net: skip external net tests on iOS

CL 113095 tried to deflake net tests on iOS by skipping the test
that uses the most sockets. That didn't work well enough and will
be reverted in CL 113555.

The flakes appeared after the iOS exec harness started to forward
environment variables, causing testenv.Builder to be non-empty on
the iOS builder. This CL attempts to fix the flakes with the more
conservative strategy of skipping tests that only run on builders.

The skipped tests happen to be those requiring external network
access; it's plausible that the iOS builder network isn't reliable
enough to run the many parallel DNS lookups and dial outs, while
keeping the number of open file descriptors below the 250 limit.

Change-Id: I9cafdaf2845dd6f3844c4819dcaaaa5970f5da15
Reviewed-on: https://go-review.googlesource.com/113575
Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/dial_test.go

@@ -749,9 +749,8 @@ func TestDialCancel(t *testing.T) {
 	switch testenv.Builder() {
 	case "linux-arm64-buildlet":
 		t.Skip("skipping on linux-arm64-buildlet; incompatible network config? issue 15191")
-	case "":
-		testenv.MustHaveExternalNetwork(t)
 	}
+	mustHaveExternalNetwork(t)
 
 	if runtime.GOOS == "nacl" {
 		// nacl doesn't have external network access.
@@ -897,9 +896,7 @@ func TestCancelAfterDial(t *testing.T) {
 // if the machine has halfway configured IPv6 such that it can bind on
 // "::" not connect back to that same address.
 func TestDialListenerAddr(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 	ln, err := Listen("tcp", ":0")
 	if err != nil {
 		t.Fatal(err)
@@ -912,3 +909,13 @@ func TestDialListenerAddr(t *testing.T) {
 	}
 	c.Close()
 }
+
+// mustHaveExternalNetwork is like testenv.MustHaveExternalNetwork
+// except that it won't skip testing on non-iOS builders.
+func mustHaveExternalNetwork(t *testing.T) {
+	t.Helper()
+	ios := runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64")
+	if testenv.Builder() == "" || ios {
+		testenv.MustHaveExternalNetwork(t)
+	}
+}

src/net/lookup_test.go

@@ -64,9 +64,7 @@ var backoffDuration = [...]time.Duration{time.Second, 5 * time.Second, 30 * time
 
 func TestLookupGoogleSRV(t *testing.T) {
 	t.Parallel()
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
 		t.Skip("no resolv.conf on iOS")
@@ -115,9 +113,7 @@ var lookupGmailMXTests = []struct {
 
 func TestLookupGmailMX(t *testing.T) {
 	t.Parallel()
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
 		t.Skip("no resolv.conf on iOS")
@@ -163,9 +159,7 @@ var lookupGmailNSTests = []struct {
 
 func TestLookupGmailNS(t *testing.T) {
 	t.Parallel()
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
 		t.Skip("no resolv.conf on iOS")
@@ -211,9 +205,7 @@ var lookupGmailTXTTests = []struct {
 
 func TestLookupGmailTXT(t *testing.T) {
 	t.Parallel()
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
 		t.Skip("no resolv.conf on iOS")
@@ -261,9 +253,7 @@ var lookupGooglePublicDNSAddrTests = []struct {
 }
 
 func TestLookupGooglePublicDNSAddr(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if !supportsIPv4() || !supportsIPv6() || !*testIPv4 || !*testIPv6 {
 		t.Skip("both IPv4 and IPv6 are required")
@@ -322,9 +312,7 @@ var lookupCNAMETests = []struct {
 }
 
 func TestLookupCNAME(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if !supportsIPv4() || !*testIPv4 {
 		t.Skip("IPv4 is required")
@@ -362,9 +350,7 @@ var lookupGoogleHostTests = []struct {
 }
 
 func TestLookupGoogleHost(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if !supportsIPv4() || !*testIPv4 {
 		t.Skip("IPv4 is required")
@@ -390,9 +376,7 @@ func TestLookupGoogleHost(t *testing.T) {
 
 func TestLookupLongTXT(t *testing.T) {
 	testenv.SkipFlaky(t, 22857)
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	defer dnsWaitGroup.Wait()
 
@@ -418,9 +402,7 @@ var lookupGoogleIPTests = []struct {
 }
 
 func TestLookupGoogleIP(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if !supportsIPv4() || !*testIPv4 {
 		t.Skip("IPv4 is required")
@@ -566,9 +548,7 @@ func TestLookupDotsWithLocalSource(t *testing.T) {
 		t.Skip("IPv4 is required")
 	}
 
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	defer dnsWaitGroup.Wait()
 
@@ -609,9 +589,7 @@ func TestLookupDotsWithLocalSource(t *testing.T) {
 }
 
 func TestLookupDotsWithRemoteSource(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 
 	if !supportsIPv4() || !*testIPv4 {
 		t.Skip("IPv4 is required")
@@ -864,9 +842,7 @@ func TestLookupNonLDH(t *testing.T) {
 }
 
 func TestLookupContextCancel(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 	if runtime.GOOS == "nacl" {
 		t.Skip("skip on nacl")
 	}
@@ -891,9 +867,7 @@ func TestLookupContextCancel(t *testing.T) {
 // Issue 24330: treat the nil *Resolver like a zero value. Verify nothing
 // crashes if nil is used.
 func TestNilResolverLookup(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 	if runtime.GOOS == "nacl" {
 		t.Skip("skip on nacl")
 	}
@@ -915,9 +889,7 @@ func TestNilResolverLookup(t *testing.T) {
 // TestLookupHostCancel verifies that lookup works even after many
 // canceled lookups (see golang.org/issue/24178 for details).
 func TestLookupHostCancel(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
 	if runtime.GOOS == "nacl" {
 		t.Skip("skip on nacl")
 	}

src/net/tcpsock_unix_test.go

@@ -8,7 +8,6 @@ package net
 
 import (
 	"context"
-	"internal/testenv"
 	"math/rand"
 	"runtime"
 	"sync"
@@ -84,9 +83,8 @@ func TestTCPSpuriousConnSetupCompletion(t *testing.T) {
 // Issue 19289.
 // Test that a canceled Dial does not cause a subsequent Dial to succeed.
 func TestTCPSpuriousConnSetupCompletionWithCancel(t *testing.T) {
-	if testenv.Builder() == "" {
-		testenv.MustHaveExternalNetwork(t)
-	}
+	mustHaveExternalNetwork(t)
+
 	defer dnsWaitGroup.Wait()
 	t.Parallel()
 	const tries = 10000