@ianlancetaylor can you explain further? 53dd0d7

[seankhliao]

#45024 makes Dial aware of the network, but this report sounds like grpc's equivalent of Dial indiscriminately uses LookupHost without passing any way of letting Resolver know what network it should restrict the results to.

[mknyszek]

CC @neild

[ianlancetaylor]

@mateusz834 What I mean is: the described behavior sounds like something we have fixed in the past. I don't know if there is a real bug here.

[gabyhelp]

Related Issues

• net: AAAA DNS queries are made despite ip4 on LookupIP #44809 (closed)
• net: make go resolver aware of network parameter #45016 (closed)
• net/http: Client.Do blocks on DNS AAAA record until timeout even after A record succeeds #57697 (closed)
• net: ipv4 chosen first when ipv6 is available #68795
• net: builtin DNS stub resolver returns query results including the second best records unconditionally #11081 (closed)
• net: Resolver doesn't use provided Dial function in all cases #60712
• net: LookupNetIP returns IPv4 in IPv6 instead of IPv4 #53554 (closed)
• net: ipv4 chosen first when both ipv4 and ipv6 are available #54928 (closed)
• net: Error when running concurrent DNS queries using cgo on MacOS #30521 (closed)

Related Code Changes

• net: make go resolver aware of network parameter

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[mateusz834]

The bug report mentions LookupHost, which does not accept the the network parameter, thus i think that this behaviour is fine.

@VovkoO

I don`t understand this:

Only A dns queries use if tcp4 usage is explicitly specified

Where the "tcp4" is explicitly specified? You mention that it uses LookupHost, which uses "ip".

[VovkoO]

I think I misunderstood something last time. I assumed that if I created an GRPC connection with a custom dialer that explicitly specified the use of tcp4, then the DNS resolver would also take this information into account.

conn, err := grpc.DialContext(ctx, "",
    grpc.WithContextDialer(func(ctx context.Context, addr string) (net.Conn, error) {
    return (&net.Dialer{}).DialContext(ctx, "tcp4", addr)
    }),
)

But it looks like these are two independent parts and grpc resolver always use LookupHost.
https://github.com/grpc/grpc-go/blob/master/internal/resolver/dns/dns_resolver.go#L319

[seankhliao]

yes grpc has its own pluggable resolver setup

[seankhliao]

I'm going to close this as it's a gRPC issue, see https://grpc.io/docs/guides/custom-name-resolution/

[ianlancetaylor]

Thanks.

[VovkoO]

Ok, thanks