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net: don't force cgo resolver for .local subdomain queries #63986

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net: don't force cgo resolver for .local subdomain queries #63986

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b535e18
net: don't force cgo resolver for .local subdomain queries
mateusz834 Nov 7, 2023
8e98e31
update docs
mateusz834 Nov 7, 2023
e2bc587
update
mateusz834 Feb 20, 2024
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17 changes: 7 additions & 10 deletions src/net/conf.go
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Original file line number Diff line number Diff line change
Expand Up @@ -338,13 +338,6 @@ func (c *conf) lookupOrder(r *Resolver, hostname string) (ret hostLookupOrder, d
if stringsHasSuffix(hostname, ".") {
hostname = hostname[:len(hostname)-1]
}
if canUseCgo && stringsHasSuffixFold(hostname, ".local") {
// Per RFC 6762, the ".local" TLD is special. And
// because Go's native resolver doesn't do mDNS or
// similar local resolution mechanisms, assume that
// libc might (via Avahi, etc) and use cgo.
return hostLookupCgo, dnsConf
}

nss := getSystemNSS()
srcs := nss.sources["hosts"]
Expand Down Expand Up @@ -404,9 +397,13 @@ func (c *conf) lookupOrder(r *Resolver, hostname string) (ret hostLookupOrder, d
}
continue
case hostname != "" && stringsHasPrefix(src.source, "mdns"):
// e.g. "mdns4", "mdns4_minimal"
// We already returned true before if it was *.local.
// libc wouldn't have found a hit on this anyway.
if stringsHasSuffixFold(hostname, ".local") {
// Per RFC 6762, the ".local" TLD is special. And
// because Go's native resolver doesn't do mDNS or
// similar local resolution mechanisms, assume that
// libc might (via Avahi, etc) and use cgo.
return hostLookupCgo, dnsConf
}

// We don't parse mdns.allow files. They're rare. If one
// exists, it might list other TLDs (besides .local) or even
Expand Down
4 changes: 2 additions & 2 deletions src/net/conf_test.go
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Expand Up @@ -257,7 +257,7 @@ func TestConfHostLookupOrder(t *testing.T) {
hostTests: []nssHostTest{
{"x.com", "myhostname", hostLookupFilesDNS},
{"x", "myhostname", hostLookupFilesDNS},
{"x.local", "myhostname", hostLookupCgo},
{"x.local", "myhostname", hostLookupFilesDNS},
},
},
{
Expand All @@ -268,7 +268,7 @@ func TestConfHostLookupOrder(t *testing.T) {
hostTests: []nssHostTest{
{"x.com", "myhostname", hostLookupDNSFiles},
{"x", "myhostname", hostLookupDNSFiles},
{"x.local", "myhostname", hostLookupCgo},
{"x.local", "myhostname", hostLookupDNSFiles},
},
},
{
Expand Down
3 changes: 1 addition & 2 deletions src/net/net.go
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Expand Up @@ -54,8 +54,7 @@ when the LOCALDOMAIN environment variable is present (even if empty),
when the RES_OPTIONS or HOSTALIASES environment variable is non-empty,
when the ASR_CONFIG environment variable is non-empty (OpenBSD only),
when /etc/resolv.conf or /etc/nsswitch.conf specify the use of features that the
Go resolver does not implement, and when the name being looked up ends in .local
or is an mDNS name.
Go resolver does not implement.

The resolver decision can be overridden by setting the netdns value of the
GODEBUG environment variable (see package runtime) to go or cgo, as in:
Expand Down