net: ipv4 chosen first when both ipv4 and ipv6 are available #54928
Description
What version of Go are you using (go version)?
$ go version go version go1.19 darwin/amd64
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
go env Output
$ go env GO111MODULE="" GOARCH="amd64" GOBIN="" GOCACHE="/Users/acruz/Library/Caches/go-build" GOENV="/Users/acruz/Library/Application Support/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GOINSECURE="" GOMODCACHE="/Users/acruz/go/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/acruz/go" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/Cellar/go/1.19/libexec" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/Cellar/go/1.19/libexec/pkg/tool/darwin_amd64" GOVCS="" GOVERSION="go1.19" GCCGO="gccgo" GOAMD64="v1" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/dev/null" GOWORK="" CGO_CFLAGS="-g -O2" CGO_CPPFLAGS="" CGO_CXXFLAGS="-g -O2" CGO_FFLAGS="-g -O2" CGO_LDFLAGS="-g -O2" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/50/p3qbm6c112v0sdym26_t_bq80000gn/T/go-build466847973=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
Connect to a host that resolves both to ipv4 and ipv6 addresses.
What did you expect to see?
According to https://github.com/golang/go/blob/master/src/net/dial.go#L71, with the default FallbackDelay of 300ms, ipv6 should be tried first and only after the configured delay ipv4 should be attempted.
What did you see instead?
ipv4 was chosen first.
The partition function uses the label of the first result, which is the DNS result that resolved first (A vs AAAA). If the A response was received first, then the primary address(es) will be ipv4, which contradicts the purpose of the Happy Eyeballs RFC.