net: make Resolver.PreferGo work more as documented

Fixes #24393

Change-Id: I8bcee34cdf30472663d866ed6056301d8445215c
Reviewed-on: https://go-review.googlesource.com/100875
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/net/conf.go b/src/net/conf.go
index c10aafe63aba51800384e8a53a58ad486c27d4b4..2c21331a00521dea430eddc1268f89d54005c08b 100644 (file)
--- a/src/net/conf.go
+++ b/src/net/conf.go
@@ -114,18 +114,19 @@ func initConfVal() {
 // canUseCgo reports whether calling cgo functions is allowed
 // for non-hostname lookups.
 func (c *conf) canUseCgo() bool {
-       return c.hostLookupOrder("") == hostLookupCgo
+       return c.hostLookupOrder(nil, "") == hostLookupCgo
 }
 
 // hostLookupOrder determines which strategy to use to resolve hostname.
-func (c *conf) hostLookupOrder(hostname string) (ret hostLookupOrder) {
+// The provided Resolver is optional. nil means to not consider its options.
+func (c *conf) hostLookupOrder(r *Resolver, hostname string) (ret hostLookupOrder) {
        if c.dnsDebugLevel > 1 {
                defer func() {
                        print("go package net: hostLookupOrder(", hostname, ") = ", ret.String(), "\n")
                }()
        }
        fallbackOrder := hostLookupCgo
-       if c.netGo {
+       if c.netGo || (r != nil && r.PreferGo) {
                fallbackOrder = hostLookupFilesDNS
        }
        if c.forceCgoLookupHost || c.resolv.unknownOpt || c.goos == "android" {

diff --git a/src/net/conf_test.go b/src/net/conf_test.go
index 17d03f4b5fc55f739a5e6017ea2eb941f5dacfb7..a6d6987b1561dd57205b3244b5d82c13477f46cc 100644 (file)
--- a/src/net/conf_test.go
+++ b/src/net/conf_test.go
@@ -33,6 +33,7 @@ func TestConfHostLookupOrder(t *testing.T) {
        tests := []struct {
                name      string
                c         *conf
+               resolver  *Resolver
                hostTests []nssHostTest
        }{
                {
@@ -322,6 +323,21 @@ func TestConfHostLookupOrder(t *testing.T) {
                                {"x.com", "myhostname", hostLookupCgo},
                        },
                },
+               // Issue 24393: make sure "Resolver.PreferGo = true" acts like netgo.
+               {
+                       name:     "resolver-prefergo",
+                       resolver: &Resolver{PreferGo: true},
+                       c: &conf{
+                               goos:               "darwin",
+                               forceCgoLookupHost: true, // always true for darwin
+                               resolv:             defaultResolvConf,
+                               nss:                nssStr(""),
+                               netCgo:             true,
+                       },
+                       hostTests: []nssHostTest{
+                               {"localhost", "myhostname", hostLookupFilesDNS},
+                       },
+               },
        }
 
        origGetHostname := getHostname
@@ -331,7 +347,7 @@ func TestConfHostLookupOrder(t *testing.T) {
                for _, ht := range tt.hostTests {
                        getHostname = func() (string, error) { return ht.localhost, nil }
 
-                       gotOrder := tt.c.hostLookupOrder(ht.host)
+                       gotOrder := tt.c.hostLookupOrder(tt.resolver, ht.host)
                        if gotOrder != ht.want {
                                t.Errorf("%s: hostLookupOrder(%q) = %v; want %v", tt.name, ht.host, gotOrder, ht.want)
                        }

diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
index d2a6dc4a811f3e63c036cfad91bd71205c17963d..7ca5d6027b5193e02b426a3c018dbce491c36e57 100644 (file)
--- a/src/net/dnsclient_unix.go
+++ b/src/net/dnsclient_unix.go
@@ -524,7 +524,7 @@ func goLookupIPFiles(name string) (addrs []IPAddr) {
 // goLookupIP is the native Go implementation of LookupIP.
 // The libc versions are in cgo_*.go.
 func (r *Resolver) goLookupIP(ctx context.Context, host string) (addrs []IPAddr, err error) {
-       order := systemConf().hostLookupOrder(host)
+       order := systemConf().hostLookupOrder(r, host)
        addrs, _, err = r.goLookupIPCNAMEOrder(ctx, host, order)
        return
 }
@@ -676,7 +676,7 @@ func (r *Resolver) goLookupIPCNAMEOrder(ctx context.Context, name string, order
 
 // goLookupCNAME is the native Go (non-cgo) implementation of LookupCNAME.
 func (r *Resolver) goLookupCNAME(ctx context.Context, host string) (string, error) {
-       order := systemConf().hostLookupOrder(host)
+       order := systemConf().hostLookupOrder(r, host)
        _, cname, err := r.goLookupIPCNAMEOrder(ctx, host, order)
        return cname.String(), err
 }

diff --git a/src/net/lookup_unix.go b/src/net/lookup_unix.go
index 0b922429079081e1d7436981582d4d89abb8c55f..8e77b8c70507a8bb117af961c6c48d1770ca3665 100644 (file)
--- a/src/net/lookup_unix.go
+++ b/src/net/lookup_unix.go
@@ -74,7 +74,7 @@ func (r *Resolver) dial(ctx context.Context, network, server string) (Conn, erro
 }
 
 func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
-       order := systemConf().hostLookupOrder(host)
+       order := systemConf().hostLookupOrder(r, host)
        if !r.PreferGo && order == hostLookupCgo {
                if addrs, err, ok := cgoLookupHost(ctx, host); ok {
                        return addrs, err
@@ -89,7 +89,7 @@ func (r *Resolver) lookupIP(ctx context.Context, host string) (addrs []IPAddr, e
        if r.PreferGo {
                return r.goLookupIP(ctx, host)
        }
-       order := systemConf().hostLookupOrder(host)
+       order := systemConf().hostLookupOrder(r, host)
        if order == hostLookupCgo {
                if addrs, err, ok := cgoLookupIP(ctx, host); ok {
                        return addrs, err