[go] net: add support for /etc/hosts aliases using go resolver

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Feb 3, 2022, 4:49:34 PM2/3/22

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net: add support for /etc/hosts aliases using go resolver

It adds support for /etc/hosts aliases and fixes the difference between the glibc cgo and the go DNS resolver.
Examples: https://pastebin.com/p6PaMVPM

Fixes: #44741

Change-Id: I98c484fced900731fbad800278b296028a45f044
GitHub-Last-Rev: c9c2946104fce6b96f3aa59a2103712f53e68e94
GitHub-Pull-Request: golang/go#51004
---
M src/net/dnsclient_unix.go
M src/net/dnsclient_unix_test.go
M src/net/hosts.go
M src/net/hosts_test.go
A src/net/testdata/aliases
5 files changed, 170 insertions(+), 20 deletions(-)

diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
index 21aa91f..d441620 100644
--- a/src/net/dnsclient_unix.go
+++ b/src/net/dnsclient_unix.go
@@ -526,7 +526,7 @@
 func (r *Resolver) goLookupHostOrder(ctx context.Context, name string, order hostLookupOrder) (addrs []string, err error) {
 	if order == hostLookupFilesDNS || order == hostLookupFiles {
 		// Use entries from /etc/hosts if they match.
-		addrs = lookupStaticHost(name)
+		addrs, _ = lookupStaticHost(name)
 		if len(addrs) > 0 || order == hostLookupFiles {
 			return
 		}
@@ -543,8 +543,9 @@
 }
 
 // lookup entries from /etc/hosts
-func goLookupIPFiles(name string) (addrs []IPAddr) {
-	for _, haddr := range lookupStaticHost(name) {
+func goLookupIPFiles(name string) (addrs []IPAddr, cname string) {
+	addr, cname := lookupStaticHost(name)
+	for _, haddr := range addr {
 		haddr, zone := splitHostZone(haddr)
 		if ip := ParseIP(haddr); ip != nil {
 			addr := IPAddr{IP: ip, Zone: zone}
@@ -565,9 +566,20 @@
 
