net: use Go's DNS resolver when system configuration permits
If the machine's network configuration files (resolv.conf,
nsswitch.conf) don't have any unsupported options, prefer Go's DNS
resolver, which doesn't have the cgo & thread over.
It means users can have more than 500 DNS requests outstanding (our
current limit for cgo lookups) and not have one blocked thread per
outstanding request.
Discussed in thread https://groups.google.com/d/msg/golang-dev/2ZUi792oztM/Q0rg_DkF5HMJ
Change-Id: I3f685d70aff6b47bec30b63e9fba674b20507f95
Reviewed-on: https://go-review.googlesource.com/8945
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/net/conf_test.go b/src/net/conf_test.go
new file mode 100644
index 0000000..46e91bc
--- /dev/null
+++ b/src/net/conf_test.go
@@ -0,0 +1,245 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package net
+
+import (
+ "os"
+ "strings"
+ "testing"
+)
+
+type nssHostTest struct {
+ host string
+ want hostLookupOrder
+}
+
+func nssStr(s string) *nssConf { return parseNSSConf(strings.NewReader(s)) }
+
+func TestConfHostLookupOrder(t *testing.T) {
+ tests := []struct {
+ name string
+ c *conf
+ goos string
+ hostTests []nssHostTest
+ }{
+ {
+ name: "force",
+ c: &conf{
+ forceCgoLookupHost: true,
+ nss: nssStr("foo: bar"),
+ },
+ hostTests: []nssHostTest{
+ {"foo.local", hostLookupCgo},
+ {"google.com", hostLookupCgo},
+ },
+ },
+ {
+ name: "ubuntu_trusty_avahi",
+ c: &conf{
+ nss: nssStr("hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4"),
+ },
+ hostTests: []nssHostTest{
+ {"foo.local", hostLookupCgo},
+ {"foo.local.", hostLookupCgo},
+ {"foo.LOCAL", hostLookupCgo},
+ {"foo.LOCAL.", hostLookupCgo},
+ {"google.com", hostLookupFilesDNS},
+ },
+ },
+ {
+ name: "freebsdlinux_no_resolv_conf",
+ c: &conf{
+ goos: "freebsd",
+ nss: nssStr("foo: bar"),
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupFilesDNS}},
+ },
+ // On OpenBSD, no resolv.conf means no DNS.
+ {
+ name: "openbsd_no_resolv_conf",
+ c: &conf{
+ goos: "openbsd",
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupFiles}},
+ },
+ {
+ name: "solaris_no_nsswitch",
+ c: &conf{
+ goos: "solaris",
+ nss: &nssConf{err: os.ErrNotExist},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupCgo}},
+ },
+ {
+ name: "openbsd_lookup_bind_file",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: []string{"bind", "file"}},
+ },
+ hostTests: []nssHostTest{
+ {"google.com", hostLookupDNSFiles},
+ {"foo.local", hostLookupDNSFiles},
+ },
+ },
+ {
+ name: "openbsd_lookup_file_bind",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: []string{"file", "bind"}},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupFilesDNS}},
+ },
+ {
+ name: "openbsd_lookup_bind",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: []string{"bind"}},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupDNS}},
+ },
+ {
+ name: "openbsd_lookup_file",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: []string{"file"}},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupFiles}},
+ },
+ {
+ name: "openbsd_lookup_yp",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: []string{"file", "bind", "yp"}},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupCgo}},
+ },
+ {
+ name: "openbsd_lookup_two",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: []string{"file", "foo"}},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupCgo}},
+ },
+ {
+ name: "openbsd_lookup_empty",
+ c: &conf{
+ goos: "openbsd",
+ resolv: &dnsConfig{lookup: nil},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupDNSFiles}},
+ },
+ // glibc lacking an nsswitch.conf, per
+ // http://www.gnu.org/software/libc/manual/html_node/Notes-on-NSS-Configuration-File.html
+ {
+ name: "linux_no_nsswitch.conf",
+ c: &conf{
+ goos: "linux",
+ nss: &nssConf{err: os.ErrNotExist},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupDNSFiles}},
+ },
+ {
+ name: "files_mdns_dns",
+ c: &conf{nss: nssStr("hosts: files mdns dns")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupFilesDNS},
+ {"x.local", hostLookupCgo},
+ },
+ },
+ {
+ name: "dns_special_hostnames",
+ c: &conf{nss: nssStr("hosts: dns")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupDNS},
+ {"x\\.com", hostLookupCgo}, // punt on weird glibc escape
+ {"foo.com%en0", hostLookupCgo}, // and IPv6 zones
+ },
+ },
+ {
+ name: "mdns_allow",
+ c: &conf{
+ nss: nssStr("hosts: files mdns dns"),
+ hasMDNSAllow: true,
+ },
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupCgo},
+ {"x.local", hostLookupCgo},
+ },
+ },
+ {
+ name: "files_dns",
+ c: &conf{nss: nssStr("hosts: files dns")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupFilesDNS},
+ {"x", hostLookupFilesDNS},
+ {"x.local", hostLookupCgo},
+ },
+ },
+ {
+ name: "dns_files",
+ c: &conf{nss: nssStr("hosts: dns files")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupDNSFiles},
+ {"x", hostLookupDNSFiles},
+ {"x.local", hostLookupCgo},
+ },
+ },
+ {
+ name: "something_custom",
+ c: &conf{nss: nssStr("hosts: dns files something_custom")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupCgo},
+ },
+ },
+ {
+ name: "myhostname",
+ c: &conf{nss: nssStr("hosts: files dns myhostname")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupFilesDNS},
+ {"somehostname", hostLookupCgo},
+ },
+ },
+ {
+ name: "ubuntu14.04.02",
+ c: &conf{nss: nssStr("hosts: files myhostname mdns4_minimal [NOTFOUND=return] dns mdns4")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupFilesDNS},
+ {"somehostname", hostLookupCgo},
+ },
+ },
+ // Debian Squeeze is just "dns,files", but lists all
+ // the default criteria for dns, but then has a
+ // non-standard but redundant notfound=return for the
+ // files.
+ {
+ name: "debian_squeeze",
+ c: &conf{nss: nssStr("hosts: dns [success=return notfound=continue unavail=continue tryagain=continue] files [notfound=return]")},
+ hostTests: []nssHostTest{
+ {"x.com", hostLookupDNSFiles},
+ {"somehostname", hostLookupDNSFiles},
+ },
+ },
+ {
+ name: "resolv.conf-unknown",
+ c: &conf{
+ nss: nssStr("foo: bar"),
+ resolv: &dnsConfig{unknownOpt: true},
+ },
+ hostTests: []nssHostTest{{"google.com", hostLookupCgo}},
+ },
+ }
+ for _, tt := range tests {
+ for _, ht := range tt.hostTests {
+ gotOrder := tt.c.hostLookupOrder(ht.host)
+ if gotOrder != ht.want {
+ t.Errorf("%s: useCgoLookupHost(%q) = %v; want %v", tt.name, ht.host, gotOrder, ht.want)
+ }
+ }
+ }
+
+}
