cherry-pick: svcb dohpath support

Merge in DNS/adguard-home from 4463-ddr-support to master

Squashed commit of the following:

commit 99a149e9024354ad0341739c3c9b08cefbd74468
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Tue Apr 12 14:13:17 2022 +0200

    imp docs

commit 26150be8df8b35e47c108f6e3319c57b39fb8e38
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Mon Apr 11 20:36:18 2022 +0200

    imp code docs

commit 5a4607f71abba83a9ac8753abd74c9fb97e4a545
Merge: 00f0abf5 9f0fdc5e
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Mon Apr 11 16:14:49 2022 +0200

    Merge remote-tracking branch 'origin/master' into 4463-ddr-support

    # Conflicts:
    #	internal/dnsforward/svcbmsg.go

commit 00f0abf5eea07aeeebc2a856a958215021a51ab7
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Mon Apr 11 16:06:42 2022 +0200

    svcb dohpath support

commit ace81ce1ea2fb96c4434c6c1fded4a79427cf17e
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Thu Apr 7 14:31:32 2022 +0200

    svcb dohpath support

commit a1b5df4fb2e87dab265d6ca55928610a6acc1c00
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Wed Apr 6 16:53:17 2022 +0200

    svcb dohpath support

internal/dnsforward/dnsrewrite_test.go

@@ -22,7 +22,7 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 		Preference: 32,
 	}
 	svcbVal := &rules.DNSSVCB{
-		Params:   map[string]string{"alpn": "h3"},
+		Params:   map[string]string{"alpn": "h3", "dohpath": "/dns-query"},
 		Target:   dns.Fqdn(domain),
 		Priority: 32,
 	}
@@ -164,10 +164,20 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 
 		require.Len(t, d.Res.Answer, 1)
 		ans, ok := d.Res.Answer[0].(*dns.SVCB)
-		require.True(t, ok)
 
-		assert.Equal(t, dns.SVCB_ALPN, ans.Value[0].Key())
-		assert.Equal(t, svcbVal.Params["alpn"], ans.Value[0].String())
+		require.True(t, ok)
+		require.Len(t, ans.Value, 2)
+
+		assert.ElementsMatch(
+			t,
+			[]dns.SVCBKey{dns.SVCB_ALPN, dns.SVCB_DOHPATH},
+			[]dns.SVCBKey{ans.Value[0].Key(), ans.Value[1].Key()},
+		)
+		assert.ElementsMatch(
+			t,
+			[]string{svcbVal.Params["alpn"], svcbVal.Params["dohpath"]},
+			[]string{ans.Value[0].String(), ans.Value[1].String()},
+		)
 		assert.Equal(t, svcbVal.Target, ans.Target)
 		assert.Equal(t, svcbVal.Priority, ans.Priority)
 	})
@@ -186,8 +196,18 @@ func TestServer_FilterDNSRewrite(t *testing.T) {
 		ans, ok := d.Res.Answer[0].(*dns.HTTPS)
 
 		require.True(t, ok)
-		assert.Equal(t, dns.SVCB_ALPN, ans.Value[0].Key())
-		assert.Equal(t, svcbVal.Params["alpn"], ans.Value[0].String())
+		require.Len(t, ans.Value, 2)
+
+		assert.ElementsMatch(
+			t,
+			[]dns.SVCBKey{dns.SVCB_ALPN, dns.SVCB_DOHPATH},
+			[]dns.SVCBKey{ans.Value[0].Key(), ans.Value[1].Key()},
+		)
+		assert.ElementsMatch(
+			t,
+			[]string{svcbVal.Params["alpn"], svcbVal.Params["dohpath"]},
+			[]string{ans.Value[0].String(), ans.Value[1].String()},
+		)
 		assert.Equal(t, svcbVal.Target, ans.Target)
 		assert.Equal(t, svcbVal.Priority, ans.Priority)
 	})

internal/dnsforward/svcbmsg.go

@@ -143,6 +143,12 @@ var svcbKeyHandlers = map[string]svcbKeyHandler{
 			ECH: ech,
 		}
 	},
+
+	"dohpath": func(valStr string) (val dns.SVCBKeyValue) {
+		return &dns.SVCBDoHPath{
+			Template: valStr,
+		}
+	},
 }
 
 // genAnswerSVCB returns a properly initialized SVCB resource record.

internal/dnsforward/svcbmsg_test.go

@@ -127,6 +127,10 @@ func TestGenAnswerHTTPS_andSVCB(t *testing.T) {
 		svcb: dnssvcb("no-default-alpn", ""),
 		want: wantsvcb(&dns.SVCBNoDefaultAlpn{}),
 		name: "no_default_alpn",
+	}, {
+		svcb: dnssvcb("dohpath", "/dns-query"),
+		want: wantsvcb(&dns.SVCBDoHPath{Template: "/dns-query"}),
+		name: "dohpath",
 	}, {
 		svcb: dnssvcb("port", "8080"),
 		want: wantsvcb(&dns.SVCBPort{Port: 8080}),