Pull request: all: update go and backend tools

Updates #2275.

Squashed commit of the following:

commit f24c26cd2b49fac00a581936da4ccb13ca341bc9
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 21:33:15 2021 +0300

    aghtest: imp docs

commit 46f5b06f9743e800b489e8c30af07d24bfdcf989
Merge: bfb852cb 55d4c7ee
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 21:32:32 2021 +0300

    Merge branch 'master' into 2275-upd

commit bfb852cbc74ec219a41e985f2dcb090d58299aee
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 19:06:32 2021 +0300

    scripts: rem unsupported platform

commit c1645e247f18d384a980c60d3a94b9363f83f174
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 18:47:57 2021 +0300

    all: rollback more

commit 989811b5e38498234dc11baf5dd153c76b9dada4
Merge: 976bdfbd 2d704242
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 18:30:42 2021 +0300

    Merge branch 'master' into 2275-upd

commit 976bdfbdd44983f4cd657a486b94ff63f5885fd5
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 18:28:23 2021 +0300

    aghtest: fix os_windows

commit 9e85080eefe882d72c939969f7008e3c46467c0c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Mar 10 18:15:37 2021 +0300

    all: rewrite windows workaround, imp code, docs

commit 35a0b1d8656640a962fe9ae019c3d665f42707ce
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Jan 21 20:38:17 2021 +0300

    all: update go and backend tools

internal/aghtest/os.go

@@ -1,14 +1,7 @@
 package aghtest
 
 import (
-	"io/ioutil"
-	"os"
-	"runtime"
 	"testing"
-	"time"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
 // PrepareTestDir returns the full path to temporary created directory and
@@ -16,30 +9,5 @@ import (
 func PrepareTestDir(t *testing.T) (dir string) {
 	t.Helper()
 
-	wd, err := os.Getwd()
-	require.Nil(t, err)
-
-	dir, err = ioutil.TempDir(wd, "agh-test")
-	require.Nil(t, err)
-	require.NotEmpty(t, dir)
-
-	t.Cleanup(func() {
-		// TODO(e.burkov): Replace with t.TempDir methods after updating
-		// go version to 1.15.
-		start := time.Now()
-		for {
-			err := os.RemoveAll(dir)
-			if err == nil {
-				break
-			}
-
-			if runtime.GOOS != "windows" || time.Since(start) >= 500*time.Millisecond {
-				break
-			}
-			time.Sleep(5 * time.Millisecond)
-		}
-		assert.Nil(t, err)
-	})
-
-	return dir
+	return prepareTestDir(t)
 }

internal/aghtest/os_others.go

@@ -0,0 +1,13 @@
+// +build !windows
+
+package aghtest
+
+import (
+	"testing"
+)
+
+func prepareTestDir(t *testing.T) (dir string) {
+	t.Helper()
+
+	return t.TempDir()
+}

internal/aghtest/os_windows.go

@@ -0,0 +1,63 @@
+// +build windows
+
+package aghtest
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	maxRetryDur = 500 * time.Millisecond
+	retryDur    = 5 * time.Millisecond
+)
+
+func prepareTestDir(t *testing.T) (dir string) {
+	// Windows, including the version of Windows Server that Github Actions
+	// uses, apparently likes to overly eagerly inspect new directories with
+	// its Windows Defender.  Disabling it might require additional
+	// workarounds, and until we've figured it out, just retry the deletion
+	// until the error goes away.
+	//
+	// The code is largely inspired by the one that has been introduced into
+	// the go command itself.  We should probably make a proposal to use the
+	// same mechanism in t.TempDir.
+	//
+	// See https://go-review.googlesource.com/c/go/+/172337.
+	//
+	// See https://github.com/golang/go/issues/44919.
+
+	t.Helper()
+
+	wd, err := os.Getwd()
+	require.Nil(t, err)
+
+	dir, err = ioutil.TempDir(wd, "agh-test")
+	require.Nil(t, err)
+	require.NotEmpty(t, dir)
+
+	t.Cleanup(func() {
+		start := time.Now()
+		for {
+			err := os.RemoveAll(dir)
+			if err == nil {
+				break
+			}
+
+			if time.Since(start) >= maxRetryDur {
+				break
+			}
+
+			time.Sleep(retryDur)
+		}
+
+		assert.Nil(t, err)
+	})
+
+	return dir
+}

internal/aghtest/resolver.go

@@ -14,23 +14,17 @@ type TestResolver struct {
 }
 
 // HostToIPs generates IPv4 and IPv6 from host.
-//
-// TODO(e.burkov): Replace with LookupIP after upgrading go to v1.15.
 func (r *TestResolver) HostToIPs(host string) (ipv4, ipv6 net.IP) {
 	hash := sha256.Sum256([]byte(host))
 
 	return net.IP(hash[:4]), net.IP(hash[4:20])
 }
 
-// LookupIPAddr implements Resolver interface for *testResolver. It returns the
-// slice of net.IPAddr with IPv4 and IPv6 instances.
-func (r *TestResolver) LookupIPAddr(_ context.Context, host string) (ips []net.IPAddr, err error) {
+// LookupIP implements Resolver interface for *testResolver. It returns the
+// slice of net.IP with IPv4 and IPv6 instances.
+func (r *TestResolver) LookupIP(_ context.Context, _, host string) (ips []net.IP, err error) {
 	ipv4, ipv6 := r.HostToIPs(host)
-	addrs := []net.IPAddr{{
-		IP: ipv4,
-	}, {
-		IP: ipv6,
-	}}
+	addrs := []net.IP{ipv4, ipv6}
 
 	r.counterLock.Lock()
 	defer r.counterLock.Unlock()