net: force cgo for myhostname and mdns nss modules for LookupAddr on unix #59921
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This PR (HEAD: d83d39b) has been imported to Gerrit for code review. Please visit https://go-review.googlesource.com/c/go/+/491235 to see it. Tip: You can toggle comments from me using the |
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…unix
Currently there is a small bug in the LookupAddr for unix systems
that causes the use of go resolver instead of the cgo one.
Example for nss myhostname:
func main() {
fmt.Println(net.LookupAddr(os.Args[1]))
}
root@arch:~# cat /etc/nsswitch.conf | grep host
hosts: myhostname dns
root@arch:~# GODEBUG=netdns=+3 go run main.go 192.168.1.200
go package net: confVal.netCgo = false netGo = false
go package net: dynamic selection of DNS resolver
go package net: hostLookupOrder() = dns
[] lookup 200.1.168.192.in-addr.arpa. on 8.8.8.8:53: no such host
root@arch:~# GODEBUG=netdns=go+3 go run main.go 192.168.1.200
go package net: confVal.netCgo = false netGo = true
go package net: GODEBUG setting forcing use of Go's resolver
go package net: hostLookupOrder() = dns
[] lookup 200.1.168.192.in-addr.arpa. on 8.8.8.8:53: no such host
root@arch:~# GODEBUG=netdns=cgo+3 go run main.go 192.168.1.200
go package net: confVal.netCgo = true netGo = false
go package net: using cgo DNS resolver
go package net: hostLookupOrder() = cgo
[arch] <nil>
The problem come from that we are only checking for hostnames that the
myhostname can resolve, but not for the addrs that it can also.
man nss-myhostname:
Please keep in mind that nss-myhostname (and nss-resolve) also
resolve in the other direction — from locally attached IP
addresses to hostnames.
Change-Id: Ic18a9f99a2214b2938463e9a95f7f3ca5db1c01b
GitHub-Last-Rev: ade40fd
GitHub-Pull-Request: #59921
Reviewed-on: https://go-review.googlesource.com/c/go/+/491235
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Run-TryBot: Mateusz Poliwczak <[email protected]>
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Message from Cherry Mui: Patch Set 3: Code-Review+1 Please don’t reply on this GitHub thread. Visit golang.org/cl/491235. |
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This PR is being closed because golang.org/cl/491235 has been merged. |
Currently there is a small bug in the LookupAddr for unix systems
that causes the use of go resolver instead of the cgo one.
Example for nss myhostname:
func main() {
fmt.Println(net.LookupAddr(os.Args[1]))
}
root@arch:
# cat /etc/nsswitch.conf | grep host# GODEBUG=netdns=+3 go run main.go 192.168.1.200hosts: myhostname dns
root@arch:
go package net: confVal.netCgo = false netGo = false
go package net: dynamic selection of DNS resolver
go package net: hostLookupOrder() = dns
[] lookup 200.1.168.192.in-addr.arpa. on 8.8.8.8:53: no such host
root@arch:
# GODEBUG=netdns=go+3 go run main.go 192.168.1.200# GODEBUG=netdns=cgo+3 go run main.go 192.168.1.200go package net: confVal.netCgo = false netGo = true
go package net: GODEBUG setting forcing use of Go's resolver
go package net: hostLookupOrder() = dns
[] lookup 200.1.168.192.in-addr.arpa. on 8.8.8.8:53: no such host
root@arch:
go package net: confVal.netCgo = true netGo = false
go package net: using cgo DNS resolver
go package net: hostLookupOrder() = cgo
[arch]
The problem come from that we are only checking for hostnames that the
myhostname can resolve, but not for the addrs that it can also.
man nss-myhostname:
Please keep in mind that nss-myhostname (and nss-resolve) also
resolve in the other direction — from locally attached IP
addresses to hostnames.