 func (r *Resolver) goLookupIPCNAMEOrder(ctx context.Context, network, name string, order hostLookupOrder) (addrs []IPAddr, cname dnsmessage.Name, err error) {
 	if order == hostLookupFilesDNS || order == hostLookupFiles {
-		addrs = goLookupIPFiles(name)
-		if len(addrs) > 0 || order == hostLookupFiles {
-			return addrs, dnsmessage.Name{}, nil
+		var canonical string
+		addrs, canonical = goLookupIPFiles(name)
+
+		if len(addrs) > 0 {
+			var err error
+			cname, err = dnsmessage.NewName(canonical)
+			if err != nil {
+				return nil, dnsmessage.Name{}, err
+			}
+			return addrs, cname, nil
+		}
+
+		if order == hostLookupFiles {
+			return nil, dnsmessage.Name{}, errors.New("no entry in /etc/hosts file")
 		}
 	}
 	if !isDomainName(name) {
@@ -723,9 +735,18 @@
 	sortByRFC6724(addrs)
 	if len(addrs) == 0 {
 		if order == hostLookupDNSFiles {
-			addrs = goLookupIPFiles(name)
+			var canonical string
+			addrs, canonical = goLookupIPFiles(name)
+			if len(addrs) > 0 {
+				var err error
+				cname, err = dnsmessage.NewName(canonical)
+				if err != nil {
+					return nil, dnsmessage.Name{}, err
+				}
+				return addrs, cname, nil
+			}
 		}
-		if len(addrs) == 0 && lastErr != nil {
+		if lastErr != nil {
 			return nil, dnsmessage.Name{}, lastErr
 		}
 	}
diff --git a/src/net/dnsclient_unix_test.go b/src/net/dnsclient_unix_test.go
index 14366ec..07e0866 100644
--- a/src/net/dnsclient_unix_test.go
+++ b/src/net/dnsclient_unix_test.go
@@ -2161,3 +2161,53 @@
 		t.Errorf("records = [%v]; want [%v]", strings.Join(records, " "), want[0])
 	}
 }
+
+func TestGoLookupIPCNAMEOrderHostsAliasesFilesOnlyMode(t *testing.T) {
+	defer func(orig string) { testHookHostsPath = orig }(testHookHostsPath)
+	testHookHostsPath = "testdata/aliases"
+	mode := hostLookupFiles
+
+	for _, v := range lookupStaticHostAliasesTest {
+		testGoLookupIPCNAMEOrderHostsAliases(t, mode, v.lookup, absDomainName(v.res))
+	}
+}
+
+func TestGoLookupIPCNAMEOrderHostsAliasesFilesDNSMode(t *testing.T) {
+	defer func(orig string) { testHookHostsPath = orig }(testHookHostsPath)
+	testHookHostsPath = "testdata/aliases"
+	mode := hostLookupFilesDNS
+
+	for _, v := range lookupStaticHostAliasesTest {
+		testGoLookupIPCNAMEOrderHostsAliases(t, mode, v.lookup, absDomainName(v.res))
+	}
+}
+
+var goLookupIPCNAMEOrderDNSFilesModeTests = []struct {
+	lookup, res string
+}{
+	//127.0.1.1
+	{"8438random7333name2", "8438random7333name2.example.test"},
+}
+
+func TestGoLookupIPCNAMEOrderHostsAliasesDNSFilesMode(t *testing.T) {
+	defer func(orig string) { testHookHostsPath = orig }(testHookHostsPath)
+	testHookHostsPath = "testdata/aliases"
+	mode := hostLookupDNSFiles
+
+	for _, v := range goLookupIPCNAMEOrderDNSFilesModeTests {
+		testGoLookupIPCNAMEOrderHostsAliases(t, mode, v.lookup, absDomainName(v.res))
+	}
+}
+
+func testGoLookupIPCNAMEOrderHostsAliases(t *testing.T, mode hostLookupOrder, lookup, lookupRes string) {
+	ins := []string{lookup, absDomainName(lookup), strings.ToLower(lookup), strings.ToUpper(lookup)}
+	for _, in := range ins {
+		_, res, err := goResolver.goLookupIPCNAMEOrder(context.Background(), "ip", in, mode)
+		if err != nil {
+			t.Errorf("expected err == nil, but got error: %v", err)
+		}
+		if res.String() != lookupRes {
+			t.Errorf("goLookupIPCNAMEOrder(%v): should be: '%v', but: '%v'", in, lookupRes, res)
+		}
+	}
+}
diff --git a/src/net/hosts.go b/src/net/hosts.go
index e604031..e74643b 100644
--- a/src/net/hosts.go
+++ b/src/net/hosts.go
@@ -28,6 +28,11 @@
 	return ip.String() + "%" + zone
 }
 
+type byName struct {
+	addrs         []string
+	canonicalName string
+}
+
 // hosts contains known host entries.
 var hosts struct {
 	sync.Mutex
@@ -36,7 +41,7 @@
 	// name. It would be part of DNS labels, a FQDN or an absolute
 	// FQDN.
 	// For now the key is converted to lower case for convenience.
-	byName map[string][]string
+	byName map[string]byName
 
 	// Key for the list of host names must be a literal IP address
 	// including IPv6 address with zone identifier.
@@ -62,8 +67,9 @@
 		return
 	}
 
-	hs := make(map[string][]string)
+	hs := make(map[string]byName)
 	is := make(map[string][]string)
+
 	var file *file
 	if file, _ = open(hp); file == nil {
 		return
@@ -81,12 +87,22 @@
 		if addr == "" {
 			continue
 		}
+
+		var canonical string
 		for i := 1; i < len(f); i++ {
 			name := absDomainName(f[i])
 			h := []byte(f[i])
 			lowerASCIIBytes(h)
 			key := absDomainName(string(h))
-			hs[key] = append(hs[key], addr)
+
+			if i == 1 {
+				canonical = key
+			}
+
+			hs[key] = byName{
+				addrs:         append(hs[key].addrs, addr),
+				canonicalName: canonical,
+			}
 			is[addr] = append(is[addr], name)
 		}
 	}
@@ -100,8 +116,8 @@
 	file.close()
 }
 
-// lookupStaticHost looks up the addresses for the given host from /etc/hosts.
-func lookupStaticHost(host string) []string {
+// lookupStaticHost looks up the addresses and the cannonical name for the given host from /etc/hosts.
+func lookupStaticHost(host string) ([]string, string) {
 	hosts.Lock()
 	defer hosts.Unlock()
 	readHosts()
@@ -111,13 +127,13 @@
 			lowerASCIIBytes(lowerHost)
 			host = string(lowerHost)
 		}
-		if ips, ok := hosts.byName[absDomainName(host)]; ok {
-			ipsCp := make([]string, len(ips))
-			copy(ipsCp, ips)
-			return ipsCp
+		if byName, ok := hosts.byName[absDomainName(host)]; ok {
+			ipsCp := make([]string, len(byName.addrs))
+			copy(ipsCp, byName.addrs)
+			return ipsCp, byName.canonicalName
 		}
 	}
-	return nil
+	return nil, ""
 }
 
 // lookupStaticAddr looks up the hosts for the given address from /etc/hosts.
diff --git a/src/net/hosts_test.go b/src/net/hosts_test.go
index 7291914..013ea78 100644
--- a/src/net/hosts_test.go
+++ b/src/net/hosts_test.go
@@ -72,7 +72,7 @@
 func testStaticHost(t *testing.T, hostsPath string, ent staticHostEntry) {
 	ins := []string{ent.in, absDomainName(ent.in), strings.ToLower(ent.in), strings.ToUpper(ent.in)}
 	for _, in := range ins {
-		addrs := lookupStaticHost(in)
+		addrs, _ := lookupStaticHost(in)
 		if !reflect.DeepEqual(addrs, ent.out) {
 			t.Errorf("%s, lookupStaticHost(%s) = %v; want %v", hostsPath, in, addrs, ent.out)
 		}
@@ -157,7 +157,7 @@
 	ent := staticHostEntry{"localhost", []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"}}
 	testStaticHost(t, testHookHostsPath, ent)
 	// Modify the addresses return by lookupStaticHost.
-	addrs := lookupStaticHost(ent.in)
+	addrs, _ := lookupStaticHost(ent.in)
 	for i := range addrs {
 		addrs[i] += "junk"
 	}
@@ -173,3 +173,42 @@
 	}
 	testStaticAddr(t, testHookHostsPath, ent)
 }
+
+var lookupStaticHostAliasesTest = []struct {
+	lookup, res string
+}{
+	//127.0.0.1
+	{"test", "test"},
+	//127.0.0.2
+	{"test2.example.com", "test2.example.com"},
+	{"test2", "test2.example.com."},
+	//127.0.0.3
+	{"test3.example.com", "test3"},
+	{"test3", "test3"},
+	//127.0.0.4
+	{"example.com", "example.com"},
+	//127.0.0.5
+	{"test5.example.com", "test4.example.com"},
+	{"test5", "test4.example.com"},
+	{"test4", "test4.example.com"},
+	{"test4.example.com", "test4.example.com"},
+}
+
+func TestLookupStaticHostAliases(t *testing.T) {
+	defer func(orig string) { testHookHostsPath = orig }(testHookHostsPath)
+
+	testHookHostsPath = "testdata/aliases"
+	for _, ent := range lookupStaticHostAliasesTest {
+			testLookupStaticHostAliases(t, ent.lookup, absDomainName(ent.res))
+	}
+}
+
+func testLookupStaticHostAliases(t *testing.T, lookup, lookupRes string) {
+	ins := []string{lookup, absDomainName(lookup), strings.ToLower(lookup), strings.ToUpper(lookup)}
+	for _, in := range ins {
+		_, res := lookupStaticHost(in)
+		if res != lookupRes {
+			t.Errorf("lookupStaticHost(%v): should be: '%v', but: '%v'", in, lookupRes, res)
+		}
+	}
+}
diff --git a/src/net/testdata/aliases b/src/net/testdata/aliases
new file mode 100644
index 0000000..e723523
--- /dev/null
+++ b/src/net/testdata/aliases
@@ -0,0 +1,8 @@
+127.0.0.1 test
+127.0.0.2 test2.example.com test2
+127.0.0.3 test3 test3.example.com
+127.0.0.4 example.com
+127.0.0.5 test4.example.com test4 test5 test5.example.com
+
+#must be a non resolvable domain on the internet
+127.0.1.1 8438random7333name2.example.test 8438random7333name2

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[go] net: add support for /etc/hosts aliases using go resolver

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